1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * INET		An implementation of the TCP/IP protocol suite for the LINUX
4  *		operating system.  INET is implemented using the  BSD Socket
5  *		interface as the means of communication with the user level.
6  *
7  *		Implementation of the Transmission Control Protocol(TCP).
8  *
9  * Authors:	Ross Biro
10  *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11  *		Mark Evans, <evansmp@uhura.aston.ac.uk>
12  *		Corey Minyard <wf-rch!minyard@relay.EU.net>
13  *		Florian La Roche, <flla@stud.uni-sb.de>
14  *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15  *		Linus Torvalds, <torvalds@cs.helsinki.fi>
16  *		Alan Cox, <gw4pts@gw4pts.ampr.org>
17  *		Matthew Dillon, <dillon@apollo.west.oic.com>
18  *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19  *		Jorge Cwik, <jorge@laser.satlink.net>
20  */
21 
22 /*
23  * Changes:
24  *		Pedro Roque	:	Fast Retransmit/Recovery.
25  *					Two receive queues.
26  *					Retransmit queue handled by TCP.
27  *					Better retransmit timer handling.
28  *					New congestion avoidance.
29  *					Header prediction.
30  *					Variable renaming.
31  *
32  *		Eric		:	Fast Retransmit.
33  *		Randy Scott	:	MSS option defines.
34  *		Eric Schenk	:	Fixes to slow start algorithm.
35  *		Eric Schenk	:	Yet another double ACK bug.
36  *		Eric Schenk	:	Delayed ACK bug fixes.
37  *		Eric Schenk	:	Floyd style fast retrans war avoidance.
38  *		David S. Miller	:	Don't allow zero congestion window.
39  *		Eric Schenk	:	Fix retransmitter so that it sends
40  *					next packet on ack of previous packet.
41  *		Andi Kleen	:	Moved open_request checking here
42  *					and process RSTs for open_requests.
43  *		Andi Kleen	:	Better prune_queue, and other fixes.
44  *		Andrey Savochkin:	Fix RTT measurements in the presence of
45  *					timestamps.
46  *		Andrey Savochkin:	Check sequence numbers correctly when
47  *					removing SACKs due to in sequence incoming
48  *					data segments.
49  *		Andi Kleen:		Make sure we never ack data there is not
50  *					enough room for. Also make this condition
51  *					a fatal error if it might still happen.
52  *		Andi Kleen:		Add tcp_measure_rcv_mss to make
53  *					connections with MSS<min(MTU,ann. MSS)
54  *					work without delayed acks.
55  *		Andi Kleen:		Process packets with PSH set in the
56  *					fast path.
57  *		J Hadi Salim:		ECN support
58  *	 	Andrei Gurtov,
59  *		Pasi Sarolahti,
60  *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
61  *					engine. Lots of bugs are found.
62  *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
63  */
64 
65 #define pr_fmt(fmt) "TCP: " fmt
66 
67 #include <linux/mm.h>
68 #include <linux/slab.h>
69 #include <linux/module.h>
70 #include <linux/sysctl.h>
71 #include <linux/kernel.h>
72 #include <linux/prefetch.h>
73 #include <net/dst.h>
74 #include <net/tcp.h>
75 #include <net/inet_common.h>
76 #include <linux/ipsec.h>
77 #include <asm/unaligned.h>
78 #include <linux/errqueue.h>
79 #include <trace/events/tcp.h>
80 #include <linux/jump_label_ratelimit.h>
81 #include <net/busy_poll.h>
82 #include <net/mptcp.h>
83 
84 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
85 
86 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
87 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
88 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
89 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
90 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
91 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
92 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
93 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
94 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
95 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
96 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
97 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
98 #define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
99 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
100 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
101 #define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
102 #define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
103 #define FLAG_DSACK_TLP		0x20000 /* DSACK for tail loss probe */
104 
105 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
106 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
107 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
108 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
109 
110 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
111 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
112 
113 #define REXMIT_NONE	0 /* no loss recovery to do */
114 #define REXMIT_LOST	1 /* retransmit packets marked lost */
115 #define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
116 
117 #if IS_ENABLED(CONFIG_TLS_DEVICE)
118 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
119 
clean_acked_data_enable(struct inet_connection_sock * icsk,void (* cad)(struct sock * sk,u32 ack_seq))120 void clean_acked_data_enable(struct inet_connection_sock *icsk,
121 			     void (*cad)(struct sock *sk, u32 ack_seq))
122 {
123 	icsk->icsk_clean_acked = cad;
124 	static_branch_deferred_inc(&clean_acked_data_enabled);
125 }
126 EXPORT_SYMBOL_GPL(clean_acked_data_enable);
127 
clean_acked_data_disable(struct inet_connection_sock * icsk)128 void clean_acked_data_disable(struct inet_connection_sock *icsk)
129 {
130 	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
131 	icsk->icsk_clean_acked = NULL;
132 }
133 EXPORT_SYMBOL_GPL(clean_acked_data_disable);
134 
clean_acked_data_flush(void)135 void clean_acked_data_flush(void)
136 {
137 	static_key_deferred_flush(&clean_acked_data_enabled);
138 }
139 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
140 #endif
141 
142 #ifdef CONFIG_CGROUP_BPF
bpf_skops_parse_hdr(struct sock * sk,struct sk_buff * skb)143 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
144 {
145 	bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
146 		BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
147 				       BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
148 	bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
149 						    BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
150 	struct bpf_sock_ops_kern sock_ops;
151 
152 	if (likely(!unknown_opt && !parse_all_opt))
153 		return;
154 
155 	/* The skb will be handled in the
156 	 * bpf_skops_established() or
157 	 * bpf_skops_write_hdr_opt().
158 	 */
159 	switch (sk->sk_state) {
160 	case TCP_SYN_RECV:
161 	case TCP_SYN_SENT:
162 	case TCP_LISTEN:
163 		return;
164 	}
165 
166 	sock_owned_by_me(sk);
167 
168 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
169 	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
170 	sock_ops.is_fullsock = 1;
171 	sock_ops.sk = sk;
172 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
173 
174 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
175 }
176 
bpf_skops_established(struct sock * sk,int bpf_op,struct sk_buff * skb)177 static void bpf_skops_established(struct sock *sk, int bpf_op,
178 				  struct sk_buff *skb)
179 {
180 	struct bpf_sock_ops_kern sock_ops;
181 
182 	sock_owned_by_me(sk);
183 
184 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
185 	sock_ops.op = bpf_op;
186 	sock_ops.is_fullsock = 1;
187 	sock_ops.sk = sk;
188 	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
189 	if (skb)
190 		bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
191 
192 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
193 }
194 #else
bpf_skops_parse_hdr(struct sock * sk,struct sk_buff * skb)195 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
196 {
197 }
198 
bpf_skops_established(struct sock * sk,int bpf_op,struct sk_buff * skb)199 static void bpf_skops_established(struct sock *sk, int bpf_op,
200 				  struct sk_buff *skb)
201 {
202 }
203 #endif
204 
tcp_gro_dev_warn(struct sock * sk,const struct sk_buff * skb,unsigned int len)205 static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
206 			     unsigned int len)
207 {
208 	static bool __once __read_mostly;
209 
210 	if (!__once) {
211 		struct net_device *dev;
212 
213 		__once = true;
214 
215 		rcu_read_lock();
216 		dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
217 		if (!dev || len >= dev->mtu)
218 			pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
219 				dev ? dev->name : "Unknown driver");
220 		rcu_read_unlock();
221 	}
222 }
223 
224 /* Adapt the MSS value used to make delayed ack decision to the
225  * real world.
226  */
tcp_measure_rcv_mss(struct sock * sk,const struct sk_buff * skb)227 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
228 {
229 	struct inet_connection_sock *icsk = inet_csk(sk);
230 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
231 	unsigned int len;
232 
233 	icsk->icsk_ack.last_seg_size = 0;
234 
235 	/* skb->len may jitter because of SACKs, even if peer
236 	 * sends good full-sized frames.
237 	 */
238 	len = skb_shinfo(skb)->gso_size ? : skb->len;
239 	if (len >= icsk->icsk_ack.rcv_mss) {
240 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
241 					       tcp_sk(sk)->advmss);
242 		/* Account for possibly-removed options */
243 		if (unlikely(len > icsk->icsk_ack.rcv_mss +
244 				   MAX_TCP_OPTION_SPACE))
245 			tcp_gro_dev_warn(sk, skb, len);
246 	} else {
247 		/* Otherwise, we make more careful check taking into account,
248 		 * that SACKs block is variable.
249 		 *
250 		 * "len" is invariant segment length, including TCP header.
251 		 */
252 		len += skb->data - skb_transport_header(skb);
253 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
254 		    /* If PSH is not set, packet should be
255 		     * full sized, provided peer TCP is not badly broken.
256 		     * This observation (if it is correct 8)) allows
257 		     * to handle super-low mtu links fairly.
258 		     */
259 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
260 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
261 			/* Subtract also invariant (if peer is RFC compliant),
262 			 * tcp header plus fixed timestamp option length.
263 			 * Resulting "len" is MSS free of SACK jitter.
264 			 */
265 			len -= tcp_sk(sk)->tcp_header_len;
266 			icsk->icsk_ack.last_seg_size = len;
267 			if (len == lss) {
268 				icsk->icsk_ack.rcv_mss = len;
269 				return;
270 			}
271 		}
272 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
273 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
274 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
275 	}
276 }
277 
tcp_incr_quickack(struct sock * sk,unsigned int max_quickacks)278 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
279 {
280 	struct inet_connection_sock *icsk = inet_csk(sk);
281 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
282 
283 	if (quickacks == 0)
284 		quickacks = 2;
285 	quickacks = min(quickacks, max_quickacks);
286 	if (quickacks > icsk->icsk_ack.quick)
287 		icsk->icsk_ack.quick = quickacks;
288 }
289 
tcp_enter_quickack_mode(struct sock * sk,unsigned int max_quickacks)290 void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
291 {
292 	struct inet_connection_sock *icsk = inet_csk(sk);
293 
294 	tcp_incr_quickack(sk, max_quickacks);
295 	inet_csk_exit_pingpong_mode(sk);
296 	icsk->icsk_ack.ato = TCP_ATO_MIN;
297 }
298 EXPORT_SYMBOL(tcp_enter_quickack_mode);
299 
300 /* Send ACKs quickly, if "quick" count is not exhausted
301  * and the session is not interactive.
302  */
303 
tcp_in_quickack_mode(struct sock * sk)304 static bool tcp_in_quickack_mode(struct sock *sk)
305 {
306 	const struct inet_connection_sock *icsk = inet_csk(sk);
307 	const struct dst_entry *dst = __sk_dst_get(sk);
308 
309 	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
310 		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
311 }
312 
tcp_ecn_queue_cwr(struct tcp_sock * tp)313 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
314 {
315 	if (tp->ecn_flags & TCP_ECN_OK)
316 		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
317 }
318 
tcp_ecn_accept_cwr(struct sock * sk,const struct sk_buff * skb)319 static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
320 {
321 	if (tcp_hdr(skb)->cwr) {
322 		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
323 
324 		/* If the sender is telling us it has entered CWR, then its
325 		 * cwnd may be very low (even just 1 packet), so we should ACK
326 		 * immediately.
327 		 */
328 		if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
329 			inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
330 	}
331 }
332 
tcp_ecn_withdraw_cwr(struct tcp_sock * tp)333 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
334 {
335 	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
336 }
337 
__tcp_ecn_check_ce(struct sock * sk,const struct sk_buff * skb)338 static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
339 {
340 	struct tcp_sock *tp = tcp_sk(sk);
341 
342 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
343 	case INET_ECN_NOT_ECT:
344 		/* Funny extension: if ECT is not set on a segment,
345 		 * and we already seen ECT on a previous segment,
346 		 * it is probably a retransmit.
347 		 */
348 		if (tp->ecn_flags & TCP_ECN_SEEN)
349 			tcp_enter_quickack_mode(sk, 2);
350 		break;
351 	case INET_ECN_CE:
352 		if (tcp_ca_needs_ecn(sk))
353 			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
354 
355 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
356 			/* Better not delay acks, sender can have a very low cwnd */
357 			tcp_enter_quickack_mode(sk, 2);
358 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
359 		}
360 		tp->ecn_flags |= TCP_ECN_SEEN;
361 		break;
362 	default:
363 		if (tcp_ca_needs_ecn(sk))
364 			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
365 		tp->ecn_flags |= TCP_ECN_SEEN;
366 		break;
367 	}
368 }
369 
tcp_ecn_check_ce(struct sock * sk,const struct sk_buff * skb)370 static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
371 {
372 	if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
373 		__tcp_ecn_check_ce(sk, skb);
374 }
375 
tcp_ecn_rcv_synack(struct tcp_sock * tp,const struct tcphdr * th)376 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
377 {
378 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
379 		tp->ecn_flags &= ~TCP_ECN_OK;
380 }
381 
tcp_ecn_rcv_syn(struct tcp_sock * tp,const struct tcphdr * th)382 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
383 {
384 	if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
385 		tp->ecn_flags &= ~TCP_ECN_OK;
386 }
387 
tcp_ecn_rcv_ecn_echo(const struct tcp_sock * tp,const struct tcphdr * th)388 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
389 {
390 	if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
391 		return true;
392 	return false;
393 }
394 
395 /* Buffer size and advertised window tuning.
396  *
397  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
398  */
399 
tcp_sndbuf_expand(struct sock * sk)400 static void tcp_sndbuf_expand(struct sock *sk)
401 {
402 	const struct tcp_sock *tp = tcp_sk(sk);
403 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
404 	int sndmem, per_mss;
405 	u32 nr_segs;
406 
407 	/* Worst case is non GSO/TSO : each frame consumes one skb
408 	 * and skb->head is kmalloced using power of two area of memory
409 	 */
410 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
411 		  MAX_TCP_HEADER +
412 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
413 
414 	per_mss = roundup_pow_of_two(per_mss) +
415 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
416 
417 	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
418 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
419 
420 	/* Fast Recovery (RFC 5681 3.2) :
421 	 * Cubic needs 1.7 factor, rounded to 2 to include
422 	 * extra cushion (application might react slowly to EPOLLOUT)
423 	 */
424 	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
425 	sndmem *= nr_segs * per_mss;
426 
427 	if (sk->sk_sndbuf < sndmem)
428 		WRITE_ONCE(sk->sk_sndbuf,
429 			   min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2])));
430 }
431 
432 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
433  *
434  * All tcp_full_space() is split to two parts: "network" buffer, allocated
435  * forward and advertised in receiver window (tp->rcv_wnd) and
436  * "application buffer", required to isolate scheduling/application
437  * latencies from network.
438  * window_clamp is maximal advertised window. It can be less than
439  * tcp_full_space(), in this case tcp_full_space() - window_clamp
440  * is reserved for "application" buffer. The less window_clamp is
441  * the smoother our behaviour from viewpoint of network, but the lower
442  * throughput and the higher sensitivity of the connection to losses. 8)
443  *
444  * rcv_ssthresh is more strict window_clamp used at "slow start"
445  * phase to predict further behaviour of this connection.
446  * It is used for two goals:
447  * - to enforce header prediction at sender, even when application
448  *   requires some significant "application buffer". It is check #1.
449  * - to prevent pruning of receive queue because of misprediction
450  *   of receiver window. Check #2.
451  *
452  * The scheme does not work when sender sends good segments opening
453  * window and then starts to feed us spaghetti. But it should work
454  * in common situations. Otherwise, we have to rely on queue collapsing.
455  */
456 
457 /* Slow part of check#2. */
__tcp_grow_window(const struct sock * sk,const struct sk_buff * skb,unsigned int skbtruesize)458 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
459 			     unsigned int skbtruesize)
460 {
461 	struct tcp_sock *tp = tcp_sk(sk);
462 	/* Optimize this! */
463 	int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
464 	int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1;
465 
466 	while (tp->rcv_ssthresh <= window) {
467 		if (truesize <= skb->len)
468 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
469 
470 		truesize >>= 1;
471 		window >>= 1;
472 	}
473 	return 0;
474 }
475 
476 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
477  * can play nice with us, as sk_buff and skb->head might be either
478  * freed or shared with up to MAX_SKB_FRAGS segments.
479  * Only give a boost to drivers using page frag(s) to hold the frame(s),
480  * and if no payload was pulled in skb->head before reaching us.
481  */
truesize_adjust(bool adjust,const struct sk_buff * skb)482 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
483 {
484 	u32 truesize = skb->truesize;
485 
486 	if (adjust && !skb_headlen(skb)) {
487 		truesize -= SKB_TRUESIZE(skb_end_offset(skb));
488 		/* paranoid check, some drivers might be buggy */
489 		if (unlikely((int)truesize < (int)skb->len))
490 			truesize = skb->truesize;
491 	}
492 	return truesize;
493 }
494 
tcp_grow_window(struct sock * sk,const struct sk_buff * skb,bool adjust)495 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
496 			    bool adjust)
497 {
498 	struct tcp_sock *tp = tcp_sk(sk);
499 	int room;
500 
501 	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
502 
503 	if (room <= 0)
504 		return;
505 
506 	/* Check #1 */
507 	if (!tcp_under_memory_pressure(sk)) {
508 		unsigned int truesize = truesize_adjust(adjust, skb);
509 		int incr;
510 
511 		/* Check #2. Increase window, if skb with such overhead
512 		 * will fit to rcvbuf in future.
513 		 */
514 		if (tcp_win_from_space(sk, truesize) <= skb->len)
515 			incr = 2 * tp->advmss;
516 		else
517 			incr = __tcp_grow_window(sk, skb, truesize);
518 
519 		if (incr) {
520 			incr = max_t(int, incr, 2 * skb->len);
521 			tp->rcv_ssthresh += min(room, incr);
522 			inet_csk(sk)->icsk_ack.quick |= 1;
523 		}
524 	} else {
525 		/* Under pressure:
526 		 * Adjust rcv_ssthresh according to reserved mem
527 		 */
528 		tcp_adjust_rcv_ssthresh(sk);
529 	}
530 }
531 
532 /* 3. Try to fixup all. It is made immediately after connection enters
533  *    established state.
534  */
tcp_init_buffer_space(struct sock * sk)535 static void tcp_init_buffer_space(struct sock *sk)
536 {
537 	int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win);
538 	struct tcp_sock *tp = tcp_sk(sk);
539 	int maxwin;
540 
541 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
542 		tcp_sndbuf_expand(sk);
543 
544 	tcp_mstamp_refresh(tp);
545 	tp->rcvq_space.time = tp->tcp_mstamp;
546 	tp->rcvq_space.seq = tp->copied_seq;
547 
548 	maxwin = tcp_full_space(sk);
549 
550 	if (tp->window_clamp >= maxwin) {
551 		tp->window_clamp = maxwin;
552 
553 		if (tcp_app_win && maxwin > 4 * tp->advmss)
554 			tp->window_clamp = max(maxwin -
555 					       (maxwin >> tcp_app_win),
556 					       4 * tp->advmss);
557 	}
558 
559 	/* Force reservation of one segment. */
560 	if (tcp_app_win &&
561 	    tp->window_clamp > 2 * tp->advmss &&
562 	    tp->window_clamp + tp->advmss > maxwin)
563 		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
564 
565 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
566 	tp->snd_cwnd_stamp = tcp_jiffies32;
567 	tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
568 				    (u32)TCP_INIT_CWND * tp->advmss);
569 }
570 
571 /* 4. Recalculate window clamp after socket hit its memory bounds. */
tcp_clamp_window(struct sock * sk)572 static void tcp_clamp_window(struct sock *sk)
573 {
574 	struct tcp_sock *tp = tcp_sk(sk);
575 	struct inet_connection_sock *icsk = inet_csk(sk);
576 	struct net *net = sock_net(sk);
577 	int rmem2;
578 
579 	icsk->icsk_ack.quick = 0;
580 	rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
581 
582 	if (sk->sk_rcvbuf < rmem2 &&
583 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
584 	    !tcp_under_memory_pressure(sk) &&
585 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
586 		WRITE_ONCE(sk->sk_rcvbuf,
587 			   min(atomic_read(&sk->sk_rmem_alloc), rmem2));
588 	}
589 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
590 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
591 }
592 
593 /* Initialize RCV_MSS value.
594  * RCV_MSS is an our guess about MSS used by the peer.
595  * We haven't any direct information about the MSS.
596  * It's better to underestimate the RCV_MSS rather than overestimate.
597  * Overestimations make us ACKing less frequently than needed.
598  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
599  */
tcp_initialize_rcv_mss(struct sock * sk)600 void tcp_initialize_rcv_mss(struct sock *sk)
601 {
602 	const struct tcp_sock *tp = tcp_sk(sk);
603 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
604 
605 	hint = min(hint, tp->rcv_wnd / 2);
606 	hint = min(hint, TCP_MSS_DEFAULT);
607 	hint = max(hint, TCP_MIN_MSS);
608 
609 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
610 }
611 EXPORT_SYMBOL(tcp_initialize_rcv_mss);
612 
613 /* Receiver "autotuning" code.
614  *
615  * The algorithm for RTT estimation w/o timestamps is based on
616  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
617  * <https://public.lanl.gov/radiant/pubs.html#DRS>
618  *
619  * More detail on this code can be found at
620  * <http://staff.psc.edu/jheffner/>,
621  * though this reference is out of date.  A new paper
622  * is pending.
623  */
tcp_rcv_rtt_update(struct tcp_sock * tp,u32 sample,int win_dep)624 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
625 {
626 	u32 new_sample = tp->rcv_rtt_est.rtt_us;
627 	long m = sample;
628 
629 	if (new_sample != 0) {
630 		/* If we sample in larger samples in the non-timestamp
631 		 * case, we could grossly overestimate the RTT especially
632 		 * with chatty applications or bulk transfer apps which
633 		 * are stalled on filesystem I/O.
634 		 *
635 		 * Also, since we are only going for a minimum in the
636 		 * non-timestamp case, we do not smooth things out
637 		 * else with timestamps disabled convergence takes too
638 		 * long.
639 		 */
640 		if (!win_dep) {
641 			m -= (new_sample >> 3);
642 			new_sample += m;
643 		} else {
644 			m <<= 3;
645 			if (m < new_sample)
646 				new_sample = m;
647 		}
648 	} else {
649 		/* No previous measure. */
650 		new_sample = m << 3;
651 	}
652 
653 	tp->rcv_rtt_est.rtt_us = new_sample;
654 }
655 
tcp_rcv_rtt_measure(struct tcp_sock * tp)656 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
657 {
658 	u32 delta_us;
659 
660 	if (tp->rcv_rtt_est.time == 0)
661 		goto new_measure;
662 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
663 		return;
664 	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
665 	if (!delta_us)
666 		delta_us = 1;
667 	tcp_rcv_rtt_update(tp, delta_us, 1);
668 
669 new_measure:
670 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
671 	tp->rcv_rtt_est.time = tp->tcp_mstamp;
672 }
673 
tcp_rcv_rtt_measure_ts(struct sock * sk,const struct sk_buff * skb)674 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
675 					  const struct sk_buff *skb)
676 {
677 	struct tcp_sock *tp = tcp_sk(sk);
678 
679 	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
680 		return;
681 	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
682 
683 	if (TCP_SKB_CB(skb)->end_seq -
684 	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
685 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
686 		u32 delta_us;
687 
688 		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
689 			if (!delta)
690 				delta = 1;
691 			delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
692 			tcp_rcv_rtt_update(tp, delta_us, 0);
693 		}
694 	}
695 }
696 
697 /*
698  * This function should be called every time data is copied to user space.
699  * It calculates the appropriate TCP receive buffer space.
700  */
tcp_rcv_space_adjust(struct sock * sk)701 void tcp_rcv_space_adjust(struct sock *sk)
702 {
703 	struct tcp_sock *tp = tcp_sk(sk);
704 	u32 copied;
705 	int time;
706 
707 	trace_tcp_rcv_space_adjust(sk);
708 
709 	tcp_mstamp_refresh(tp);
710 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
711 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
712 		return;
713 
714 	/* Number of bytes copied to user in last RTT */
715 	copied = tp->copied_seq - tp->rcvq_space.seq;
716 	if (copied <= tp->rcvq_space.space)
717 		goto new_measure;
718 
719 	/* A bit of theory :
720 	 * copied = bytes received in previous RTT, our base window
721 	 * To cope with packet losses, we need a 2x factor
722 	 * To cope with slow start, and sender growing its cwin by 100 %
723 	 * every RTT, we need a 4x factor, because the ACK we are sending
724 	 * now is for the next RTT, not the current one :
725 	 * <prev RTT . ><current RTT .. ><next RTT .... >
726 	 */
727 
728 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
729 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
730 		int rcvmem, rcvbuf;
731 		u64 rcvwin, grow;
732 
733 		/* minimal window to cope with packet losses, assuming
734 		 * steady state. Add some cushion because of small variations.
735 		 */
736 		rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
737 
738 		/* Accommodate for sender rate increase (eg. slow start) */
739 		grow = rcvwin * (copied - tp->rcvq_space.space);
740 		do_div(grow, tp->rcvq_space.space);
741 		rcvwin += (grow << 1);
742 
743 		rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
744 		while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
745 			rcvmem += 128;
746 
747 		do_div(rcvwin, tp->advmss);
748 		rcvbuf = min_t(u64, rcvwin * rcvmem,
749 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
750 		if (rcvbuf > sk->sk_rcvbuf) {
751 			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
752 
753 			/* Make the window clamp follow along.  */
754 			tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
755 		}
756 	}
757 	tp->rcvq_space.space = copied;
758 
759 new_measure:
760 	tp->rcvq_space.seq = tp->copied_seq;
761 	tp->rcvq_space.time = tp->tcp_mstamp;
762 }
763 
764 /* There is something which you must keep in mind when you analyze the
765  * behavior of the tp->ato delayed ack timeout interval.  When a
766  * connection starts up, we want to ack as quickly as possible.  The
767  * problem is that "good" TCP's do slow start at the beginning of data
768  * transmission.  The means that until we send the first few ACK's the
769  * sender will sit on his end and only queue most of his data, because
770  * he can only send snd_cwnd unacked packets at any given time.  For
771  * each ACK we send, he increments snd_cwnd and transmits more of his
772  * queue.  -DaveM
773  */
tcp_event_data_recv(struct sock * sk,struct sk_buff * skb)774 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
775 {
776 	struct tcp_sock *tp = tcp_sk(sk);
777 	struct inet_connection_sock *icsk = inet_csk(sk);
778 	u32 now;
779 
780 	inet_csk_schedule_ack(sk);
781 
782 	tcp_measure_rcv_mss(sk, skb);
783 
784 	tcp_rcv_rtt_measure(tp);
785 
786 	now = tcp_jiffies32;
787 
788 	if (!icsk->icsk_ack.ato) {
789 		/* The _first_ data packet received, initialize
790 		 * delayed ACK engine.
791 		 */
792 		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
793 		icsk->icsk_ack.ato = TCP_ATO_MIN;
794 	} else {
795 		int m = now - icsk->icsk_ack.lrcvtime;
796 
797 		if (m <= TCP_ATO_MIN / 2) {
798 			/* The fastest case is the first. */
799 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
800 		} else if (m < icsk->icsk_ack.ato) {
801 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
802 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
803 				icsk->icsk_ack.ato = icsk->icsk_rto;
804 		} else if (m > icsk->icsk_rto) {
805 			/* Too long gap. Apparently sender failed to
806 			 * restart window, so that we send ACKs quickly.
807 			 */
808 			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
809 		}
810 	}
811 	icsk->icsk_ack.lrcvtime = now;
812 
813 	tcp_ecn_check_ce(sk, skb);
814 
815 	if (skb->len >= 128)
816 		tcp_grow_window(sk, skb, true);
817 }
818 
819 /* Called to compute a smoothed rtt estimate. The data fed to this
820  * routine either comes from timestamps, or from segments that were
821  * known _not_ to have been retransmitted [see Karn/Partridge
822  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
823  * piece by Van Jacobson.
824  * NOTE: the next three routines used to be one big routine.
825  * To save cycles in the RFC 1323 implementation it was better to break
826  * it up into three procedures. -- erics
827  */
tcp_rtt_estimator(struct sock * sk,long mrtt_us)828 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
829 {
830 	struct tcp_sock *tp = tcp_sk(sk);
831 	long m = mrtt_us; /* RTT */
832 	u32 srtt = tp->srtt_us;
833 
834 	/*	The following amusing code comes from Jacobson's
835 	 *	article in SIGCOMM '88.  Note that rtt and mdev
836 	 *	are scaled versions of rtt and mean deviation.
837 	 *	This is designed to be as fast as possible
838 	 *	m stands for "measurement".
839 	 *
840 	 *	On a 1990 paper the rto value is changed to:
841 	 *	RTO = rtt + 4 * mdev
842 	 *
843 	 * Funny. This algorithm seems to be very broken.
844 	 * These formulae increase RTO, when it should be decreased, increase
845 	 * too slowly, when it should be increased quickly, decrease too quickly
846 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
847 	 * does not matter how to _calculate_ it. Seems, it was trap
848 	 * that VJ failed to avoid. 8)
849 	 */
850 	if (srtt != 0) {
851 		m -= (srtt >> 3);	/* m is now error in rtt est */
852 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
853 		if (m < 0) {
854 			m = -m;		/* m is now abs(error) */
855 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
856 			/* This is similar to one of Eifel findings.
857 			 * Eifel blocks mdev updates when rtt decreases.
858 			 * This solution is a bit different: we use finer gain
859 			 * for mdev in this case (alpha*beta).
860 			 * Like Eifel it also prevents growth of rto,
861 			 * but also it limits too fast rto decreases,
862 			 * happening in pure Eifel.
863 			 */
864 			if (m > 0)
865 				m >>= 3;
866 		} else {
867 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
868 		}
869 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
870 		if (tp->mdev_us > tp->mdev_max_us) {
871 			tp->mdev_max_us = tp->mdev_us;
872 			if (tp->mdev_max_us > tp->rttvar_us)
873 				tp->rttvar_us = tp->mdev_max_us;
874 		}
875 		if (after(tp->snd_una, tp->rtt_seq)) {
876 			if (tp->mdev_max_us < tp->rttvar_us)
877 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
878 			tp->rtt_seq = tp->snd_nxt;
879 			tp->mdev_max_us = tcp_rto_min_us(sk);
880 
881 			tcp_bpf_rtt(sk);
882 		}
883 	} else {
884 		/* no previous measure. */
885 		srtt = m << 3;		/* take the measured time to be rtt */
886 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
887 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
888 		tp->mdev_max_us = tp->rttvar_us;
889 		tp->rtt_seq = tp->snd_nxt;
890 
891 		tcp_bpf_rtt(sk);
892 	}
893 	tp->srtt_us = max(1U, srtt);
894 }
895 
tcp_update_pacing_rate(struct sock * sk)896 static void tcp_update_pacing_rate(struct sock *sk)
897 {
898 	const struct tcp_sock *tp = tcp_sk(sk);
899 	u64 rate;
900 
901 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
902 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
903 
904 	/* current rate is (cwnd * mss) / srtt
905 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
906 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
907 	 *
908 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
909 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
910 	 *	 end of slow start and should slow down.
911 	 */
912 	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
913 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio);
914 	else
915 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio);
916 
917 	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
918 
919 	if (likely(tp->srtt_us))
920 		do_div(rate, tp->srtt_us);
921 
922 	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
923 	 * without any lock. We want to make sure compiler wont store
924 	 * intermediate values in this location.
925 	 */
926 	WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
927 					     sk->sk_max_pacing_rate));
928 }
929 
930 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
931  * routine referred to above.
932  */
tcp_set_rto(struct sock * sk)933 static void tcp_set_rto(struct sock *sk)
934 {
935 	const struct tcp_sock *tp = tcp_sk(sk);
936 	/* Old crap is replaced with new one. 8)
937 	 *
938 	 * More seriously:
939 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
940 	 *    It cannot be less due to utterly erratic ACK generation made
941 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
942 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
943 	 *    is invisible. Actually, Linux-2.4 also generates erratic
944 	 *    ACKs in some circumstances.
945 	 */
946 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
947 
948 	/* 2. Fixups made earlier cannot be right.
949 	 *    If we do not estimate RTO correctly without them,
950 	 *    all the algo is pure shit and should be replaced
951 	 *    with correct one. It is exactly, which we pretend to do.
952 	 */
953 
954 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
955 	 * guarantees that rto is higher.
956 	 */
957 	tcp_bound_rto(sk);
958 }
959 
tcp_init_cwnd(const struct tcp_sock * tp,const struct dst_entry * dst)960 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
961 {
962 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
963 
964 	if (!cwnd)
965 		cwnd = TCP_INIT_CWND;
966 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
967 }
968 
969 struct tcp_sacktag_state {
970 	/* Timestamps for earliest and latest never-retransmitted segment
971 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
972 	 * but congestion control should still get an accurate delay signal.
973 	 */
974 	u64	first_sackt;
975 	u64	last_sackt;
976 	u32	reord;
977 	u32	sack_delivered;
978 	int	flag;
979 	unsigned int mss_now;
980 	struct rate_sample *rate;
981 };
982 
983 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery
984  * and spurious retransmission information if this DSACK is unlikely caused by
985  * sender's action:
986  * - DSACKed sequence range is larger than maximum receiver's window.
987  * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
988  */
tcp_dsack_seen(struct tcp_sock * tp,u32 start_seq,u32 end_seq,struct tcp_sacktag_state * state)989 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
990 			  u32 end_seq, struct tcp_sacktag_state *state)
991 {
992 	u32 seq_len, dup_segs = 1;
993 
994 	if (!before(start_seq, end_seq))
995 		return 0;
996 
997 	seq_len = end_seq - start_seq;
998 	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
999 	if (seq_len > tp->max_window)
1000 		return 0;
1001 	if (seq_len > tp->mss_cache)
1002 		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1003 	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1004 		state->flag |= FLAG_DSACK_TLP;
1005 
1006 	tp->dsack_dups += dup_segs;
1007 	/* Skip the DSACK if dup segs weren't retransmitted by sender */
1008 	if (tp->dsack_dups > tp->total_retrans)
1009 		return 0;
1010 
1011 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1012 	/* We increase the RACK ordering window in rounds where we receive
1013 	 * DSACKs that may have been due to reordering causing RACK to trigger
1014 	 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1015 	 * without having seen reordering, or that match TLP probes (TLP
1016 	 * is timer-driven, not triggered by RACK).
1017 	 */
1018 	if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1019 		tp->rack.dsack_seen = 1;
1020 
1021 	state->flag |= FLAG_DSACKING_ACK;
1022 	/* A spurious retransmission is delivered */
1023 	state->sack_delivered += dup_segs;
1024 
1025 	return dup_segs;
1026 }
1027 
1028 /* It's reordering when higher sequence was delivered (i.e. sacked) before
1029  * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1030  * distance is approximated in full-mss packet distance ("reordering").
1031  */
tcp_check_sack_reordering(struct sock * sk,const u32 low_seq,const int ts)1032 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1033 				      const int ts)
1034 {
1035 	struct tcp_sock *tp = tcp_sk(sk);
1036 	const u32 mss = tp->mss_cache;
1037 	u32 fack, metric;
1038 
1039 	fack = tcp_highest_sack_seq(tp);
1040 	if (!before(low_seq, fack))
1041 		return;
1042 
1043 	metric = fack - low_seq;
1044 	if ((metric > tp->reordering * mss) && mss) {
1045 #if FASTRETRANS_DEBUG > 1
1046 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1047 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1048 			 tp->reordering,
1049 			 0,
1050 			 tp->sacked_out,
1051 			 tp->undo_marker ? tp->undo_retrans : 0);
1052 #endif
1053 		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1054 				       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
1055 	}
1056 
1057 	/* This exciting event is worth to be remembered. 8) */
1058 	tp->reord_seen++;
1059 	NET_INC_STATS(sock_net(sk),
1060 		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1061 }
1062 
1063  /* This must be called before lost_out or retrans_out are updated
1064   * on a new loss, because we want to know if all skbs previously
1065   * known to be lost have already been retransmitted, indicating
1066   * that this newly lost skb is our next skb to retransmit.
1067   */
tcp_verify_retransmit_hint(struct tcp_sock * tp,struct sk_buff * skb)1068 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1069 {
1070 	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1071 	    (tp->retransmit_skb_hint &&
1072 	     before(TCP_SKB_CB(skb)->seq,
1073 		    TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1074 		tp->retransmit_skb_hint = skb;
1075 }
1076 
1077 /* Sum the number of packets on the wire we have marked as lost, and
1078  * notify the congestion control module that the given skb was marked lost.
1079  */
tcp_notify_skb_loss_event(struct tcp_sock * tp,const struct sk_buff * skb)1080 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1081 {
1082 	tp->lost += tcp_skb_pcount(skb);
1083 }
1084 
tcp_mark_skb_lost(struct sock * sk,struct sk_buff * skb)1085 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1086 {
1087 	__u8 sacked = TCP_SKB_CB(skb)->sacked;
1088 	struct tcp_sock *tp = tcp_sk(sk);
1089 
1090 	if (sacked & TCPCB_SACKED_ACKED)
1091 		return;
1092 
1093 	tcp_verify_retransmit_hint(tp, skb);
1094 	if (sacked & TCPCB_LOST) {
1095 		if (sacked & TCPCB_SACKED_RETRANS) {
1096 			/* Account for retransmits that are lost again */
1097 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1098 			tp->retrans_out -= tcp_skb_pcount(skb);
1099 			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1100 				      tcp_skb_pcount(skb));
1101 			tcp_notify_skb_loss_event(tp, skb);
1102 		}
1103 	} else {
1104 		tp->lost_out += tcp_skb_pcount(skb);
1105 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1106 		tcp_notify_skb_loss_event(tp, skb);
1107 	}
1108 }
1109 
1110 /* Updates the delivered and delivered_ce counts */
tcp_count_delivered(struct tcp_sock * tp,u32 delivered,bool ece_ack)1111 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
1112 				bool ece_ack)
1113 {
1114 	tp->delivered += delivered;
1115 	if (ece_ack)
1116 		tp->delivered_ce += delivered;
1117 }
1118 
1119 /* This procedure tags the retransmission queue when SACKs arrive.
1120  *
1121  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1122  * Packets in queue with these bits set are counted in variables
1123  * sacked_out, retrans_out and lost_out, correspondingly.
1124  *
1125  * Valid combinations are:
1126  * Tag  InFlight	Description
1127  * 0	1		- orig segment is in flight.
1128  * S	0		- nothing flies, orig reached receiver.
1129  * L	0		- nothing flies, orig lost by net.
1130  * R	2		- both orig and retransmit are in flight.
1131  * L|R	1		- orig is lost, retransmit is in flight.
1132  * S|R  1		- orig reached receiver, retrans is still in flight.
1133  * (L|S|R is logically valid, it could occur when L|R is sacked,
1134  *  but it is equivalent to plain S and code short-curcuits it to S.
1135  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1136  *
1137  * These 6 states form finite state machine, controlled by the following events:
1138  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1139  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1140  * 3. Loss detection event of two flavors:
1141  *	A. Scoreboard estimator decided the packet is lost.
1142  *	   A'. Reno "three dupacks" marks head of queue lost.
1143  *	B. SACK arrives sacking SND.NXT at the moment, when the
1144  *	   segment was retransmitted.
1145  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1146  *
1147  * It is pleasant to note, that state diagram turns out to be commutative,
1148  * so that we are allowed not to be bothered by order of our actions,
1149  * when multiple events arrive simultaneously. (see the function below).
1150  *
1151  * Reordering detection.
1152  * --------------------
1153  * Reordering metric is maximal distance, which a packet can be displaced
1154  * in packet stream. With SACKs we can estimate it:
1155  *
1156  * 1. SACK fills old hole and the corresponding segment was not
1157  *    ever retransmitted -> reordering. Alas, we cannot use it
1158  *    when segment was retransmitted.
1159  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1160  *    for retransmitted and already SACKed segment -> reordering..
1161  * Both of these heuristics are not used in Loss state, when we cannot
1162  * account for retransmits accurately.
1163  *
1164  * SACK block validation.
1165  * ----------------------
1166  *
1167  * SACK block range validation checks that the received SACK block fits to
1168  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1169  * Note that SND.UNA is not included to the range though being valid because
1170  * it means that the receiver is rather inconsistent with itself reporting
1171  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1172  * perfectly valid, however, in light of RFC2018 which explicitly states
1173  * that "SACK block MUST reflect the newest segment.  Even if the newest
1174  * segment is going to be discarded ...", not that it looks very clever
1175  * in case of head skb. Due to potentional receiver driven attacks, we
1176  * choose to avoid immediate execution of a walk in write queue due to
1177  * reneging and defer head skb's loss recovery to standard loss recovery
1178  * procedure that will eventually trigger (nothing forbids us doing this).
1179  *
1180  * Implements also blockage to start_seq wrap-around. Problem lies in the
1181  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1182  * there's no guarantee that it will be before snd_nxt (n). The problem
1183  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1184  * wrap (s_w):
1185  *
1186  *         <- outs wnd ->                          <- wrapzone ->
1187  *         u     e      n                         u_w   e_w  s n_w
1188  *         |     |      |                          |     |   |  |
1189  * |<------------+------+----- TCP seqno space --------------+---------->|
1190  * ...-- <2^31 ->|                                           |<--------...
1191  * ...---- >2^31 ------>|                                    |<--------...
1192  *
1193  * Current code wouldn't be vulnerable but it's better still to discard such
1194  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1195  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1196  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1197  * equal to the ideal case (infinite seqno space without wrap caused issues).
1198  *
1199  * With D-SACK the lower bound is extended to cover sequence space below
1200  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1201  * again, D-SACK block must not to go across snd_una (for the same reason as
1202  * for the normal SACK blocks, explained above). But there all simplicity
1203  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1204  * fully below undo_marker they do not affect behavior in anyway and can
1205  * therefore be safely ignored. In rare cases (which are more or less
1206  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1207  * fragmentation and packet reordering past skb's retransmission. To consider
1208  * them correctly, the acceptable range must be extended even more though
1209  * the exact amount is rather hard to quantify. However, tp->max_window can
1210  * be used as an exaggerated estimate.
1211  */
tcp_is_sackblock_valid(struct tcp_sock * tp,bool is_dsack,u32 start_seq,u32 end_seq)1212 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1213 				   u32 start_seq, u32 end_seq)
1214 {
1215 	/* Too far in future, or reversed (interpretation is ambiguous) */
1216 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1217 		return false;
1218 
1219 	/* Nasty start_seq wrap-around check (see comments above) */
1220 	if (!before(start_seq, tp->snd_nxt))
1221 		return false;
1222 
1223 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1224 	 * start_seq == snd_una is non-sensical (see comments above)
1225 	 */
1226 	if (after(start_seq, tp->snd_una))
1227 		return true;
1228 
1229 	if (!is_dsack || !tp->undo_marker)
1230 		return false;
1231 
1232 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1233 	if (after(end_seq, tp->snd_una))
1234 		return false;
1235 
1236 	if (!before(start_seq, tp->undo_marker))
1237 		return true;
1238 
1239 	/* Too old */
1240 	if (!after(end_seq, tp->undo_marker))
1241 		return false;
1242 
1243 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1244 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1245 	 */
1246 	return !before(start_seq, end_seq - tp->max_window);
1247 }
1248 
tcp_check_dsack(struct sock * sk,const struct sk_buff * ack_skb,struct tcp_sack_block_wire * sp,int num_sacks,u32 prior_snd_una,struct tcp_sacktag_state * state)1249 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1250 			    struct tcp_sack_block_wire *sp, int num_sacks,
1251 			    u32 prior_snd_una, struct tcp_sacktag_state *state)
1252 {
1253 	struct tcp_sock *tp = tcp_sk(sk);
1254 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1255 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1256 	u32 dup_segs;
1257 
1258 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1259 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1260 	} else if (num_sacks > 1) {
1261 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1262 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1263 
1264 		if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1265 			return false;
1266 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1267 	} else {
1268 		return false;
1269 	}
1270 
1271 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1272 	if (!dup_segs) {	/* Skip dubious DSACK */
1273 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1274 		return false;
1275 	}
1276 
1277 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1278 
1279 	/* D-SACK for already forgotten data... Do dumb counting. */
1280 	if (tp->undo_marker && tp->undo_retrans > 0 &&
1281 	    !after(end_seq_0, prior_snd_una) &&
1282 	    after(end_seq_0, tp->undo_marker))
1283 		tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1284 
1285 	return true;
1286 }
1287 
1288 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1289  * the incoming SACK may not exactly match but we can find smaller MSS
1290  * aligned portion of it that matches. Therefore we might need to fragment
1291  * which may fail and creates some hassle (caller must handle error case
1292  * returns).
1293  *
1294  * FIXME: this could be merged to shift decision code
1295  */
tcp_match_skb_to_sack(struct sock * sk,struct sk_buff * skb,u32 start_seq,u32 end_seq)1296 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1297 				  u32 start_seq, u32 end_seq)
1298 {
1299 	int err;
1300 	bool in_sack;
1301 	unsigned int pkt_len;
1302 	unsigned int mss;
1303 
1304 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1305 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1306 
1307 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1308 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1309 		mss = tcp_skb_mss(skb);
1310 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1311 
1312 		if (!in_sack) {
1313 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1314 			if (pkt_len < mss)
1315 				pkt_len = mss;
1316 		} else {
1317 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1318 			if (pkt_len < mss)
1319 				return -EINVAL;
1320 		}
1321 
1322 		/* Round if necessary so that SACKs cover only full MSSes
1323 		 * and/or the remaining small portion (if present)
1324 		 */
1325 		if (pkt_len > mss) {
1326 			unsigned int new_len = (pkt_len / mss) * mss;
1327 			if (!in_sack && new_len < pkt_len)
1328 				new_len += mss;
1329 			pkt_len = new_len;
1330 		}
1331 
1332 		if (pkt_len >= skb->len && !in_sack)
1333 			return 0;
1334 
1335 		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1336 				   pkt_len, mss, GFP_ATOMIC);
1337 		if (err < 0)
1338 			return err;
1339 	}
1340 
1341 	return in_sack;
1342 }
1343 
1344 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
tcp_sacktag_one(struct sock * sk,struct tcp_sacktag_state * state,u8 sacked,u32 start_seq,u32 end_seq,int dup_sack,int pcount,u64 xmit_time)1345 static u8 tcp_sacktag_one(struct sock *sk,
1346 			  struct tcp_sacktag_state *state, u8 sacked,
1347 			  u32 start_seq, u32 end_seq,
1348 			  int dup_sack, int pcount,
1349 			  u64 xmit_time)
1350 {
1351 	struct tcp_sock *tp = tcp_sk(sk);
1352 
1353 	/* Account D-SACK for retransmitted packet. */
1354 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1355 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1356 		    after(end_seq, tp->undo_marker))
1357 			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1358 		if ((sacked & TCPCB_SACKED_ACKED) &&
1359 		    before(start_seq, state->reord))
1360 				state->reord = start_seq;
1361 	}
1362 
1363 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1364 	if (!after(end_seq, tp->snd_una))
1365 		return sacked;
1366 
1367 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1368 		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1369 
1370 		if (sacked & TCPCB_SACKED_RETRANS) {
1371 			/* If the segment is not tagged as lost,
1372 			 * we do not clear RETRANS, believing
1373 			 * that retransmission is still in flight.
1374 			 */
1375 			if (sacked & TCPCB_LOST) {
1376 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1377 				tp->lost_out -= pcount;
1378 				tp->retrans_out -= pcount;
1379 			}
1380 		} else {
1381 			if (!(sacked & TCPCB_RETRANS)) {
1382 				/* New sack for not retransmitted frame,
1383 				 * which was in hole. It is reordering.
1384 				 */
1385 				if (before(start_seq,
1386 					   tcp_highest_sack_seq(tp)) &&
1387 				    before(start_seq, state->reord))
1388 					state->reord = start_seq;
1389 
1390 				if (!after(end_seq, tp->high_seq))
1391 					state->flag |= FLAG_ORIG_SACK_ACKED;
1392 				if (state->first_sackt == 0)
1393 					state->first_sackt = xmit_time;
1394 				state->last_sackt = xmit_time;
1395 			}
1396 
1397 			if (sacked & TCPCB_LOST) {
1398 				sacked &= ~TCPCB_LOST;
1399 				tp->lost_out -= pcount;
1400 			}
1401 		}
1402 
1403 		sacked |= TCPCB_SACKED_ACKED;
1404 		state->flag |= FLAG_DATA_SACKED;
1405 		tp->sacked_out += pcount;
1406 		/* Out-of-order packets delivered */
1407 		state->sack_delivered += pcount;
1408 
1409 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1410 		if (tp->lost_skb_hint &&
1411 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1412 			tp->lost_cnt_hint += pcount;
1413 	}
1414 
1415 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1416 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1417 	 * are accounted above as well.
1418 	 */
1419 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1420 		sacked &= ~TCPCB_SACKED_RETRANS;
1421 		tp->retrans_out -= pcount;
1422 	}
1423 
1424 	return sacked;
1425 }
1426 
1427 /* Shift newly-SACKed bytes from this skb to the immediately previous
1428  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1429  */
tcp_shifted_skb(struct sock * sk,struct sk_buff * prev,struct sk_buff * skb,struct tcp_sacktag_state * state,unsigned int pcount,int shifted,int mss,bool dup_sack)1430 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1431 			    struct sk_buff *skb,
1432 			    struct tcp_sacktag_state *state,
1433 			    unsigned int pcount, int shifted, int mss,
1434 			    bool dup_sack)
1435 {
1436 	struct tcp_sock *tp = tcp_sk(sk);
1437 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1438 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1439 
1440 	BUG_ON(!pcount);
1441 
1442 	/* Adjust counters and hints for the newly sacked sequence
1443 	 * range but discard the return value since prev is already
1444 	 * marked. We must tag the range first because the seq
1445 	 * advancement below implicitly advances
1446 	 * tcp_highest_sack_seq() when skb is highest_sack.
1447 	 */
1448 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1449 			start_seq, end_seq, dup_sack, pcount,
1450 			tcp_skb_timestamp_us(skb));
1451 	tcp_rate_skb_delivered(sk, skb, state->rate);
1452 
1453 	if (skb == tp->lost_skb_hint)
1454 		tp->lost_cnt_hint += pcount;
1455 
1456 	TCP_SKB_CB(prev)->end_seq += shifted;
1457 	TCP_SKB_CB(skb)->seq += shifted;
1458 
1459 	tcp_skb_pcount_add(prev, pcount);
1460 	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1461 	tcp_skb_pcount_add(skb, -pcount);
1462 
1463 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1464 	 * in theory this shouldn't be necessary but as long as DSACK
1465 	 * code can come after this skb later on it's better to keep
1466 	 * setting gso_size to something.
1467 	 */
1468 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1469 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1470 
1471 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1472 	if (tcp_skb_pcount(skb) <= 1)
1473 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1474 
1475 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1476 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1477 
1478 	if (skb->len > 0) {
1479 		BUG_ON(!tcp_skb_pcount(skb));
1480 		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1481 		return false;
1482 	}
1483 
1484 	/* Whole SKB was eaten :-) */
1485 
1486 	if (skb == tp->retransmit_skb_hint)
1487 		tp->retransmit_skb_hint = prev;
1488 	if (skb == tp->lost_skb_hint) {
1489 		tp->lost_skb_hint = prev;
1490 		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1491 	}
1492 
1493 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1494 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1495 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1496 		TCP_SKB_CB(prev)->end_seq++;
1497 
1498 	if (skb == tcp_highest_sack(sk))
1499 		tcp_advance_highest_sack(sk, skb);
1500 
1501 	tcp_skb_collapse_tstamp(prev, skb);
1502 	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1503 		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1504 
1505 	tcp_rtx_queue_unlink_and_free(skb, sk);
1506 
1507 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1508 
1509 	return true;
1510 }
1511 
1512 /* I wish gso_size would have a bit more sane initialization than
1513  * something-or-zero which complicates things
1514  */
tcp_skb_seglen(const struct sk_buff * skb)1515 static int tcp_skb_seglen(const struct sk_buff *skb)
1516 {
1517 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1518 }
1519 
1520 /* Shifting pages past head area doesn't work */
skb_can_shift(const struct sk_buff * skb)1521 static int skb_can_shift(const struct sk_buff *skb)
1522 {
1523 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1524 }
1525 
tcp_skb_shift(struct sk_buff * to,struct sk_buff * from,int pcount,int shiftlen)1526 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1527 		  int pcount, int shiftlen)
1528 {
1529 	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1530 	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1531 	 * to make sure not storing more than 65535 * 8 bytes per skb,
1532 	 * even if current MSS is bigger.
1533 	 */
1534 	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1535 		return 0;
1536 	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1537 		return 0;
1538 	return skb_shift(to, from, shiftlen);
1539 }
1540 
1541 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1542  * skb.
1543  */
tcp_shift_skb_data(struct sock * sk,struct sk_buff * skb,struct tcp_sacktag_state * state,u32 start_seq,u32 end_seq,bool dup_sack)1544 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1545 					  struct tcp_sacktag_state *state,
1546 					  u32 start_seq, u32 end_seq,
1547 					  bool dup_sack)
1548 {
1549 	struct tcp_sock *tp = tcp_sk(sk);
1550 	struct sk_buff *prev;
1551 	int mss;
1552 	int pcount = 0;
1553 	int len;
1554 	int in_sack;
1555 
1556 	/* Normally R but no L won't result in plain S */
1557 	if (!dup_sack &&
1558 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1559 		goto fallback;
1560 	if (!skb_can_shift(skb))
1561 		goto fallback;
1562 	/* This frame is about to be dropped (was ACKed). */
1563 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1564 		goto fallback;
1565 
1566 	/* Can only happen with delayed DSACK + discard craziness */
1567 	prev = skb_rb_prev(skb);
1568 	if (!prev)
1569 		goto fallback;
1570 
1571 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1572 		goto fallback;
1573 
1574 	if (!tcp_skb_can_collapse(prev, skb))
1575 		goto fallback;
1576 
1577 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1578 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1579 
1580 	if (in_sack) {
1581 		len = skb->len;
1582 		pcount = tcp_skb_pcount(skb);
1583 		mss = tcp_skb_seglen(skb);
1584 
1585 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1586 		 * drop this restriction as unnecessary
1587 		 */
1588 		if (mss != tcp_skb_seglen(prev))
1589 			goto fallback;
1590 	} else {
1591 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1592 			goto noop;
1593 		/* CHECKME: This is non-MSS split case only?, this will
1594 		 * cause skipped skbs due to advancing loop btw, original
1595 		 * has that feature too
1596 		 */
1597 		if (tcp_skb_pcount(skb) <= 1)
1598 			goto noop;
1599 
1600 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1601 		if (!in_sack) {
1602 			/* TODO: head merge to next could be attempted here
1603 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1604 			 * though it might not be worth of the additional hassle
1605 			 *
1606 			 * ...we can probably just fallback to what was done
1607 			 * previously. We could try merging non-SACKed ones
1608 			 * as well but it probably isn't going to buy off
1609 			 * because later SACKs might again split them, and
1610 			 * it would make skb timestamp tracking considerably
1611 			 * harder problem.
1612 			 */
1613 			goto fallback;
1614 		}
1615 
1616 		len = end_seq - TCP_SKB_CB(skb)->seq;
1617 		BUG_ON(len < 0);
1618 		BUG_ON(len > skb->len);
1619 
1620 		/* MSS boundaries should be honoured or else pcount will
1621 		 * severely break even though it makes things bit trickier.
1622 		 * Optimize common case to avoid most of the divides
1623 		 */
1624 		mss = tcp_skb_mss(skb);
1625 
1626 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1627 		 * drop this restriction as unnecessary
1628 		 */
1629 		if (mss != tcp_skb_seglen(prev))
1630 			goto fallback;
1631 
1632 		if (len == mss) {
1633 			pcount = 1;
1634 		} else if (len < mss) {
1635 			goto noop;
1636 		} else {
1637 			pcount = len / mss;
1638 			len = pcount * mss;
1639 		}
1640 	}
1641 
1642 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1643 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1644 		goto fallback;
1645 
1646 	if (!tcp_skb_shift(prev, skb, pcount, len))
1647 		goto fallback;
1648 	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1649 		goto out;
1650 
1651 	/* Hole filled allows collapsing with the next as well, this is very
1652 	 * useful when hole on every nth skb pattern happens
1653 	 */
1654 	skb = skb_rb_next(prev);
1655 	if (!skb)
1656 		goto out;
1657 
1658 	if (!skb_can_shift(skb) ||
1659 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1660 	    (mss != tcp_skb_seglen(skb)))
1661 		goto out;
1662 
1663 	if (!tcp_skb_can_collapse(prev, skb))
1664 		goto out;
1665 	len = skb->len;
1666 	pcount = tcp_skb_pcount(skb);
1667 	if (tcp_skb_shift(prev, skb, pcount, len))
1668 		tcp_shifted_skb(sk, prev, skb, state, pcount,
1669 				len, mss, 0);
1670 
1671 out:
1672 	return prev;
1673 
1674 noop:
1675 	return skb;
1676 
1677 fallback:
1678 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1679 	return NULL;
1680 }
1681 
tcp_sacktag_walk(struct sk_buff * skb,struct sock * sk,struct tcp_sack_block * next_dup,struct tcp_sacktag_state * state,u32 start_seq,u32 end_seq,bool dup_sack_in)1682 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1683 					struct tcp_sack_block *next_dup,
1684 					struct tcp_sacktag_state *state,
1685 					u32 start_seq, u32 end_seq,
1686 					bool dup_sack_in)
1687 {
1688 	struct tcp_sock *tp = tcp_sk(sk);
1689 	struct sk_buff *tmp;
1690 
1691 	skb_rbtree_walk_from(skb) {
1692 		int in_sack = 0;
1693 		bool dup_sack = dup_sack_in;
1694 
1695 		/* queue is in-order => we can short-circuit the walk early */
1696 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1697 			break;
1698 
1699 		if (next_dup  &&
1700 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1701 			in_sack = tcp_match_skb_to_sack(sk, skb,
1702 							next_dup->start_seq,
1703 							next_dup->end_seq);
1704 			if (in_sack > 0)
1705 				dup_sack = true;
1706 		}
1707 
1708 		/* skb reference here is a bit tricky to get right, since
1709 		 * shifting can eat and free both this skb and the next,
1710 		 * so not even _safe variant of the loop is enough.
1711 		 */
1712 		if (in_sack <= 0) {
1713 			tmp = tcp_shift_skb_data(sk, skb, state,
1714 						 start_seq, end_seq, dup_sack);
1715 			if (tmp) {
1716 				if (tmp != skb) {
1717 					skb = tmp;
1718 					continue;
1719 				}
1720 
1721 				in_sack = 0;
1722 			} else {
1723 				in_sack = tcp_match_skb_to_sack(sk, skb,
1724 								start_seq,
1725 								end_seq);
1726 			}
1727 		}
1728 
1729 		if (unlikely(in_sack < 0))
1730 			break;
1731 
1732 		if (in_sack) {
1733 			TCP_SKB_CB(skb)->sacked =
1734 				tcp_sacktag_one(sk,
1735 						state,
1736 						TCP_SKB_CB(skb)->sacked,
1737 						TCP_SKB_CB(skb)->seq,
1738 						TCP_SKB_CB(skb)->end_seq,
1739 						dup_sack,
1740 						tcp_skb_pcount(skb),
1741 						tcp_skb_timestamp_us(skb));
1742 			tcp_rate_skb_delivered(sk, skb, state->rate);
1743 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1744 				list_del_init(&skb->tcp_tsorted_anchor);
1745 
1746 			if (!before(TCP_SKB_CB(skb)->seq,
1747 				    tcp_highest_sack_seq(tp)))
1748 				tcp_advance_highest_sack(sk, skb);
1749 		}
1750 	}
1751 	return skb;
1752 }
1753 
tcp_sacktag_bsearch(struct sock * sk,u32 seq)1754 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1755 {
1756 	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1757 	struct sk_buff *skb;
1758 
1759 	while (*p) {
1760 		parent = *p;
1761 		skb = rb_to_skb(parent);
1762 		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1763 			p = &parent->rb_left;
1764 			continue;
1765 		}
1766 		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1767 			p = &parent->rb_right;
1768 			continue;
1769 		}
1770 		return skb;
1771 	}
1772 	return NULL;
1773 }
1774 
tcp_sacktag_skip(struct sk_buff * skb,struct sock * sk,u32 skip_to_seq)1775 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1776 					u32 skip_to_seq)
1777 {
1778 	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1779 		return skb;
1780 
1781 	return tcp_sacktag_bsearch(sk, skip_to_seq);
1782 }
1783 
tcp_maybe_skipping_dsack(struct sk_buff * skb,struct sock * sk,struct tcp_sack_block * next_dup,struct tcp_sacktag_state * state,u32 skip_to_seq)1784 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1785 						struct sock *sk,
1786 						struct tcp_sack_block *next_dup,
1787 						struct tcp_sacktag_state *state,
1788 						u32 skip_to_seq)
1789 {
1790 	if (!next_dup)
1791 		return skb;
1792 
1793 	if (before(next_dup->start_seq, skip_to_seq)) {
1794 		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1795 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1796 				       next_dup->start_seq, next_dup->end_seq,
1797 				       1);
1798 	}
1799 
1800 	return skb;
1801 }
1802 
tcp_sack_cache_ok(const struct tcp_sock * tp,const struct tcp_sack_block * cache)1803 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1804 {
1805 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1806 }
1807 
1808 static int
tcp_sacktag_write_queue(struct sock * sk,const struct sk_buff * ack_skb,u32 prior_snd_una,struct tcp_sacktag_state * state)1809 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1810 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1811 {
1812 	struct tcp_sock *tp = tcp_sk(sk);
1813 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1814 				    TCP_SKB_CB(ack_skb)->sacked);
1815 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1816 	struct tcp_sack_block sp[TCP_NUM_SACKS];
1817 	struct tcp_sack_block *cache;
1818 	struct sk_buff *skb;
1819 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1820 	int used_sacks;
1821 	bool found_dup_sack = false;
1822 	int i, j;
1823 	int first_sack_index;
1824 
1825 	state->flag = 0;
1826 	state->reord = tp->snd_nxt;
1827 
1828 	if (!tp->sacked_out)
1829 		tcp_highest_sack_reset(sk);
1830 
1831 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1832 					 num_sacks, prior_snd_una, state);
1833 
1834 	/* Eliminate too old ACKs, but take into
1835 	 * account more or less fresh ones, they can
1836 	 * contain valid SACK info.
1837 	 */
1838 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1839 		return 0;
1840 
1841 	if (!tp->packets_out)
1842 		goto out;
1843 
1844 	used_sacks = 0;
1845 	first_sack_index = 0;
1846 	for (i = 0; i < num_sacks; i++) {
1847 		bool dup_sack = !i && found_dup_sack;
1848 
1849 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1850 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1851 
1852 		if (!tcp_is_sackblock_valid(tp, dup_sack,
1853 					    sp[used_sacks].start_seq,
1854 					    sp[used_sacks].end_seq)) {
1855 			int mib_idx;
1856 
1857 			if (dup_sack) {
1858 				if (!tp->undo_marker)
1859 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1860 				else
1861 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1862 			} else {
1863 				/* Don't count olds caused by ACK reordering */
1864 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1865 				    !after(sp[used_sacks].end_seq, tp->snd_una))
1866 					continue;
1867 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1868 			}
1869 
1870 			NET_INC_STATS(sock_net(sk), mib_idx);
1871 			if (i == 0)
1872 				first_sack_index = -1;
1873 			continue;
1874 		}
1875 
1876 		/* Ignore very old stuff early */
1877 		if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
1878 			if (i == 0)
1879 				first_sack_index = -1;
1880 			continue;
1881 		}
1882 
1883 		used_sacks++;
1884 	}
1885 
1886 	/* order SACK blocks to allow in order walk of the retrans queue */
1887 	for (i = used_sacks - 1; i > 0; i--) {
1888 		for (j = 0; j < i; j++) {
1889 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1890 				swap(sp[j], sp[j + 1]);
1891 
1892 				/* Track where the first SACK block goes to */
1893 				if (j == first_sack_index)
1894 					first_sack_index = j + 1;
1895 			}
1896 		}
1897 	}
1898 
1899 	state->mss_now = tcp_current_mss(sk);
1900 	skb = NULL;
1901 	i = 0;
1902 
1903 	if (!tp->sacked_out) {
1904 		/* It's already past, so skip checking against it */
1905 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1906 	} else {
1907 		cache = tp->recv_sack_cache;
1908 		/* Skip empty blocks in at head of the cache */
1909 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1910 		       !cache->end_seq)
1911 			cache++;
1912 	}
1913 
1914 	while (i < used_sacks) {
1915 		u32 start_seq = sp[i].start_seq;
1916 		u32 end_seq = sp[i].end_seq;
1917 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1918 		struct tcp_sack_block *next_dup = NULL;
1919 
1920 		if (found_dup_sack && ((i + 1) == first_sack_index))
1921 			next_dup = &sp[i + 1];
1922 
1923 		/* Skip too early cached blocks */
1924 		while (tcp_sack_cache_ok(tp, cache) &&
1925 		       !before(start_seq, cache->end_seq))
1926 			cache++;
1927 
1928 		/* Can skip some work by looking recv_sack_cache? */
1929 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1930 		    after(end_seq, cache->start_seq)) {
1931 
1932 			/* Head todo? */
1933 			if (before(start_seq, cache->start_seq)) {
1934 				skb = tcp_sacktag_skip(skb, sk, start_seq);
1935 				skb = tcp_sacktag_walk(skb, sk, next_dup,
1936 						       state,
1937 						       start_seq,
1938 						       cache->start_seq,
1939 						       dup_sack);
1940 			}
1941 
1942 			/* Rest of the block already fully processed? */
1943 			if (!after(end_seq, cache->end_seq))
1944 				goto advance_sp;
1945 
1946 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1947 						       state,
1948 						       cache->end_seq);
1949 
1950 			/* ...tail remains todo... */
1951 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1952 				/* ...but better entrypoint exists! */
1953 				skb = tcp_highest_sack(sk);
1954 				if (!skb)
1955 					break;
1956 				cache++;
1957 				goto walk;
1958 			}
1959 
1960 			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1961 			/* Check overlap against next cached too (past this one already) */
1962 			cache++;
1963 			continue;
1964 		}
1965 
1966 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1967 			skb = tcp_highest_sack(sk);
1968 			if (!skb)
1969 				break;
1970 		}
1971 		skb = tcp_sacktag_skip(skb, sk, start_seq);
1972 
1973 walk:
1974 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
1975 				       start_seq, end_seq, dup_sack);
1976 
1977 advance_sp:
1978 		i++;
1979 	}
1980 
1981 	/* Clear the head of the cache sack blocks so we can skip it next time */
1982 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1983 		tp->recv_sack_cache[i].start_seq = 0;
1984 		tp->recv_sack_cache[i].end_seq = 0;
1985 	}
1986 	for (j = 0; j < used_sacks; j++)
1987 		tp->recv_sack_cache[i++] = sp[j];
1988 
1989 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
1990 		tcp_check_sack_reordering(sk, state->reord, 0);
1991 
1992 	tcp_verify_left_out(tp);
1993 out:
1994 
1995 #if FASTRETRANS_DEBUG > 0
1996 	WARN_ON((int)tp->sacked_out < 0);
1997 	WARN_ON((int)tp->lost_out < 0);
1998 	WARN_ON((int)tp->retrans_out < 0);
1999 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2000 #endif
2001 	return state->flag;
2002 }
2003 
2004 /* Limits sacked_out so that sum with lost_out isn't ever larger than
2005  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2006  */
tcp_limit_reno_sacked(struct tcp_sock * tp)2007 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2008 {
2009 	u32 holes;
2010 
2011 	holes = max(tp->lost_out, 1U);
2012 	holes = min(holes, tp->packets_out);
2013 
2014 	if ((tp->sacked_out + holes) > tp->packets_out) {
2015 		tp->sacked_out = tp->packets_out - holes;
2016 		return true;
2017 	}
2018 	return false;
2019 }
2020 
2021 /* If we receive more dupacks than we expected counting segments
2022  * in assumption of absent reordering, interpret this as reordering.
2023  * The only another reason could be bug in receiver TCP.
2024  */
tcp_check_reno_reordering(struct sock * sk,const int addend)2025 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2026 {
2027 	struct tcp_sock *tp = tcp_sk(sk);
2028 
2029 	if (!tcp_limit_reno_sacked(tp))
2030 		return;
2031 
2032 	tp->reordering = min_t(u32, tp->packets_out + addend,
2033 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
2034 	tp->reord_seen++;
2035 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2036 }
2037 
2038 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2039 
tcp_add_reno_sack(struct sock * sk,int num_dupack,bool ece_ack)2040 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2041 {
2042 	if (num_dupack) {
2043 		struct tcp_sock *tp = tcp_sk(sk);
2044 		u32 prior_sacked = tp->sacked_out;
2045 		s32 delivered;
2046 
2047 		tp->sacked_out += num_dupack;
2048 		tcp_check_reno_reordering(sk, 0);
2049 		delivered = tp->sacked_out - prior_sacked;
2050 		if (delivered > 0)
2051 			tcp_count_delivered(tp, delivered, ece_ack);
2052 		tcp_verify_left_out(tp);
2053 	}
2054 }
2055 
2056 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2057 
tcp_remove_reno_sacks(struct sock * sk,int acked,bool ece_ack)2058 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2059 {
2060 	struct tcp_sock *tp = tcp_sk(sk);
2061 
2062 	if (acked > 0) {
2063 		/* One ACK acked hole. The rest eat duplicate ACKs. */
2064 		tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2065 				    ece_ack);
2066 		if (acked - 1 >= tp->sacked_out)
2067 			tp->sacked_out = 0;
2068 		else
2069 			tp->sacked_out -= acked - 1;
2070 	}
2071 	tcp_check_reno_reordering(sk, acked);
2072 	tcp_verify_left_out(tp);
2073 }
2074 
tcp_reset_reno_sack(struct tcp_sock * tp)2075 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2076 {
2077 	tp->sacked_out = 0;
2078 }
2079 
tcp_clear_retrans(struct tcp_sock * tp)2080 void tcp_clear_retrans(struct tcp_sock *tp)
2081 {
2082 	tp->retrans_out = 0;
2083 	tp->lost_out = 0;
2084 	tp->undo_marker = 0;
2085 	tp->undo_retrans = -1;
2086 	tp->sacked_out = 0;
2087 }
2088 
tcp_init_undo(struct tcp_sock * tp)2089 static inline void tcp_init_undo(struct tcp_sock *tp)
2090 {
2091 	tp->undo_marker = tp->snd_una;
2092 	/* Retransmission still in flight may cause DSACKs later. */
2093 	tp->undo_retrans = tp->retrans_out ? : -1;
2094 }
2095 
tcp_is_rack(const struct sock * sk)2096 static bool tcp_is_rack(const struct sock *sk)
2097 {
2098 	return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
2099 		TCP_RACK_LOSS_DETECTION;
2100 }
2101 
2102 /* If we detect SACK reneging, forget all SACK information
2103  * and reset tags completely, otherwise preserve SACKs. If receiver
2104  * dropped its ofo queue, we will know this due to reneging detection.
2105  */
tcp_timeout_mark_lost(struct sock * sk)2106 static void tcp_timeout_mark_lost(struct sock *sk)
2107 {
2108 	struct tcp_sock *tp = tcp_sk(sk);
2109 	struct sk_buff *skb, *head;
2110 	bool is_reneg;			/* is receiver reneging on SACKs? */
2111 
2112 	head = tcp_rtx_queue_head(sk);
2113 	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2114 	if (is_reneg) {
2115 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2116 		tp->sacked_out = 0;
2117 		/* Mark SACK reneging until we recover from this loss event. */
2118 		tp->is_sack_reneg = 1;
2119 	} else if (tcp_is_reno(tp)) {
2120 		tcp_reset_reno_sack(tp);
2121 	}
2122 
2123 	skb = head;
2124 	skb_rbtree_walk_from(skb) {
2125 		if (is_reneg)
2126 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2127 		else if (tcp_is_rack(sk) && skb != head &&
2128 			 tcp_rack_skb_timeout(tp, skb, 0) > 0)
2129 			continue; /* Don't mark recently sent ones lost yet */
2130 		tcp_mark_skb_lost(sk, skb);
2131 	}
2132 	tcp_verify_left_out(tp);
2133 	tcp_clear_all_retrans_hints(tp);
2134 }
2135 
2136 /* Enter Loss state. */
tcp_enter_loss(struct sock * sk)2137 void tcp_enter_loss(struct sock *sk)
2138 {
2139 	const struct inet_connection_sock *icsk = inet_csk(sk);
2140 	struct tcp_sock *tp = tcp_sk(sk);
2141 	struct net *net = sock_net(sk);
2142 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2143 	u8 reordering;
2144 
2145 	tcp_timeout_mark_lost(sk);
2146 
2147 	/* Reduce ssthresh if it has not yet been made inside this window. */
2148 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2149 	    !after(tp->high_seq, tp->snd_una) ||
2150 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2151 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2152 		tp->prior_cwnd = tcp_snd_cwnd(tp);
2153 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2154 		tcp_ca_event(sk, CA_EVENT_LOSS);
2155 		tcp_init_undo(tp);
2156 	}
2157 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2158 	tp->snd_cwnd_cnt   = 0;
2159 	tp->snd_cwnd_stamp = tcp_jiffies32;
2160 
2161 	/* Timeout in disordered state after receiving substantial DUPACKs
2162 	 * suggests that the degree of reordering is over-estimated.
2163 	 */
2164 	reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2165 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2166 	    tp->sacked_out >= reordering)
2167 		tp->reordering = min_t(unsigned int, tp->reordering,
2168 				       reordering);
2169 
2170 	tcp_set_ca_state(sk, TCP_CA_Loss);
2171 	tp->high_seq = tp->snd_nxt;
2172 	tcp_ecn_queue_cwr(tp);
2173 
2174 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2175 	 * loss recovery is underway except recurring timeout(s) on
2176 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2177 	 */
2178 	tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
2179 		   (new_recovery || icsk->icsk_retransmits) &&
2180 		   !inet_csk(sk)->icsk_mtup.probe_size;
2181 }
2182 
2183 /* If ACK arrived pointing to a remembered SACK, it means that our
2184  * remembered SACKs do not reflect real state of receiver i.e.
2185  * receiver _host_ is heavily congested (or buggy).
2186  *
2187  * To avoid big spurious retransmission bursts due to transient SACK
2188  * scoreboard oddities that look like reneging, we give the receiver a
2189  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2190  * restore sanity to the SACK scoreboard. If the apparent reneging
2191  * persists until this RTO then we'll clear the SACK scoreboard.
2192  */
tcp_check_sack_reneging(struct sock * sk,int flag)2193 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
2194 {
2195 	if (flag & FLAG_SACK_RENEGING &&
2196 	    flag & FLAG_SND_UNA_ADVANCED) {
2197 		struct tcp_sock *tp = tcp_sk(sk);
2198 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2199 					  msecs_to_jiffies(10));
2200 
2201 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2202 					  delay, TCP_RTO_MAX);
2203 		return true;
2204 	}
2205 	return false;
2206 }
2207 
2208 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2209  * counter when SACK is enabled (without SACK, sacked_out is used for
2210  * that purpose).
2211  *
2212  * With reordering, holes may still be in flight, so RFC3517 recovery
2213  * uses pure sacked_out (total number of SACKed segments) even though
2214  * it violates the RFC that uses duplicate ACKs, often these are equal
2215  * but when e.g. out-of-window ACKs or packet duplication occurs,
2216  * they differ. Since neither occurs due to loss, TCP should really
2217  * ignore them.
2218  */
tcp_dupack_heuristics(const struct tcp_sock * tp)2219 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2220 {
2221 	return tp->sacked_out + 1;
2222 }
2223 
2224 /* Linux NewReno/SACK/ECN state machine.
2225  * --------------------------------------
2226  *
2227  * "Open"	Normal state, no dubious events, fast path.
2228  * "Disorder"   In all the respects it is "Open",
2229  *		but requires a bit more attention. It is entered when
2230  *		we see some SACKs or dupacks. It is split of "Open"
2231  *		mainly to move some processing from fast path to slow one.
2232  * "CWR"	CWND was reduced due to some Congestion Notification event.
2233  *		It can be ECN, ICMP source quench, local device congestion.
2234  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2235  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2236  *
2237  * tcp_fastretrans_alert() is entered:
2238  * - each incoming ACK, if state is not "Open"
2239  * - when arrived ACK is unusual, namely:
2240  *	* SACK
2241  *	* Duplicate ACK.
2242  *	* ECN ECE.
2243  *
2244  * Counting packets in flight is pretty simple.
2245  *
2246  *	in_flight = packets_out - left_out + retrans_out
2247  *
2248  *	packets_out is SND.NXT-SND.UNA counted in packets.
2249  *
2250  *	retrans_out is number of retransmitted segments.
2251  *
2252  *	left_out is number of segments left network, but not ACKed yet.
2253  *
2254  *		left_out = sacked_out + lost_out
2255  *
2256  *     sacked_out: Packets, which arrived to receiver out of order
2257  *		   and hence not ACKed. With SACKs this number is simply
2258  *		   amount of SACKed data. Even without SACKs
2259  *		   it is easy to give pretty reliable estimate of this number,
2260  *		   counting duplicate ACKs.
2261  *
2262  *       lost_out: Packets lost by network. TCP has no explicit
2263  *		   "loss notification" feedback from network (for now).
2264  *		   It means that this number can be only _guessed_.
2265  *		   Actually, it is the heuristics to predict lossage that
2266  *		   distinguishes different algorithms.
2267  *
2268  *	F.e. after RTO, when all the queue is considered as lost,
2269  *	lost_out = packets_out and in_flight = retrans_out.
2270  *
2271  *		Essentially, we have now a few algorithms detecting
2272  *		lost packets.
2273  *
2274  *		If the receiver supports SACK:
2275  *
2276  *		RFC6675/3517: It is the conventional algorithm. A packet is
2277  *		considered lost if the number of higher sequence packets
2278  *		SACKed is greater than or equal the DUPACK thoreshold
2279  *		(reordering). This is implemented in tcp_mark_head_lost and
2280  *		tcp_update_scoreboard.
2281  *
2282  *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2283  *		(2017-) that checks timing instead of counting DUPACKs.
2284  *		Essentially a packet is considered lost if it's not S/ACKed
2285  *		after RTT + reordering_window, where both metrics are
2286  *		dynamically measured and adjusted. This is implemented in
2287  *		tcp_rack_mark_lost.
2288  *
2289  *		If the receiver does not support SACK:
2290  *
2291  *		NewReno (RFC6582): in Recovery we assume that one segment
2292  *		is lost (classic Reno). While we are in Recovery and
2293  *		a partial ACK arrives, we assume that one more packet
2294  *		is lost (NewReno). This heuristics are the same in NewReno
2295  *		and SACK.
2296  *
2297  * Really tricky (and requiring careful tuning) part of algorithm
2298  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2299  * The first determines the moment _when_ we should reduce CWND and,
2300  * hence, slow down forward transmission. In fact, it determines the moment
2301  * when we decide that hole is caused by loss, rather than by a reorder.
2302  *
2303  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2304  * holes, caused by lost packets.
2305  *
2306  * And the most logically complicated part of algorithm is undo
2307  * heuristics. We detect false retransmits due to both too early
2308  * fast retransmit (reordering) and underestimated RTO, analyzing
2309  * timestamps and D-SACKs. When we detect that some segments were
2310  * retransmitted by mistake and CWND reduction was wrong, we undo
2311  * window reduction and abort recovery phase. This logic is hidden
2312  * inside several functions named tcp_try_undo_<something>.
2313  */
2314 
2315 /* This function decides, when we should leave Disordered state
2316  * and enter Recovery phase, reducing congestion window.
2317  *
2318  * Main question: may we further continue forward transmission
2319  * with the same cwnd?
2320  */
tcp_time_to_recover(struct sock * sk,int flag)2321 static bool tcp_time_to_recover(struct sock *sk, int flag)
2322 {
2323 	struct tcp_sock *tp = tcp_sk(sk);
2324 
2325 	/* Trick#1: The loss is proven. */
2326 	if (tp->lost_out)
2327 		return true;
2328 
2329 	/* Not-A-Trick#2 : Classic rule... */
2330 	if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2331 		return true;
2332 
2333 	return false;
2334 }
2335 
2336 /* Detect loss in event "A" above by marking head of queue up as lost.
2337  * For RFC3517 SACK, a segment is considered lost if it
2338  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2339  * the maximum SACKed segments to pass before reaching this limit.
2340  */
tcp_mark_head_lost(struct sock * sk,int packets,int mark_head)2341 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2342 {
2343 	struct tcp_sock *tp = tcp_sk(sk);
2344 	struct sk_buff *skb;
2345 	int cnt;
2346 	/* Use SACK to deduce losses of new sequences sent during recovery */
2347 	const u32 loss_high = tp->snd_nxt;
2348 
2349 	WARN_ON(packets > tp->packets_out);
2350 	skb = tp->lost_skb_hint;
2351 	if (skb) {
2352 		/* Head already handled? */
2353 		if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2354 			return;
2355 		cnt = tp->lost_cnt_hint;
2356 	} else {
2357 		skb = tcp_rtx_queue_head(sk);
2358 		cnt = 0;
2359 	}
2360 
2361 	skb_rbtree_walk_from(skb) {
2362 		/* TODO: do this better */
2363 		/* this is not the most efficient way to do this... */
2364 		tp->lost_skb_hint = skb;
2365 		tp->lost_cnt_hint = cnt;
2366 
2367 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2368 			break;
2369 
2370 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2371 			cnt += tcp_skb_pcount(skb);
2372 
2373 		if (cnt > packets)
2374 			break;
2375 
2376 		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST))
2377 			tcp_mark_skb_lost(sk, skb);
2378 
2379 		if (mark_head)
2380 			break;
2381 	}
2382 	tcp_verify_left_out(tp);
2383 }
2384 
2385 /* Account newly detected lost packet(s) */
2386 
tcp_update_scoreboard(struct sock * sk,int fast_rexmit)2387 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2388 {
2389 	struct tcp_sock *tp = tcp_sk(sk);
2390 
2391 	if (tcp_is_sack(tp)) {
2392 		int sacked_upto = tp->sacked_out - tp->reordering;
2393 		if (sacked_upto >= 0)
2394 			tcp_mark_head_lost(sk, sacked_upto, 0);
2395 		else if (fast_rexmit)
2396 			tcp_mark_head_lost(sk, 1, 1);
2397 	}
2398 }
2399 
tcp_tsopt_ecr_before(const struct tcp_sock * tp,u32 when)2400 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2401 {
2402 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2403 	       before(tp->rx_opt.rcv_tsecr, when);
2404 }
2405 
2406 /* skb is spurious retransmitted if the returned timestamp echo
2407  * reply is prior to the skb transmission time
2408  */
tcp_skb_spurious_retrans(const struct tcp_sock * tp,const struct sk_buff * skb)2409 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2410 				     const struct sk_buff *skb)
2411 {
2412 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2413 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
2414 }
2415 
2416 /* Nothing was retransmitted or returned timestamp is less
2417  * than timestamp of the first retransmission.
2418  */
tcp_packet_delayed(const struct tcp_sock * tp)2419 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2420 {
2421 	return tp->retrans_stamp &&
2422 	       tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2423 }
2424 
2425 /* Undo procedures. */
2426 
2427 /* We can clear retrans_stamp when there are no retransmissions in the
2428  * window. It would seem that it is trivially available for us in
2429  * tp->retrans_out, however, that kind of assumptions doesn't consider
2430  * what will happen if errors occur when sending retransmission for the
2431  * second time. ...It could the that such segment has only
2432  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2433  * the head skb is enough except for some reneging corner cases that
2434  * are not worth the effort.
2435  *
2436  * Main reason for all this complexity is the fact that connection dying
2437  * time now depends on the validity of the retrans_stamp, in particular,
2438  * that successive retransmissions of a segment must not advance
2439  * retrans_stamp under any conditions.
2440  */
tcp_any_retrans_done(const struct sock * sk)2441 static bool tcp_any_retrans_done(const struct sock *sk)
2442 {
2443 	const struct tcp_sock *tp = tcp_sk(sk);
2444 	struct sk_buff *skb;
2445 
2446 	if (tp->retrans_out)
2447 		return true;
2448 
2449 	skb = tcp_rtx_queue_head(sk);
2450 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2451 		return true;
2452 
2453 	return false;
2454 }
2455 
DBGUNDO(struct sock * sk,const char * msg)2456 static void DBGUNDO(struct sock *sk, const char *msg)
2457 {
2458 #if FASTRETRANS_DEBUG > 1
2459 	struct tcp_sock *tp = tcp_sk(sk);
2460 	struct inet_sock *inet = inet_sk(sk);
2461 
2462 	if (sk->sk_family == AF_INET) {
2463 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2464 			 msg,
2465 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2466 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2467 			 tp->snd_ssthresh, tp->prior_ssthresh,
2468 			 tp->packets_out);
2469 	}
2470 #if IS_ENABLED(CONFIG_IPV6)
2471 	else if (sk->sk_family == AF_INET6) {
2472 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2473 			 msg,
2474 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2475 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2476 			 tp->snd_ssthresh, tp->prior_ssthresh,
2477 			 tp->packets_out);
2478 	}
2479 #endif
2480 #endif
2481 }
2482 
tcp_undo_cwnd_reduction(struct sock * sk,bool unmark_loss)2483 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2484 {
2485 	struct tcp_sock *tp = tcp_sk(sk);
2486 
2487 	if (unmark_loss) {
2488 		struct sk_buff *skb;
2489 
2490 		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2491 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2492 		}
2493 		tp->lost_out = 0;
2494 		tcp_clear_all_retrans_hints(tp);
2495 	}
2496 
2497 	if (tp->prior_ssthresh) {
2498 		const struct inet_connection_sock *icsk = inet_csk(sk);
2499 
2500 		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2501 
2502 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2503 			tp->snd_ssthresh = tp->prior_ssthresh;
2504 			tcp_ecn_withdraw_cwr(tp);
2505 		}
2506 	}
2507 	tp->snd_cwnd_stamp = tcp_jiffies32;
2508 	tp->undo_marker = 0;
2509 	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2510 }
2511 
tcp_may_undo(const struct tcp_sock * tp)2512 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2513 {
2514 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2515 }
2516 
tcp_is_non_sack_preventing_reopen(struct sock * sk)2517 static bool tcp_is_non_sack_preventing_reopen(struct sock *sk)
2518 {
2519 	struct tcp_sock *tp = tcp_sk(sk);
2520 
2521 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2522 		/* Hold old state until something *above* high_seq
2523 		 * is ACKed. For Reno it is MUST to prevent false
2524 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2525 		if (!tcp_any_retrans_done(sk))
2526 			tp->retrans_stamp = 0;
2527 		return true;
2528 	}
2529 	return false;
2530 }
2531 
2532 /* People celebrate: "We love our President!" */
tcp_try_undo_recovery(struct sock * sk)2533 static bool tcp_try_undo_recovery(struct sock *sk)
2534 {
2535 	struct tcp_sock *tp = tcp_sk(sk);
2536 
2537 	if (tcp_may_undo(tp)) {
2538 		int mib_idx;
2539 
2540 		/* Happy end! We did not retransmit anything
2541 		 * or our original transmission succeeded.
2542 		 */
2543 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2544 		tcp_undo_cwnd_reduction(sk, false);
2545 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2546 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2547 		else
2548 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2549 
2550 		NET_INC_STATS(sock_net(sk), mib_idx);
2551 	} else if (tp->rack.reo_wnd_persist) {
2552 		tp->rack.reo_wnd_persist--;
2553 	}
2554 	if (tcp_is_non_sack_preventing_reopen(sk))
2555 		return true;
2556 	tcp_set_ca_state(sk, TCP_CA_Open);
2557 	tp->is_sack_reneg = 0;
2558 	return false;
2559 }
2560 
2561 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
tcp_try_undo_dsack(struct sock * sk)2562 static bool tcp_try_undo_dsack(struct sock *sk)
2563 {
2564 	struct tcp_sock *tp = tcp_sk(sk);
2565 
2566 	if (tp->undo_marker && !tp->undo_retrans) {
2567 		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2568 					       tp->rack.reo_wnd_persist + 1);
2569 		DBGUNDO(sk, "D-SACK");
2570 		tcp_undo_cwnd_reduction(sk, false);
2571 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2572 		return true;
2573 	}
2574 	return false;
2575 }
2576 
2577 /* Undo during loss recovery after partial ACK or using F-RTO. */
tcp_try_undo_loss(struct sock * sk,bool frto_undo)2578 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2579 {
2580 	struct tcp_sock *tp = tcp_sk(sk);
2581 
2582 	if (frto_undo || tcp_may_undo(tp)) {
2583 		tcp_undo_cwnd_reduction(sk, true);
2584 
2585 		DBGUNDO(sk, "partial loss");
2586 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2587 		if (frto_undo)
2588 			NET_INC_STATS(sock_net(sk),
2589 					LINUX_MIB_TCPSPURIOUSRTOS);
2590 		inet_csk(sk)->icsk_retransmits = 0;
2591 		if (tcp_is_non_sack_preventing_reopen(sk))
2592 			return true;
2593 		if (frto_undo || tcp_is_sack(tp)) {
2594 			tcp_set_ca_state(sk, TCP_CA_Open);
2595 			tp->is_sack_reneg = 0;
2596 		}
2597 		return true;
2598 	}
2599 	return false;
2600 }
2601 
2602 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2603  * It computes the number of packets to send (sndcnt) based on packets newly
2604  * delivered:
2605  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2606  *	cwnd reductions across a full RTT.
2607  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2608  *      But when SND_UNA is acked without further losses,
2609  *      slow starts cwnd up to ssthresh to speed up the recovery.
2610  */
tcp_init_cwnd_reduction(struct sock * sk)2611 static void tcp_init_cwnd_reduction(struct sock *sk)
2612 {
2613 	struct tcp_sock *tp = tcp_sk(sk);
2614 
2615 	tp->high_seq = tp->snd_nxt;
2616 	tp->tlp_high_seq = 0;
2617 	tp->snd_cwnd_cnt = 0;
2618 	tp->prior_cwnd = tcp_snd_cwnd(tp);
2619 	tp->prr_delivered = 0;
2620 	tp->prr_out = 0;
2621 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2622 	tcp_ecn_queue_cwr(tp);
2623 }
2624 
tcp_cwnd_reduction(struct sock * sk,int newly_acked_sacked,int newly_lost,int flag)2625 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2626 {
2627 	struct tcp_sock *tp = tcp_sk(sk);
2628 	int sndcnt = 0;
2629 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2630 
2631 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2632 		return;
2633 
2634 	tp->prr_delivered += newly_acked_sacked;
2635 	if (delta < 0) {
2636 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2637 			       tp->prior_cwnd - 1;
2638 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2639 	} else {
2640 		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2641 			       newly_acked_sacked);
2642 		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2643 			sndcnt++;
2644 		sndcnt = min(delta, sndcnt);
2645 	}
2646 	/* Force a fast retransmit upon entering fast recovery */
2647 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2648 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2649 }
2650 
tcp_end_cwnd_reduction(struct sock * sk)2651 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2652 {
2653 	struct tcp_sock *tp = tcp_sk(sk);
2654 
2655 	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2656 		return;
2657 
2658 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2659 	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2660 	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2661 		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2662 		tp->snd_cwnd_stamp = tcp_jiffies32;
2663 	}
2664 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2665 }
2666 
2667 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
tcp_enter_cwr(struct sock * sk)2668 void tcp_enter_cwr(struct sock *sk)
2669 {
2670 	struct tcp_sock *tp = tcp_sk(sk);
2671 
2672 	tp->prior_ssthresh = 0;
2673 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2674 		tp->undo_marker = 0;
2675 		tcp_init_cwnd_reduction(sk);
2676 		tcp_set_ca_state(sk, TCP_CA_CWR);
2677 	}
2678 }
2679 EXPORT_SYMBOL(tcp_enter_cwr);
2680 
tcp_try_keep_open(struct sock * sk)2681 static void tcp_try_keep_open(struct sock *sk)
2682 {
2683 	struct tcp_sock *tp = tcp_sk(sk);
2684 	int state = TCP_CA_Open;
2685 
2686 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2687 		state = TCP_CA_Disorder;
2688 
2689 	if (inet_csk(sk)->icsk_ca_state != state) {
2690 		tcp_set_ca_state(sk, state);
2691 		tp->high_seq = tp->snd_nxt;
2692 	}
2693 }
2694 
tcp_try_to_open(struct sock * sk,int flag)2695 static void tcp_try_to_open(struct sock *sk, int flag)
2696 {
2697 	struct tcp_sock *tp = tcp_sk(sk);
2698 
2699 	tcp_verify_left_out(tp);
2700 
2701 	if (!tcp_any_retrans_done(sk))
2702 		tp->retrans_stamp = 0;
2703 
2704 	if (flag & FLAG_ECE)
2705 		tcp_enter_cwr(sk);
2706 
2707 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2708 		tcp_try_keep_open(sk);
2709 	}
2710 }
2711 
tcp_mtup_probe_failed(struct sock * sk)2712 static void tcp_mtup_probe_failed(struct sock *sk)
2713 {
2714 	struct inet_connection_sock *icsk = inet_csk(sk);
2715 
2716 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2717 	icsk->icsk_mtup.probe_size = 0;
2718 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2719 }
2720 
tcp_mtup_probe_success(struct sock * sk)2721 static void tcp_mtup_probe_success(struct sock *sk)
2722 {
2723 	struct tcp_sock *tp = tcp_sk(sk);
2724 	struct inet_connection_sock *icsk = inet_csk(sk);
2725 	u64 val;
2726 
2727 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2728 
2729 	val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2730 	do_div(val, icsk->icsk_mtup.probe_size);
2731 	DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2732 	tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2733 
2734 	tp->snd_cwnd_cnt = 0;
2735 	tp->snd_cwnd_stamp = tcp_jiffies32;
2736 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2737 
2738 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2739 	icsk->icsk_mtup.probe_size = 0;
2740 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2741 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2742 }
2743 
2744 /* Do a simple retransmit without using the backoff mechanisms in
2745  * tcp_timer. This is used for path mtu discovery.
2746  * The socket is already locked here.
2747  */
tcp_simple_retransmit(struct sock * sk)2748 void tcp_simple_retransmit(struct sock *sk)
2749 {
2750 	const struct inet_connection_sock *icsk = inet_csk(sk);
2751 	struct tcp_sock *tp = tcp_sk(sk);
2752 	struct sk_buff *skb;
2753 	int mss;
2754 
2755 	/* A fastopen SYN request is stored as two separate packets within
2756 	 * the retransmit queue, this is done by tcp_send_syn_data().
2757 	 * As a result simply checking the MSS of the frames in the queue
2758 	 * will not work for the SYN packet.
2759 	 *
2760 	 * Us being here is an indication of a path MTU issue so we can
2761 	 * assume that the fastopen SYN was lost and just mark all the
2762 	 * frames in the retransmit queue as lost. We will use an MSS of
2763 	 * -1 to mark all frames as lost, otherwise compute the current MSS.
2764 	 */
2765 	if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2766 		mss = -1;
2767 	else
2768 		mss = tcp_current_mss(sk);
2769 
2770 	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2771 		if (tcp_skb_seglen(skb) > mss)
2772 			tcp_mark_skb_lost(sk, skb);
2773 	}
2774 
2775 	tcp_clear_retrans_hints_partial(tp);
2776 
2777 	if (!tp->lost_out)
2778 		return;
2779 
2780 	if (tcp_is_reno(tp))
2781 		tcp_limit_reno_sacked(tp);
2782 
2783 	tcp_verify_left_out(tp);
2784 
2785 	/* Don't muck with the congestion window here.
2786 	 * Reason is that we do not increase amount of _data_
2787 	 * in network, but units changed and effective
2788 	 * cwnd/ssthresh really reduced now.
2789 	 */
2790 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2791 		tp->high_seq = tp->snd_nxt;
2792 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2793 		tp->prior_ssthresh = 0;
2794 		tp->undo_marker = 0;
2795 		tcp_set_ca_state(sk, TCP_CA_Loss);
2796 	}
2797 	tcp_xmit_retransmit_queue(sk);
2798 }
2799 EXPORT_SYMBOL(tcp_simple_retransmit);
2800 
tcp_enter_recovery(struct sock * sk,bool ece_ack)2801 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2802 {
2803 	struct tcp_sock *tp = tcp_sk(sk);
2804 	int mib_idx;
2805 
2806 	if (tcp_is_reno(tp))
2807 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2808 	else
2809 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2810 
2811 	NET_INC_STATS(sock_net(sk), mib_idx);
2812 
2813 	tp->prior_ssthresh = 0;
2814 	tcp_init_undo(tp);
2815 
2816 	if (!tcp_in_cwnd_reduction(sk)) {
2817 		if (!ece_ack)
2818 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2819 		tcp_init_cwnd_reduction(sk);
2820 	}
2821 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2822 }
2823 
2824 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2825  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2826  */
tcp_process_loss(struct sock * sk,int flag,int num_dupack,int * rexmit)2827 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2828 			     int *rexmit)
2829 {
2830 	struct tcp_sock *tp = tcp_sk(sk);
2831 	bool recovered = !before(tp->snd_una, tp->high_seq);
2832 
2833 	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2834 	    tcp_try_undo_loss(sk, false))
2835 		return;
2836 
2837 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2838 		/* Step 3.b. A timeout is spurious if not all data are
2839 		 * lost, i.e., never-retransmitted data are (s)acked.
2840 		 */
2841 		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2842 		    tcp_try_undo_loss(sk, true))
2843 			return;
2844 
2845 		if (after(tp->snd_nxt, tp->high_seq)) {
2846 			if (flag & FLAG_DATA_SACKED || num_dupack)
2847 				tp->frto = 0; /* Step 3.a. loss was real */
2848 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2849 			tp->high_seq = tp->snd_nxt;
2850 			/* Step 2.b. Try send new data (but deferred until cwnd
2851 			 * is updated in tcp_ack()). Otherwise fall back to
2852 			 * the conventional recovery.
2853 			 */
2854 			if (!tcp_write_queue_empty(sk) &&
2855 			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2856 				*rexmit = REXMIT_NEW;
2857 				return;
2858 			}
2859 			tp->frto = 0;
2860 		}
2861 	}
2862 
2863 	if (recovered) {
2864 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2865 		tcp_try_undo_recovery(sk);
2866 		return;
2867 	}
2868 	if (tcp_is_reno(tp)) {
2869 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2870 		 * delivered. Lower inflight to clock out (re)tranmissions.
2871 		 */
2872 		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2873 			tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
2874 		else if (flag & FLAG_SND_UNA_ADVANCED)
2875 			tcp_reset_reno_sack(tp);
2876 	}
2877 	*rexmit = REXMIT_LOST;
2878 }
2879 
tcp_force_fast_retransmit(struct sock * sk)2880 static bool tcp_force_fast_retransmit(struct sock *sk)
2881 {
2882 	struct tcp_sock *tp = tcp_sk(sk);
2883 
2884 	return after(tcp_highest_sack_seq(tp),
2885 		     tp->snd_una + tp->reordering * tp->mss_cache);
2886 }
2887 
2888 /* Undo during fast recovery after partial ACK. */
tcp_try_undo_partial(struct sock * sk,u32 prior_snd_una,bool * do_lost)2889 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
2890 				 bool *do_lost)
2891 {
2892 	struct tcp_sock *tp = tcp_sk(sk);
2893 
2894 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
2895 		/* Plain luck! Hole if filled with delayed
2896 		 * packet, rather than with a retransmit. Check reordering.
2897 		 */
2898 		tcp_check_sack_reordering(sk, prior_snd_una, 1);
2899 
2900 		/* We are getting evidence that the reordering degree is higher
2901 		 * than we realized. If there are no retransmits out then we
2902 		 * can undo. Otherwise we clock out new packets but do not
2903 		 * mark more packets lost or retransmit more.
2904 		 */
2905 		if (tp->retrans_out)
2906 			return true;
2907 
2908 		if (!tcp_any_retrans_done(sk))
2909 			tp->retrans_stamp = 0;
2910 
2911 		DBGUNDO(sk, "partial recovery");
2912 		tcp_undo_cwnd_reduction(sk, true);
2913 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2914 		tcp_try_keep_open(sk);
2915 	} else {
2916 		/* Partial ACK arrived. Force fast retransmit. */
2917 		*do_lost = tcp_force_fast_retransmit(sk);
2918 	}
2919 	return false;
2920 }
2921 
tcp_identify_packet_loss(struct sock * sk,int * ack_flag)2922 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
2923 {
2924 	struct tcp_sock *tp = tcp_sk(sk);
2925 
2926 	if (tcp_rtx_queue_empty(sk))
2927 		return;
2928 
2929 	if (unlikely(tcp_is_reno(tp))) {
2930 		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
2931 	} else if (tcp_is_rack(sk)) {
2932 		u32 prior_retrans = tp->retrans_out;
2933 
2934 		if (tcp_rack_mark_lost(sk))
2935 			*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2936 		if (prior_retrans > tp->retrans_out)
2937 			*ack_flag |= FLAG_LOST_RETRANS;
2938 	}
2939 }
2940 
2941 /* Process an event, which can update packets-in-flight not trivially.
2942  * Main goal of this function is to calculate new estimate for left_out,
2943  * taking into account both packets sitting in receiver's buffer and
2944  * packets lost by network.
2945  *
2946  * Besides that it updates the congestion state when packet loss or ECN
2947  * is detected. But it does not reduce the cwnd, it is done by the
2948  * congestion control later.
2949  *
2950  * It does _not_ decide what to send, it is made in function
2951  * tcp_xmit_retransmit_queue().
2952  */
tcp_fastretrans_alert(struct sock * sk,const u32 prior_snd_una,int num_dupack,int * ack_flag,int * rexmit)2953 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
2954 				  int num_dupack, int *ack_flag, int *rexmit)
2955 {
2956 	struct inet_connection_sock *icsk = inet_csk(sk);
2957 	struct tcp_sock *tp = tcp_sk(sk);
2958 	int fast_rexmit = 0, flag = *ack_flag;
2959 	bool ece_ack = flag & FLAG_ECE;
2960 	bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
2961 				      tcp_force_fast_retransmit(sk));
2962 
2963 	if (!tp->packets_out && tp->sacked_out)
2964 		tp->sacked_out = 0;
2965 
2966 	/* Now state machine starts.
2967 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2968 	if (ece_ack)
2969 		tp->prior_ssthresh = 0;
2970 
2971 	/* B. In all the states check for reneging SACKs. */
2972 	if (tcp_check_sack_reneging(sk, flag))
2973 		return;
2974 
2975 	/* C. Check consistency of the current state. */
2976 	tcp_verify_left_out(tp);
2977 
2978 	/* D. Check state exit conditions. State can be terminated
2979 	 *    when high_seq is ACKed. */
2980 	if (icsk->icsk_ca_state == TCP_CA_Open) {
2981 		WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
2982 		tp->retrans_stamp = 0;
2983 	} else if (!before(tp->snd_una, tp->high_seq)) {
2984 		switch (icsk->icsk_ca_state) {
2985 		case TCP_CA_CWR:
2986 			/* CWR is to be held something *above* high_seq
2987 			 * is ACKed for CWR bit to reach receiver. */
2988 			if (tp->snd_una != tp->high_seq) {
2989 				tcp_end_cwnd_reduction(sk);
2990 				tcp_set_ca_state(sk, TCP_CA_Open);
2991 			}
2992 			break;
2993 
2994 		case TCP_CA_Recovery:
2995 			if (tcp_is_reno(tp))
2996 				tcp_reset_reno_sack(tp);
2997 			if (tcp_try_undo_recovery(sk))
2998 				return;
2999 			tcp_end_cwnd_reduction(sk);
3000 			break;
3001 		}
3002 	}
3003 
3004 	/* E. Process state. */
3005 	switch (icsk->icsk_ca_state) {
3006 	case TCP_CA_Recovery:
3007 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3008 			if (tcp_is_reno(tp))
3009 				tcp_add_reno_sack(sk, num_dupack, ece_ack);
3010 		} else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost))
3011 			return;
3012 
3013 		if (tcp_try_undo_dsack(sk))
3014 			tcp_try_keep_open(sk);
3015 
3016 		tcp_identify_packet_loss(sk, ack_flag);
3017 		if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3018 			if (!tcp_time_to_recover(sk, flag))
3019 				return;
3020 			/* Undo reverts the recovery state. If loss is evident,
3021 			 * starts a new recovery (e.g. reordering then loss);
3022 			 */
3023 			tcp_enter_recovery(sk, ece_ack);
3024 		}
3025 		break;
3026 	case TCP_CA_Loss:
3027 		tcp_process_loss(sk, flag, num_dupack, rexmit);
3028 		tcp_identify_packet_loss(sk, ack_flag);
3029 		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3030 		      (*ack_flag & FLAG_LOST_RETRANS)))
3031 			return;
3032 		/* Change state if cwnd is undone or retransmits are lost */
3033 		fallthrough;
3034 	default:
3035 		if (tcp_is_reno(tp)) {
3036 			if (flag & FLAG_SND_UNA_ADVANCED)
3037 				tcp_reset_reno_sack(tp);
3038 			tcp_add_reno_sack(sk, num_dupack, ece_ack);
3039 		}
3040 
3041 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3042 			tcp_try_undo_dsack(sk);
3043 
3044 		tcp_identify_packet_loss(sk, ack_flag);
3045 		if (!tcp_time_to_recover(sk, flag)) {
3046 			tcp_try_to_open(sk, flag);
3047 			return;
3048 		}
3049 
3050 		/* MTU probe failure: don't reduce cwnd */
3051 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3052 		    icsk->icsk_mtup.probe_size &&
3053 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3054 			tcp_mtup_probe_failed(sk);
3055 			/* Restores the reduction we did in tcp_mtup_probe() */
3056 			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3057 			tcp_simple_retransmit(sk);
3058 			return;
3059 		}
3060 
3061 		/* Otherwise enter Recovery state */
3062 		tcp_enter_recovery(sk, ece_ack);
3063 		fast_rexmit = 1;
3064 	}
3065 
3066 	if (!tcp_is_rack(sk) && do_lost)
3067 		tcp_update_scoreboard(sk, fast_rexmit);
3068 	*rexmit = REXMIT_LOST;
3069 }
3070 
tcp_update_rtt_min(struct sock * sk,u32 rtt_us,const int flag)3071 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3072 {
3073 	u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ;
3074 	struct tcp_sock *tp = tcp_sk(sk);
3075 
3076 	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3077 		/* If the remote keeps returning delayed ACKs, eventually
3078 		 * the min filter would pick it up and overestimate the
3079 		 * prop. delay when it expires. Skip suspected delayed ACKs.
3080 		 */
3081 		return;
3082 	}
3083 	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3084 			   rtt_us ? : jiffies_to_usecs(1));
3085 }
3086 
tcp_ack_update_rtt(struct sock * sk,const int flag,long seq_rtt_us,long sack_rtt_us,long ca_rtt_us,struct rate_sample * rs)3087 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3088 			       long seq_rtt_us, long sack_rtt_us,
3089 			       long ca_rtt_us, struct rate_sample *rs)
3090 {
3091 	const struct tcp_sock *tp = tcp_sk(sk);
3092 
3093 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3094 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3095 	 * Karn's algorithm forbids taking RTT if some retransmitted data
3096 	 * is acked (RFC6298).
3097 	 */
3098 	if (seq_rtt_us < 0)
3099 		seq_rtt_us = sack_rtt_us;
3100 
3101 	/* RTTM Rule: A TSecr value received in a segment is used to
3102 	 * update the averaged RTT measurement only if the segment
3103 	 * acknowledges some new data, i.e., only if it advances the
3104 	 * left edge of the send window.
3105 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3106 	 */
3107 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
3108 	    flag & FLAG_ACKED) {
3109 		u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
3110 
3111 		if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
3112 			if (!delta)
3113 				delta = 1;
3114 			seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
3115 			ca_rtt_us = seq_rtt_us;
3116 		}
3117 	}
3118 	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3119 	if (seq_rtt_us < 0)
3120 		return false;
3121 
3122 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3123 	 * always taken together with ACK, SACK, or TS-opts. Any negative
3124 	 * values will be skipped with the seq_rtt_us < 0 check above.
3125 	 */
3126 	tcp_update_rtt_min(sk, ca_rtt_us, flag);
3127 	tcp_rtt_estimator(sk, seq_rtt_us);
3128 	tcp_set_rto(sk);
3129 
3130 	/* RFC6298: only reset backoff on valid RTT measurement. */
3131 	inet_csk(sk)->icsk_backoff = 0;
3132 	return true;
3133 }
3134 
3135 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
tcp_synack_rtt_meas(struct sock * sk,struct request_sock * req)3136 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3137 {
3138 	struct rate_sample rs;
3139 	long rtt_us = -1L;
3140 
3141 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3142 		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3143 
3144 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3145 }
3146 
3147 
tcp_cong_avoid(struct sock * sk,u32 ack,u32 acked)3148 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3149 {
3150 	const struct inet_connection_sock *icsk = inet_csk(sk);
3151 
3152 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3153 	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3154 }
3155 
3156 /* Restart timer after forward progress on connection.
3157  * RFC2988 recommends to restart timer to now+rto.
3158  */
tcp_rearm_rto(struct sock * sk)3159 void tcp_rearm_rto(struct sock *sk)
3160 {
3161 	const struct inet_connection_sock *icsk = inet_csk(sk);
3162 	struct tcp_sock *tp = tcp_sk(sk);
3163 
3164 	/* If the retrans timer is currently being used by Fast Open
3165 	 * for SYN-ACK retrans purpose, stay put.
3166 	 */
3167 	if (rcu_access_pointer(tp->fastopen_rsk))
3168 		return;
3169 
3170 	if (!tp->packets_out) {
3171 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3172 	} else {
3173 		u32 rto = inet_csk(sk)->icsk_rto;
3174 		/* Offset the time elapsed after installing regular RTO */
3175 		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3176 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3177 			s64 delta_us = tcp_rto_delta_us(sk);
3178 			/* delta_us may not be positive if the socket is locked
3179 			 * when the retrans timer fires and is rescheduled.
3180 			 */
3181 			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3182 		}
3183 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
3184 				     TCP_RTO_MAX);
3185 	}
3186 }
3187 
3188 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
tcp_set_xmit_timer(struct sock * sk)3189 static void tcp_set_xmit_timer(struct sock *sk)
3190 {
3191 	if (!tcp_schedule_loss_probe(sk, true))
3192 		tcp_rearm_rto(sk);
3193 }
3194 
3195 /* If we get here, the whole TSO packet has not been acked. */
tcp_tso_acked(struct sock * sk,struct sk_buff * skb)3196 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3197 {
3198 	struct tcp_sock *tp = tcp_sk(sk);
3199 	u32 packets_acked;
3200 
3201 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3202 
3203 	packets_acked = tcp_skb_pcount(skb);
3204 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3205 		return 0;
3206 	packets_acked -= tcp_skb_pcount(skb);
3207 
3208 	if (packets_acked) {
3209 		BUG_ON(tcp_skb_pcount(skb) == 0);
3210 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3211 	}
3212 
3213 	return packets_acked;
3214 }
3215 
tcp_ack_tstamp(struct sock * sk,struct sk_buff * skb,const struct sk_buff * ack_skb,u32 prior_snd_una)3216 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3217 			   const struct sk_buff *ack_skb, u32 prior_snd_una)
3218 {
3219 	const struct skb_shared_info *shinfo;
3220 
3221 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3222 	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3223 		return;
3224 
3225 	shinfo = skb_shinfo(skb);
3226 	if (!before(shinfo->tskey, prior_snd_una) &&
3227 	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3228 		tcp_skb_tsorted_save(skb) {
3229 			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3230 		} tcp_skb_tsorted_restore(skb);
3231 	}
3232 }
3233 
3234 /* Remove acknowledged frames from the retransmission queue. If our packet
3235  * is before the ack sequence we can discard it as it's confirmed to have
3236  * arrived at the other end.
3237  */
tcp_clean_rtx_queue(struct sock * sk,const struct sk_buff * ack_skb,u32 prior_fack,u32 prior_snd_una,struct tcp_sacktag_state * sack,bool ece_ack)3238 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3239 			       u32 prior_fack, u32 prior_snd_una,
3240 			       struct tcp_sacktag_state *sack, bool ece_ack)
3241 {
3242 	const struct inet_connection_sock *icsk = inet_csk(sk);
3243 	u64 first_ackt, last_ackt;
3244 	struct tcp_sock *tp = tcp_sk(sk);
3245 	u32 prior_sacked = tp->sacked_out;
3246 	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3247 	struct sk_buff *skb, *next;
3248 	bool fully_acked = true;
3249 	long sack_rtt_us = -1L;
3250 	long seq_rtt_us = -1L;
3251 	long ca_rtt_us = -1L;
3252 	u32 pkts_acked = 0;
3253 	bool rtt_update;
3254 	int flag = 0;
3255 
3256 	first_ackt = 0;
3257 
3258 	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3259 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3260 		const u32 start_seq = scb->seq;
3261 		u8 sacked = scb->sacked;
3262 		u32 acked_pcount;
3263 
3264 		/* Determine how many packets and what bytes were acked, tso and else */
3265 		if (after(scb->end_seq, tp->snd_una)) {
3266 			if (tcp_skb_pcount(skb) == 1 ||
3267 			    !after(tp->snd_una, scb->seq))
3268 				break;
3269 
3270 			acked_pcount = tcp_tso_acked(sk, skb);
3271 			if (!acked_pcount)
3272 				break;
3273 			fully_acked = false;
3274 		} else {
3275 			acked_pcount = tcp_skb_pcount(skb);
3276 		}
3277 
3278 		if (unlikely(sacked & TCPCB_RETRANS)) {
3279 			if (sacked & TCPCB_SACKED_RETRANS)
3280 				tp->retrans_out -= acked_pcount;
3281 			flag |= FLAG_RETRANS_DATA_ACKED;
3282 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3283 			last_ackt = tcp_skb_timestamp_us(skb);
3284 			WARN_ON_ONCE(last_ackt == 0);
3285 			if (!first_ackt)
3286 				first_ackt = last_ackt;
3287 
3288 			if (before(start_seq, reord))
3289 				reord = start_seq;
3290 			if (!after(scb->end_seq, tp->high_seq))
3291 				flag |= FLAG_ORIG_SACK_ACKED;
3292 		}
3293 
3294 		if (sacked & TCPCB_SACKED_ACKED) {
3295 			tp->sacked_out -= acked_pcount;
3296 		} else if (tcp_is_sack(tp)) {
3297 			tcp_count_delivered(tp, acked_pcount, ece_ack);
3298 			if (!tcp_skb_spurious_retrans(tp, skb))
3299 				tcp_rack_advance(tp, sacked, scb->end_seq,
3300 						 tcp_skb_timestamp_us(skb));
3301 		}
3302 		if (sacked & TCPCB_LOST)
3303 			tp->lost_out -= acked_pcount;
3304 
3305 		tp->packets_out -= acked_pcount;
3306 		pkts_acked += acked_pcount;
3307 		tcp_rate_skb_delivered(sk, skb, sack->rate);
3308 
3309 		/* Initial outgoing SYN's get put onto the write_queue
3310 		 * just like anything else we transmit.  It is not
3311 		 * true data, and if we misinform our callers that
3312 		 * this ACK acks real data, we will erroneously exit
3313 		 * connection startup slow start one packet too
3314 		 * quickly.  This is severely frowned upon behavior.
3315 		 */
3316 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3317 			flag |= FLAG_DATA_ACKED;
3318 		} else {
3319 			flag |= FLAG_SYN_ACKED;
3320 			tp->retrans_stamp = 0;
3321 		}
3322 
3323 		if (!fully_acked)
3324 			break;
3325 
3326 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3327 
3328 		next = skb_rb_next(skb);
3329 		if (unlikely(skb == tp->retransmit_skb_hint))
3330 			tp->retransmit_skb_hint = NULL;
3331 		if (unlikely(skb == tp->lost_skb_hint))
3332 			tp->lost_skb_hint = NULL;
3333 		tcp_highest_sack_replace(sk, skb, next);
3334 		tcp_rtx_queue_unlink_and_free(skb, sk);
3335 	}
3336 
3337 	if (!skb)
3338 		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3339 
3340 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3341 		tp->snd_up = tp->snd_una;
3342 
3343 	if (skb) {
3344 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3345 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3346 			flag |= FLAG_SACK_RENEGING;
3347 	}
3348 
3349 	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3350 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3351 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3352 
3353 		if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3354 		    (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3355 		    sack->rate->prior_delivered + 1 == tp->delivered &&
3356 		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3357 			/* Conservatively mark a delayed ACK. It's typically
3358 			 * from a lone runt packet over the round trip to
3359 			 * a receiver w/o out-of-order or CE events.
3360 			 */
3361 			flag |= FLAG_ACK_MAYBE_DELAYED;
3362 		}
3363 	}
3364 	if (sack->first_sackt) {
3365 		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3366 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3367 	}
3368 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3369 					ca_rtt_us, sack->rate);
3370 
3371 	if (flag & FLAG_ACKED) {
3372 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3373 		if (unlikely(icsk->icsk_mtup.probe_size &&
3374 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3375 			tcp_mtup_probe_success(sk);
3376 		}
3377 
3378 		if (tcp_is_reno(tp)) {
3379 			tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3380 
3381 			/* If any of the cumulatively ACKed segments was
3382 			 * retransmitted, non-SACK case cannot confirm that
3383 			 * progress was due to original transmission due to
3384 			 * lack of TCPCB_SACKED_ACKED bits even if some of
3385 			 * the packets may have been never retransmitted.
3386 			 */
3387 			if (flag & FLAG_RETRANS_DATA_ACKED)
3388 				flag &= ~FLAG_ORIG_SACK_ACKED;
3389 		} else {
3390 			int delta;
3391 
3392 			/* Non-retransmitted hole got filled? That's reordering */
3393 			if (before(reord, prior_fack))
3394 				tcp_check_sack_reordering(sk, reord, 0);
3395 
3396 			delta = prior_sacked - tp->sacked_out;
3397 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3398 		}
3399 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3400 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3401 						    tcp_skb_timestamp_us(skb))) {
3402 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3403 		 * after when the head was last (re)transmitted. Otherwise the
3404 		 * timeout may continue to extend in loss recovery.
3405 		 */
3406 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3407 	}
3408 
3409 	if (icsk->icsk_ca_ops->pkts_acked) {
3410 		struct ack_sample sample = { .pkts_acked = pkts_acked,
3411 					     .rtt_us = sack->rate->rtt_us };
3412 
3413 		sample.in_flight = tp->mss_cache *
3414 			(tp->delivered - sack->rate->prior_delivered);
3415 		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3416 	}
3417 
3418 #if FASTRETRANS_DEBUG > 0
3419 	WARN_ON((int)tp->sacked_out < 0);
3420 	WARN_ON((int)tp->lost_out < 0);
3421 	WARN_ON((int)tp->retrans_out < 0);
3422 	if (!tp->packets_out && tcp_is_sack(tp)) {
3423 		icsk = inet_csk(sk);
3424 		if (tp->lost_out) {
3425 			pr_debug("Leak l=%u %d\n",
3426 				 tp->lost_out, icsk->icsk_ca_state);
3427 			tp->lost_out = 0;
3428 		}
3429 		if (tp->sacked_out) {
3430 			pr_debug("Leak s=%u %d\n",
3431 				 tp->sacked_out, icsk->icsk_ca_state);
3432 			tp->sacked_out = 0;
3433 		}
3434 		if (tp->retrans_out) {
3435 			pr_debug("Leak r=%u %d\n",
3436 				 tp->retrans_out, icsk->icsk_ca_state);
3437 			tp->retrans_out = 0;
3438 		}
3439 	}
3440 #endif
3441 	return flag;
3442 }
3443 
tcp_ack_probe(struct sock * sk)3444 static void tcp_ack_probe(struct sock *sk)
3445 {
3446 	struct inet_connection_sock *icsk = inet_csk(sk);
3447 	struct sk_buff *head = tcp_send_head(sk);
3448 	const struct tcp_sock *tp = tcp_sk(sk);
3449 
3450 	/* Was it a usable window open? */
3451 	if (!head)
3452 		return;
3453 	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3454 		icsk->icsk_backoff = 0;
3455 		icsk->icsk_probes_tstamp = 0;
3456 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3457 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3458 		 * This function is not for random using!
3459 		 */
3460 	} else {
3461 		unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
3462 
3463 		when = tcp_clamp_probe0_to_user_timeout(sk, when);
3464 		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX);
3465 	}
3466 }
3467 
tcp_ack_is_dubious(const struct sock * sk,const int flag)3468 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3469 {
3470 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3471 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3472 }
3473 
3474 /* Decide wheather to run the increase function of congestion control. */
tcp_may_raise_cwnd(const struct sock * sk,const int flag)3475 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3476 {
3477 	/* If reordering is high then always grow cwnd whenever data is
3478 	 * delivered regardless of its ordering. Otherwise stay conservative
3479 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3480 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3481 	 * cwnd in tcp_fastretrans_alert() based on more states.
3482 	 */
3483 	if (tcp_sk(sk)->reordering >
3484 	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3485 		return flag & FLAG_FORWARD_PROGRESS;
3486 
3487 	return flag & FLAG_DATA_ACKED;
3488 }
3489 
3490 /* The "ultimate" congestion control function that aims to replace the rigid
3491  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3492  * It's called toward the end of processing an ACK with precise rate
3493  * information. All transmission or retransmission are delayed afterwards.
3494  */
tcp_cong_control(struct sock * sk,u32 ack,u32 acked_sacked,int flag,const struct rate_sample * rs)3495 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3496 			     int flag, const struct rate_sample *rs)
3497 {
3498 	const struct inet_connection_sock *icsk = inet_csk(sk);
3499 
3500 	if (icsk->icsk_ca_ops->cong_control) {
3501 		icsk->icsk_ca_ops->cong_control(sk, rs);
3502 		return;
3503 	}
3504 
3505 	if (tcp_in_cwnd_reduction(sk)) {
3506 		/* Reduce cwnd if state mandates */
3507 		tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3508 	} else if (tcp_may_raise_cwnd(sk, flag)) {
3509 		/* Advance cwnd if state allows */
3510 		tcp_cong_avoid(sk, ack, acked_sacked);
3511 	}
3512 	tcp_update_pacing_rate(sk);
3513 }
3514 
3515 /* Check that window update is acceptable.
3516  * The function assumes that snd_una<=ack<=snd_next.
3517  */
tcp_may_update_window(const struct tcp_sock * tp,const u32 ack,const u32 ack_seq,const u32 nwin)3518 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3519 					const u32 ack, const u32 ack_seq,
3520 					const u32 nwin)
3521 {
3522 	return	after(ack, tp->snd_una) ||
3523 		after(ack_seq, tp->snd_wl1) ||
3524 		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3525 }
3526 
3527 /* If we update tp->snd_una, also update tp->bytes_acked */
tcp_snd_una_update(struct tcp_sock * tp,u32 ack)3528 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3529 {
3530 	u32 delta = ack - tp->snd_una;
3531 
3532 	sock_owned_by_me((struct sock *)tp);
3533 	tp->bytes_acked += delta;
3534 	tp->snd_una = ack;
3535 }
3536 
3537 /* If we update tp->rcv_nxt, also update tp->bytes_received */
tcp_rcv_nxt_update(struct tcp_sock * tp,u32 seq)3538 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3539 {
3540 	u32 delta = seq - tp->rcv_nxt;
3541 
3542 	sock_owned_by_me((struct sock *)tp);
3543 	tp->bytes_received += delta;
3544 	WRITE_ONCE(tp->rcv_nxt, seq);
3545 }
3546 
3547 /* Update our send window.
3548  *
3549  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3550  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3551  */
tcp_ack_update_window(struct sock * sk,const struct sk_buff * skb,u32 ack,u32 ack_seq)3552 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3553 				 u32 ack_seq)
3554 {
3555 	struct tcp_sock *tp = tcp_sk(sk);
3556 	int flag = 0;
3557 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3558 
3559 	if (likely(!tcp_hdr(skb)->syn))
3560 		nwin <<= tp->rx_opt.snd_wscale;
3561 
3562 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3563 		flag |= FLAG_WIN_UPDATE;
3564 		tcp_update_wl(tp, ack_seq);
3565 
3566 		if (tp->snd_wnd != nwin) {
3567 			tp->snd_wnd = nwin;
3568 
3569 			/* Note, it is the only place, where
3570 			 * fast path is recovered for sending TCP.
3571 			 */
3572 			tp->pred_flags = 0;
3573 			tcp_fast_path_check(sk);
3574 
3575 			if (!tcp_write_queue_empty(sk))
3576 				tcp_slow_start_after_idle_check(sk);
3577 
3578 			if (nwin > tp->max_window) {
3579 				tp->max_window = nwin;
3580 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3581 			}
3582 		}
3583 	}
3584 
3585 	tcp_snd_una_update(tp, ack);
3586 
3587 	return flag;
3588 }
3589 
__tcp_oow_rate_limited(struct net * net,int mib_idx,u32 * last_oow_ack_time)3590 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3591 				   u32 *last_oow_ack_time)
3592 {
3593 	if (*last_oow_ack_time) {
3594 		s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
3595 
3596 		if (0 <= elapsed &&
3597 		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
3598 			NET_INC_STATS(net, mib_idx);
3599 			return true;	/* rate-limited: don't send yet! */
3600 		}
3601 	}
3602 
3603 	*last_oow_ack_time = tcp_jiffies32;
3604 
3605 	return false;	/* not rate-limited: go ahead, send dupack now! */
3606 }
3607 
3608 /* Return true if we're currently rate-limiting out-of-window ACKs and
3609  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3610  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3611  * attacks that send repeated SYNs or ACKs for the same connection. To
3612  * do this, we do not send a duplicate SYNACK or ACK if the remote
3613  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3614  */
tcp_oow_rate_limited(struct net * net,const struct sk_buff * skb,int mib_idx,u32 * last_oow_ack_time)3615 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3616 			  int mib_idx, u32 *last_oow_ack_time)
3617 {
3618 	/* Data packets without SYNs are not likely part of an ACK loop. */
3619 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3620 	    !tcp_hdr(skb)->syn)
3621 		return false;
3622 
3623 	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3624 }
3625 
3626 /* RFC 5961 7 [ACK Throttling] */
tcp_send_challenge_ack(struct sock * sk)3627 static void tcp_send_challenge_ack(struct sock *sk)
3628 {
3629 	struct tcp_sock *tp = tcp_sk(sk);
3630 	struct net *net = sock_net(sk);
3631 	u32 count, now, ack_limit;
3632 
3633 	/* First check our per-socket dupack rate limit. */
3634 	if (__tcp_oow_rate_limited(net,
3635 				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3636 				   &tp->last_oow_ack_time))
3637 		return;
3638 
3639 	ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
3640 	if (ack_limit == INT_MAX)
3641 		goto send_ack;
3642 
3643 	/* Then check host-wide RFC 5961 rate limit. */
3644 	now = jiffies / HZ;
3645 	if (now != READ_ONCE(net->ipv4.tcp_challenge_timestamp)) {
3646 		u32 half = (ack_limit + 1) >> 1;
3647 
3648 		WRITE_ONCE(net->ipv4.tcp_challenge_timestamp, now);
3649 		WRITE_ONCE(net->ipv4.tcp_challenge_count, half + prandom_u32_max(ack_limit));
3650 	}
3651 	count = READ_ONCE(net->ipv4.tcp_challenge_count);
3652 	if (count > 0) {
3653 		WRITE_ONCE(net->ipv4.tcp_challenge_count, count - 1);
3654 send_ack:
3655 		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3656 		tcp_send_ack(sk);
3657 	}
3658 }
3659 
tcp_store_ts_recent(struct tcp_sock * tp)3660 static void tcp_store_ts_recent(struct tcp_sock *tp)
3661 {
3662 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3663 	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3664 }
3665 
tcp_replace_ts_recent(struct tcp_sock * tp,u32 seq)3666 static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3667 {
3668 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3669 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3670 		 * extra check below makes sure this can only happen
3671 		 * for pure ACK frames.  -DaveM
3672 		 *
3673 		 * Not only, also it occurs for expired timestamps.
3674 		 */
3675 
3676 		if (tcp_paws_check(&tp->rx_opt, 0))
3677 			tcp_store_ts_recent(tp);
3678 	}
3679 }
3680 
3681 /* This routine deals with acks during a TLP episode and ends an episode by
3682  * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
3683  */
tcp_process_tlp_ack(struct sock * sk,u32 ack,int flag)3684 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3685 {
3686 	struct tcp_sock *tp = tcp_sk(sk);
3687 
3688 	if (before(ack, tp->tlp_high_seq))
3689 		return;
3690 
3691 	if (!tp->tlp_retrans) {
3692 		/* TLP of new data has been acknowledged */
3693 		tp->tlp_high_seq = 0;
3694 	} else if (flag & FLAG_DSACK_TLP) {
3695 		/* This DSACK means original and TLP probe arrived; no loss */
3696 		tp->tlp_high_seq = 0;
3697 	} else if (after(ack, tp->tlp_high_seq)) {
3698 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3699 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3700 		 */
3701 		tcp_init_cwnd_reduction(sk);
3702 		tcp_set_ca_state(sk, TCP_CA_CWR);
3703 		tcp_end_cwnd_reduction(sk);
3704 		tcp_try_keep_open(sk);
3705 		NET_INC_STATS(sock_net(sk),
3706 				LINUX_MIB_TCPLOSSPROBERECOVERY);
3707 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3708 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3709 		/* Pure dupack: original and TLP probe arrived; no loss */
3710 		tp->tlp_high_seq = 0;
3711 	}
3712 }
3713 
tcp_in_ack_event(struct sock * sk,u32 flags)3714 static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
3715 {
3716 	const struct inet_connection_sock *icsk = inet_csk(sk);
3717 
3718 	if (icsk->icsk_ca_ops->in_ack_event)
3719 		icsk->icsk_ca_ops->in_ack_event(sk, flags);
3720 }
3721 
3722 /* Congestion control has updated the cwnd already. So if we're in
3723  * loss recovery then now we do any new sends (for FRTO) or
3724  * retransmits (for CA_Loss or CA_recovery) that make sense.
3725  */
tcp_xmit_recovery(struct sock * sk,int rexmit)3726 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3727 {
3728 	struct tcp_sock *tp = tcp_sk(sk);
3729 
3730 	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3731 		return;
3732 
3733 	if (unlikely(rexmit == REXMIT_NEW)) {
3734 		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3735 					  TCP_NAGLE_OFF);
3736 		if (after(tp->snd_nxt, tp->high_seq))
3737 			return;
3738 		tp->frto = 0;
3739 	}
3740 	tcp_xmit_retransmit_queue(sk);
3741 }
3742 
3743 /* Returns the number of packets newly acked or sacked by the current ACK */
tcp_newly_delivered(struct sock * sk,u32 prior_delivered,int flag)3744 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3745 {
3746 	const struct net *net = sock_net(sk);
3747 	struct tcp_sock *tp = tcp_sk(sk);
3748 	u32 delivered;
3749 
3750 	delivered = tp->delivered - prior_delivered;
3751 	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3752 	if (flag & FLAG_ECE)
3753 		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3754 
3755 	return delivered;
3756 }
3757 
3758 /* This routine deals with incoming acks, but not outgoing ones. */
tcp_ack(struct sock * sk,const struct sk_buff * skb,int flag)3759 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3760 {
3761 	struct inet_connection_sock *icsk = inet_csk(sk);
3762 	struct tcp_sock *tp = tcp_sk(sk);
3763 	struct tcp_sacktag_state sack_state;
3764 	struct rate_sample rs = { .prior_delivered = 0 };
3765 	u32 prior_snd_una = tp->snd_una;
3766 	bool is_sack_reneg = tp->is_sack_reneg;
3767 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3768 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3769 	int num_dupack = 0;
3770 	int prior_packets = tp->packets_out;
3771 	u32 delivered = tp->delivered;
3772 	u32 lost = tp->lost;
3773 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3774 	u32 prior_fack;
3775 
3776 	sack_state.first_sackt = 0;
3777 	sack_state.rate = &rs;
3778 	sack_state.sack_delivered = 0;
3779 
3780 	/* We very likely will need to access rtx queue. */
3781 	prefetch(sk->tcp_rtx_queue.rb_node);
3782 
3783 	/* If the ack is older than previous acks
3784 	 * then we can probably ignore it.
3785 	 */
3786 	if (before(ack, prior_snd_una)) {
3787 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3788 		if (before(ack, prior_snd_una - tp->max_window)) {
3789 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3790 				tcp_send_challenge_ack(sk);
3791 			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
3792 		}
3793 		goto old_ack;
3794 	}
3795 
3796 	/* If the ack includes data we haven't sent yet, discard
3797 	 * this segment (RFC793 Section 3.9).
3798 	 */
3799 	if (after(ack, tp->snd_nxt))
3800 		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
3801 
3802 	if (after(ack, prior_snd_una)) {
3803 		flag |= FLAG_SND_UNA_ADVANCED;
3804 		icsk->icsk_retransmits = 0;
3805 
3806 #if IS_ENABLED(CONFIG_TLS_DEVICE)
3807 		if (static_branch_unlikely(&clean_acked_data_enabled.key))
3808 			if (icsk->icsk_clean_acked)
3809 				icsk->icsk_clean_acked(sk, ack);
3810 #endif
3811 	}
3812 
3813 	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3814 	rs.prior_in_flight = tcp_packets_in_flight(tp);
3815 
3816 	/* ts_recent update must be made after we are sure that the packet
3817 	 * is in window.
3818 	 */
3819 	if (flag & FLAG_UPDATE_TS_RECENT)
3820 		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
3821 
3822 	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
3823 	    FLAG_SND_UNA_ADVANCED) {
3824 		/* Window is constant, pure forward advance.
3825 		 * No more checks are required.
3826 		 * Note, we use the fact that SND.UNA>=SND.WL2.
3827 		 */
3828 		tcp_update_wl(tp, ack_seq);
3829 		tcp_snd_una_update(tp, ack);
3830 		flag |= FLAG_WIN_UPDATE;
3831 
3832 		tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
3833 
3834 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
3835 	} else {
3836 		u32 ack_ev_flags = CA_ACK_SLOWPATH;
3837 
3838 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3839 			flag |= FLAG_DATA;
3840 		else
3841 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3842 
3843 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3844 
3845 		if (TCP_SKB_CB(skb)->sacked)
3846 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3847 							&sack_state);
3848 
3849 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
3850 			flag |= FLAG_ECE;
3851 			ack_ev_flags |= CA_ACK_ECE;
3852 		}
3853 
3854 		if (sack_state.sack_delivered)
3855 			tcp_count_delivered(tp, sack_state.sack_delivered,
3856 					    flag & FLAG_ECE);
3857 
3858 		if (flag & FLAG_WIN_UPDATE)
3859 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3860 
3861 		tcp_in_ack_event(sk, ack_ev_flags);
3862 	}
3863 
3864 	/* This is a deviation from RFC3168 since it states that:
3865 	 * "When the TCP data sender is ready to set the CWR bit after reducing
3866 	 * the congestion window, it SHOULD set the CWR bit only on the first
3867 	 * new data packet that it transmits."
3868 	 * We accept CWR on pure ACKs to be more robust
3869 	 * with widely-deployed TCP implementations that do this.
3870 	 */
3871 	tcp_ecn_accept_cwr(sk, skb);
3872 
3873 	/* We passed data and got it acked, remove any soft error
3874 	 * log. Something worked...
3875 	 */
3876 	sk->sk_err_soft = 0;
3877 	icsk->icsk_probes_out = 0;
3878 	tp->rcv_tstamp = tcp_jiffies32;
3879 	if (!prior_packets)
3880 		goto no_queue;
3881 
3882 	/* See if we can take anything off of the retransmit queue. */
3883 	flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
3884 				    &sack_state, flag & FLAG_ECE);
3885 
3886 	tcp_rack_update_reo_wnd(sk, &rs);
3887 
3888 	if (tp->tlp_high_seq)
3889 		tcp_process_tlp_ack(sk, ack, flag);
3890 
3891 	if (tcp_ack_is_dubious(sk, flag)) {
3892 		if (!(flag & (FLAG_SND_UNA_ADVANCED |
3893 			      FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
3894 			num_dupack = 1;
3895 			/* Consider if pure acks were aggregated in tcp_add_backlog() */
3896 			if (!(flag & FLAG_DATA))
3897 				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
3898 		}
3899 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3900 				      &rexmit);
3901 	}
3902 
3903 	/* If needed, reset TLP/RTO timer when RACK doesn't set. */
3904 	if (flag & FLAG_SET_XMIT_TIMER)
3905 		tcp_set_xmit_timer(sk);
3906 
3907 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3908 		sk_dst_confirm(sk);
3909 
3910 	delivered = tcp_newly_delivered(sk, delivered, flag);
3911 	lost = tp->lost - lost;			/* freshly marked lost */
3912 	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
3913 	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
3914 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
3915 	tcp_xmit_recovery(sk, rexmit);
3916 	return 1;
3917 
3918 no_queue:
3919 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
3920 	if (flag & FLAG_DSACKING_ACK) {
3921 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3922 				      &rexmit);
3923 		tcp_newly_delivered(sk, delivered, flag);
3924 	}
3925 	/* If this ack opens up a zero window, clear backoff.  It was
3926 	 * being used to time the probes, and is probably far higher than
3927 	 * it needs to be for normal retransmission.
3928 	 */
3929 	tcp_ack_probe(sk);
3930 
3931 	if (tp->tlp_high_seq)
3932 		tcp_process_tlp_ack(sk, ack, flag);
3933 	return 1;
3934 
3935 old_ack:
3936 	/* If data was SACKed, tag it and see if we should send more data.
3937 	 * If data was DSACKed, see if we can undo a cwnd reduction.
3938 	 */
3939 	if (TCP_SKB_CB(skb)->sacked) {
3940 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
3941 						&sack_state);
3942 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
3943 				      &rexmit);
3944 		tcp_newly_delivered(sk, delivered, flag);
3945 		tcp_xmit_recovery(sk, rexmit);
3946 	}
3947 
3948 	return 0;
3949 }
3950 
tcp_parse_fastopen_option(int len,const unsigned char * cookie,bool syn,struct tcp_fastopen_cookie * foc,bool exp_opt)3951 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
3952 				      bool syn, struct tcp_fastopen_cookie *foc,
3953 				      bool exp_opt)
3954 {
3955 	/* Valid only in SYN or SYN-ACK with an even length.  */
3956 	if (!foc || !syn || len < 0 || (len & 1))
3957 		return;
3958 
3959 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
3960 	    len <= TCP_FASTOPEN_COOKIE_MAX)
3961 		memcpy(foc->val, cookie, len);
3962 	else if (len != 0)
3963 		len = -1;
3964 	foc->len = len;
3965 	foc->exp = exp_opt;
3966 }
3967 
smc_parse_options(const struct tcphdr * th,struct tcp_options_received * opt_rx,const unsigned char * ptr,int opsize)3968 static bool smc_parse_options(const struct tcphdr *th,
3969 			      struct tcp_options_received *opt_rx,
3970 			      const unsigned char *ptr,
3971 			      int opsize)
3972 {
3973 #if IS_ENABLED(CONFIG_SMC)
3974 	if (static_branch_unlikely(&tcp_have_smc)) {
3975 		if (th->syn && !(opsize & 1) &&
3976 		    opsize >= TCPOLEN_EXP_SMC_BASE &&
3977 		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
3978 			opt_rx->smc_ok = 1;
3979 			return true;
3980 		}
3981 	}
3982 #endif
3983 	return false;
3984 }
3985 
3986 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
3987  * value on success.
3988  */
tcp_parse_mss_option(const struct tcphdr * th,u16 user_mss)3989 u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
3990 {
3991 	const unsigned char *ptr = (const unsigned char *)(th + 1);
3992 	int length = (th->doff * 4) - sizeof(struct tcphdr);
3993 	u16 mss = 0;
3994 
3995 	while (length > 0) {
3996 		int opcode = *ptr++;
3997 		int opsize;
3998 
3999 		switch (opcode) {
4000 		case TCPOPT_EOL:
4001 			return mss;
4002 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4003 			length--;
4004 			continue;
4005 		default:
4006 			if (length < 2)
4007 				return mss;
4008 			opsize = *ptr++;
4009 			if (opsize < 2) /* "silly options" */
4010 				return mss;
4011 			if (opsize > length)
4012 				return mss;	/* fail on partial options */
4013 			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4014 				u16 in_mss = get_unaligned_be16(ptr);
4015 
4016 				if (in_mss) {
4017 					if (user_mss && user_mss < in_mss)
4018 						in_mss = user_mss;
4019 					mss = in_mss;
4020 				}
4021 			}
4022 			ptr += opsize - 2;
4023 			length -= opsize;
4024 		}
4025 	}
4026 	return mss;
4027 }
4028 EXPORT_SYMBOL_GPL(tcp_parse_mss_option);
4029 
4030 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
4031  * But, this can also be called on packets in the established flow when
4032  * the fast version below fails.
4033  */
tcp_parse_options(const struct net * net,const struct sk_buff * skb,struct tcp_options_received * opt_rx,int estab,struct tcp_fastopen_cookie * foc)4034 void tcp_parse_options(const struct net *net,
4035 		       const struct sk_buff *skb,
4036 		       struct tcp_options_received *opt_rx, int estab,
4037 		       struct tcp_fastopen_cookie *foc)
4038 {
4039 	const unsigned char *ptr;
4040 	const struct tcphdr *th = tcp_hdr(skb);
4041 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4042 
4043 	ptr = (const unsigned char *)(th + 1);
4044 	opt_rx->saw_tstamp = 0;
4045 	opt_rx->saw_unknown = 0;
4046 
4047 	while (length > 0) {
4048 		int opcode = *ptr++;
4049 		int opsize;
4050 
4051 		switch (opcode) {
4052 		case TCPOPT_EOL:
4053 			return;
4054 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4055 			length--;
4056 			continue;
4057 		default:
4058 			if (length < 2)
4059 				return;
4060 			opsize = *ptr++;
4061 			if (opsize < 2) /* "silly options" */
4062 				return;
4063 			if (opsize > length)
4064 				return;	/* don't parse partial options */
4065 			switch (opcode) {
4066 			case TCPOPT_MSS:
4067 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4068 					u16 in_mss = get_unaligned_be16(ptr);
4069 					if (in_mss) {
4070 						if (opt_rx->user_mss &&
4071 						    opt_rx->user_mss < in_mss)
4072 							in_mss = opt_rx->user_mss;
4073 						opt_rx->mss_clamp = in_mss;
4074 					}
4075 				}
4076 				break;
4077 			case TCPOPT_WINDOW:
4078 				if (opsize == TCPOLEN_WINDOW && th->syn &&
4079 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4080 					__u8 snd_wscale = *(__u8 *)ptr;
4081 					opt_rx->wscale_ok = 1;
4082 					if (snd_wscale > TCP_MAX_WSCALE) {
4083 						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4084 								     __func__,
4085 								     snd_wscale,
4086 								     TCP_MAX_WSCALE);
4087 						snd_wscale = TCP_MAX_WSCALE;
4088 					}
4089 					opt_rx->snd_wscale = snd_wscale;
4090 				}
4091 				break;
4092 			case TCPOPT_TIMESTAMP:
4093 				if ((opsize == TCPOLEN_TIMESTAMP) &&
4094 				    ((estab && opt_rx->tstamp_ok) ||
4095 				     (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4096 					opt_rx->saw_tstamp = 1;
4097 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4098 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4099 				}
4100 				break;
4101 			case TCPOPT_SACK_PERM:
4102 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4103 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4104 					opt_rx->sack_ok = TCP_SACK_SEEN;
4105 					tcp_sack_reset(opt_rx);
4106 				}
4107 				break;
4108 
4109 			case TCPOPT_SACK:
4110 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4111 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4112 				   opt_rx->sack_ok) {
4113 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4114 				}
4115 				break;
4116 #ifdef CONFIG_TCP_MD5SIG
4117 			case TCPOPT_MD5SIG:
4118 				/*
4119 				 * The MD5 Hash has already been
4120 				 * checked (see tcp_v{4,6}_do_rcv()).
4121 				 */
4122 				break;
4123 #endif
4124 			case TCPOPT_FASTOPEN:
4125 				tcp_parse_fastopen_option(
4126 					opsize - TCPOLEN_FASTOPEN_BASE,
4127 					ptr, th->syn, foc, false);
4128 				break;
4129 
4130 			case TCPOPT_EXP:
4131 				/* Fast Open option shares code 254 using a
4132 				 * 16 bits magic number.
4133 				 */
4134 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4135 				    get_unaligned_be16(ptr) ==
4136 				    TCPOPT_FASTOPEN_MAGIC) {
4137 					tcp_parse_fastopen_option(opsize -
4138 						TCPOLEN_EXP_FASTOPEN_BASE,
4139 						ptr + 2, th->syn, foc, true);
4140 					break;
4141 				}
4142 
4143 				if (smc_parse_options(th, opt_rx, ptr, opsize))
4144 					break;
4145 
4146 				opt_rx->saw_unknown = 1;
4147 				break;
4148 
4149 			default:
4150 				opt_rx->saw_unknown = 1;
4151 			}
4152 			ptr += opsize-2;
4153 			length -= opsize;
4154 		}
4155 	}
4156 }
4157 EXPORT_SYMBOL(tcp_parse_options);
4158 
tcp_parse_aligned_timestamp(struct tcp_sock * tp,const struct tcphdr * th)4159 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4160 {
4161 	const __be32 *ptr = (const __be32 *)(th + 1);
4162 
4163 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4164 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4165 		tp->rx_opt.saw_tstamp = 1;
4166 		++ptr;
4167 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4168 		++ptr;
4169 		if (*ptr)
4170 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4171 		else
4172 			tp->rx_opt.rcv_tsecr = 0;
4173 		return true;
4174 	}
4175 	return false;
4176 }
4177 
4178 /* Fast parse options. This hopes to only see timestamps.
4179  * If it is wrong it falls back on tcp_parse_options().
4180  */
tcp_fast_parse_options(const struct net * net,const struct sk_buff * skb,const struct tcphdr * th,struct tcp_sock * tp)4181 static bool tcp_fast_parse_options(const struct net *net,
4182 				   const struct sk_buff *skb,
4183 				   const struct tcphdr *th, struct tcp_sock *tp)
4184 {
4185 	/* In the spirit of fast parsing, compare doff directly to constant
4186 	 * values.  Because equality is used, short doff can be ignored here.
4187 	 */
4188 	if (th->doff == (sizeof(*th) / 4)) {
4189 		tp->rx_opt.saw_tstamp = 0;
4190 		return false;
4191 	} else if (tp->rx_opt.tstamp_ok &&
4192 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4193 		if (tcp_parse_aligned_timestamp(tp, th))
4194 			return true;
4195 	}
4196 
4197 	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4198 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4199 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4200 
4201 	return true;
4202 }
4203 
4204 #ifdef CONFIG_TCP_MD5SIG
4205 /*
4206  * Parse MD5 Signature option
4207  */
tcp_parse_md5sig_option(const struct tcphdr * th)4208 const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
4209 {
4210 	int length = (th->doff << 2) - sizeof(*th);
4211 	const u8 *ptr = (const u8 *)(th + 1);
4212 
4213 	/* If not enough data remaining, we can short cut */
4214 	while (length >= TCPOLEN_MD5SIG) {
4215 		int opcode = *ptr++;
4216 		int opsize;
4217 
4218 		switch (opcode) {
4219 		case TCPOPT_EOL:
4220 			return NULL;
4221 		case TCPOPT_NOP:
4222 			length--;
4223 			continue;
4224 		default:
4225 			opsize = *ptr++;
4226 			if (opsize < 2 || opsize > length)
4227 				return NULL;
4228 			if (opcode == TCPOPT_MD5SIG)
4229 				return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
4230 		}
4231 		ptr += opsize - 2;
4232 		length -= opsize;
4233 	}
4234 	return NULL;
4235 }
4236 EXPORT_SYMBOL(tcp_parse_md5sig_option);
4237 #endif
4238 
4239 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4240  *
4241  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4242  * it can pass through stack. So, the following predicate verifies that
4243  * this segment is not used for anything but congestion avoidance or
4244  * fast retransmit. Moreover, we even are able to eliminate most of such
4245  * second order effects, if we apply some small "replay" window (~RTO)
4246  * to timestamp space.
4247  *
4248  * All these measures still do not guarantee that we reject wrapped ACKs
4249  * on networks with high bandwidth, when sequence space is recycled fastly,
4250  * but it guarantees that such events will be very rare and do not affect
4251  * connection seriously. This doesn't look nice, but alas, PAWS is really
4252  * buggy extension.
4253  *
4254  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4255  * states that events when retransmit arrives after original data are rare.
4256  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4257  * the biggest problem on large power networks even with minor reordering.
4258  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4259  * up to bandwidth of 18Gigabit/sec. 8) ]
4260  */
4261 
tcp_disordered_ack(const struct sock * sk,const struct sk_buff * skb)4262 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4263 {
4264 	const struct tcp_sock *tp = tcp_sk(sk);
4265 	const struct tcphdr *th = tcp_hdr(skb);
4266 	u32 seq = TCP_SKB_CB(skb)->seq;
4267 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4268 
4269 	return (/* 1. Pure ACK with correct sequence number. */
4270 		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4271 
4272 		/* 2. ... and duplicate ACK. */
4273 		ack == tp->snd_una &&
4274 
4275 		/* 3. ... and does not update window. */
4276 		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4277 
4278 		/* 4. ... and sits in replay window. */
4279 		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4280 }
4281 
tcp_paws_discard(const struct sock * sk,const struct sk_buff * skb)4282 static inline bool tcp_paws_discard(const struct sock *sk,
4283 				   const struct sk_buff *skb)
4284 {
4285 	const struct tcp_sock *tp = tcp_sk(sk);
4286 
4287 	return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4288 	       !tcp_disordered_ack(sk, skb);
4289 }
4290 
4291 /* Check segment sequence number for validity.
4292  *
4293  * Segment controls are considered valid, if the segment
4294  * fits to the window after truncation to the window. Acceptability
4295  * of data (and SYN, FIN, of course) is checked separately.
4296  * See tcp_data_queue(), for example.
4297  *
4298  * Also, controls (RST is main one) are accepted using RCV.WUP instead
4299  * of RCV.NXT. Peer still did not advance his SND.UNA when we
4300  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4301  * (borrowed from freebsd)
4302  */
4303 
tcp_sequence(const struct tcp_sock * tp,u32 seq,u32 end_seq)4304 static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4305 {
4306 	return	!before(end_seq, tp->rcv_wup) &&
4307 		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4308 }
4309 
4310 /* When we get a reset we do this. */
tcp_reset(struct sock * sk,struct sk_buff * skb)4311 void tcp_reset(struct sock *sk, struct sk_buff *skb)
4312 {
4313 	trace_tcp_receive_reset(sk);
4314 
4315 	/* mptcp can't tell us to ignore reset pkts,
4316 	 * so just ignore the return value of mptcp_incoming_options().
4317 	 */
4318 	if (sk_is_mptcp(sk))
4319 		mptcp_incoming_options(sk, skb);
4320 
4321 	/* We want the right error as BSD sees it (and indeed as we do). */
4322 	switch (sk->sk_state) {
4323 	case TCP_SYN_SENT:
4324 		sk->sk_err = ECONNREFUSED;
4325 		break;
4326 	case TCP_CLOSE_WAIT:
4327 		sk->sk_err = EPIPE;
4328 		break;
4329 	case TCP_CLOSE:
4330 		return;
4331 	default:
4332 		sk->sk_err = ECONNRESET;
4333 	}
4334 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4335 	smp_wmb();
4336 
4337 	tcp_write_queue_purge(sk);
4338 	tcp_done(sk);
4339 
4340 	if (!sock_flag(sk, SOCK_DEAD))
4341 		sk_error_report(sk);
4342 }
4343 
4344 /*
4345  * 	Process the FIN bit. This now behaves as it is supposed to work
4346  *	and the FIN takes effect when it is validly part of sequence
4347  *	space. Not before when we get holes.
4348  *
4349  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4350  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4351  *	TIME-WAIT)
4352  *
4353  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4354  *	close and we go into CLOSING (and later onto TIME-WAIT)
4355  *
4356  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4357  */
tcp_fin(struct sock * sk)4358 void tcp_fin(struct sock *sk)
4359 {
4360 	struct tcp_sock *tp = tcp_sk(sk);
4361 
4362 	inet_csk_schedule_ack(sk);
4363 
4364 	sk->sk_shutdown |= RCV_SHUTDOWN;
4365 	sock_set_flag(sk, SOCK_DONE);
4366 
4367 	switch (sk->sk_state) {
4368 	case TCP_SYN_RECV:
4369 	case TCP_ESTABLISHED:
4370 		/* Move to CLOSE_WAIT */
4371 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4372 		inet_csk_enter_pingpong_mode(sk);
4373 		break;
4374 
4375 	case TCP_CLOSE_WAIT:
4376 	case TCP_CLOSING:
4377 		/* Received a retransmission of the FIN, do
4378 		 * nothing.
4379 		 */
4380 		break;
4381 	case TCP_LAST_ACK:
4382 		/* RFC793: Remain in the LAST-ACK state. */
4383 		break;
4384 
4385 	case TCP_FIN_WAIT1:
4386 		/* This case occurs when a simultaneous close
4387 		 * happens, we must ack the received FIN and
4388 		 * enter the CLOSING state.
4389 		 */
4390 		tcp_send_ack(sk);
4391 		tcp_set_state(sk, TCP_CLOSING);
4392 		break;
4393 	case TCP_FIN_WAIT2:
4394 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4395 		tcp_send_ack(sk);
4396 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4397 		break;
4398 	default:
4399 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4400 		 * cases we should never reach this piece of code.
4401 		 */
4402 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4403 		       __func__, sk->sk_state);
4404 		break;
4405 	}
4406 
4407 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4408 	 * Probably, we should reset in this case. For now drop them.
4409 	 */
4410 	skb_rbtree_purge(&tp->out_of_order_queue);
4411 	if (tcp_is_sack(tp))
4412 		tcp_sack_reset(&tp->rx_opt);
4413 
4414 	if (!sock_flag(sk, SOCK_DEAD)) {
4415 		sk->sk_state_change(sk);
4416 
4417 		/* Do not send POLL_HUP for half duplex close. */
4418 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4419 		    sk->sk_state == TCP_CLOSE)
4420 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4421 		else
4422 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4423 	}
4424 }
4425 
tcp_sack_extend(struct tcp_sack_block * sp,u32 seq,u32 end_seq)4426 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4427 				  u32 end_seq)
4428 {
4429 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4430 		if (before(seq, sp->start_seq))
4431 			sp->start_seq = seq;
4432 		if (after(end_seq, sp->end_seq))
4433 			sp->end_seq = end_seq;
4434 		return true;
4435 	}
4436 	return false;
4437 }
4438 
tcp_dsack_set(struct sock * sk,u32 seq,u32 end_seq)4439 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4440 {
4441 	struct tcp_sock *tp = tcp_sk(sk);
4442 
4443 	if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4444 		int mib_idx;
4445 
4446 		if (before(seq, tp->rcv_nxt))
4447 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4448 		else
4449 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4450 
4451 		NET_INC_STATS(sock_net(sk), mib_idx);
4452 
4453 		tp->rx_opt.dsack = 1;
4454 		tp->duplicate_sack[0].start_seq = seq;
4455 		tp->duplicate_sack[0].end_seq = end_seq;
4456 	}
4457 }
4458 
tcp_dsack_extend(struct sock * sk,u32 seq,u32 end_seq)4459 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4460 {
4461 	struct tcp_sock *tp = tcp_sk(sk);
4462 
4463 	if (!tp->rx_opt.dsack)
4464 		tcp_dsack_set(sk, seq, end_seq);
4465 	else
4466 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4467 }
4468 
tcp_rcv_spurious_retrans(struct sock * sk,const struct sk_buff * skb)4469 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4470 {
4471 	/* When the ACK path fails or drops most ACKs, the sender would
4472 	 * timeout and spuriously retransmit the same segment repeatedly.
4473 	 * The receiver remembers and reflects via DSACKs. Leverage the
4474 	 * DSACK state and change the txhash to re-route speculatively.
4475 	 */
4476 	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
4477 	    sk_rethink_txhash(sk))
4478 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
4479 }
4480 
tcp_send_dupack(struct sock * sk,const struct sk_buff * skb)4481 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4482 {
4483 	struct tcp_sock *tp = tcp_sk(sk);
4484 
4485 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4486 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4487 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4488 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4489 
4490 		if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4491 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4492 
4493 			tcp_rcv_spurious_retrans(sk, skb);
4494 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4495 				end_seq = tp->rcv_nxt;
4496 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4497 		}
4498 	}
4499 
4500 	tcp_send_ack(sk);
4501 }
4502 
4503 /* These routines update the SACK block as out-of-order packets arrive or
4504  * in-order packets close up the sequence space.
4505  */
tcp_sack_maybe_coalesce(struct tcp_sock * tp)4506 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4507 {
4508 	int this_sack;
4509 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4510 	struct tcp_sack_block *swalk = sp + 1;
4511 
4512 	/* See if the recent change to the first SACK eats into
4513 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4514 	 */
4515 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4516 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4517 			int i;
4518 
4519 			/* Zap SWALK, by moving every further SACK up by one slot.
4520 			 * Decrease num_sacks.
4521 			 */
4522 			tp->rx_opt.num_sacks--;
4523 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4524 				sp[i] = sp[i + 1];
4525 			continue;
4526 		}
4527 		this_sack++;
4528 		swalk++;
4529 	}
4530 }
4531 
tcp_sack_compress_send_ack(struct sock * sk)4532 static void tcp_sack_compress_send_ack(struct sock *sk)
4533 {
4534 	struct tcp_sock *tp = tcp_sk(sk);
4535 
4536 	if (!tp->compressed_ack)
4537 		return;
4538 
4539 	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4540 		__sock_put(sk);
4541 
4542 	/* Since we have to send one ack finally,
4543 	 * substract one from tp->compressed_ack to keep
4544 	 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4545 	 */
4546 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4547 		      tp->compressed_ack - 1);
4548 
4549 	tp->compressed_ack = 0;
4550 	tcp_send_ack(sk);
4551 }
4552 
4553 /* Reasonable amount of sack blocks included in TCP SACK option
4554  * The max is 4, but this becomes 3 if TCP timestamps are there.
4555  * Given that SACK packets might be lost, be conservative and use 2.
4556  */
4557 #define TCP_SACK_BLOCKS_EXPECTED 2
4558 
tcp_sack_new_ofo_skb(struct sock * sk,u32 seq,u32 end_seq)4559 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4560 {
4561 	struct tcp_sock *tp = tcp_sk(sk);
4562 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4563 	int cur_sacks = tp->rx_opt.num_sacks;
4564 	int this_sack;
4565 
4566 	if (!cur_sacks)
4567 		goto new_sack;
4568 
4569 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4570 		if (tcp_sack_extend(sp, seq, end_seq)) {
4571 			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4572 				tcp_sack_compress_send_ack(sk);
4573 			/* Rotate this_sack to the first one. */
4574 			for (; this_sack > 0; this_sack--, sp--)
4575 				swap(*sp, *(sp - 1));
4576 			if (cur_sacks > 1)
4577 				tcp_sack_maybe_coalesce(tp);
4578 			return;
4579 		}
4580 	}
4581 
4582 	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4583 		tcp_sack_compress_send_ack(sk);
4584 
4585 	/* Could not find an adjacent existing SACK, build a new one,
4586 	 * put it at the front, and shift everyone else down.  We
4587 	 * always know there is at least one SACK present already here.
4588 	 *
4589 	 * If the sack array is full, forget about the last one.
4590 	 */
4591 	if (this_sack >= TCP_NUM_SACKS) {
4592 		this_sack--;
4593 		tp->rx_opt.num_sacks--;
4594 		sp--;
4595 	}
4596 	for (; this_sack > 0; this_sack--, sp--)
4597 		*sp = *(sp - 1);
4598 
4599 new_sack:
4600 	/* Build the new head SACK, and we're done. */
4601 	sp->start_seq = seq;
4602 	sp->end_seq = end_seq;
4603 	tp->rx_opt.num_sacks++;
4604 }
4605 
4606 /* RCV.NXT advances, some SACKs should be eaten. */
4607 
tcp_sack_remove(struct tcp_sock * tp)4608 static void tcp_sack_remove(struct tcp_sock *tp)
4609 {
4610 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4611 	int num_sacks = tp->rx_opt.num_sacks;
4612 	int this_sack;
4613 
4614 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4615 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4616 		tp->rx_opt.num_sacks = 0;
4617 		return;
4618 	}
4619 
4620 	for (this_sack = 0; this_sack < num_sacks;) {
4621 		/* Check if the start of the sack is covered by RCV.NXT. */
4622 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4623 			int i;
4624 
4625 			/* RCV.NXT must cover all the block! */
4626 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4627 
4628 			/* Zap this SACK, by moving forward any other SACKS. */
4629 			for (i = this_sack+1; i < num_sacks; i++)
4630 				tp->selective_acks[i-1] = tp->selective_acks[i];
4631 			num_sacks--;
4632 			continue;
4633 		}
4634 		this_sack++;
4635 		sp++;
4636 	}
4637 	tp->rx_opt.num_sacks = num_sacks;
4638 }
4639 
4640 /**
4641  * tcp_try_coalesce - try to merge skb to prior one
4642  * @sk: socket
4643  * @to: prior buffer
4644  * @from: buffer to add in queue
4645  * @fragstolen: pointer to boolean
4646  *
4647  * Before queueing skb @from after @to, try to merge them
4648  * to reduce overall memory use and queue lengths, if cost is small.
4649  * Packets in ofo or receive queues can stay a long time.
4650  * Better try to coalesce them right now to avoid future collapses.
4651  * Returns true if caller should free @from instead of queueing it
4652  */
tcp_try_coalesce(struct sock * sk,struct sk_buff * to,struct sk_buff * from,bool * fragstolen)4653 static bool tcp_try_coalesce(struct sock *sk,
4654 			     struct sk_buff *to,
4655 			     struct sk_buff *from,
4656 			     bool *fragstolen)
4657 {
4658 	int delta;
4659 
4660 	*fragstolen = false;
4661 
4662 	/* Its possible this segment overlaps with prior segment in queue */
4663 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4664 		return false;
4665 
4666 	if (!mptcp_skb_can_collapse(to, from))
4667 		return false;
4668 
4669 #ifdef CONFIG_TLS_DEVICE
4670 	if (from->decrypted != to->decrypted)
4671 		return false;
4672 #endif
4673 
4674 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4675 		return false;
4676 
4677 	atomic_add(delta, &sk->sk_rmem_alloc);
4678 	sk_mem_charge(sk, delta);
4679 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4680 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4681 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4682 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4683 
4684 	if (TCP_SKB_CB(from)->has_rxtstamp) {
4685 		TCP_SKB_CB(to)->has_rxtstamp = true;
4686 		to->tstamp = from->tstamp;
4687 		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4688 	}
4689 
4690 	return true;
4691 }
4692 
tcp_ooo_try_coalesce(struct sock * sk,struct sk_buff * to,struct sk_buff * from,bool * fragstolen)4693 static bool tcp_ooo_try_coalesce(struct sock *sk,
4694 			     struct sk_buff *to,
4695 			     struct sk_buff *from,
4696 			     bool *fragstolen)
4697 {
4698 	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4699 
4700 	/* In case tcp_drop_reason() is called later, update to->gso_segs */
4701 	if (res) {
4702 		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4703 			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
4704 
4705 		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4706 	}
4707 	return res;
4708 }
4709 
tcp_drop_reason(struct sock * sk,struct sk_buff * skb,enum skb_drop_reason reason)4710 static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
4711 			    enum skb_drop_reason reason)
4712 {
4713 	sk_drops_add(sk, skb);
4714 	kfree_skb_reason(skb, reason);
4715 }
4716 
4717 /* This one checks to see if we can put data from the
4718  * out_of_order queue into the receive_queue.
4719  */
tcp_ofo_queue(struct sock * sk)4720 static void tcp_ofo_queue(struct sock *sk)
4721 {
4722 	struct tcp_sock *tp = tcp_sk(sk);
4723 	__u32 dsack_high = tp->rcv_nxt;
4724 	bool fin, fragstolen, eaten;
4725 	struct sk_buff *skb, *tail;
4726 	struct rb_node *p;
4727 
4728 	p = rb_first(&tp->out_of_order_queue);
4729 	while (p) {
4730 		skb = rb_to_skb(p);
4731 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4732 			break;
4733 
4734 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4735 			__u32 dsack = dsack_high;
4736 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4737 				dsack_high = TCP_SKB_CB(skb)->end_seq;
4738 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4739 		}
4740 		p = rb_next(p);
4741 		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4742 
4743 		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4744 			tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
4745 			continue;
4746 		}
4747 
4748 		tail = skb_peek_tail(&sk->sk_receive_queue);
4749 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4750 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4751 		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4752 		if (!eaten)
4753 			__skb_queue_tail(&sk->sk_receive_queue, skb);
4754 		else
4755 			kfree_skb_partial(skb, fragstolen);
4756 
4757 		if (unlikely(fin)) {
4758 			tcp_fin(sk);
4759 			/* tcp_fin() purges tp->out_of_order_queue,
4760 			 * so we must end this loop right now.
4761 			 */
4762 			break;
4763 		}
4764 	}
4765 }
4766 
4767 static bool tcp_prune_ofo_queue(struct sock *sk);
4768 static int tcp_prune_queue(struct sock *sk);
4769 
tcp_try_rmem_schedule(struct sock * sk,struct sk_buff * skb,unsigned int size)4770 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
4771 				 unsigned int size)
4772 {
4773 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4774 	    !sk_rmem_schedule(sk, skb, size)) {
4775 
4776 		if (tcp_prune_queue(sk) < 0)
4777 			return -1;
4778 
4779 		while (!sk_rmem_schedule(sk, skb, size)) {
4780 			if (!tcp_prune_ofo_queue(sk))
4781 				return -1;
4782 		}
4783 	}
4784 	return 0;
4785 }
4786 
tcp_data_queue_ofo(struct sock * sk,struct sk_buff * skb)4787 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
4788 {
4789 	struct tcp_sock *tp = tcp_sk(sk);
4790 	struct rb_node **p, *parent;
4791 	struct sk_buff *skb1;
4792 	u32 seq, end_seq;
4793 	bool fragstolen;
4794 
4795 	tcp_ecn_check_ce(sk, skb);
4796 
4797 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
4798 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
4799 		sk->sk_data_ready(sk);
4800 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
4801 		return;
4802 	}
4803 
4804 	/* Disable header prediction. */
4805 	tp->pred_flags = 0;
4806 	inet_csk_schedule_ack(sk);
4807 
4808 	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4809 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
4810 	seq = TCP_SKB_CB(skb)->seq;
4811 	end_seq = TCP_SKB_CB(skb)->end_seq;
4812 
4813 	p = &tp->out_of_order_queue.rb_node;
4814 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4815 		/* Initial out of order segment, build 1 SACK. */
4816 		if (tcp_is_sack(tp)) {
4817 			tp->rx_opt.num_sacks = 1;
4818 			tp->selective_acks[0].start_seq = seq;
4819 			tp->selective_acks[0].end_seq = end_seq;
4820 		}
4821 		rb_link_node(&skb->rbnode, NULL, p);
4822 		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4823 		tp->ooo_last_skb = skb;
4824 		goto end;
4825 	}
4826 
4827 	/* In the typical case, we are adding an skb to the end of the list.
4828 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
4829 	 */
4830 	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
4831 				 skb, &fragstolen)) {
4832 coalesce_done:
4833 		/* For non sack flows, do not grow window to force DUPACK
4834 		 * and trigger fast retransmit.
4835 		 */
4836 		if (tcp_is_sack(tp))
4837 			tcp_grow_window(sk, skb, true);
4838 		kfree_skb_partial(skb, fragstolen);
4839 		skb = NULL;
4840 		goto add_sack;
4841 	}
4842 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
4843 	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
4844 		parent = &tp->ooo_last_skb->rbnode;
4845 		p = &parent->rb_right;
4846 		goto insert;
4847 	}
4848 
4849 	/* Find place to insert this segment. Handle overlaps on the way. */
4850 	parent = NULL;
4851 	while (*p) {
4852 		parent = *p;
4853 		skb1 = rb_to_skb(parent);
4854 		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
4855 			p = &parent->rb_left;
4856 			continue;
4857 		}
4858 		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4859 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4860 				/* All the bits are present. Drop. */
4861 				NET_INC_STATS(sock_net(sk),
4862 					      LINUX_MIB_TCPOFOMERGE);
4863 				tcp_drop_reason(sk, skb,
4864 						SKB_DROP_REASON_TCP_OFOMERGE);
4865 				skb = NULL;
4866 				tcp_dsack_set(sk, seq, end_seq);
4867 				goto add_sack;
4868 			}
4869 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4870 				/* Partial overlap. */
4871 				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
4872 			} else {
4873 				/* skb's seq == skb1's seq and skb covers skb1.
4874 				 * Replace skb1 with skb.
4875 				 */
4876 				rb_replace_node(&skb1->rbnode, &skb->rbnode,
4877 						&tp->out_of_order_queue);
4878 				tcp_dsack_extend(sk,
4879 						 TCP_SKB_CB(skb1)->seq,
4880 						 TCP_SKB_CB(skb1)->end_seq);
4881 				NET_INC_STATS(sock_net(sk),
4882 					      LINUX_MIB_TCPOFOMERGE);
4883 				tcp_drop_reason(sk, skb1,
4884 						SKB_DROP_REASON_TCP_OFOMERGE);
4885 				goto merge_right;
4886 			}
4887 		} else if (tcp_ooo_try_coalesce(sk, skb1,
4888 						skb, &fragstolen)) {
4889 			goto coalesce_done;
4890 		}
4891 		p = &parent->rb_right;
4892 	}
4893 insert:
4894 	/* Insert segment into RB tree. */
4895 	rb_link_node(&skb->rbnode, parent, p);
4896 	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
4897 
4898 merge_right:
4899 	/* Remove other segments covered by skb. */
4900 	while ((skb1 = skb_rb_next(skb)) != NULL) {
4901 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4902 			break;
4903 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4904 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4905 					 end_seq);
4906 			break;
4907 		}
4908 		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
4909 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4910 				 TCP_SKB_CB(skb1)->end_seq);
4911 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
4912 		tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
4913 	}
4914 	/* If there is no skb after us, we are the last_skb ! */
4915 	if (!skb1)
4916 		tp->ooo_last_skb = skb;
4917 
4918 add_sack:
4919 	if (tcp_is_sack(tp))
4920 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
4921 end:
4922 	if (skb) {
4923 		/* For non sack flows, do not grow window to force DUPACK
4924 		 * and trigger fast retransmit.
4925 		 */
4926 		if (tcp_is_sack(tp))
4927 			tcp_grow_window(sk, skb, false);
4928 		skb_condense(skb);
4929 		skb_set_owner_r(skb, sk);
4930 	}
4931 }
4932 
tcp_queue_rcv(struct sock * sk,struct sk_buff * skb,bool * fragstolen)4933 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
4934 				      bool *fragstolen)
4935 {
4936 	int eaten;
4937 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
4938 
4939 	eaten = (tail &&
4940 		 tcp_try_coalesce(sk, tail,
4941 				  skb, fragstolen)) ? 1 : 0;
4942 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
4943 	if (!eaten) {
4944 		__skb_queue_tail(&sk->sk_receive_queue, skb);
4945 		skb_set_owner_r(skb, sk);
4946 	}
4947 	return eaten;
4948 }
4949 
tcp_send_rcvq(struct sock * sk,struct msghdr * msg,size_t size)4950 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
4951 {
4952 	struct sk_buff *skb;
4953 	int err = -ENOMEM;
4954 	int data_len = 0;
4955 	bool fragstolen;
4956 
4957 	if (size == 0)
4958 		return 0;
4959 
4960 	if (size > PAGE_SIZE) {
4961 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
4962 
4963 		data_len = npages << PAGE_SHIFT;
4964 		size = data_len + (size & ~PAGE_MASK);
4965 	}
4966 	skb = alloc_skb_with_frags(size - data_len, data_len,
4967 				   PAGE_ALLOC_COSTLY_ORDER,
4968 				   &err, sk->sk_allocation);
4969 	if (!skb)
4970 		goto err;
4971 
4972 	skb_put(skb, size - data_len);
4973 	skb->data_len = data_len;
4974 	skb->len = size;
4975 
4976 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
4977 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
4978 		goto err_free;
4979 	}
4980 
4981 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
4982 	if (err)
4983 		goto err_free;
4984 
4985 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
4986 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
4987 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
4988 
4989 	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
4990 		WARN_ON_ONCE(fragstolen); /* should not happen */
4991 		__kfree_skb(skb);
4992 	}
4993 	return size;
4994 
4995 err_free:
4996 	kfree_skb(skb);
4997 err:
4998 	return err;
4999 
5000 }
5001 
tcp_data_ready(struct sock * sk)5002 void tcp_data_ready(struct sock *sk)
5003 {
5004 	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
5005 		sk->sk_data_ready(sk);
5006 }
5007 
tcp_data_queue(struct sock * sk,struct sk_buff * skb)5008 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
5009 {
5010 	struct tcp_sock *tp = tcp_sk(sk);
5011 	enum skb_drop_reason reason;
5012 	bool fragstolen;
5013 	int eaten;
5014 
5015 	/* If a subflow has been reset, the packet should not continue
5016 	 * to be processed, drop the packet.
5017 	 */
5018 	if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5019 		__kfree_skb(skb);
5020 		return;
5021 	}
5022 
5023 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5024 		__kfree_skb(skb);
5025 		return;
5026 	}
5027 	skb_dst_drop(skb);
5028 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
5029 
5030 	reason = SKB_DROP_REASON_NOT_SPECIFIED;
5031 	tp->rx_opt.dsack = 0;
5032 
5033 	/*  Queue data for delivery to the user.
5034 	 *  Packets in sequence go to the receive queue.
5035 	 *  Out of sequence packets to the out_of_order_queue.
5036 	 */
5037 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5038 		if (tcp_receive_window(tp) == 0) {
5039 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5040 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5041 			goto out_of_window;
5042 		}
5043 
5044 		/* Ok. In sequence. In window. */
5045 queue_and_out:
5046 		if (skb_queue_len(&sk->sk_receive_queue) == 0)
5047 			sk_forced_mem_schedule(sk, skb->truesize);
5048 		else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5049 			reason = SKB_DROP_REASON_PROTO_MEM;
5050 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5051 			sk->sk_data_ready(sk);
5052 			goto drop;
5053 		}
5054 
5055 		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5056 		if (skb->len)
5057 			tcp_event_data_recv(sk, skb);
5058 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5059 			tcp_fin(sk);
5060 
5061 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5062 			tcp_ofo_queue(sk);
5063 
5064 			/* RFC5681. 4.2. SHOULD send immediate ACK, when
5065 			 * gap in queue is filled.
5066 			 */
5067 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5068 				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5069 		}
5070 
5071 		if (tp->rx_opt.num_sacks)
5072 			tcp_sack_remove(tp);
5073 
5074 		tcp_fast_path_check(sk);
5075 
5076 		if (eaten > 0)
5077 			kfree_skb_partial(skb, fragstolen);
5078 		if (!sock_flag(sk, SOCK_DEAD))
5079 			tcp_data_ready(sk);
5080 		return;
5081 	}
5082 
5083 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5084 		tcp_rcv_spurious_retrans(sk, skb);
5085 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
5086 		reason = SKB_DROP_REASON_TCP_OLD_DATA;
5087 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5088 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5089 
5090 out_of_window:
5091 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5092 		inet_csk_schedule_ack(sk);
5093 drop:
5094 		tcp_drop_reason(sk, skb, reason);
5095 		return;
5096 	}
5097 
5098 	/* Out of window. F.e. zero window probe. */
5099 	if (!before(TCP_SKB_CB(skb)->seq,
5100 		    tp->rcv_nxt + tcp_receive_window(tp))) {
5101 		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5102 		goto out_of_window;
5103 	}
5104 
5105 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5106 		/* Partial packet, seq < rcv_next < end_seq */
5107 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5108 
5109 		/* If window is closed, drop tail of packet. But after
5110 		 * remembering D-SACK for its head made in previous line.
5111 		 */
5112 		if (!tcp_receive_window(tp)) {
5113 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5114 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5115 			goto out_of_window;
5116 		}
5117 		goto queue_and_out;
5118 	}
5119 
5120 	tcp_data_queue_ofo(sk, skb);
5121 }
5122 
tcp_skb_next(struct sk_buff * skb,struct sk_buff_head * list)5123 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5124 {
5125 	if (list)
5126 		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5127 
5128 	return skb_rb_next(skb);
5129 }
5130 
tcp_collapse_one(struct sock * sk,struct sk_buff * skb,struct sk_buff_head * list,struct rb_root * root)5131 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5132 					struct sk_buff_head *list,
5133 					struct rb_root *root)
5134 {
5135 	struct sk_buff *next = tcp_skb_next(skb, list);
5136 
5137 	if (list)
5138 		__skb_unlink(skb, list);
5139 	else
5140 		rb_erase(&skb->rbnode, root);
5141 
5142 	__kfree_skb(skb);
5143 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5144 
5145 	return next;
5146 }
5147 
5148 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
tcp_rbtree_insert(struct rb_root * root,struct sk_buff * skb)5149 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5150 {
5151 	struct rb_node **p = &root->rb_node;
5152 	struct rb_node *parent = NULL;
5153 	struct sk_buff *skb1;
5154 
5155 	while (*p) {
5156 		parent = *p;
5157 		skb1 = rb_to_skb(parent);
5158 		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5159 			p = &parent->rb_left;
5160 		else
5161 			p = &parent->rb_right;
5162 	}
5163 	rb_link_node(&skb->rbnode, parent, p);
5164 	rb_insert_color(&skb->rbnode, root);
5165 }
5166 
5167 /* Collapse contiguous sequence of skbs head..tail with
5168  * sequence numbers start..end.
5169  *
5170  * If tail is NULL, this means until the end of the queue.
5171  *
5172  * Segments with FIN/SYN are not collapsed (only because this
5173  * simplifies code)
5174  */
5175 static void
tcp_collapse(struct sock * sk,struct sk_buff_head * list,struct rb_root * root,struct sk_buff * head,struct sk_buff * tail,u32 start,u32 end)5176 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5177 	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5178 {
5179 	struct sk_buff *skb = head, *n;
5180 	struct sk_buff_head tmp;
5181 	bool end_of_skbs;
5182 
5183 	/* First, check that queue is collapsible and find
5184 	 * the point where collapsing can be useful.
5185 	 */
5186 restart:
5187 	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5188 		n = tcp_skb_next(skb, list);
5189 
5190 		/* No new bits? It is possible on ofo queue. */
5191 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5192 			skb = tcp_collapse_one(sk, skb, list, root);
5193 			if (!skb)
5194 				break;
5195 			goto restart;
5196 		}
5197 
5198 		/* The first skb to collapse is:
5199 		 * - not SYN/FIN and
5200 		 * - bloated or contains data before "start" or
5201 		 *   overlaps to the next one and mptcp allow collapsing.
5202 		 */
5203 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5204 		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5205 		     before(TCP_SKB_CB(skb)->seq, start))) {
5206 			end_of_skbs = false;
5207 			break;
5208 		}
5209 
5210 		if (n && n != tail && mptcp_skb_can_collapse(skb, n) &&
5211 		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5212 			end_of_skbs = false;
5213 			break;
5214 		}
5215 
5216 		/* Decided to skip this, advance start seq. */
5217 		start = TCP_SKB_CB(skb)->end_seq;
5218 	}
5219 	if (end_of_skbs ||
5220 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5221 		return;
5222 
5223 	__skb_queue_head_init(&tmp);
5224 
5225 	while (before(start, end)) {
5226 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5227 		struct sk_buff *nskb;
5228 
5229 		nskb = alloc_skb(copy, GFP_ATOMIC);
5230 		if (!nskb)
5231 			break;
5232 
5233 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5234 #ifdef CONFIG_TLS_DEVICE
5235 		nskb->decrypted = skb->decrypted;
5236 #endif
5237 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5238 		if (list)
5239 			__skb_queue_before(list, skb, nskb);
5240 		else
5241 			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5242 		skb_set_owner_r(nskb, sk);
5243 		mptcp_skb_ext_move(nskb, skb);
5244 
5245 		/* Copy data, releasing collapsed skbs. */
5246 		while (copy > 0) {
5247 			int offset = start - TCP_SKB_CB(skb)->seq;
5248 			int size = TCP_SKB_CB(skb)->end_seq - start;
5249 
5250 			BUG_ON(offset < 0);
5251 			if (size > 0) {
5252 				size = min(copy, size);
5253 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5254 					BUG();
5255 				TCP_SKB_CB(nskb)->end_seq += size;
5256 				copy -= size;
5257 				start += size;
5258 			}
5259 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5260 				skb = tcp_collapse_one(sk, skb, list, root);
5261 				if (!skb ||
5262 				    skb == tail ||
5263 				    !mptcp_skb_can_collapse(nskb, skb) ||
5264 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
5265 					goto end;
5266 #ifdef CONFIG_TLS_DEVICE
5267 				if (skb->decrypted != nskb->decrypted)
5268 					goto end;
5269 #endif
5270 			}
5271 		}
5272 	}
5273 end:
5274 	skb_queue_walk_safe(&tmp, skb, n)
5275 		tcp_rbtree_insert(root, skb);
5276 }
5277 
5278 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5279  * and tcp_collapse() them until all the queue is collapsed.
5280  */
tcp_collapse_ofo_queue(struct sock * sk)5281 static void tcp_collapse_ofo_queue(struct sock *sk)
5282 {
5283 	struct tcp_sock *tp = tcp_sk(sk);
5284 	u32 range_truesize, sum_tiny = 0;
5285 	struct sk_buff *skb, *head;
5286 	u32 start, end;
5287 
5288 	skb = skb_rb_first(&tp->out_of_order_queue);
5289 new_range:
5290 	if (!skb) {
5291 		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5292 		return;
5293 	}
5294 	start = TCP_SKB_CB(skb)->seq;
5295 	end = TCP_SKB_CB(skb)->end_seq;
5296 	range_truesize = skb->truesize;
5297 
5298 	for (head = skb;;) {
5299 		skb = skb_rb_next(skb);
5300 
5301 		/* Range is terminated when we see a gap or when
5302 		 * we are at the queue end.
5303 		 */
5304 		if (!skb ||
5305 		    after(TCP_SKB_CB(skb)->seq, end) ||
5306 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5307 			/* Do not attempt collapsing tiny skbs */
5308 			if (range_truesize != head->truesize ||
5309 			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
5310 				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5311 					     head, skb, start, end);
5312 			} else {
5313 				sum_tiny += range_truesize;
5314 				if (sum_tiny > sk->sk_rcvbuf >> 3)
5315 					return;
5316 			}
5317 			goto new_range;
5318 		}
5319 
5320 		range_truesize += skb->truesize;
5321 		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5322 			start = TCP_SKB_CB(skb)->seq;
5323 		if (after(TCP_SKB_CB(skb)->end_seq, end))
5324 			end = TCP_SKB_CB(skb)->end_seq;
5325 	}
5326 }
5327 
5328 /*
5329  * Clean the out-of-order queue to make room.
5330  * We drop high sequences packets to :
5331  * 1) Let a chance for holes to be filled.
5332  * 2) not add too big latencies if thousands of packets sit there.
5333  *    (But if application shrinks SO_RCVBUF, we could still end up
5334  *     freeing whole queue here)
5335  * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5336  *
5337  * Return true if queue has shrunk.
5338  */
tcp_prune_ofo_queue(struct sock * sk)5339 static bool tcp_prune_ofo_queue(struct sock *sk)
5340 {
5341 	struct tcp_sock *tp = tcp_sk(sk);
5342 	struct rb_node *node, *prev;
5343 	int goal;
5344 
5345 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5346 		return false;
5347 
5348 	NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5349 	goal = sk->sk_rcvbuf >> 3;
5350 	node = &tp->ooo_last_skb->rbnode;
5351 	do {
5352 		prev = rb_prev(node);
5353 		rb_erase(node, &tp->out_of_order_queue);
5354 		goal -= rb_to_skb(node)->truesize;
5355 		tcp_drop_reason(sk, rb_to_skb(node),
5356 				SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5357 		if (!prev || goal <= 0) {
5358 			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5359 			    !tcp_under_memory_pressure(sk))
5360 				break;
5361 			goal = sk->sk_rcvbuf >> 3;
5362 		}
5363 		node = prev;
5364 	} while (node);
5365 	tp->ooo_last_skb = rb_to_skb(prev);
5366 
5367 	/* Reset SACK state.  A conforming SACK implementation will
5368 	 * do the same at a timeout based retransmit.  When a connection
5369 	 * is in a sad state like this, we care only about integrity
5370 	 * of the connection not performance.
5371 	 */
5372 	if (tp->rx_opt.sack_ok)
5373 		tcp_sack_reset(&tp->rx_opt);
5374 	return true;
5375 }
5376 
5377 /* Reduce allocated memory if we can, trying to get
5378  * the socket within its memory limits again.
5379  *
5380  * Return less than zero if we should start dropping frames
5381  * until the socket owning process reads some of the data
5382  * to stabilize the situation.
5383  */
tcp_prune_queue(struct sock * sk)5384 static int tcp_prune_queue(struct sock *sk)
5385 {
5386 	struct tcp_sock *tp = tcp_sk(sk);
5387 
5388 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5389 
5390 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5391 		tcp_clamp_window(sk);
5392 	else if (tcp_under_memory_pressure(sk))
5393 		tcp_adjust_rcv_ssthresh(sk);
5394 
5395 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5396 		return 0;
5397 
5398 	tcp_collapse_ofo_queue(sk);
5399 	if (!skb_queue_empty(&sk->sk_receive_queue))
5400 		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5401 			     skb_peek(&sk->sk_receive_queue),
5402 			     NULL,
5403 			     tp->copied_seq, tp->rcv_nxt);
5404 
5405 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5406 		return 0;
5407 
5408 	/* Collapsing did not help, destructive actions follow.
5409 	 * This must not ever occur. */
5410 
5411 	tcp_prune_ofo_queue(sk);
5412 
5413 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5414 		return 0;
5415 
5416 	/* If we are really being abused, tell the caller to silently
5417 	 * drop receive data on the floor.  It will get retransmitted
5418 	 * and hopefully then we'll have sufficient space.
5419 	 */
5420 	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5421 
5422 	/* Massive buffer overcommit. */
5423 	tp->pred_flags = 0;
5424 	return -1;
5425 }
5426 
tcp_should_expand_sndbuf(struct sock * sk)5427 static bool tcp_should_expand_sndbuf(struct sock *sk)
5428 {
5429 	const struct tcp_sock *tp = tcp_sk(sk);
5430 
5431 	/* If the user specified a specific send buffer setting, do
5432 	 * not modify it.
5433 	 */
5434 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5435 		return false;
5436 
5437 	/* If we are under global TCP memory pressure, do not expand.  */
5438 	if (tcp_under_memory_pressure(sk)) {
5439 		int unused_mem = sk_unused_reserved_mem(sk);
5440 
5441 		/* Adjust sndbuf according to reserved mem. But make sure
5442 		 * it never goes below SOCK_MIN_SNDBUF.
5443 		 * See sk_stream_moderate_sndbuf() for more details.
5444 		 */
5445 		if (unused_mem > SOCK_MIN_SNDBUF)
5446 			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5447 
5448 		return false;
5449 	}
5450 
5451 	/* If we are under soft global TCP memory pressure, do not expand.  */
5452 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5453 		return false;
5454 
5455 	/* If we filled the congestion window, do not expand.  */
5456 	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5457 		return false;
5458 
5459 	return true;
5460 }
5461 
tcp_new_space(struct sock * sk)5462 static void tcp_new_space(struct sock *sk)
5463 {
5464 	struct tcp_sock *tp = tcp_sk(sk);
5465 
5466 	if (tcp_should_expand_sndbuf(sk)) {
5467 		tcp_sndbuf_expand(sk);
5468 		tp->snd_cwnd_stamp = tcp_jiffies32;
5469 	}
5470 
5471 	INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5472 }
5473 
5474 /* Caller made space either from:
5475  * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5476  * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5477  *
5478  * We might be able to generate EPOLLOUT to the application if:
5479  * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5480  * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5481  *    small enough that tcp_stream_memory_free() decides it
5482  *    is time to generate EPOLLOUT.
5483  */
tcp_check_space(struct sock * sk)5484 void tcp_check_space(struct sock *sk)
5485 {
5486 	/* pairs with tcp_poll() */
5487 	smp_mb();
5488 	if (sk->sk_socket &&
5489 	    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5490 		tcp_new_space(sk);
5491 		if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5492 			tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5493 	}
5494 }
5495 
tcp_data_snd_check(struct sock * sk)5496 static inline void tcp_data_snd_check(struct sock *sk)
5497 {
5498 	tcp_push_pending_frames(sk);
5499 	tcp_check_space(sk);
5500 }
5501 
5502 /*
5503  * Check if sending an ack is needed.
5504  */
__tcp_ack_snd_check(struct sock * sk,int ofo_possible)5505 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5506 {
5507 	struct tcp_sock *tp = tcp_sk(sk);
5508 	unsigned long rtt, delay;
5509 
5510 	    /* More than one full frame received... */
5511 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5512 	     /* ... and right edge of window advances far enough.
5513 	      * (tcp_recvmsg() will send ACK otherwise).
5514 	      * If application uses SO_RCVLOWAT, we want send ack now if
5515 	      * we have not received enough bytes to satisfy the condition.
5516 	      */
5517 	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5518 	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5519 	    /* We ACK each frame or... */
5520 	    tcp_in_quickack_mode(sk) ||
5521 	    /* Protocol state mandates a one-time immediate ACK */
5522 	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5523 send_now:
5524 		tcp_send_ack(sk);
5525 		return;
5526 	}
5527 
5528 	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5529 		tcp_send_delayed_ack(sk);
5530 		return;
5531 	}
5532 
5533 	if (!tcp_is_sack(tp) ||
5534 	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
5535 		goto send_now;
5536 
5537 	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5538 		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5539 		tp->dup_ack_counter = 0;
5540 	}
5541 	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5542 		tp->dup_ack_counter++;
5543 		goto send_now;
5544 	}
5545 	tp->compressed_ack++;
5546 	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5547 		return;
5548 
5549 	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5550 
5551 	rtt = tp->rcv_rtt_est.rtt_us;
5552 	if (tp->srtt_us && tp->srtt_us < rtt)
5553 		rtt = tp->srtt_us;
5554 
5555 	delay = min_t(unsigned long,
5556 		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
5557 		      rtt * (NSEC_PER_USEC >> 3)/20);
5558 	sock_hold(sk);
5559 	hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5560 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns),
5561 			       HRTIMER_MODE_REL_PINNED_SOFT);
5562 }
5563 
tcp_ack_snd_check(struct sock * sk)5564 static inline void tcp_ack_snd_check(struct sock *sk)
5565 {
5566 	if (!inet_csk_ack_scheduled(sk)) {
5567 		/* We sent a data segment already. */
5568 		return;
5569 	}
5570 	__tcp_ack_snd_check(sk, 1);
5571 }
5572 
5573 /*
5574  *	This routine is only called when we have urgent data
5575  *	signaled. Its the 'slow' part of tcp_urg. It could be
5576  *	moved inline now as tcp_urg is only called from one
5577  *	place. We handle URGent data wrong. We have to - as
5578  *	BSD still doesn't use the correction from RFC961.
5579  *	For 1003.1g we should support a new option TCP_STDURG to permit
5580  *	either form (or just set the sysctl tcp_stdurg).
5581  */
5582 
tcp_check_urg(struct sock * sk,const struct tcphdr * th)5583 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5584 {
5585 	struct tcp_sock *tp = tcp_sk(sk);
5586 	u32 ptr = ntohs(th->urg_ptr);
5587 
5588 	if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5589 		ptr--;
5590 	ptr += ntohl(th->seq);
5591 
5592 	/* Ignore urgent data that we've already seen and read. */
5593 	if (after(tp->copied_seq, ptr))
5594 		return;
5595 
5596 	/* Do not replay urg ptr.
5597 	 *
5598 	 * NOTE: interesting situation not covered by specs.
5599 	 * Misbehaving sender may send urg ptr, pointing to segment,
5600 	 * which we already have in ofo queue. We are not able to fetch
5601 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5602 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5603 	 * situations. But it is worth to think about possibility of some
5604 	 * DoSes using some hypothetical application level deadlock.
5605 	 */
5606 	if (before(ptr, tp->rcv_nxt))
5607 		return;
5608 
5609 	/* Do we already have a newer (or duplicate) urgent pointer? */
5610 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5611 		return;
5612 
5613 	/* Tell the world about our new urgent pointer. */
5614 	sk_send_sigurg(sk);
5615 
5616 	/* We may be adding urgent data when the last byte read was
5617 	 * urgent. To do this requires some care. We cannot just ignore
5618 	 * tp->copied_seq since we would read the last urgent byte again
5619 	 * as data, nor can we alter copied_seq until this data arrives
5620 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5621 	 *
5622 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5623 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5624 	 * and expect that both A and B disappear from stream. This is _wrong_.
5625 	 * Though this happens in BSD with high probability, this is occasional.
5626 	 * Any application relying on this is buggy. Note also, that fix "works"
5627 	 * only in this artificial test. Insert some normal data between A and B and we will
5628 	 * decline of BSD again. Verdict: it is better to remove to trap
5629 	 * buggy users.
5630 	 */
5631 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5632 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5633 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5634 		tp->copied_seq++;
5635 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5636 			__skb_unlink(skb, &sk->sk_receive_queue);
5637 			__kfree_skb(skb);
5638 		}
5639 	}
5640 
5641 	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
5642 	WRITE_ONCE(tp->urg_seq, ptr);
5643 
5644 	/* Disable header prediction. */
5645 	tp->pred_flags = 0;
5646 }
5647 
5648 /* This is the 'fast' part of urgent handling. */
tcp_urg(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th)5649 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5650 {
5651 	struct tcp_sock *tp = tcp_sk(sk);
5652 
5653 	/* Check if we get a new urgent pointer - normally not. */
5654 	if (unlikely(th->urg))
5655 		tcp_check_urg(sk, th);
5656 
5657 	/* Do we wait for any urgent data? - normally not... */
5658 	if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
5659 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5660 			  th->syn;
5661 
5662 		/* Is the urgent pointer pointing into this packet? */
5663 		if (ptr < skb->len) {
5664 			u8 tmp;
5665 			if (skb_copy_bits(skb, ptr, &tmp, 1))
5666 				BUG();
5667 			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
5668 			if (!sock_flag(sk, SOCK_DEAD))
5669 				sk->sk_data_ready(sk);
5670 		}
5671 	}
5672 }
5673 
5674 /* Accept RST for rcv_nxt - 1 after a FIN.
5675  * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5676  * FIN is sent followed by a RST packet. The RST is sent with the same
5677  * sequence number as the FIN, and thus according to RFC 5961 a challenge
5678  * ACK should be sent. However, Mac OSX rate limits replies to challenge
5679  * ACKs on the closed socket. In addition middleboxes can drop either the
5680  * challenge ACK or a subsequent RST.
5681  */
tcp_reset_check(const struct sock * sk,const struct sk_buff * skb)5682 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5683 {
5684 	struct tcp_sock *tp = tcp_sk(sk);
5685 
5686 	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5687 			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5688 					       TCPF_CLOSING));
5689 }
5690 
5691 /* Does PAWS and seqno based validation of an incoming segment, flags will
5692  * play significant role here.
5693  */
tcp_validate_incoming(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th,int syn_inerr)5694 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5695 				  const struct tcphdr *th, int syn_inerr)
5696 {
5697 	struct tcp_sock *tp = tcp_sk(sk);
5698 	SKB_DR(reason);
5699 
5700 	/* RFC1323: H1. Apply PAWS check first. */
5701 	if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
5702 	    tp->rx_opt.saw_tstamp &&
5703 	    tcp_paws_discard(sk, skb)) {
5704 		if (!th->rst) {
5705 			NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
5706 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5707 						  LINUX_MIB_TCPACKSKIPPEDPAWS,
5708 						  &tp->last_oow_ack_time))
5709 				tcp_send_dupack(sk, skb);
5710 			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
5711 			goto discard;
5712 		}
5713 		/* Reset is accepted even if it did not pass PAWS. */
5714 	}
5715 
5716 	/* Step 1: check sequence number */
5717 	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5718 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
5719 		 * (RST) segments are validated by checking their SEQ-fields."
5720 		 * And page 69: "If an incoming segment is not acceptable,
5721 		 * an acknowledgment should be sent in reply (unless the RST
5722 		 * bit is set, if so drop the segment and return)".
5723 		 */
5724 		if (!th->rst) {
5725 			if (th->syn)
5726 				goto syn_challenge;
5727 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
5728 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
5729 						  &tp->last_oow_ack_time))
5730 				tcp_send_dupack(sk, skb);
5731 		} else if (tcp_reset_check(sk, skb)) {
5732 			goto reset;
5733 		}
5734 		SKB_DR_SET(reason, TCP_INVALID_SEQUENCE);
5735 		goto discard;
5736 	}
5737 
5738 	/* Step 2: check RST bit */
5739 	if (th->rst) {
5740 		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
5741 		 * FIN and SACK too if available):
5742 		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
5743 		 * the right-most SACK block,
5744 		 * then
5745 		 *     RESET the connection
5746 		 * else
5747 		 *     Send a challenge ACK
5748 		 */
5749 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
5750 		    tcp_reset_check(sk, skb))
5751 			goto reset;
5752 
5753 		if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
5754 			struct tcp_sack_block *sp = &tp->selective_acks[0];
5755 			int max_sack = sp[0].end_seq;
5756 			int this_sack;
5757 
5758 			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
5759 			     ++this_sack) {
5760 				max_sack = after(sp[this_sack].end_seq,
5761 						 max_sack) ?
5762 					sp[this_sack].end_seq : max_sack;
5763 			}
5764 
5765 			if (TCP_SKB_CB(skb)->seq == max_sack)
5766 				goto reset;
5767 		}
5768 
5769 		/* Disable TFO if RST is out-of-order
5770 		 * and no data has been received
5771 		 * for current active TFO socket
5772 		 */
5773 		if (tp->syn_fastopen && !tp->data_segs_in &&
5774 		    sk->sk_state == TCP_ESTABLISHED)
5775 			tcp_fastopen_active_disable(sk);
5776 		tcp_send_challenge_ack(sk);
5777 		SKB_DR_SET(reason, TCP_RESET);
5778 		goto discard;
5779 	}
5780 
5781 	/* step 3: check security and precedence [ignored] */
5782 
5783 	/* step 4: Check for a SYN
5784 	 * RFC 5961 4.2 : Send a challenge ack
5785 	 */
5786 	if (th->syn) {
5787 syn_challenge:
5788 		if (syn_inerr)
5789 			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5790 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
5791 		tcp_send_challenge_ack(sk);
5792 		SKB_DR_SET(reason, TCP_INVALID_SYN);
5793 		goto discard;
5794 	}
5795 
5796 	bpf_skops_parse_hdr(sk, skb);
5797 
5798 	return true;
5799 
5800 discard:
5801 	tcp_drop_reason(sk, skb, reason);
5802 	return false;
5803 
5804 reset:
5805 	tcp_reset(sk, skb);
5806 	__kfree_skb(skb);
5807 	return false;
5808 }
5809 
5810 /*
5811  *	TCP receive function for the ESTABLISHED state.
5812  *
5813  *	It is split into a fast path and a slow path. The fast path is
5814  * 	disabled when:
5815  *	- A zero window was announced from us - zero window probing
5816  *        is only handled properly in the slow path.
5817  *	- Out of order segments arrived.
5818  *	- Urgent data is expected.
5819  *	- There is no buffer space left
5820  *	- Unexpected TCP flags/window values/header lengths are received
5821  *	  (detected by checking the TCP header against pred_flags)
5822  *	- Data is sent in both directions. Fast path only supports pure senders
5823  *	  or pure receivers (this means either the sequence number or the ack
5824  *	  value must stay constant)
5825  *	- Unexpected TCP option.
5826  *
5827  *	When these conditions are not satisfied it drops into a standard
5828  *	receive procedure patterned after RFC793 to handle all cases.
5829  *	The first three cases are guaranteed by proper pred_flags setting,
5830  *	the rest is checked inline. Fast processing is turned on in
5831  *	tcp_data_queue when everything is OK.
5832  */
tcp_rcv_established(struct sock * sk,struct sk_buff * skb)5833 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
5834 {
5835 	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
5836 	const struct tcphdr *th = (const struct tcphdr *)skb->data;
5837 	struct tcp_sock *tp = tcp_sk(sk);
5838 	unsigned int len = skb->len;
5839 
5840 	/* TCP congestion window tracking */
5841 	trace_tcp_probe(sk, skb);
5842 
5843 	tcp_mstamp_refresh(tp);
5844 	if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
5845 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
5846 	/*
5847 	 *	Header prediction.
5848 	 *	The code loosely follows the one in the famous
5849 	 *	"30 instruction TCP receive" Van Jacobson mail.
5850 	 *
5851 	 *	Van's trick is to deposit buffers into socket queue
5852 	 *	on a device interrupt, to call tcp_recv function
5853 	 *	on the receive process context and checksum and copy
5854 	 *	the buffer to user space. smart...
5855 	 *
5856 	 *	Our current scheme is not silly either but we take the
5857 	 *	extra cost of the net_bh soft interrupt processing...
5858 	 *	We do checksum and copy also but from device to kernel.
5859 	 */
5860 
5861 	tp->rx_opt.saw_tstamp = 0;
5862 
5863 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
5864 	 *	if header_prediction is to be made
5865 	 *	'S' will always be tp->tcp_header_len >> 2
5866 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
5867 	 *  turn it off	(when there are holes in the receive
5868 	 *	 space for instance)
5869 	 *	PSH flag is ignored.
5870 	 */
5871 
5872 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
5873 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
5874 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
5875 		int tcp_header_len = tp->tcp_header_len;
5876 
5877 		/* Timestamp header prediction: tcp_header_len
5878 		 * is automatically equal to th->doff*4 due to pred_flags
5879 		 * match.
5880 		 */
5881 
5882 		/* Check timestamp */
5883 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
5884 			/* No? Slow path! */
5885 			if (!tcp_parse_aligned_timestamp(tp, th))
5886 				goto slow_path;
5887 
5888 			/* If PAWS failed, check it more carefully in slow path */
5889 			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
5890 				goto slow_path;
5891 
5892 			/* DO NOT update ts_recent here, if checksum fails
5893 			 * and timestamp was corrupted part, it will result
5894 			 * in a hung connection since we will drop all
5895 			 * future packets due to the PAWS test.
5896 			 */
5897 		}
5898 
5899 		if (len <= tcp_header_len) {
5900 			/* Bulk data transfer: sender */
5901 			if (len == tcp_header_len) {
5902 				/* Predicted packet is in window by definition.
5903 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5904 				 * Hence, check seq<=rcv_wup reduces to:
5905 				 */
5906 				if (tcp_header_len ==
5907 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5908 				    tp->rcv_nxt == tp->rcv_wup)
5909 					tcp_store_ts_recent(tp);
5910 
5911 				/* We know that such packets are checksummed
5912 				 * on entry.
5913 				 */
5914 				tcp_ack(sk, skb, 0);
5915 				__kfree_skb(skb);
5916 				tcp_data_snd_check(sk);
5917 				/* When receiving pure ack in fast path, update
5918 				 * last ts ecr directly instead of calling
5919 				 * tcp_rcv_rtt_measure_ts()
5920 				 */
5921 				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
5922 				return;
5923 			} else { /* Header too small */
5924 				reason = SKB_DROP_REASON_PKT_TOO_SMALL;
5925 				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
5926 				goto discard;
5927 			}
5928 		} else {
5929 			int eaten = 0;
5930 			bool fragstolen = false;
5931 
5932 			if (tcp_checksum_complete(skb))
5933 				goto csum_error;
5934 
5935 			if ((int)skb->truesize > sk->sk_forward_alloc)
5936 				goto step5;
5937 
5938 			/* Predicted packet is in window by definition.
5939 			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
5940 			 * Hence, check seq<=rcv_wup reduces to:
5941 			 */
5942 			if (tcp_header_len ==
5943 			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
5944 			    tp->rcv_nxt == tp->rcv_wup)
5945 				tcp_store_ts_recent(tp);
5946 
5947 			tcp_rcv_rtt_measure_ts(sk, skb);
5948 
5949 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
5950 
5951 			/* Bulk data transfer: receiver */
5952 			skb_dst_drop(skb);
5953 			__skb_pull(skb, tcp_header_len);
5954 			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5955 
5956 			tcp_event_data_recv(sk, skb);
5957 
5958 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
5959 				/* Well, only one small jumplet in fast path... */
5960 				tcp_ack(sk, skb, FLAG_DATA);
5961 				tcp_data_snd_check(sk);
5962 				if (!inet_csk_ack_scheduled(sk))
5963 					goto no_ack;
5964 			} else {
5965 				tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
5966 			}
5967 
5968 			__tcp_ack_snd_check(sk, 0);
5969 no_ack:
5970 			if (eaten)
5971 				kfree_skb_partial(skb, fragstolen);
5972 			tcp_data_ready(sk);
5973 			return;
5974 		}
5975 	}
5976 
5977 slow_path:
5978 	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
5979 		goto csum_error;
5980 
5981 	if (!th->ack && !th->rst && !th->syn) {
5982 		reason = SKB_DROP_REASON_TCP_FLAGS;
5983 		goto discard;
5984 	}
5985 
5986 	/*
5987 	 *	Standard slow path.
5988 	 */
5989 
5990 	if (!tcp_validate_incoming(sk, skb, th, 1))
5991 		return;
5992 
5993 step5:
5994 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
5995 	if ((int)reason < 0) {
5996 		reason = -reason;
5997 		goto discard;
5998 	}
5999 	tcp_rcv_rtt_measure_ts(sk, skb);
6000 
6001 	/* Process urgent data. */
6002 	tcp_urg(sk, skb, th);
6003 
6004 	/* step 7: process the segment text */
6005 	tcp_data_queue(sk, skb);
6006 
6007 	tcp_data_snd_check(sk);
6008 	tcp_ack_snd_check(sk);
6009 	return;
6010 
6011 csum_error:
6012 	reason = SKB_DROP_REASON_TCP_CSUM;
6013 	trace_tcp_bad_csum(skb);
6014 	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6015 	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6016 
6017 discard:
6018 	tcp_drop_reason(sk, skb, reason);
6019 }
6020 EXPORT_SYMBOL(tcp_rcv_established);
6021 
tcp_init_transfer(struct sock * sk,int bpf_op,struct sk_buff * skb)6022 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6023 {
6024 	struct inet_connection_sock *icsk = inet_csk(sk);
6025 	struct tcp_sock *tp = tcp_sk(sk);
6026 
6027 	tcp_mtup_init(sk);
6028 	icsk->icsk_af_ops->rebuild_header(sk);
6029 	tcp_init_metrics(sk);
6030 
6031 	/* Initialize the congestion window to start the transfer.
6032 	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6033 	 * retransmitted. In light of RFC6298 more aggressive 1sec
6034 	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6035 	 * retransmission has occurred.
6036 	 */
6037 	if (tp->total_retrans > 1 && tp->undo_marker)
6038 		tcp_snd_cwnd_set(tp, 1);
6039 	else
6040 		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6041 	tp->snd_cwnd_stamp = tcp_jiffies32;
6042 
6043 	bpf_skops_established(sk, bpf_op, skb);
6044 	/* Initialize congestion control unless BPF initialized it already: */
6045 	if (!icsk->icsk_ca_initialized)
6046 		tcp_init_congestion_control(sk);
6047 	tcp_init_buffer_space(sk);
6048 }
6049 
tcp_finish_connect(struct sock * sk,struct sk_buff * skb)6050 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6051 {
6052 	struct tcp_sock *tp = tcp_sk(sk);
6053 	struct inet_connection_sock *icsk = inet_csk(sk);
6054 
6055 	tcp_set_state(sk, TCP_ESTABLISHED);
6056 	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6057 
6058 	if (skb) {
6059 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6060 		security_inet_conn_established(sk, skb);
6061 		sk_mark_napi_id(sk, skb);
6062 	}
6063 
6064 	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6065 
6066 	/* Prevent spurious tcp_cwnd_restart() on first data
6067 	 * packet.
6068 	 */
6069 	tp->lsndtime = tcp_jiffies32;
6070 
6071 	if (sock_flag(sk, SOCK_KEEPOPEN))
6072 		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
6073 
6074 	if (!tp->rx_opt.snd_wscale)
6075 		__tcp_fast_path_on(tp, tp->snd_wnd);
6076 	else
6077 		tp->pred_flags = 0;
6078 }
6079 
tcp_rcv_fastopen_synack(struct sock * sk,struct sk_buff * synack,struct tcp_fastopen_cookie * cookie)6080 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6081 				    struct tcp_fastopen_cookie *cookie)
6082 {
6083 	struct tcp_sock *tp = tcp_sk(sk);
6084 	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6085 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6086 	bool syn_drop = false;
6087 
6088 	if (mss == tp->rx_opt.user_mss) {
6089 		struct tcp_options_received opt;
6090 
6091 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
6092 		tcp_clear_options(&opt);
6093 		opt.user_mss = opt.mss_clamp = 0;
6094 		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6095 		mss = opt.mss_clamp;
6096 	}
6097 
6098 	if (!tp->syn_fastopen) {
6099 		/* Ignore an unsolicited cookie */
6100 		cookie->len = -1;
6101 	} else if (tp->total_retrans) {
6102 		/* SYN timed out and the SYN-ACK neither has a cookie nor
6103 		 * acknowledges data. Presumably the remote received only
6104 		 * the retransmitted (regular) SYNs: either the original
6105 		 * SYN-data or the corresponding SYN-ACK was dropped.
6106 		 */
6107 		syn_drop = (cookie->len < 0 && data);
6108 	} else if (cookie->len < 0 && !tp->syn_data) {
6109 		/* We requested a cookie but didn't get it. If we did not use
6110 		 * the (old) exp opt format then try so next time (try_exp=1).
6111 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6112 		 */
6113 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
6114 	}
6115 
6116 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6117 
6118 	if (data) { /* Retransmit unacked data in SYN */
6119 		if (tp->total_retrans)
6120 			tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6121 		else
6122 			tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6123 		skb_rbtree_walk_from(data)
6124 			 tcp_mark_skb_lost(sk, data);
6125 		tcp_xmit_retransmit_queue(sk);
6126 		NET_INC_STATS(sock_net(sk),
6127 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6128 		return true;
6129 	}
6130 	tp->syn_data_acked = tp->syn_data;
6131 	if (tp->syn_data_acked) {
6132 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6133 		/* SYN-data is counted as two separate packets in tcp_ack() */
6134 		if (tp->delivered > 1)
6135 			--tp->delivered;
6136 	}
6137 
6138 	tcp_fastopen_add_skb(sk, synack);
6139 
6140 	return false;
6141 }
6142 
smc_check_reset_syn(struct tcp_sock * tp)6143 static void smc_check_reset_syn(struct tcp_sock *tp)
6144 {
6145 #if IS_ENABLED(CONFIG_SMC)
6146 	if (static_branch_unlikely(&tcp_have_smc)) {
6147 		if (tp->syn_smc && !tp->rx_opt.smc_ok)
6148 			tp->syn_smc = 0;
6149 	}
6150 #endif
6151 }
6152 
tcp_try_undo_spurious_syn(struct sock * sk)6153 static void tcp_try_undo_spurious_syn(struct sock *sk)
6154 {
6155 	struct tcp_sock *tp = tcp_sk(sk);
6156 	u32 syn_stamp;
6157 
6158 	/* undo_marker is set when SYN or SYNACK times out. The timeout is
6159 	 * spurious if the ACK's timestamp option echo value matches the
6160 	 * original SYN timestamp.
6161 	 */
6162 	syn_stamp = tp->retrans_stamp;
6163 	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6164 	    syn_stamp == tp->rx_opt.rcv_tsecr)
6165 		tp->undo_marker = 0;
6166 }
6167 
tcp_rcv_synsent_state_process(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th)6168 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6169 					 const struct tcphdr *th)
6170 {
6171 	struct inet_connection_sock *icsk = inet_csk(sk);
6172 	struct tcp_sock *tp = tcp_sk(sk);
6173 	struct tcp_fastopen_cookie foc = { .len = -1 };
6174 	int saved_clamp = tp->rx_opt.mss_clamp;
6175 	bool fastopen_fail;
6176 	SKB_DR(reason);
6177 
6178 	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6179 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6180 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6181 
6182 	if (th->ack) {
6183 		/* rfc793:
6184 		 * "If the state is SYN-SENT then
6185 		 *    first check the ACK bit
6186 		 *      If the ACK bit is set
6187 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6188 		 *        a reset (unless the RST bit is set, if so drop
6189 		 *        the segment and return)"
6190 		 */
6191 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6192 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6193 			/* Previous FIN/ACK or RST/ACK might be ignored. */
6194 			if (icsk->icsk_retransmits == 0)
6195 				inet_csk_reset_xmit_timer(sk,
6196 						ICSK_TIME_RETRANS,
6197 						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
6198 			goto reset_and_undo;
6199 		}
6200 
6201 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6202 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6203 			     tcp_time_stamp(tp))) {
6204 			NET_INC_STATS(sock_net(sk),
6205 					LINUX_MIB_PAWSACTIVEREJECTED);
6206 			goto reset_and_undo;
6207 		}
6208 
6209 		/* Now ACK is acceptable.
6210 		 *
6211 		 * "If the RST bit is set
6212 		 *    If the ACK was acceptable then signal the user "error:
6213 		 *    connection reset", drop the segment, enter CLOSED state,
6214 		 *    delete TCB, and return."
6215 		 */
6216 
6217 		if (th->rst) {
6218 			tcp_reset(sk, skb);
6219 consume:
6220 			__kfree_skb(skb);
6221 			return 0;
6222 		}
6223 
6224 		/* rfc793:
6225 		 *   "fifth, if neither of the SYN or RST bits is set then
6226 		 *    drop the segment and return."
6227 		 *
6228 		 *    See note below!
6229 		 *                                        --ANK(990513)
6230 		 */
6231 		if (!th->syn) {
6232 			SKB_DR_SET(reason, TCP_FLAGS);
6233 			goto discard_and_undo;
6234 		}
6235 		/* rfc793:
6236 		 *   "If the SYN bit is on ...
6237 		 *    are acceptable then ...
6238 		 *    (our SYN has been ACKed), change the connection
6239 		 *    state to ESTABLISHED..."
6240 		 */
6241 
6242 		tcp_ecn_rcv_synack(tp, th);
6243 
6244 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6245 		tcp_try_undo_spurious_syn(sk);
6246 		tcp_ack(sk, skb, FLAG_SLOWPATH);
6247 
6248 		/* Ok.. it's good. Set up sequence numbers and
6249 		 * move to established.
6250 		 */
6251 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6252 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6253 
6254 		/* RFC1323: The window in SYN & SYN/ACK segments is
6255 		 * never scaled.
6256 		 */
6257 		tp->snd_wnd = ntohs(th->window);
6258 
6259 		if (!tp->rx_opt.wscale_ok) {
6260 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6261 			tp->window_clamp = min(tp->window_clamp, 65535U);
6262 		}
6263 
6264 		if (tp->rx_opt.saw_tstamp) {
6265 			tp->rx_opt.tstamp_ok	   = 1;
6266 			tp->tcp_header_len =
6267 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6268 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
6269 			tcp_store_ts_recent(tp);
6270 		} else {
6271 			tp->tcp_header_len = sizeof(struct tcphdr);
6272 		}
6273 
6274 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6275 		tcp_initialize_rcv_mss(sk);
6276 
6277 		/* Remember, tcp_poll() does not lock socket!
6278 		 * Change state from SYN-SENT only after copied_seq
6279 		 * is initialized. */
6280 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6281 
6282 		smc_check_reset_syn(tp);
6283 
6284 		smp_mb();
6285 
6286 		tcp_finish_connect(sk, skb);
6287 
6288 		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6289 				tcp_rcv_fastopen_synack(sk, skb, &foc);
6290 
6291 		if (!sock_flag(sk, SOCK_DEAD)) {
6292 			sk->sk_state_change(sk);
6293 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6294 		}
6295 		if (fastopen_fail)
6296 			return -1;
6297 		if (sk->sk_write_pending ||
6298 		    icsk->icsk_accept_queue.rskq_defer_accept ||
6299 		    inet_csk_in_pingpong_mode(sk)) {
6300 			/* Save one ACK. Data will be ready after
6301 			 * several ticks, if write_pending is set.
6302 			 *
6303 			 * It may be deleted, but with this feature tcpdumps
6304 			 * look so _wonderfully_ clever, that I was not able
6305 			 * to stand against the temptation 8)     --ANK
6306 			 */
6307 			inet_csk_schedule_ack(sk);
6308 			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6309 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
6310 						  TCP_DELACK_MAX, TCP_RTO_MAX);
6311 			goto consume;
6312 		}
6313 		tcp_send_ack(sk);
6314 		return -1;
6315 	}
6316 
6317 	/* No ACK in the segment */
6318 
6319 	if (th->rst) {
6320 		/* rfc793:
6321 		 * "If the RST bit is set
6322 		 *
6323 		 *      Otherwise (no ACK) drop the segment and return."
6324 		 */
6325 		SKB_DR_SET(reason, TCP_RESET);
6326 		goto discard_and_undo;
6327 	}
6328 
6329 	/* PAWS check. */
6330 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6331 	    tcp_paws_reject(&tp->rx_opt, 0)) {
6332 		SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6333 		goto discard_and_undo;
6334 	}
6335 	if (th->syn) {
6336 		/* We see SYN without ACK. It is attempt of
6337 		 * simultaneous connect with crossed SYNs.
6338 		 * Particularly, it can be connect to self.
6339 		 */
6340 		tcp_set_state(sk, TCP_SYN_RECV);
6341 
6342 		if (tp->rx_opt.saw_tstamp) {
6343 			tp->rx_opt.tstamp_ok = 1;
6344 			tcp_store_ts_recent(tp);
6345 			tp->tcp_header_len =
6346 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6347 		} else {
6348 			tp->tcp_header_len = sizeof(struct tcphdr);
6349 		}
6350 
6351 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6352 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6353 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6354 
6355 		/* RFC1323: The window in SYN & SYN/ACK segments is
6356 		 * never scaled.
6357 		 */
6358 		tp->snd_wnd    = ntohs(th->window);
6359 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6360 		tp->max_window = tp->snd_wnd;
6361 
6362 		tcp_ecn_rcv_syn(tp, th);
6363 
6364 		tcp_mtup_init(sk);
6365 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6366 		tcp_initialize_rcv_mss(sk);
6367 
6368 		tcp_send_synack(sk);
6369 #if 0
6370 		/* Note, we could accept data and URG from this segment.
6371 		 * There are no obstacles to make this (except that we must
6372 		 * either change tcp_recvmsg() to prevent it from returning data
6373 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6374 		 *
6375 		 * However, if we ignore data in ACKless segments sometimes,
6376 		 * we have no reasons to accept it sometimes.
6377 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6378 		 * is not flawless. So, discard packet for sanity.
6379 		 * Uncomment this return to process the data.
6380 		 */
6381 		return -1;
6382 #else
6383 		goto consume;
6384 #endif
6385 	}
6386 	/* "fifth, if neither of the SYN or RST bits is set then
6387 	 * drop the segment and return."
6388 	 */
6389 
6390 discard_and_undo:
6391 	tcp_clear_options(&tp->rx_opt);
6392 	tp->rx_opt.mss_clamp = saved_clamp;
6393 	tcp_drop_reason(sk, skb, reason);
6394 	return 0;
6395 
6396 reset_and_undo:
6397 	tcp_clear_options(&tp->rx_opt);
6398 	tp->rx_opt.mss_clamp = saved_clamp;
6399 	return 1;
6400 }
6401 
tcp_rcv_synrecv_state_fastopen(struct sock * sk)6402 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6403 {
6404 	struct request_sock *req;
6405 
6406 	/* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6407 	 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6408 	 */
6409 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
6410 		tcp_try_undo_loss(sk, false);
6411 
6412 	/* Reset rtx states to prevent spurious retransmits_timed_out() */
6413 	tcp_sk(sk)->retrans_stamp = 0;
6414 	inet_csk(sk)->icsk_retransmits = 0;
6415 
6416 	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6417 	 * we no longer need req so release it.
6418 	 */
6419 	req = rcu_dereference_protected(tcp_sk(sk)->fastopen_rsk,
6420 					lockdep_sock_is_held(sk));
6421 	reqsk_fastopen_remove(sk, req, false);
6422 
6423 	/* Re-arm the timer because data may have been sent out.
6424 	 * This is similar to the regular data transmission case
6425 	 * when new data has just been ack'ed.
6426 	 *
6427 	 * (TFO) - we could try to be more aggressive and
6428 	 * retransmitting any data sooner based on when they
6429 	 * are sent out.
6430 	 */
6431 	tcp_rearm_rto(sk);
6432 }
6433 
6434 /*
6435  *	This function implements the receiving procedure of RFC 793 for
6436  *	all states except ESTABLISHED and TIME_WAIT.
6437  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6438  *	address independent.
6439  */
6440 
tcp_rcv_state_process(struct sock * sk,struct sk_buff * skb)6441 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6442 {
6443 	struct tcp_sock *tp = tcp_sk(sk);
6444 	struct inet_connection_sock *icsk = inet_csk(sk);
6445 	const struct tcphdr *th = tcp_hdr(skb);
6446 	struct request_sock *req;
6447 	int queued = 0;
6448 	bool acceptable;
6449 	SKB_DR(reason);
6450 
6451 	switch (sk->sk_state) {
6452 	case TCP_CLOSE:
6453 		SKB_DR_SET(reason, TCP_CLOSE);
6454 		goto discard;
6455 
6456 	case TCP_LISTEN:
6457 		if (th->ack)
6458 			return 1;
6459 
6460 		if (th->rst) {
6461 			SKB_DR_SET(reason, TCP_RESET);
6462 			goto discard;
6463 		}
6464 		if (th->syn) {
6465 			if (th->fin) {
6466 				SKB_DR_SET(reason, TCP_FLAGS);
6467 				goto discard;
6468 			}
6469 			/* It is possible that we process SYN packets from backlog,
6470 			 * so we need to make sure to disable BH and RCU right there.
6471 			 */
6472 			rcu_read_lock();
6473 			local_bh_disable();
6474 			acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
6475 			local_bh_enable();
6476 			rcu_read_unlock();
6477 
6478 			if (!acceptable)
6479 				return 1;
6480 			consume_skb(skb);
6481 			return 0;
6482 		}
6483 		SKB_DR_SET(reason, TCP_FLAGS);
6484 		goto discard;
6485 
6486 	case TCP_SYN_SENT:
6487 		tp->rx_opt.saw_tstamp = 0;
6488 		tcp_mstamp_refresh(tp);
6489 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6490 		if (queued >= 0)
6491 			return queued;
6492 
6493 		/* Do step6 onward by hand. */
6494 		tcp_urg(sk, skb, th);
6495 		__kfree_skb(skb);
6496 		tcp_data_snd_check(sk);
6497 		return 0;
6498 	}
6499 
6500 	tcp_mstamp_refresh(tp);
6501 	tp->rx_opt.saw_tstamp = 0;
6502 	req = rcu_dereference_protected(tp->fastopen_rsk,
6503 					lockdep_sock_is_held(sk));
6504 	if (req) {
6505 		bool req_stolen;
6506 
6507 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6508 		    sk->sk_state != TCP_FIN_WAIT1);
6509 
6510 		if (!tcp_check_req(sk, skb, req, true, &req_stolen)) {
6511 			SKB_DR_SET(reason, TCP_FASTOPEN);
6512 			goto discard;
6513 		}
6514 	}
6515 
6516 	if (!th->ack && !th->rst && !th->syn) {
6517 		SKB_DR_SET(reason, TCP_FLAGS);
6518 		goto discard;
6519 	}
6520 	if (!tcp_validate_incoming(sk, skb, th, 0))
6521 		return 0;
6522 
6523 	/* step 5: check the ACK field */
6524 	acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
6525 				      FLAG_UPDATE_TS_RECENT |
6526 				      FLAG_NO_CHALLENGE_ACK) > 0;
6527 
6528 	if (!acceptable) {
6529 		if (sk->sk_state == TCP_SYN_RECV)
6530 			return 1;	/* send one RST */
6531 		tcp_send_challenge_ack(sk);
6532 		SKB_DR_SET(reason, TCP_OLD_ACK);
6533 		goto discard;
6534 	}
6535 	switch (sk->sk_state) {
6536 	case TCP_SYN_RECV:
6537 		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6538 		if (!tp->srtt_us)
6539 			tcp_synack_rtt_meas(sk, req);
6540 
6541 		if (req) {
6542 			tcp_rcv_synrecv_state_fastopen(sk);
6543 		} else {
6544 			tcp_try_undo_spurious_syn(sk);
6545 			tp->retrans_stamp = 0;
6546 			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
6547 					  skb);
6548 			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6549 		}
6550 		smp_mb();
6551 		tcp_set_state(sk, TCP_ESTABLISHED);
6552 		sk->sk_state_change(sk);
6553 
6554 		/* Note, that this wakeup is only for marginal crossed SYN case.
6555 		 * Passively open sockets are not waked up, because
6556 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6557 		 */
6558 		if (sk->sk_socket)
6559 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6560 
6561 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6562 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6563 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6564 
6565 		if (tp->rx_opt.tstamp_ok)
6566 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6567 
6568 		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6569 			tcp_update_pacing_rate(sk);
6570 
6571 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6572 		tp->lsndtime = tcp_jiffies32;
6573 
6574 		tcp_initialize_rcv_mss(sk);
6575 		tcp_fast_path_on(tp);
6576 		break;
6577 
6578 	case TCP_FIN_WAIT1: {
6579 		int tmo;
6580 
6581 		if (req)
6582 			tcp_rcv_synrecv_state_fastopen(sk);
6583 
6584 		if (tp->snd_una != tp->write_seq)
6585 			break;
6586 
6587 		tcp_set_state(sk, TCP_FIN_WAIT2);
6588 		sk->sk_shutdown |= SEND_SHUTDOWN;
6589 
6590 		sk_dst_confirm(sk);
6591 
6592 		if (!sock_flag(sk, SOCK_DEAD)) {
6593 			/* Wake up lingering close() */
6594 			sk->sk_state_change(sk);
6595 			break;
6596 		}
6597 
6598 		if (tp->linger2 < 0) {
6599 			tcp_done(sk);
6600 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6601 			return 1;
6602 		}
6603 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6604 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6605 			/* Receive out of order FIN after close() */
6606 			if (tp->syn_fastopen && th->fin)
6607 				tcp_fastopen_active_disable(sk);
6608 			tcp_done(sk);
6609 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6610 			return 1;
6611 		}
6612 
6613 		tmo = tcp_fin_time(sk);
6614 		if (tmo > TCP_TIMEWAIT_LEN) {
6615 			inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6616 		} else if (th->fin || sock_owned_by_user(sk)) {
6617 			/* Bad case. We could lose such FIN otherwise.
6618 			 * It is not a big problem, but it looks confusing
6619 			 * and not so rare event. We still can lose it now,
6620 			 * if it spins in bh_lock_sock(), but it is really
6621 			 * marginal case.
6622 			 */
6623 			inet_csk_reset_keepalive_timer(sk, tmo);
6624 		} else {
6625 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6626 			goto consume;
6627 		}
6628 		break;
6629 	}
6630 
6631 	case TCP_CLOSING:
6632 		if (tp->snd_una == tp->write_seq) {
6633 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6634 			goto consume;
6635 		}
6636 		break;
6637 
6638 	case TCP_LAST_ACK:
6639 		if (tp->snd_una == tp->write_seq) {
6640 			tcp_update_metrics(sk);
6641 			tcp_done(sk);
6642 			goto consume;
6643 		}
6644 		break;
6645 	}
6646 
6647 	/* step 6: check the URG bit */
6648 	tcp_urg(sk, skb, th);
6649 
6650 	/* step 7: process the segment text */
6651 	switch (sk->sk_state) {
6652 	case TCP_CLOSE_WAIT:
6653 	case TCP_CLOSING:
6654 	case TCP_LAST_ACK:
6655 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
6656 			/* If a subflow has been reset, the packet should not
6657 			 * continue to be processed, drop the packet.
6658 			 */
6659 			if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
6660 				goto discard;
6661 			break;
6662 		}
6663 		fallthrough;
6664 	case TCP_FIN_WAIT1:
6665 	case TCP_FIN_WAIT2:
6666 		/* RFC 793 says to queue data in these states,
6667 		 * RFC 1122 says we MUST send a reset.
6668 		 * BSD 4.4 also does reset.
6669 		 */
6670 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
6671 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6672 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6673 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6674 				tcp_reset(sk, skb);
6675 				return 1;
6676 			}
6677 		}
6678 		fallthrough;
6679 	case TCP_ESTABLISHED:
6680 		tcp_data_queue(sk, skb);
6681 		queued = 1;
6682 		break;
6683 	}
6684 
6685 	/* tcp_data could move socket to TIME-WAIT */
6686 	if (sk->sk_state != TCP_CLOSE) {
6687 		tcp_data_snd_check(sk);
6688 		tcp_ack_snd_check(sk);
6689 	}
6690 
6691 	if (!queued) {
6692 discard:
6693 		tcp_drop_reason(sk, skb, reason);
6694 	}
6695 	return 0;
6696 
6697 consume:
6698 	__kfree_skb(skb);
6699 	return 0;
6700 }
6701 EXPORT_SYMBOL(tcp_rcv_state_process);
6702 
pr_drop_req(struct request_sock * req,__u16 port,int family)6703 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
6704 {
6705 	struct inet_request_sock *ireq = inet_rsk(req);
6706 
6707 	if (family == AF_INET)
6708 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
6709 				    &ireq->ir_rmt_addr, port);
6710 #if IS_ENABLED(CONFIG_IPV6)
6711 	else if (family == AF_INET6)
6712 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
6713 				    &ireq->ir_v6_rmt_addr, port);
6714 #endif
6715 }
6716 
6717 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
6718  *
6719  * If we receive a SYN packet with these bits set, it means a
6720  * network is playing bad games with TOS bits. In order to
6721  * avoid possible false congestion notifications, we disable
6722  * TCP ECN negotiation.
6723  *
6724  * Exception: tcp_ca wants ECN. This is required for DCTCP
6725  * congestion control: Linux DCTCP asserts ECT on all packets,
6726  * including SYN, which is most optimal solution; however,
6727  * others, such as FreeBSD do not.
6728  *
6729  * Exception: At least one of the reserved bits of the TCP header (th->res1) is
6730  * set, indicating the use of a future TCP extension (such as AccECN). See
6731  * RFC8311 §4.3 which updates RFC3168 to allow the development of such
6732  * extensions.
6733  */
tcp_ecn_create_request(struct request_sock * req,const struct sk_buff * skb,const struct sock * listen_sk,const struct dst_entry * dst)6734 static void tcp_ecn_create_request(struct request_sock *req,
6735 				   const struct sk_buff *skb,
6736 				   const struct sock *listen_sk,
6737 				   const struct dst_entry *dst)
6738 {
6739 	const struct tcphdr *th = tcp_hdr(skb);
6740 	const struct net *net = sock_net(listen_sk);
6741 	bool th_ecn = th->ece && th->cwr;
6742 	bool ect, ecn_ok;
6743 	u32 ecn_ok_dst;
6744 
6745 	if (!th_ecn)
6746 		return;
6747 
6748 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
6749 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
6750 	ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
6751 
6752 	if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
6753 	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
6754 	    tcp_bpf_ca_needs_ecn((struct sock *)req))
6755 		inet_rsk(req)->ecn_ok = 1;
6756 }
6757 
tcp_openreq_init(struct request_sock * req,const struct tcp_options_received * rx_opt,struct sk_buff * skb,const struct sock * sk)6758 static void tcp_openreq_init(struct request_sock *req,
6759 			     const struct tcp_options_received *rx_opt,
6760 			     struct sk_buff *skb, const struct sock *sk)
6761 {
6762 	struct inet_request_sock *ireq = inet_rsk(req);
6763 
6764 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
6765 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
6766 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
6767 	tcp_rsk(req)->snt_synack = 0;
6768 	tcp_rsk(req)->last_oow_ack_time = 0;
6769 	req->mss = rx_opt->mss_clamp;
6770 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
6771 	ireq->tstamp_ok = rx_opt->tstamp_ok;
6772 	ireq->sack_ok = rx_opt->sack_ok;
6773 	ireq->snd_wscale = rx_opt->snd_wscale;
6774 	ireq->wscale_ok = rx_opt->wscale_ok;
6775 	ireq->acked = 0;
6776 	ireq->ecn_ok = 0;
6777 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
6778 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
6779 	ireq->ir_mark = inet_request_mark(sk, skb);
6780 #if IS_ENABLED(CONFIG_SMC)
6781 	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
6782 			tcp_sk(sk)->smc_hs_congested(sk));
6783 #endif
6784 }
6785 
inet_reqsk_alloc(const struct request_sock_ops * ops,struct sock * sk_listener,bool attach_listener)6786 struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
6787 				      struct sock *sk_listener,
6788 				      bool attach_listener)
6789 {
6790 	struct request_sock *req = reqsk_alloc(ops, sk_listener,
6791 					       attach_listener);
6792 
6793 	if (req) {
6794 		struct inet_request_sock *ireq = inet_rsk(req);
6795 
6796 		ireq->ireq_opt = NULL;
6797 #if IS_ENABLED(CONFIG_IPV6)
6798 		ireq->pktopts = NULL;
6799 #endif
6800 		atomic64_set(&ireq->ir_cookie, 0);
6801 		ireq->ireq_state = TCP_NEW_SYN_RECV;
6802 		write_pnet(&ireq->ireq_net, sock_net(sk_listener));
6803 		ireq->ireq_family = sk_listener->sk_family;
6804 		req->timeout = TCP_TIMEOUT_INIT;
6805 	}
6806 
6807 	return req;
6808 }
6809 EXPORT_SYMBOL(inet_reqsk_alloc);
6810 
6811 /*
6812  * Return true if a syncookie should be sent
6813  */
tcp_syn_flood_action(const struct sock * sk,const char * proto)6814 static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
6815 {
6816 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
6817 	const char *msg = "Dropping request";
6818 	struct net *net = sock_net(sk);
6819 	bool want_cookie = false;
6820 	u8 syncookies;
6821 
6822 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6823 
6824 #ifdef CONFIG_SYN_COOKIES
6825 	if (syncookies) {
6826 		msg = "Sending cookies";
6827 		want_cookie = true;
6828 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
6829 	} else
6830 #endif
6831 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
6832 
6833 	if (!queue->synflood_warned && syncookies != 2 &&
6834 	    xchg(&queue->synflood_warned, 1) == 0)
6835 		net_info_ratelimited("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
6836 				     proto, sk->sk_num, msg);
6837 
6838 	return want_cookie;
6839 }
6840 
tcp_reqsk_record_syn(const struct sock * sk,struct request_sock * req,const struct sk_buff * skb)6841 static void tcp_reqsk_record_syn(const struct sock *sk,
6842 				 struct request_sock *req,
6843 				 const struct sk_buff *skb)
6844 {
6845 	if (tcp_sk(sk)->save_syn) {
6846 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
6847 		struct saved_syn *saved_syn;
6848 		u32 mac_hdrlen;
6849 		void *base;
6850 
6851 		if (tcp_sk(sk)->save_syn == 2) {  /* Save full header. */
6852 			base = skb_mac_header(skb);
6853 			mac_hdrlen = skb_mac_header_len(skb);
6854 			len += mac_hdrlen;
6855 		} else {
6856 			base = skb_network_header(skb);
6857 			mac_hdrlen = 0;
6858 		}
6859 
6860 		saved_syn = kmalloc(struct_size(saved_syn, data, len),
6861 				    GFP_ATOMIC);
6862 		if (saved_syn) {
6863 			saved_syn->mac_hdrlen = mac_hdrlen;
6864 			saved_syn->network_hdrlen = skb_network_header_len(skb);
6865 			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
6866 			memcpy(saved_syn->data, base, len);
6867 			req->saved_syn = saved_syn;
6868 		}
6869 	}
6870 }
6871 
6872 /* If a SYN cookie is required and supported, returns a clamped MSS value to be
6873  * used for SYN cookie generation.
6874  */
tcp_get_syncookie_mss(struct request_sock_ops * rsk_ops,const struct tcp_request_sock_ops * af_ops,struct sock * sk,struct tcphdr * th)6875 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
6876 			  const struct tcp_request_sock_ops *af_ops,
6877 			  struct sock *sk, struct tcphdr *th)
6878 {
6879 	struct tcp_sock *tp = tcp_sk(sk);
6880 	u16 mss;
6881 
6882 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
6883 	    !inet_csk_reqsk_queue_is_full(sk))
6884 		return 0;
6885 
6886 	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
6887 		return 0;
6888 
6889 	if (sk_acceptq_is_full(sk)) {
6890 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6891 		return 0;
6892 	}
6893 
6894 	mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
6895 	if (!mss)
6896 		mss = af_ops->mss_clamp;
6897 
6898 	return mss;
6899 }
6900 EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss);
6901 
tcp_conn_request(struct request_sock_ops * rsk_ops,const struct tcp_request_sock_ops * af_ops,struct sock * sk,struct sk_buff * skb)6902 int tcp_conn_request(struct request_sock_ops *rsk_ops,
6903 		     const struct tcp_request_sock_ops *af_ops,
6904 		     struct sock *sk, struct sk_buff *skb)
6905 {
6906 	struct tcp_fastopen_cookie foc = { .len = -1 };
6907 	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
6908 	struct tcp_options_received tmp_opt;
6909 	struct tcp_sock *tp = tcp_sk(sk);
6910 	struct net *net = sock_net(sk);
6911 	struct sock *fastopen_sk = NULL;
6912 	struct request_sock *req;
6913 	bool want_cookie = false;
6914 	struct dst_entry *dst;
6915 	struct flowi fl;
6916 	u8 syncookies;
6917 
6918 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
6919 
6920 	/* TW buckets are converted to open requests without
6921 	 * limitations, they conserve resources and peer is
6922 	 * evidently real one.
6923 	 */
6924 	if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
6925 		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
6926 		if (!want_cookie)
6927 			goto drop;
6928 	}
6929 
6930 	if (sk_acceptq_is_full(sk)) {
6931 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
6932 		goto drop;
6933 	}
6934 
6935 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
6936 	if (!req)
6937 		goto drop;
6938 
6939 	req->syncookie = want_cookie;
6940 	tcp_rsk(req)->af_specific = af_ops;
6941 	tcp_rsk(req)->ts_off = 0;
6942 #if IS_ENABLED(CONFIG_MPTCP)
6943 	tcp_rsk(req)->is_mptcp = 0;
6944 #endif
6945 
6946 	tcp_clear_options(&tmp_opt);
6947 	tmp_opt.mss_clamp = af_ops->mss_clamp;
6948 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
6949 	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
6950 			  want_cookie ? NULL : &foc);
6951 
6952 	if (want_cookie && !tmp_opt.saw_tstamp)
6953 		tcp_clear_options(&tmp_opt);
6954 
6955 	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
6956 		tmp_opt.smc_ok = 0;
6957 
6958 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
6959 	tcp_openreq_init(req, &tmp_opt, skb, sk);
6960 	inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
6961 
6962 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
6963 	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
6964 
6965 	dst = af_ops->route_req(sk, skb, &fl, req);
6966 	if (!dst)
6967 		goto drop_and_free;
6968 
6969 	if (tmp_opt.tstamp_ok)
6970 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
6971 
6972 	if (!want_cookie && !isn) {
6973 		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
6974 
6975 		/* Kill the following clause, if you dislike this way. */
6976 		if (!syncookies &&
6977 		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
6978 		     (max_syn_backlog >> 2)) &&
6979 		    !tcp_peer_is_proven(req, dst)) {
6980 			/* Without syncookies last quarter of
6981 			 * backlog is filled with destinations,
6982 			 * proven to be alive.
6983 			 * It means that we continue to communicate
6984 			 * to destinations, already remembered
6985 			 * to the moment of synflood.
6986 			 */
6987 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
6988 				    rsk_ops->family);
6989 			goto drop_and_release;
6990 		}
6991 
6992 		isn = af_ops->init_seq(skb);
6993 	}
6994 
6995 	tcp_ecn_create_request(req, skb, sk, dst);
6996 
6997 	if (want_cookie) {
6998 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
6999 		if (!tmp_opt.tstamp_ok)
7000 			inet_rsk(req)->ecn_ok = 0;
7001 	}
7002 
7003 	tcp_rsk(req)->snt_isn = isn;
7004 	tcp_rsk(req)->txhash = net_tx_rndhash();
7005 	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
7006 	tcp_openreq_init_rwin(req, sk, dst);
7007 	sk_rx_queue_set(req_to_sk(req), skb);
7008 	if (!want_cookie) {
7009 		tcp_reqsk_record_syn(sk, req, skb);
7010 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7011 	}
7012 	if (fastopen_sk) {
7013 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
7014 				    &foc, TCP_SYNACK_FASTOPEN, skb);
7015 		/* Add the child socket directly into the accept queue */
7016 		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7017 			reqsk_fastopen_remove(fastopen_sk, req, false);
7018 			bh_unlock_sock(fastopen_sk);
7019 			sock_put(fastopen_sk);
7020 			goto drop_and_free;
7021 		}
7022 		sk->sk_data_ready(sk);
7023 		bh_unlock_sock(fastopen_sk);
7024 		sock_put(fastopen_sk);
7025 	} else {
7026 		tcp_rsk(req)->tfo_listener = false;
7027 		if (!want_cookie) {
7028 			req->timeout = tcp_timeout_init((struct sock *)req);
7029 			inet_csk_reqsk_queue_hash_add(sk, req, req->timeout);
7030 		}
7031 		af_ops->send_synack(sk, dst, &fl, req, &foc,
7032 				    !want_cookie ? TCP_SYNACK_NORMAL :
7033 						   TCP_SYNACK_COOKIE,
7034 				    skb);
7035 		if (want_cookie) {
7036 			reqsk_free(req);
7037 			return 0;
7038 		}
7039 	}
7040 	reqsk_put(req);
7041 	return 0;
7042 
7043 drop_and_release:
7044 	dst_release(dst);
7045 drop_and_free:
7046 	__reqsk_free(req);
7047 drop:
7048 	tcp_listendrop(sk);
7049 	return 0;
7050 }
7051 EXPORT_SYMBOL(tcp_conn_request);
7052