1 // SPDX-License-Identifier: GPL-2.0-only
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:	Pedro Roque	:	Retransmit queue handled by TCP.
24  *				:	Fragmentation on mtu decrease
25  *				:	Segment collapse on retransmit
26  *				:	AF independence
27  *
28  *		Linus Torvalds	:	send_delayed_ack
29  *		David S. Miller	:	Charge memory using the right skb
30  *					during syn/ack processing.
31  *		David S. Miller :	Output engine completely rewritten.
32  *		Andrea Arcangeli:	SYNACK carry ts_recent in tsecr.
33  *		Cacophonix Gaul :	draft-minshall-nagle-01
34  *		J Hadi Salim	:	ECN support
35  *
36  */
37 
38 #define pr_fmt(fmt) "TCP: " fmt
39 
40 #include <net/tcp.h>
41 #include <net/mptcp.h>
42 
43 #include <linux/compiler.h>
44 #include <linux/gfp.h>
45 #include <linux/module.h>
46 #include <linux/static_key.h>
47 
48 #include <trace/events/tcp.h>
49 
50 /* Refresh clocks of a TCP socket,
51  * ensuring monotically increasing values.
52  */
tcp_mstamp_refresh(struct tcp_sock * tp)53 void tcp_mstamp_refresh(struct tcp_sock *tp)
54 {
55 	u64 val = tcp_clock_ns();
56 
57 	tp->tcp_clock_cache = val;
58 	tp->tcp_mstamp = div_u64(val, NSEC_PER_USEC);
59 }
60 
61 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
62 			   int push_one, gfp_t gfp);
63 
64 /* Account for new data that has been sent to the network. */
tcp_event_new_data_sent(struct sock * sk,struct sk_buff * skb)65 static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
66 {
67 	struct inet_connection_sock *icsk = inet_csk(sk);
68 	struct tcp_sock *tp = tcp_sk(sk);
69 	unsigned int prior_packets = tp->packets_out;
70 
71 	WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(skb)->end_seq);
72 
73 	__skb_unlink(skb, &sk->sk_write_queue);
74 	tcp_rbtree_insert(&sk->tcp_rtx_queue, skb);
75 
76 	if (tp->highest_sack == NULL)
77 		tp->highest_sack = skb;
78 
79 	tp->packets_out += tcp_skb_pcount(skb);
80 	if (!prior_packets || icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
81 		tcp_rearm_rto(sk);
82 
83 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
84 		      tcp_skb_pcount(skb));
85 	tcp_check_space(sk);
86 }
87 
88 /* SND.NXT, if window was not shrunk or the amount of shrunk was less than one
89  * window scaling factor due to loss of precision.
90  * If window has been shrunk, what should we make? It is not clear at all.
91  * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
92  * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
93  * invalid. OK, let's make this for now:
94  */
tcp_acceptable_seq(const struct sock * sk)95 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
96 {
97 	const struct tcp_sock *tp = tcp_sk(sk);
98 
99 	if (!before(tcp_wnd_end(tp), tp->snd_nxt) ||
100 	    (tp->rx_opt.wscale_ok &&
101 	     ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale))))
102 		return tp->snd_nxt;
103 	else
104 		return tcp_wnd_end(tp);
105 }
106 
107 /* Calculate mss to advertise in SYN segment.
108  * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
109  *
110  * 1. It is independent of path mtu.
111  * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
112  * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
113  *    attached devices, because some buggy hosts are confused by
114  *    large MSS.
115  * 4. We do not make 3, we advertise MSS, calculated from first
116  *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
117  *    This may be overridden via information stored in routing table.
118  * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
119  *    probably even Jumbo".
120  */
tcp_advertise_mss(struct sock * sk)121 static __u16 tcp_advertise_mss(struct sock *sk)
122 {
123 	struct tcp_sock *tp = tcp_sk(sk);
124 	const struct dst_entry *dst = __sk_dst_get(sk);
125 	int mss = tp->advmss;
126 
127 	if (dst) {
128 		unsigned int metric = dst_metric_advmss(dst);
129 
130 		if (metric < mss) {
131 			mss = metric;
132 			tp->advmss = mss;
133 		}
134 	}
135 
136 	return (__u16)mss;
137 }
138 
139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
140  * This is the first part of cwnd validation mechanism.
141  */
tcp_cwnd_restart(struct sock * sk,s32 delta)142 void tcp_cwnd_restart(struct sock *sk, s32 delta)
143 {
144 	struct tcp_sock *tp = tcp_sk(sk);
145 	u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
146 	u32 cwnd = tcp_snd_cwnd(tp);
147 
148 	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
149 
150 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
151 	restart_cwnd = min(restart_cwnd, cwnd);
152 
153 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
154 		cwnd >>= 1;
155 	tcp_snd_cwnd_set(tp, max(cwnd, restart_cwnd));
156 	tp->snd_cwnd_stamp = tcp_jiffies32;
157 	tp->snd_cwnd_used = 0;
158 }
159 
160 /* Congestion state accounting after a packet has been sent. */
tcp_event_data_sent(struct tcp_sock * tp,struct sock * sk)161 static void tcp_event_data_sent(struct tcp_sock *tp,
162 				struct sock *sk)
163 {
164 	struct inet_connection_sock *icsk = inet_csk(sk);
165 	const u32 now = tcp_jiffies32;
166 
167 	if (tcp_packets_in_flight(tp) == 0)
168 		tcp_ca_event(sk, CA_EVENT_TX_START);
169 
170 	tp->lsndtime = now;
171 
172 	/* If it is a reply for ato after last received
173 	 * packet, enter pingpong mode.
174 	 */
175 	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
176 		inet_csk_enter_pingpong_mode(sk);
177 }
178 
179 /* Account for an ACK we sent. */
tcp_event_ack_sent(struct sock * sk,unsigned int pkts,u32 rcv_nxt)180 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts,
181 				      u32 rcv_nxt)
182 {
183 	struct tcp_sock *tp = tcp_sk(sk);
184 
185 	if (unlikely(tp->compressed_ack)) {
186 		NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
187 			      tp->compressed_ack);
188 		tp->compressed_ack = 0;
189 		if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
190 			__sock_put(sk);
191 	}
192 
193 	if (unlikely(rcv_nxt != tp->rcv_nxt))
194 		return;  /* Special ACK sent by DCTCP to reflect ECN */
195 	tcp_dec_quickack_mode(sk, pkts);
196 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
197 }
198 
199 /* Determine a window scaling and initial window to offer.
200  * Based on the assumption that the given amount of space
201  * will be offered. Store the results in the tp structure.
202  * NOTE: for smooth operation initial space offering should
203  * be a multiple of mss if possible. We assume here that mss >= 1.
204  * This MUST be enforced by all callers.
205  */
tcp_select_initial_window(const struct sock * sk,int __space,__u32 mss,__u32 * rcv_wnd,__u32 * window_clamp,int wscale_ok,__u8 * rcv_wscale,__u32 init_rcv_wnd)206 void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
207 			       __u32 *rcv_wnd, __u32 *window_clamp,
208 			       int wscale_ok, __u8 *rcv_wscale,
209 			       __u32 init_rcv_wnd)
210 {
211 	unsigned int space = (__space < 0 ? 0 : __space);
212 
213 	/* If no clamp set the clamp to the max possible scaled window */
214 	if (*window_clamp == 0)
215 		(*window_clamp) = (U16_MAX << TCP_MAX_WSCALE);
216 	space = min(*window_clamp, space);
217 
218 	/* Quantize space offering to a multiple of mss if possible. */
219 	if (space > mss)
220 		space = rounddown(space, mss);
221 
222 	/* NOTE: offering an initial window larger than 32767
223 	 * will break some buggy TCP stacks. If the admin tells us
224 	 * it is likely we could be speaking with such a buggy stack
225 	 * we will truncate our initial window offering to 32K-1
226 	 * unless the remote has sent us a window scaling option,
227 	 * which we interpret as a sign the remote TCP is not
228 	 * misinterpreting the window field as a signed quantity.
229 	 */
230 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows))
231 		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
232 	else
233 		(*rcv_wnd) = min_t(u32, space, U16_MAX);
234 
235 	if (init_rcv_wnd)
236 		*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
237 
238 	*rcv_wscale = 0;
239 	if (wscale_ok) {
240 		/* Set window scaling on max possible window */
241 		space = max_t(u32, space, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
242 		space = max_t(u32, space, READ_ONCE(sysctl_rmem_max));
243 		space = min_t(u32, space, *window_clamp);
244 		*rcv_wscale = clamp_t(int, ilog2(space) - 15,
245 				      0, TCP_MAX_WSCALE);
246 	}
247 	/* Set the clamp no higher than max representable value */
248 	(*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale), *window_clamp);
249 }
250 EXPORT_SYMBOL(tcp_select_initial_window);
251 
252 /* Chose a new window to advertise, update state in tcp_sock for the
253  * socket, and return result with RFC1323 scaling applied.  The return
254  * value can be stuffed directly into th->window for an outgoing
255  * frame.
256  */
tcp_select_window(struct sock * sk)257 static u16 tcp_select_window(struct sock *sk)
258 {
259 	struct tcp_sock *tp = tcp_sk(sk);
260 	u32 old_win = tp->rcv_wnd;
261 	u32 cur_win = tcp_receive_window(tp);
262 	u32 new_win = __tcp_select_window(sk);
263 
264 	/* Never shrink the offered window */
265 	if (new_win < cur_win) {
266 		/* Danger Will Robinson!
267 		 * Don't update rcv_wup/rcv_wnd here or else
268 		 * we will not be able to advertise a zero
269 		 * window in time.  --DaveM
270 		 *
271 		 * Relax Will Robinson.
272 		 */
273 		if (new_win == 0)
274 			NET_INC_STATS(sock_net(sk),
275 				      LINUX_MIB_TCPWANTZEROWINDOWADV);
276 		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
277 	}
278 	tp->rcv_wnd = new_win;
279 	tp->rcv_wup = tp->rcv_nxt;
280 
281 	/* Make sure we do not exceed the maximum possible
282 	 * scaled window.
283 	 */
284 	if (!tp->rx_opt.rcv_wscale &&
285 	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_workaround_signed_windows))
286 		new_win = min(new_win, MAX_TCP_WINDOW);
287 	else
288 		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
289 
290 	/* RFC1323 scaling applied */
291 	new_win >>= tp->rx_opt.rcv_wscale;
292 
293 	/* If we advertise zero window, disable fast path. */
294 	if (new_win == 0) {
295 		tp->pred_flags = 0;
296 		if (old_win)
297 			NET_INC_STATS(sock_net(sk),
298 				      LINUX_MIB_TCPTOZEROWINDOWADV);
299 	} else if (old_win == 0) {
300 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
301 	}
302 
303 	return new_win;
304 }
305 
306 /* Packet ECN state for a SYN-ACK */
tcp_ecn_send_synack(struct sock * sk,struct sk_buff * skb)307 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
308 {
309 	const struct tcp_sock *tp = tcp_sk(sk);
310 
311 	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
312 	if (!(tp->ecn_flags & TCP_ECN_OK))
313 		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
314 	else if (tcp_ca_needs_ecn(sk) ||
315 		 tcp_bpf_ca_needs_ecn(sk))
316 		INET_ECN_xmit(sk);
317 }
318 
319 /* Packet ECN state for a SYN.  */
tcp_ecn_send_syn(struct sock * sk,struct sk_buff * skb)320 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
321 {
322 	struct tcp_sock *tp = tcp_sk(sk);
323 	bool bpf_needs_ecn = tcp_bpf_ca_needs_ecn(sk);
324 	bool use_ecn = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn) == 1 ||
325 		tcp_ca_needs_ecn(sk) || bpf_needs_ecn;
326 
327 	if (!use_ecn) {
328 		const struct dst_entry *dst = __sk_dst_get(sk);
329 
330 		if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
331 			use_ecn = true;
332 	}
333 
334 	tp->ecn_flags = 0;
335 
336 	if (use_ecn) {
337 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
338 		tp->ecn_flags = TCP_ECN_OK;
339 		if (tcp_ca_needs_ecn(sk) || bpf_needs_ecn)
340 			INET_ECN_xmit(sk);
341 	}
342 }
343 
tcp_ecn_clear_syn(struct sock * sk,struct sk_buff * skb)344 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
345 {
346 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback))
347 		/* tp->ecn_flags are cleared at a later point in time when
348 		 * SYN ACK is ultimatively being received.
349 		 */
350 		TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
351 }
352 
353 static void
tcp_ecn_make_synack(const struct request_sock * req,struct tcphdr * th)354 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
355 {
356 	if (inet_rsk(req)->ecn_ok)
357 		th->ece = 1;
358 }
359 
360 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
361  * be sent.
362  */
tcp_ecn_send(struct sock * sk,struct sk_buff * skb,struct tcphdr * th,int tcp_header_len)363 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
364 			 struct tcphdr *th, int tcp_header_len)
365 {
366 	struct tcp_sock *tp = tcp_sk(sk);
367 
368 	if (tp->ecn_flags & TCP_ECN_OK) {
369 		/* Not-retransmitted data segment: set ECT and inject CWR. */
370 		if (skb->len != tcp_header_len &&
371 		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
372 			INET_ECN_xmit(sk);
373 			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
374 				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
375 				th->cwr = 1;
376 				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
377 			}
378 		} else if (!tcp_ca_needs_ecn(sk)) {
379 			/* ACK or retransmitted segment: clear ECT|CE */
380 			INET_ECN_dontxmit(sk);
381 		}
382 		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
383 			th->ece = 1;
384 	}
385 }
386 
387 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
388  * auto increment end seqno.
389  */
tcp_init_nondata_skb(struct sk_buff * skb,u32 seq,u8 flags)390 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
391 {
392 	skb->ip_summed = CHECKSUM_PARTIAL;
393 
394 	TCP_SKB_CB(skb)->tcp_flags = flags;
395 
396 	tcp_skb_pcount_set(skb, 1);
397 
398 	TCP_SKB_CB(skb)->seq = seq;
399 	if (flags & (TCPHDR_SYN | TCPHDR_FIN))
400 		seq++;
401 	TCP_SKB_CB(skb)->end_seq = seq;
402 }
403 
tcp_urg_mode(const struct tcp_sock * tp)404 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
405 {
406 	return tp->snd_una != tp->snd_up;
407 }
408 
409 #define OPTION_SACK_ADVERTISE	BIT(0)
410 #define OPTION_TS		BIT(1)
411 #define OPTION_MD5		BIT(2)
412 #define OPTION_WSCALE		BIT(3)
413 #define OPTION_FAST_OPEN_COOKIE	BIT(8)
414 #define OPTION_SMC		BIT(9)
415 #define OPTION_MPTCP		BIT(10)
416 
smc_options_write(__be32 * ptr,u16 * options)417 static void smc_options_write(__be32 *ptr, u16 *options)
418 {
419 #if IS_ENABLED(CONFIG_SMC)
420 	if (static_branch_unlikely(&tcp_have_smc)) {
421 		if (unlikely(OPTION_SMC & *options)) {
422 			*ptr++ = htonl((TCPOPT_NOP  << 24) |
423 				       (TCPOPT_NOP  << 16) |
424 				       (TCPOPT_EXP <<  8) |
425 				       (TCPOLEN_EXP_SMC_BASE));
426 			*ptr++ = htonl(TCPOPT_SMC_MAGIC);
427 		}
428 	}
429 #endif
430 }
431 
432 struct tcp_out_options {
433 	u16 options;		/* bit field of OPTION_* */
434 	u16 mss;		/* 0 to disable */
435 	u8 ws;			/* window scale, 0 to disable */
436 	u8 num_sack_blocks;	/* number of SACK blocks to include */
437 	u8 hash_size;		/* bytes in hash_location */
438 	u8 bpf_opt_len;		/* length of BPF hdr option */
439 	__u8 *hash_location;	/* temporary pointer, overloaded */
440 	__u32 tsval, tsecr;	/* need to include OPTION_TS */
441 	struct tcp_fastopen_cookie *fastopen_cookie;	/* Fast open cookie */
442 	struct mptcp_out_options mptcp;
443 };
444 
mptcp_options_write(struct tcphdr * th,__be32 * ptr,struct tcp_sock * tp,struct tcp_out_options * opts)445 static void mptcp_options_write(struct tcphdr *th, __be32 *ptr,
446 				struct tcp_sock *tp,
447 				struct tcp_out_options *opts)
448 {
449 #if IS_ENABLED(CONFIG_MPTCP)
450 	if (unlikely(OPTION_MPTCP & opts->options))
451 		mptcp_write_options(th, ptr, tp, &opts->mptcp);
452 #endif
453 }
454 
455 #ifdef CONFIG_CGROUP_BPF
bpf_skops_write_hdr_opt_arg0(struct sk_buff * skb,enum tcp_synack_type synack_type)456 static int bpf_skops_write_hdr_opt_arg0(struct sk_buff *skb,
457 					enum tcp_synack_type synack_type)
458 {
459 	if (unlikely(!skb))
460 		return BPF_WRITE_HDR_TCP_CURRENT_MSS;
461 
462 	if (unlikely(synack_type == TCP_SYNACK_COOKIE))
463 		return BPF_WRITE_HDR_TCP_SYNACK_COOKIE;
464 
465 	return 0;
466 }
467 
468 /* req, syn_skb and synack_type are used when writing synack */
bpf_skops_hdr_opt_len(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct sk_buff * syn_skb,enum tcp_synack_type synack_type,struct tcp_out_options * opts,unsigned int * remaining)469 static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb,
470 				  struct request_sock *req,
471 				  struct sk_buff *syn_skb,
472 				  enum tcp_synack_type synack_type,
473 				  struct tcp_out_options *opts,
474 				  unsigned int *remaining)
475 {
476 	struct bpf_sock_ops_kern sock_ops;
477 	int err;
478 
479 	if (likely(!BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
480 					   BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG)) ||
481 	    !*remaining)
482 		return;
483 
484 	/* *remaining has already been aligned to 4 bytes, so *remaining >= 4 */
485 
486 	/* init sock_ops */
487 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
488 
489 	sock_ops.op = BPF_SOCK_OPS_HDR_OPT_LEN_CB;
490 
491 	if (req) {
492 		/* The listen "sk" cannot be passed here because
493 		 * it is not locked.  It would not make too much
494 		 * sense to do bpf_setsockopt(listen_sk) based
495 		 * on individual connection request also.
496 		 *
497 		 * Thus, "req" is passed here and the cgroup-bpf-progs
498 		 * of the listen "sk" will be run.
499 		 *
500 		 * "req" is also used here for fastopen even the "sk" here is
501 		 * a fullsock "child" sk.  It is to keep the behavior
502 		 * consistent between fastopen and non-fastopen on
503 		 * the bpf programming side.
504 		 */
505 		sock_ops.sk = (struct sock *)req;
506 		sock_ops.syn_skb = syn_skb;
507 	} else {
508 		sock_owned_by_me(sk);
509 
510 		sock_ops.is_fullsock = 1;
511 		sock_ops.sk = sk;
512 	}
513 
514 	sock_ops.args[0] = bpf_skops_write_hdr_opt_arg0(skb, synack_type);
515 	sock_ops.remaining_opt_len = *remaining;
516 	/* tcp_current_mss() does not pass a skb */
517 	if (skb)
518 		bpf_skops_init_skb(&sock_ops, skb, 0);
519 
520 	err = BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk);
521 
522 	if (err || sock_ops.remaining_opt_len == *remaining)
523 		return;
524 
525 	opts->bpf_opt_len = *remaining - sock_ops.remaining_opt_len;
526 	/* round up to 4 bytes */
527 	opts->bpf_opt_len = (opts->bpf_opt_len + 3) & ~3;
528 
529 	*remaining -= opts->bpf_opt_len;
530 }
531 
bpf_skops_write_hdr_opt(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct sk_buff * syn_skb,enum tcp_synack_type synack_type,struct tcp_out_options * opts)532 static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb,
533 				    struct request_sock *req,
534 				    struct sk_buff *syn_skb,
535 				    enum tcp_synack_type synack_type,
536 				    struct tcp_out_options *opts)
537 {
538 	u8 first_opt_off, nr_written, max_opt_len = opts->bpf_opt_len;
539 	struct bpf_sock_ops_kern sock_ops;
540 	int err;
541 
542 	if (likely(!max_opt_len))
543 		return;
544 
545 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
546 
547 	sock_ops.op = BPF_SOCK_OPS_WRITE_HDR_OPT_CB;
548 
549 	if (req) {
550 		sock_ops.sk = (struct sock *)req;
551 		sock_ops.syn_skb = syn_skb;
552 	} else {
553 		sock_owned_by_me(sk);
554 
555 		sock_ops.is_fullsock = 1;
556 		sock_ops.sk = sk;
557 	}
558 
559 	sock_ops.args[0] = bpf_skops_write_hdr_opt_arg0(skb, synack_type);
560 	sock_ops.remaining_opt_len = max_opt_len;
561 	first_opt_off = tcp_hdrlen(skb) - max_opt_len;
562 	bpf_skops_init_skb(&sock_ops, skb, first_opt_off);
563 
564 	err = BPF_CGROUP_RUN_PROG_SOCK_OPS_SK(&sock_ops, sk);
565 
566 	if (err)
567 		nr_written = 0;
568 	else
569 		nr_written = max_opt_len - sock_ops.remaining_opt_len;
570 
571 	if (nr_written < max_opt_len)
572 		memset(skb->data + first_opt_off + nr_written, TCPOPT_NOP,
573 		       max_opt_len - nr_written);
574 }
575 #else
bpf_skops_hdr_opt_len(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct sk_buff * syn_skb,enum tcp_synack_type synack_type,struct tcp_out_options * opts,unsigned int * remaining)576 static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb,
577 				  struct request_sock *req,
578 				  struct sk_buff *syn_skb,
579 				  enum tcp_synack_type synack_type,
580 				  struct tcp_out_options *opts,
581 				  unsigned int *remaining)
582 {
583 }
584 
bpf_skops_write_hdr_opt(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct sk_buff * syn_skb,enum tcp_synack_type synack_type,struct tcp_out_options * opts)585 static void bpf_skops_write_hdr_opt(struct sock *sk, struct sk_buff *skb,
586 				    struct request_sock *req,
587 				    struct sk_buff *syn_skb,
588 				    enum tcp_synack_type synack_type,
589 				    struct tcp_out_options *opts)
590 {
591 }
592 #endif
593 
594 /* Write previously computed TCP options to the packet.
595  *
596  * Beware: Something in the Internet is very sensitive to the ordering of
597  * TCP options, we learned this through the hard way, so be careful here.
598  * Luckily we can at least blame others for their non-compliance but from
599  * inter-operability perspective it seems that we're somewhat stuck with
600  * the ordering which we have been using if we want to keep working with
601  * those broken things (not that it currently hurts anybody as there isn't
602  * particular reason why the ordering would need to be changed).
603  *
604  * At least SACK_PERM as the first option is known to lead to a disaster
605  * (but it may well be that other scenarios fail similarly).
606  */
tcp_options_write(struct tcphdr * th,struct tcp_sock * tp,struct tcp_out_options * opts)607 static void tcp_options_write(struct tcphdr *th, struct tcp_sock *tp,
608 			      struct tcp_out_options *opts)
609 {
610 	__be32 *ptr = (__be32 *)(th + 1);
611 	u16 options = opts->options;	/* mungable copy */
612 
613 	if (unlikely(OPTION_MD5 & options)) {
614 		*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
615 			       (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
616 		/* overload cookie hash location */
617 		opts->hash_location = (__u8 *)ptr;
618 		ptr += 4;
619 	}
620 
621 	if (unlikely(opts->mss)) {
622 		*ptr++ = htonl((TCPOPT_MSS << 24) |
623 			       (TCPOLEN_MSS << 16) |
624 			       opts->mss);
625 	}
626 
627 	if (likely(OPTION_TS & options)) {
628 		if (unlikely(OPTION_SACK_ADVERTISE & options)) {
629 			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
630 				       (TCPOLEN_SACK_PERM << 16) |
631 				       (TCPOPT_TIMESTAMP << 8) |
632 				       TCPOLEN_TIMESTAMP);
633 			options &= ~OPTION_SACK_ADVERTISE;
634 		} else {
635 			*ptr++ = htonl((TCPOPT_NOP << 24) |
636 				       (TCPOPT_NOP << 16) |
637 				       (TCPOPT_TIMESTAMP << 8) |
638 				       TCPOLEN_TIMESTAMP);
639 		}
640 		*ptr++ = htonl(opts->tsval);
641 		*ptr++ = htonl(opts->tsecr);
642 	}
643 
644 	if (unlikely(OPTION_SACK_ADVERTISE & options)) {
645 		*ptr++ = htonl((TCPOPT_NOP << 24) |
646 			       (TCPOPT_NOP << 16) |
647 			       (TCPOPT_SACK_PERM << 8) |
648 			       TCPOLEN_SACK_PERM);
649 	}
650 
651 	if (unlikely(OPTION_WSCALE & options)) {
652 		*ptr++ = htonl((TCPOPT_NOP << 24) |
653 			       (TCPOPT_WINDOW << 16) |
654 			       (TCPOLEN_WINDOW << 8) |
655 			       opts->ws);
656 	}
657 
658 	if (unlikely(opts->num_sack_blocks)) {
659 		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
660 			tp->duplicate_sack : tp->selective_acks;
661 		int this_sack;
662 
663 		*ptr++ = htonl((TCPOPT_NOP  << 24) |
664 			       (TCPOPT_NOP  << 16) |
665 			       (TCPOPT_SACK <<  8) |
666 			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
667 						     TCPOLEN_SACK_PERBLOCK)));
668 
669 		for (this_sack = 0; this_sack < opts->num_sack_blocks;
670 		     ++this_sack) {
671 			*ptr++ = htonl(sp[this_sack].start_seq);
672 			*ptr++ = htonl(sp[this_sack].end_seq);
673 		}
674 
675 		tp->rx_opt.dsack = 0;
676 	}
677 
678 	if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
679 		struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
680 		u8 *p = (u8 *)ptr;
681 		u32 len; /* Fast Open option length */
682 
683 		if (foc->exp) {
684 			len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
685 			*ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
686 				     TCPOPT_FASTOPEN_MAGIC);
687 			p += TCPOLEN_EXP_FASTOPEN_BASE;
688 		} else {
689 			len = TCPOLEN_FASTOPEN_BASE + foc->len;
690 			*p++ = TCPOPT_FASTOPEN;
691 			*p++ = len;
692 		}
693 
694 		memcpy(p, foc->val, foc->len);
695 		if ((len & 3) == 2) {
696 			p[foc->len] = TCPOPT_NOP;
697 			p[foc->len + 1] = TCPOPT_NOP;
698 		}
699 		ptr += (len + 3) >> 2;
700 	}
701 
702 	smc_options_write(ptr, &options);
703 
704 	mptcp_options_write(th, ptr, tp, opts);
705 }
706 
smc_set_option(const struct tcp_sock * tp,struct tcp_out_options * opts,unsigned int * remaining)707 static void smc_set_option(const struct tcp_sock *tp,
708 			   struct tcp_out_options *opts,
709 			   unsigned int *remaining)
710 {
711 #if IS_ENABLED(CONFIG_SMC)
712 	if (static_branch_unlikely(&tcp_have_smc)) {
713 		if (tp->syn_smc) {
714 			if (*remaining >= TCPOLEN_EXP_SMC_BASE_ALIGNED) {
715 				opts->options |= OPTION_SMC;
716 				*remaining -= TCPOLEN_EXP_SMC_BASE_ALIGNED;
717 			}
718 		}
719 	}
720 #endif
721 }
722 
smc_set_option_cond(const struct tcp_sock * tp,const struct inet_request_sock * ireq,struct tcp_out_options * opts,unsigned int * remaining)723 static void smc_set_option_cond(const struct tcp_sock *tp,
724 				const struct inet_request_sock *ireq,
725 				struct tcp_out_options *opts,
726 				unsigned int *remaining)
727 {
728 #if IS_ENABLED(CONFIG_SMC)
729 	if (static_branch_unlikely(&tcp_have_smc)) {
730 		if (tp->syn_smc && ireq->smc_ok) {
731 			if (*remaining >= TCPOLEN_EXP_SMC_BASE_ALIGNED) {
732 				opts->options |= OPTION_SMC;
733 				*remaining -= TCPOLEN_EXP_SMC_BASE_ALIGNED;
734 			}
735 		}
736 	}
737 #endif
738 }
739 
mptcp_set_option_cond(const struct request_sock * req,struct tcp_out_options * opts,unsigned int * remaining)740 static void mptcp_set_option_cond(const struct request_sock *req,
741 				  struct tcp_out_options *opts,
742 				  unsigned int *remaining)
743 {
744 	if (rsk_is_mptcp(req)) {
745 		unsigned int size;
746 
747 		if (mptcp_synack_options(req, &size, &opts->mptcp)) {
748 			if (*remaining >= size) {
749 				opts->options |= OPTION_MPTCP;
750 				*remaining -= size;
751 			}
752 		}
753 	}
754 }
755 
756 /* Compute TCP options for SYN packets. This is not the final
757  * network wire format yet.
758  */
tcp_syn_options(struct sock * sk,struct sk_buff * skb,struct tcp_out_options * opts,struct tcp_md5sig_key ** md5)759 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
760 				struct tcp_out_options *opts,
761 				struct tcp_md5sig_key **md5)
762 {
763 	struct tcp_sock *tp = tcp_sk(sk);
764 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
765 	struct tcp_fastopen_request *fastopen = tp->fastopen_req;
766 
767 	*md5 = NULL;
768 #ifdef CONFIG_TCP_MD5SIG
769 	if (static_branch_unlikely(&tcp_md5_needed) &&
770 	    rcu_access_pointer(tp->md5sig_info)) {
771 		*md5 = tp->af_specific->md5_lookup(sk, sk);
772 		if (*md5) {
773 			opts->options |= OPTION_MD5;
774 			remaining -= TCPOLEN_MD5SIG_ALIGNED;
775 		}
776 	}
777 #endif
778 
779 	/* We always get an MSS option.  The option bytes which will be seen in
780 	 * normal data packets should timestamps be used, must be in the MSS
781 	 * advertised.  But we subtract them from tp->mss_cache so that
782 	 * calculations in tcp_sendmsg are simpler etc.  So account for this
783 	 * fact here if necessary.  If we don't do this correctly, as a
784 	 * receiver we won't recognize data packets as being full sized when we
785 	 * should, and thus we won't abide by the delayed ACK rules correctly.
786 	 * SACKs don't matter, we never delay an ACK when we have any of those
787 	 * going out.  */
788 	opts->mss = tcp_advertise_mss(sk);
789 	remaining -= TCPOLEN_MSS_ALIGNED;
790 
791 	if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_timestamps) && !*md5)) {
792 		opts->options |= OPTION_TS;
793 		opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
794 		opts->tsecr = tp->rx_opt.ts_recent;
795 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
796 	}
797 	if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_window_scaling))) {
798 		opts->ws = tp->rx_opt.rcv_wscale;
799 		opts->options |= OPTION_WSCALE;
800 		remaining -= TCPOLEN_WSCALE_ALIGNED;
801 	}
802 	if (likely(READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_sack))) {
803 		opts->options |= OPTION_SACK_ADVERTISE;
804 		if (unlikely(!(OPTION_TS & opts->options)))
805 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
806 	}
807 
808 	if (fastopen && fastopen->cookie.len >= 0) {
809 		u32 need = fastopen->cookie.len;
810 
811 		need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
812 					       TCPOLEN_FASTOPEN_BASE;
813 		need = (need + 3) & ~3U;  /* Align to 32 bits */
814 		if (remaining >= need) {
815 			opts->options |= OPTION_FAST_OPEN_COOKIE;
816 			opts->fastopen_cookie = &fastopen->cookie;
817 			remaining -= need;
818 			tp->syn_fastopen = 1;
819 			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
820 		}
821 	}
822 
823 	smc_set_option(tp, opts, &remaining);
824 
825 	if (sk_is_mptcp(sk)) {
826 		unsigned int size;
827 
828 		if (mptcp_syn_options(sk, skb, &size, &opts->mptcp)) {
829 			opts->options |= OPTION_MPTCP;
830 			remaining -= size;
831 		}
832 	}
833 
834 	bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining);
835 
836 	return MAX_TCP_OPTION_SPACE - remaining;
837 }
838 
839 /* Set up TCP options for SYN-ACKs. */
tcp_synack_options(const struct sock * sk,struct request_sock * req,unsigned int mss,struct sk_buff * skb,struct tcp_out_options * opts,const struct tcp_md5sig_key * md5,struct tcp_fastopen_cookie * foc,enum tcp_synack_type synack_type,struct sk_buff * syn_skb)840 static unsigned int tcp_synack_options(const struct sock *sk,
841 				       struct request_sock *req,
842 				       unsigned int mss, struct sk_buff *skb,
843 				       struct tcp_out_options *opts,
844 				       const struct tcp_md5sig_key *md5,
845 				       struct tcp_fastopen_cookie *foc,
846 				       enum tcp_synack_type synack_type,
847 				       struct sk_buff *syn_skb)
848 {
849 	struct inet_request_sock *ireq = inet_rsk(req);
850 	unsigned int remaining = MAX_TCP_OPTION_SPACE;
851 
852 #ifdef CONFIG_TCP_MD5SIG
853 	if (md5) {
854 		opts->options |= OPTION_MD5;
855 		remaining -= TCPOLEN_MD5SIG_ALIGNED;
856 
857 		/* We can't fit any SACK blocks in a packet with MD5 + TS
858 		 * options. There was discussion about disabling SACK
859 		 * rather than TS in order to fit in better with old,
860 		 * buggy kernels, but that was deemed to be unnecessary.
861 		 */
862 		if (synack_type != TCP_SYNACK_COOKIE)
863 			ireq->tstamp_ok &= !ireq->sack_ok;
864 	}
865 #endif
866 
867 	/* We always send an MSS option. */
868 	opts->mss = mss;
869 	remaining -= TCPOLEN_MSS_ALIGNED;
870 
871 	if (likely(ireq->wscale_ok)) {
872 		opts->ws = ireq->rcv_wscale;
873 		opts->options |= OPTION_WSCALE;
874 		remaining -= TCPOLEN_WSCALE_ALIGNED;
875 	}
876 	if (likely(ireq->tstamp_ok)) {
877 		opts->options |= OPTION_TS;
878 		opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off;
879 		opts->tsecr = req->ts_recent;
880 		remaining -= TCPOLEN_TSTAMP_ALIGNED;
881 	}
882 	if (likely(ireq->sack_ok)) {
883 		opts->options |= OPTION_SACK_ADVERTISE;
884 		if (unlikely(!ireq->tstamp_ok))
885 			remaining -= TCPOLEN_SACKPERM_ALIGNED;
886 	}
887 	if (foc != NULL && foc->len >= 0) {
888 		u32 need = foc->len;
889 
890 		need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
891 				   TCPOLEN_FASTOPEN_BASE;
892 		need = (need + 3) & ~3U;  /* Align to 32 bits */
893 		if (remaining >= need) {
894 			opts->options |= OPTION_FAST_OPEN_COOKIE;
895 			opts->fastopen_cookie = foc;
896 			remaining -= need;
897 		}
898 	}
899 
900 	mptcp_set_option_cond(req, opts, &remaining);
901 
902 	smc_set_option_cond(tcp_sk(sk), ireq, opts, &remaining);
903 
904 	bpf_skops_hdr_opt_len((struct sock *)sk, skb, req, syn_skb,
905 			      synack_type, opts, &remaining);
906 
907 	return MAX_TCP_OPTION_SPACE - remaining;
908 }
909 
910 /* Compute TCP options for ESTABLISHED sockets. This is not the
911  * final wire format yet.
912  */
tcp_established_options(struct sock * sk,struct sk_buff * skb,struct tcp_out_options * opts,struct tcp_md5sig_key ** md5)913 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
914 					struct tcp_out_options *opts,
915 					struct tcp_md5sig_key **md5)
916 {
917 	struct tcp_sock *tp = tcp_sk(sk);
918 	unsigned int size = 0;
919 	unsigned int eff_sacks;
920 
921 	opts->options = 0;
922 
923 	*md5 = NULL;
924 #ifdef CONFIG_TCP_MD5SIG
925 	if (static_branch_unlikely(&tcp_md5_needed) &&
926 	    rcu_access_pointer(tp->md5sig_info)) {
927 		*md5 = tp->af_specific->md5_lookup(sk, sk);
928 		if (*md5) {
929 			opts->options |= OPTION_MD5;
930 			size += TCPOLEN_MD5SIG_ALIGNED;
931 		}
932 	}
933 #endif
934 
935 	if (likely(tp->rx_opt.tstamp_ok)) {
936 		opts->options |= OPTION_TS;
937 		opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
938 		opts->tsecr = tp->rx_opt.ts_recent;
939 		size += TCPOLEN_TSTAMP_ALIGNED;
940 	}
941 
942 	/* MPTCP options have precedence over SACK for the limited TCP
943 	 * option space because a MPTCP connection would be forced to
944 	 * fall back to regular TCP if a required multipath option is
945 	 * missing. SACK still gets a chance to use whatever space is
946 	 * left.
947 	 */
948 	if (sk_is_mptcp(sk)) {
949 		unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
950 		unsigned int opt_size = 0;
951 
952 		if (mptcp_established_options(sk, skb, &opt_size, remaining,
953 					      &opts->mptcp)) {
954 			opts->options |= OPTION_MPTCP;
955 			size += opt_size;
956 		}
957 	}
958 
959 	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
960 	if (unlikely(eff_sacks)) {
961 		const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
962 		if (unlikely(remaining < TCPOLEN_SACK_BASE_ALIGNED +
963 					 TCPOLEN_SACK_PERBLOCK))
964 			return size;
965 
966 		opts->num_sack_blocks =
967 			min_t(unsigned int, eff_sacks,
968 			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
969 			      TCPOLEN_SACK_PERBLOCK);
970 
971 		size += TCPOLEN_SACK_BASE_ALIGNED +
972 			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
973 	}
974 
975 	if (unlikely(BPF_SOCK_OPS_TEST_FLAG(tp,
976 					    BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG))) {
977 		unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
978 
979 		bpf_skops_hdr_opt_len(sk, skb, NULL, NULL, 0, opts, &remaining);
980 
981 		size = MAX_TCP_OPTION_SPACE - remaining;
982 	}
983 
984 	return size;
985 }
986 
987 
988 /* TCP SMALL QUEUES (TSQ)
989  *
990  * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
991  * to reduce RTT and bufferbloat.
992  * We do this using a special skb destructor (tcp_wfree).
993  *
994  * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
995  * needs to be reallocated in a driver.
996  * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
997  *
998  * Since transmit from skb destructor is forbidden, we use a tasklet
999  * to process all sockets that eventually need to send more skbs.
1000  * We use one tasklet per cpu, with its own queue of sockets.
1001  */
1002 struct tsq_tasklet {
1003 	struct tasklet_struct	tasklet;
1004 	struct list_head	head; /* queue of tcp sockets */
1005 };
1006 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
1007 
tcp_tsq_write(struct sock * sk)1008 static void tcp_tsq_write(struct sock *sk)
1009 {
1010 	if ((1 << sk->sk_state) &
1011 	    (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
1012 	     TCPF_CLOSE_WAIT  | TCPF_LAST_ACK)) {
1013 		struct tcp_sock *tp = tcp_sk(sk);
1014 
1015 		if (tp->lost_out > tp->retrans_out &&
1016 		    tcp_snd_cwnd(tp) > tcp_packets_in_flight(tp)) {
1017 			tcp_mstamp_refresh(tp);
1018 			tcp_xmit_retransmit_queue(sk);
1019 		}
1020 
1021 		tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle,
1022 			       0, GFP_ATOMIC);
1023 	}
1024 }
1025 
tcp_tsq_handler(struct sock * sk)1026 static void tcp_tsq_handler(struct sock *sk)
1027 {
1028 	bh_lock_sock(sk);
1029 	if (!sock_owned_by_user(sk))
1030 		tcp_tsq_write(sk);
1031 	else if (!test_and_set_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags))
1032 		sock_hold(sk);
1033 	bh_unlock_sock(sk);
1034 }
1035 /*
1036  * One tasklet per cpu tries to send more skbs.
1037  * We run in tasklet context but need to disable irqs when
1038  * transferring tsq->head because tcp_wfree() might
1039  * interrupt us (non NAPI drivers)
1040  */
tcp_tasklet_func(struct tasklet_struct * t)1041 static void tcp_tasklet_func(struct tasklet_struct *t)
1042 {
1043 	struct tsq_tasklet *tsq = from_tasklet(tsq,  t, tasklet);
1044 	LIST_HEAD(list);
1045 	unsigned long flags;
1046 	struct list_head *q, *n;
1047 	struct tcp_sock *tp;
1048 	struct sock *sk;
1049 
1050 	local_irq_save(flags);
1051 	list_splice_init(&tsq->head, &list);
1052 	local_irq_restore(flags);
1053 
1054 	list_for_each_safe(q, n, &list) {
1055 		tp = list_entry(q, struct tcp_sock, tsq_node);
1056 		list_del(&tp->tsq_node);
1057 
1058 		sk = (struct sock *)tp;
1059 		smp_mb__before_atomic();
1060 		clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags);
1061 
1062 		tcp_tsq_handler(sk);
1063 		sk_free(sk);
1064 	}
1065 }
1066 
1067 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED |		\
1068 			  TCPF_WRITE_TIMER_DEFERRED |	\
1069 			  TCPF_DELACK_TIMER_DEFERRED |	\
1070 			  TCPF_MTU_REDUCED_DEFERRED)
1071 /**
1072  * tcp_release_cb - tcp release_sock() callback
1073  * @sk: socket
1074  *
1075  * called from release_sock() to perform protocol dependent
1076  * actions before socket release.
1077  */
tcp_release_cb(struct sock * sk)1078 void tcp_release_cb(struct sock *sk)
1079 {
1080 	unsigned long flags, nflags;
1081 
1082 	/* perform an atomic operation only if at least one flag is set */
1083 	do {
1084 		flags = sk->sk_tsq_flags;
1085 		if (!(flags & TCP_DEFERRED_ALL))
1086 			return;
1087 		nflags = flags & ~TCP_DEFERRED_ALL;
1088 	} while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);
1089 
1090 	if (flags & TCPF_TSQ_DEFERRED) {
1091 		tcp_tsq_write(sk);
1092 		__sock_put(sk);
1093 	}
1094 	/* Here begins the tricky part :
1095 	 * We are called from release_sock() with :
1096 	 * 1) BH disabled
1097 	 * 2) sk_lock.slock spinlock held
1098 	 * 3) socket owned by us (sk->sk_lock.owned == 1)
1099 	 *
1100 	 * But following code is meant to be called from BH handlers,
1101 	 * so we should keep BH disabled, but early release socket ownership
1102 	 */
1103 	sock_release_ownership(sk);
1104 
1105 	if (flags & TCPF_WRITE_TIMER_DEFERRED) {
1106 		tcp_write_timer_handler(sk);
1107 		__sock_put(sk);
1108 	}
1109 	if (flags & TCPF_DELACK_TIMER_DEFERRED) {
1110 		tcp_delack_timer_handler(sk);
1111 		__sock_put(sk);
1112 	}
1113 	if (flags & TCPF_MTU_REDUCED_DEFERRED) {
1114 		inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
1115 		__sock_put(sk);
1116 	}
1117 }
1118 EXPORT_SYMBOL(tcp_release_cb);
1119 
tcp_tasklet_init(void)1120 void __init tcp_tasklet_init(void)
1121 {
1122 	int i;
1123 
1124 	for_each_possible_cpu(i) {
1125 		struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
1126 
1127 		INIT_LIST_HEAD(&tsq->head);
1128 		tasklet_setup(&tsq->tasklet, tcp_tasklet_func);
1129 	}
1130 }
1131 
1132 /*
1133  * Write buffer destructor automatically called from kfree_skb.
1134  * We can't xmit new skbs from this context, as we might already
1135  * hold qdisc lock.
1136  */
tcp_wfree(struct sk_buff * skb)1137 void tcp_wfree(struct sk_buff *skb)
1138 {
1139 	struct sock *sk = skb->sk;
1140 	struct tcp_sock *tp = tcp_sk(sk);
1141 	unsigned long flags, nval, oval;
1142 
1143 	/* Keep one reference on sk_wmem_alloc.
1144 	 * Will be released by sk_free() from here or tcp_tasklet_func()
1145 	 */
1146 	WARN_ON(refcount_sub_and_test(skb->truesize - 1, &sk->sk_wmem_alloc));
1147 
1148 	/* If this softirq is serviced by ksoftirqd, we are likely under stress.
1149 	 * Wait until our queues (qdisc + devices) are drained.
1150 	 * This gives :
1151 	 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
1152 	 * - chance for incoming ACK (processed by another cpu maybe)
1153 	 *   to migrate this flow (skb->ooo_okay will be eventually set)
1154 	 */
1155 	if (refcount_read(&sk->sk_wmem_alloc) >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
1156 		goto out;
1157 
1158 	for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) {
1159 		struct tsq_tasklet *tsq;
1160 		bool empty;
1161 
1162 		if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
1163 			goto out;
1164 
1165 		nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED;
1166 		nval = cmpxchg(&sk->sk_tsq_flags, oval, nval);
1167 		if (nval != oval)
1168 			continue;
1169 
1170 		/* queue this socket to tasklet queue */
1171 		local_irq_save(flags);
1172 		tsq = this_cpu_ptr(&tsq_tasklet);
1173 		empty = list_empty(&tsq->head);
1174 		list_add(&tp->tsq_node, &tsq->head);
1175 		if (empty)
1176 			tasklet_schedule(&tsq->tasklet);
1177 		local_irq_restore(flags);
1178 		return;
1179 	}
1180 out:
1181 	sk_free(sk);
1182 }
1183 
1184 /* Note: Called under soft irq.
1185  * We can call TCP stack right away, unless socket is owned by user.
1186  */
tcp_pace_kick(struct hrtimer * timer)1187 enum hrtimer_restart tcp_pace_kick(struct hrtimer *timer)
1188 {
1189 	struct tcp_sock *tp = container_of(timer, struct tcp_sock, pacing_timer);
1190 	struct sock *sk = (struct sock *)tp;
1191 
1192 	tcp_tsq_handler(sk);
1193 	sock_put(sk);
1194 
1195 	return HRTIMER_NORESTART;
1196 }
1197 
tcp_update_skb_after_send(struct sock * sk,struct sk_buff * skb,u64 prior_wstamp)1198 static void tcp_update_skb_after_send(struct sock *sk, struct sk_buff *skb,
1199 				      u64 prior_wstamp)
1200 {
1201 	struct tcp_sock *tp = tcp_sk(sk);
1202 
1203 	if (sk->sk_pacing_status != SK_PACING_NONE) {
1204 		unsigned long rate = sk->sk_pacing_rate;
1205 
1206 		/* Original sch_fq does not pace first 10 MSS
1207 		 * Note that tp->data_segs_out overflows after 2^32 packets,
1208 		 * this is a minor annoyance.
1209 		 */
1210 		if (rate != ~0UL && rate && tp->data_segs_out >= 10) {
1211 			u64 len_ns = div64_ul((u64)skb->len * NSEC_PER_SEC, rate);
1212 			u64 credit = tp->tcp_wstamp_ns - prior_wstamp;
1213 
1214 			/* take into account OS jitter */
1215 			len_ns -= min_t(u64, len_ns / 2, credit);
1216 			tp->tcp_wstamp_ns += len_ns;
1217 		}
1218 	}
1219 	list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
1220 }
1221 
1222 INDIRECT_CALLABLE_DECLARE(int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl));
1223 INDIRECT_CALLABLE_DECLARE(int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl));
1224 INDIRECT_CALLABLE_DECLARE(void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb));
1225 
1226 /* This routine actually transmits TCP packets queued in by
1227  * tcp_do_sendmsg().  This is used by both the initial
1228  * transmission and possible later retransmissions.
1229  * All SKB's seen here are completely headerless.  It is our
1230  * job to build the TCP header, and pass the packet down to
1231  * IP so it can do the same plus pass the packet off to the
1232  * device.
1233  *
1234  * We are working here with either a clone of the original
1235  * SKB, or a fresh unique copy made by the retransmit engine.
1236  */
__tcp_transmit_skb(struct sock * sk,struct sk_buff * skb,int clone_it,gfp_t gfp_mask,u32 rcv_nxt)1237 static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
1238 			      int clone_it, gfp_t gfp_mask, u32 rcv_nxt)
1239 {
1240 	const struct inet_connection_sock *icsk = inet_csk(sk);
1241 	struct inet_sock *inet;
1242 	struct tcp_sock *tp;
1243 	struct tcp_skb_cb *tcb;
1244 	struct tcp_out_options opts;
1245 	unsigned int tcp_options_size, tcp_header_size;
1246 	struct sk_buff *oskb = NULL;
1247 	struct tcp_md5sig_key *md5;
1248 	struct tcphdr *th;
1249 	u64 prior_wstamp;
1250 	int err;
1251 
1252 	BUG_ON(!skb || !tcp_skb_pcount(skb));
1253 	tp = tcp_sk(sk);
1254 	prior_wstamp = tp->tcp_wstamp_ns;
1255 	tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
1256 	skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
1257 	if (clone_it) {
1258 		oskb = skb;
1259 
1260 		tcp_skb_tsorted_save(oskb) {
1261 			if (unlikely(skb_cloned(oskb)))
1262 				skb = pskb_copy(oskb, gfp_mask);
1263 			else
1264 				skb = skb_clone(oskb, gfp_mask);
1265 		} tcp_skb_tsorted_restore(oskb);
1266 
1267 		if (unlikely(!skb))
1268 			return -ENOBUFS;
1269 		/* retransmit skbs might have a non zero value in skb->dev
1270 		 * because skb->dev is aliased with skb->rbnode.rb_left
1271 		 */
1272 		skb->dev = NULL;
1273 	}
1274 
1275 	inet = inet_sk(sk);
1276 	tcb = TCP_SKB_CB(skb);
1277 	memset(&opts, 0, sizeof(opts));
1278 
1279 	if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
1280 		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
1281 	} else {
1282 		tcp_options_size = tcp_established_options(sk, skb, &opts,
1283 							   &md5);
1284 		/* Force a PSH flag on all (GSO) packets to expedite GRO flush
1285 		 * at receiver : This slightly improve GRO performance.
1286 		 * Note that we do not force the PSH flag for non GSO packets,
1287 		 * because they might be sent under high congestion events,
1288 		 * and in this case it is better to delay the delivery of 1-MSS
1289 		 * packets and thus the corresponding ACK packet that would
1290 		 * release the following packet.
1291 		 */
1292 		if (tcp_skb_pcount(skb) > 1)
1293 			tcb->tcp_flags |= TCPHDR_PSH;
1294 	}
1295 	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
1296 
1297 	/* if no packet is in qdisc/device queue, then allow XPS to select
1298 	 * another queue. We can be called from tcp_tsq_handler()
1299 	 * which holds one reference to sk.
1300 	 *
1301 	 * TODO: Ideally, in-flight pure ACK packets should not matter here.
1302 	 * One way to get this would be to set skb->truesize = 2 on them.
1303 	 */
1304 	skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
1305 
1306 	/* If we had to use memory reserve to allocate this skb,
1307 	 * this might cause drops if packet is looped back :
1308 	 * Other socket might not have SOCK_MEMALLOC.
1309 	 * Packets not looped back do not care about pfmemalloc.
1310 	 */
1311 	skb->pfmemalloc = 0;
1312 
1313 	skb_push(skb, tcp_header_size);
1314 	skb_reset_transport_header(skb);
1315 
1316 	skb_orphan(skb);
1317 	skb->sk = sk;
1318 	skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree;
1319 	refcount_add(skb->truesize, &sk->sk_wmem_alloc);
1320 
1321 	skb_set_dst_pending_confirm(skb, sk->sk_dst_pending_confirm);
1322 
1323 	/* Build TCP header and checksum it. */
1324 	th = (struct tcphdr *)skb->data;
1325 	th->source		= inet->inet_sport;
1326 	th->dest		= inet->inet_dport;
1327 	th->seq			= htonl(tcb->seq);
1328 	th->ack_seq		= htonl(rcv_nxt);
1329 	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
1330 					tcb->tcp_flags);
1331 
1332 	th->check		= 0;
1333 	th->urg_ptr		= 0;
1334 
1335 	/* The urg_mode check is necessary during a below snd_una win probe */
1336 	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
1337 		if (before(tp->snd_up, tcb->seq + 0x10000)) {
1338 			th->urg_ptr = htons(tp->snd_up - tcb->seq);
1339 			th->urg = 1;
1340 		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
1341 			th->urg_ptr = htons(0xFFFF);
1342 			th->urg = 1;
1343 		}
1344 	}
1345 
1346 	skb_shinfo(skb)->gso_type = sk->sk_gso_type;
1347 	if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) {
1348 		th->window      = htons(tcp_select_window(sk));
1349 		tcp_ecn_send(sk, skb, th, tcp_header_size);
1350 	} else {
1351 		/* RFC1323: The window in SYN & SYN/ACK segments
1352 		 * is never scaled.
1353 		 */
1354 		th->window	= htons(min(tp->rcv_wnd, 65535U));
1355 	}
1356 
1357 	tcp_options_write(th, tp, &opts);
1358 
1359 #ifdef CONFIG_TCP_MD5SIG
1360 	/* Calculate the MD5 hash, as we have all we need now */
1361 	if (md5) {
1362 		sk_gso_disable(sk);
1363 		tp->af_specific->calc_md5_hash(opts.hash_location,
1364 					       md5, sk, skb);
1365 	}
1366 #endif
1367 
1368 	/* BPF prog is the last one writing header option */
1369 	bpf_skops_write_hdr_opt(sk, skb, NULL, NULL, 0, &opts);
1370 
1371 	INDIRECT_CALL_INET(icsk->icsk_af_ops->send_check,
1372 			   tcp_v6_send_check, tcp_v4_send_check,
1373 			   sk, skb);
1374 
1375 	if (likely(tcb->tcp_flags & TCPHDR_ACK))
1376 		tcp_event_ack_sent(sk, tcp_skb_pcount(skb), rcv_nxt);
1377 
1378 	if (skb->len != tcp_header_size) {
1379 		tcp_event_data_sent(tp, sk);
1380 		tp->data_segs_out += tcp_skb_pcount(skb);
1381 		tp->bytes_sent += skb->len - tcp_header_size;
1382 	}
1383 
1384 	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1385 		TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1386 			      tcp_skb_pcount(skb));
1387 
1388 	tp->segs_out += tcp_skb_pcount(skb);
1389 	skb_set_hash_from_sk(skb, sk);
1390 	/* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1391 	skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1392 	skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1393 
1394 	/* Leave earliest departure time in skb->tstamp (skb->skb_mstamp_ns) */
1395 
1396 	/* Cleanup our debris for IP stacks */
1397 	memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1398 			       sizeof(struct inet6_skb_parm)));
1399 
1400 	tcp_add_tx_delay(skb, tp);
1401 
1402 	err = INDIRECT_CALL_INET(icsk->icsk_af_ops->queue_xmit,
1403 				 inet6_csk_xmit, ip_queue_xmit,
1404 				 sk, skb, &inet->cork.fl);
1405 
1406 	if (unlikely(err > 0)) {
1407 		tcp_enter_cwr(sk);
1408 		err = net_xmit_eval(err);
1409 	}
1410 	if (!err && oskb) {
1411 		tcp_update_skb_after_send(sk, oskb, prior_wstamp);
1412 		tcp_rate_skb_sent(sk, oskb);
1413 	}
1414 	return err;
1415 }
1416 
tcp_transmit_skb(struct sock * sk,struct sk_buff * skb,int clone_it,gfp_t gfp_mask)1417 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
1418 			    gfp_t gfp_mask)
1419 {
1420 	return __tcp_transmit_skb(sk, skb, clone_it, gfp_mask,
1421 				  tcp_sk(sk)->rcv_nxt);
1422 }
1423 
1424 /* This routine just queues the buffer for sending.
1425  *
1426  * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1427  * otherwise socket can stall.
1428  */
tcp_queue_skb(struct sock * sk,struct sk_buff * skb)1429 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1430 {
1431 	struct tcp_sock *tp = tcp_sk(sk);
1432 
1433 	/* Advance write_seq and place onto the write_queue. */
1434 	WRITE_ONCE(tp->write_seq, TCP_SKB_CB(skb)->end_seq);
1435 	__skb_header_release(skb);
1436 	tcp_add_write_queue_tail(sk, skb);
1437 	sk_wmem_queued_add(sk, skb->truesize);
1438 	sk_mem_charge(sk, skb->truesize);
1439 }
1440 
1441 /* Initialize TSO segments for a packet. */
tcp_set_skb_tso_segs(struct sk_buff * skb,unsigned int mss_now)1442 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1443 {
1444 	if (skb->len <= mss_now) {
1445 		/* Avoid the costly divide in the normal
1446 		 * non-TSO case.
1447 		 */
1448 		tcp_skb_pcount_set(skb, 1);
1449 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1450 	} else {
1451 		tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1452 		TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1453 	}
1454 }
1455 
1456 /* Pcount in the middle of the write queue got changed, we need to do various
1457  * tweaks to fix counters
1458  */
tcp_adjust_pcount(struct sock * sk,const struct sk_buff * skb,int decr)1459 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1460 {
1461 	struct tcp_sock *tp = tcp_sk(sk);
1462 
1463 	tp->packets_out -= decr;
1464 
1465 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1466 		tp->sacked_out -= decr;
1467 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1468 		tp->retrans_out -= decr;
1469 	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1470 		tp->lost_out -= decr;
1471 
1472 	/* Reno case is special. Sigh... */
1473 	if (tcp_is_reno(tp) && decr > 0)
1474 		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1475 
1476 	if (tp->lost_skb_hint &&
1477 	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1478 	    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
1479 		tp->lost_cnt_hint -= decr;
1480 
1481 	tcp_verify_left_out(tp);
1482 }
1483 
tcp_has_tx_tstamp(const struct sk_buff * skb)1484 static bool tcp_has_tx_tstamp(const struct sk_buff *skb)
1485 {
1486 	return TCP_SKB_CB(skb)->txstamp_ack ||
1487 		(skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP);
1488 }
1489 
tcp_fragment_tstamp(struct sk_buff * skb,struct sk_buff * skb2)1490 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1491 {
1492 	struct skb_shared_info *shinfo = skb_shinfo(skb);
1493 
1494 	if (unlikely(tcp_has_tx_tstamp(skb)) &&
1495 	    !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1496 		struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1497 		u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1498 
1499 		shinfo->tx_flags &= ~tsflags;
1500 		shinfo2->tx_flags |= tsflags;
1501 		swap(shinfo->tskey, shinfo2->tskey);
1502 		TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack;
1503 		TCP_SKB_CB(skb)->txstamp_ack = 0;
1504 	}
1505 }
1506 
tcp_skb_fragment_eor(struct sk_buff * skb,struct sk_buff * skb2)1507 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2)
1508 {
1509 	TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor;
1510 	TCP_SKB_CB(skb)->eor = 0;
1511 }
1512 
1513 /* Insert buff after skb on the write or rtx queue of sk.  */
tcp_insert_write_queue_after(struct sk_buff * skb,struct sk_buff * buff,struct sock * sk,enum tcp_queue tcp_queue)1514 static void tcp_insert_write_queue_after(struct sk_buff *skb,
1515 					 struct sk_buff *buff,
1516 					 struct sock *sk,
1517 					 enum tcp_queue tcp_queue)
1518 {
1519 	if (tcp_queue == TCP_FRAG_IN_WRITE_QUEUE)
1520 		__skb_queue_after(&sk->sk_write_queue, skb, buff);
1521 	else
1522 		tcp_rbtree_insert(&sk->tcp_rtx_queue, buff);
1523 }
1524 
1525 /* Function to create two new TCP segments.  Shrinks the given segment
1526  * to the specified size and appends a new segment with the rest of the
1527  * packet to the list.  This won't be called frequently, I hope.
1528  * Remember, these are still headerless SKBs at this point.
1529  */
tcp_fragment(struct sock * sk,enum tcp_queue tcp_queue,struct sk_buff * skb,u32 len,unsigned int mss_now,gfp_t gfp)1530 int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
1531 		 struct sk_buff *skb, u32 len,
1532 		 unsigned int mss_now, gfp_t gfp)
1533 {
1534 	struct tcp_sock *tp = tcp_sk(sk);
1535 	struct sk_buff *buff;
1536 	int nsize, old_factor;
1537 	long limit;
1538 	int nlen;
1539 	u8 flags;
1540 
1541 	if (WARN_ON(len > skb->len))
1542 		return -EINVAL;
1543 
1544 	nsize = skb_headlen(skb) - len;
1545 	if (nsize < 0)
1546 		nsize = 0;
1547 
1548 	/* tcp_sendmsg() can overshoot sk_wmem_queued by one full size skb.
1549 	 * We need some allowance to not penalize applications setting small
1550 	 * SO_SNDBUF values.
1551 	 * Also allow first and last skb in retransmit queue to be split.
1552 	 */
1553 	limit = sk->sk_sndbuf + 2 * SKB_TRUESIZE(GSO_LEGACY_MAX_SIZE);
1554 	if (unlikely((sk->sk_wmem_queued >> 1) > limit &&
1555 		     tcp_queue != TCP_FRAG_IN_WRITE_QUEUE &&
1556 		     skb != tcp_rtx_queue_head(sk) &&
1557 		     skb != tcp_rtx_queue_tail(sk))) {
1558 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
1559 		return -ENOMEM;
1560 	}
1561 
1562 	if (skb_unclone_keeptruesize(skb, gfp))
1563 		return -ENOMEM;
1564 
1565 	/* Get a new skb... force flag on. */
1566 	buff = tcp_stream_alloc_skb(sk, nsize, gfp, true);
1567 	if (!buff)
1568 		return -ENOMEM; /* We'll just try again later. */
1569 	skb_copy_decrypted(buff, skb);
1570 	mptcp_skb_ext_copy(buff, skb);
1571 
1572 	sk_wmem_queued_add(sk, buff->truesize);
1573 	sk_mem_charge(sk, buff->truesize);
1574 	nlen = skb->len - len - nsize;
1575 	buff->truesize += nlen;
1576 	skb->truesize -= nlen;
1577 
1578 	/* Correct the sequence numbers. */
1579 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1580 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1581 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1582 
1583 	/* PSH and FIN should only be set in the second packet. */
1584 	flags = TCP_SKB_CB(skb)->tcp_flags;
1585 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1586 	TCP_SKB_CB(buff)->tcp_flags = flags;
1587 	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1588 	tcp_skb_fragment_eor(skb, buff);
1589 
1590 	skb_split(skb, buff, len);
1591 
1592 	skb_set_delivery_time(buff, skb->tstamp, true);
1593 	tcp_fragment_tstamp(skb, buff);
1594 
1595 	old_factor = tcp_skb_pcount(skb);
1596 
1597 	/* Fix up tso_factor for both original and new SKB.  */
1598 	tcp_set_skb_tso_segs(skb, mss_now);
1599 	tcp_set_skb_tso_segs(buff, mss_now);
1600 
1601 	/* Update delivered info for the new segment */
1602 	TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
1603 
1604 	/* If this packet has been sent out already, we must
1605 	 * adjust the various packet counters.
1606 	 */
1607 	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1608 		int diff = old_factor - tcp_skb_pcount(skb) -
1609 			tcp_skb_pcount(buff);
1610 
1611 		if (diff)
1612 			tcp_adjust_pcount(sk, skb, diff);
1613 	}
1614 
1615 	/* Link BUFF into the send queue. */
1616 	__skb_header_release(buff);
1617 	tcp_insert_write_queue_after(skb, buff, sk, tcp_queue);
1618 	if (tcp_queue == TCP_FRAG_IN_RTX_QUEUE)
1619 		list_add(&buff->tcp_tsorted_anchor, &skb->tcp_tsorted_anchor);
1620 
1621 	return 0;
1622 }
1623 
1624 /* This is similar to __pskb_pull_tail(). The difference is that pulled
1625  * data is not copied, but immediately discarded.
1626  */
__pskb_trim_head(struct sk_buff * skb,int len)1627 static int __pskb_trim_head(struct sk_buff *skb, int len)
1628 {
1629 	struct skb_shared_info *shinfo;
1630 	int i, k, eat;
1631 
1632 	eat = min_t(int, len, skb_headlen(skb));
1633 	if (eat) {
1634 		__skb_pull(skb, eat);
1635 		len -= eat;
1636 		if (!len)
1637 			return 0;
1638 	}
1639 	eat = len;
1640 	k = 0;
1641 	shinfo = skb_shinfo(skb);
1642 	for (i = 0; i < shinfo->nr_frags; i++) {
1643 		int size = skb_frag_size(&shinfo->frags[i]);
1644 
1645 		if (size <= eat) {
1646 			skb_frag_unref(skb, i);
1647 			eat -= size;
1648 		} else {
1649 			shinfo->frags[k] = shinfo->frags[i];
1650 			if (eat) {
1651 				skb_frag_off_add(&shinfo->frags[k], eat);
1652 				skb_frag_size_sub(&shinfo->frags[k], eat);
1653 				eat = 0;
1654 			}
1655 			k++;
1656 		}
1657 	}
1658 	shinfo->nr_frags = k;
1659 
1660 	skb->data_len -= len;
1661 	skb->len = skb->data_len;
1662 	return len;
1663 }
1664 
1665 /* Remove acked data from a packet in the transmit queue. */
tcp_trim_head(struct sock * sk,struct sk_buff * skb,u32 len)1666 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1667 {
1668 	u32 delta_truesize;
1669 
1670 	if (skb_unclone_keeptruesize(skb, GFP_ATOMIC))
1671 		return -ENOMEM;
1672 
1673 	delta_truesize = __pskb_trim_head(skb, len);
1674 
1675 	TCP_SKB_CB(skb)->seq += len;
1676 
1677 	if (delta_truesize) {
1678 		skb->truesize	   -= delta_truesize;
1679 		sk_wmem_queued_add(sk, -delta_truesize);
1680 		if (!skb_zcopy_pure(skb))
1681 			sk_mem_uncharge(sk, delta_truesize);
1682 	}
1683 
1684 	/* Any change of skb->len requires recalculation of tso factor. */
1685 	if (tcp_skb_pcount(skb) > 1)
1686 		tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1687 
1688 	return 0;
1689 }
1690 
1691 /* Calculate MSS not accounting any TCP options.  */
__tcp_mtu_to_mss(struct sock * sk,int pmtu)1692 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1693 {
1694 	const struct tcp_sock *tp = tcp_sk(sk);
1695 	const struct inet_connection_sock *icsk = inet_csk(sk);
1696 	int mss_now;
1697 
1698 	/* Calculate base mss without TCP options:
1699 	   It is MMS_S - sizeof(tcphdr) of rfc1122
1700 	 */
1701 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1702 
1703 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1704 	if (icsk->icsk_af_ops->net_frag_header_len) {
1705 		const struct dst_entry *dst = __sk_dst_get(sk);
1706 
1707 		if (dst && dst_allfrag(dst))
1708 			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1709 	}
1710 
1711 	/* Clamp it (mss_clamp does not include tcp options) */
1712 	if (mss_now > tp->rx_opt.mss_clamp)
1713 		mss_now = tp->rx_opt.mss_clamp;
1714 
1715 	/* Now subtract optional transport overhead */
1716 	mss_now -= icsk->icsk_ext_hdr_len;
1717 
1718 	/* Then reserve room for full set of TCP options and 8 bytes of data */
1719 	mss_now = max(mss_now,
1720 		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss));
1721 	return mss_now;
1722 }
1723 
1724 /* Calculate MSS. Not accounting for SACKs here.  */
tcp_mtu_to_mss(struct sock * sk,int pmtu)1725 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1726 {
1727 	/* Subtract TCP options size, not including SACKs */
1728 	return __tcp_mtu_to_mss(sk, pmtu) -
1729 	       (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1730 }
1731 EXPORT_SYMBOL(tcp_mtu_to_mss);
1732 
1733 /* Inverse of above */
tcp_mss_to_mtu(struct sock * sk,int mss)1734 int tcp_mss_to_mtu(struct sock *sk, int mss)
1735 {
1736 	const struct tcp_sock *tp = tcp_sk(sk);
1737 	const struct inet_connection_sock *icsk = inet_csk(sk);
1738 	int mtu;
1739 
1740 	mtu = mss +
1741 	      tp->tcp_header_len +
1742 	      icsk->icsk_ext_hdr_len +
1743 	      icsk->icsk_af_ops->net_header_len;
1744 
1745 	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1746 	if (icsk->icsk_af_ops->net_frag_header_len) {
1747 		const struct dst_entry *dst = __sk_dst_get(sk);
1748 
1749 		if (dst && dst_allfrag(dst))
1750 			mtu += icsk->icsk_af_ops->net_frag_header_len;
1751 	}
1752 	return mtu;
1753 }
1754 EXPORT_SYMBOL(tcp_mss_to_mtu);
1755 
1756 /* MTU probing init per socket */
tcp_mtup_init(struct sock * sk)1757 void tcp_mtup_init(struct sock *sk)
1758 {
1759 	struct tcp_sock *tp = tcp_sk(sk);
1760 	struct inet_connection_sock *icsk = inet_csk(sk);
1761 	struct net *net = sock_net(sk);
1762 
1763 	icsk->icsk_mtup.enabled = READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing) > 1;
1764 	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1765 			       icsk->icsk_af_ops->net_header_len;
1766 	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, READ_ONCE(net->ipv4.sysctl_tcp_base_mss));
1767 	icsk->icsk_mtup.probe_size = 0;
1768 	if (icsk->icsk_mtup.enabled)
1769 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
1770 }
1771 EXPORT_SYMBOL(tcp_mtup_init);
1772 
1773 /* This function synchronize snd mss to current pmtu/exthdr set.
1774 
1775    tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1776    for TCP options, but includes only bare TCP header.
1777 
1778    tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1779    It is minimum of user_mss and mss received with SYN.
1780    It also does not include TCP options.
1781 
1782    inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1783 
1784    tp->mss_cache is current effective sending mss, including
1785    all tcp options except for SACKs. It is evaluated,
1786    taking into account current pmtu, but never exceeds
1787    tp->rx_opt.mss_clamp.
1788 
1789    NOTE1. rfc1122 clearly states that advertised MSS
1790    DOES NOT include either tcp or ip options.
1791 
1792    NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1793    are READ ONLY outside this function.		--ANK (980731)
1794  */
tcp_sync_mss(struct sock * sk,u32 pmtu)1795 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1796 {
1797 	struct tcp_sock *tp = tcp_sk(sk);
1798 	struct inet_connection_sock *icsk = inet_csk(sk);
1799 	int mss_now;
1800 
1801 	if (icsk->icsk_mtup.search_high > pmtu)
1802 		icsk->icsk_mtup.search_high = pmtu;
1803 
1804 	mss_now = tcp_mtu_to_mss(sk, pmtu);
1805 	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1806 
1807 	/* And store cached results */
1808 	icsk->icsk_pmtu_cookie = pmtu;
1809 	if (icsk->icsk_mtup.enabled)
1810 		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1811 	tp->mss_cache = mss_now;
1812 
1813 	return mss_now;
1814 }
1815 EXPORT_SYMBOL(tcp_sync_mss);
1816 
1817 /* Compute the current effective MSS, taking SACKs and IP options,
1818  * and even PMTU discovery events into account.
1819  */
tcp_current_mss(struct sock * sk)1820 unsigned int tcp_current_mss(struct sock *sk)
1821 {
1822 	const struct tcp_sock *tp = tcp_sk(sk);
1823 	const struct dst_entry *dst = __sk_dst_get(sk);
1824 	u32 mss_now;
1825 	unsigned int header_len;
1826 	struct tcp_out_options opts;
1827 	struct tcp_md5sig_key *md5;
1828 
1829 	mss_now = tp->mss_cache;
1830 
1831 	if (dst) {
1832 		u32 mtu = dst_mtu(dst);
1833 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1834 			mss_now = tcp_sync_mss(sk, mtu);
1835 	}
1836 
1837 	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1838 		     sizeof(struct tcphdr);
1839 	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
1840 	 * some common options. If this is an odd packet (because we have SACK
1841 	 * blocks etc) then our calculated header_len will be different, and
1842 	 * we have to adjust mss_now correspondingly */
1843 	if (header_len != tp->tcp_header_len) {
1844 		int delta = (int) header_len - tp->tcp_header_len;
1845 		mss_now -= delta;
1846 	}
1847 
1848 	return mss_now;
1849 }
1850 
1851 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1852  * As additional protections, we do not touch cwnd in retransmission phases,
1853  * and if application hit its sndbuf limit recently.
1854  */
tcp_cwnd_application_limited(struct sock * sk)1855 static void tcp_cwnd_application_limited(struct sock *sk)
1856 {
1857 	struct tcp_sock *tp = tcp_sk(sk);
1858 
1859 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1860 	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1861 		/* Limited by application or receiver window. */
1862 		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1863 		u32 win_used = max(tp->snd_cwnd_used, init_win);
1864 		if (win_used < tcp_snd_cwnd(tp)) {
1865 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
1866 			tcp_snd_cwnd_set(tp, (tcp_snd_cwnd(tp) + win_used) >> 1);
1867 		}
1868 		tp->snd_cwnd_used = 0;
1869 	}
1870 	tp->snd_cwnd_stamp = tcp_jiffies32;
1871 }
1872 
tcp_cwnd_validate(struct sock * sk,bool is_cwnd_limited)1873 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1874 {
1875 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1876 	struct tcp_sock *tp = tcp_sk(sk);
1877 
1878 	/* Track the strongest available signal of the degree to which the cwnd
1879 	 * is fully utilized. If cwnd-limited then remember that fact for the
1880 	 * current window. If not cwnd-limited then track the maximum number of
1881 	 * outstanding packets in the current window. (If cwnd-limited then we
1882 	 * chose to not update tp->max_packets_out to avoid an extra else
1883 	 * clause with no functional impact.)
1884 	 */
1885 	if (!before(tp->snd_una, tp->cwnd_usage_seq) ||
1886 	    is_cwnd_limited ||
1887 	    (!tp->is_cwnd_limited &&
1888 	     tp->packets_out > tp->max_packets_out)) {
1889 		tp->is_cwnd_limited = is_cwnd_limited;
1890 		tp->max_packets_out = tp->packets_out;
1891 		tp->cwnd_usage_seq = tp->snd_nxt;
1892 	}
1893 
1894 	if (tcp_is_cwnd_limited(sk)) {
1895 		/* Network is feed fully. */
1896 		tp->snd_cwnd_used = 0;
1897 		tp->snd_cwnd_stamp = tcp_jiffies32;
1898 	} else {
1899 		/* Network starves. */
1900 		if (tp->packets_out > tp->snd_cwnd_used)
1901 			tp->snd_cwnd_used = tp->packets_out;
1902 
1903 		if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_slow_start_after_idle) &&
1904 		    (s32)(tcp_jiffies32 - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto &&
1905 		    !ca_ops->cong_control)
1906 			tcp_cwnd_application_limited(sk);
1907 
1908 		/* The following conditions together indicate the starvation
1909 		 * is caused by insufficient sender buffer:
1910 		 * 1) just sent some data (see tcp_write_xmit)
1911 		 * 2) not cwnd limited (this else condition)
1912 		 * 3) no more data to send (tcp_write_queue_empty())
1913 		 * 4) application is hitting buffer limit (SOCK_NOSPACE)
1914 		 */
1915 		if (tcp_write_queue_empty(sk) && sk->sk_socket &&
1916 		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
1917 		    (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
1918 			tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
1919 	}
1920 }
1921 
1922 /* Minshall's variant of the Nagle send check. */
tcp_minshall_check(const struct tcp_sock * tp)1923 static bool tcp_minshall_check(const struct tcp_sock *tp)
1924 {
1925 	return after(tp->snd_sml, tp->snd_una) &&
1926 		!after(tp->snd_sml, tp->snd_nxt);
1927 }
1928 
1929 /* Update snd_sml if this skb is under mss
1930  * Note that a TSO packet might end with a sub-mss segment
1931  * The test is really :
1932  * if ((skb->len % mss) != 0)
1933  *        tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1934  * But we can avoid doing the divide again given we already have
1935  *  skb_pcount = skb->len / mss_now
1936  */
tcp_minshall_update(struct tcp_sock * tp,unsigned int mss_now,const struct sk_buff * skb)1937 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1938 				const struct sk_buff *skb)
1939 {
1940 	if (skb->len < tcp_skb_pcount(skb) * mss_now)
1941 		tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1942 }
1943 
1944 /* Return false, if packet can be sent now without violation Nagle's rules:
1945  * 1. It is full sized. (provided by caller in %partial bool)
1946  * 2. Or it contains FIN. (already checked by caller)
1947  * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1948  * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1949  *    With Minshall's modification: all sent small packets are ACKed.
1950  */
tcp_nagle_check(bool partial,const struct tcp_sock * tp,int nonagle)1951 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1952 			    int nonagle)
1953 {
1954 	return partial &&
1955 		((nonagle & TCP_NAGLE_CORK) ||
1956 		 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1957 }
1958 
1959 /* Return how many segs we'd like on a TSO packet,
1960  * depending on current pacing rate, and how close the peer is.
1961  *
1962  * Rationale is:
1963  * - For close peers, we rather send bigger packets to reduce
1964  *   cpu costs, because occasional losses will be repaired fast.
1965  * - For long distance/rtt flows, we would like to get ACK clocking
1966  *   with 1 ACK per ms.
1967  *
1968  * Use min_rtt to help adapt TSO burst size, with smaller min_rtt resulting
1969  * in bigger TSO bursts. We we cut the RTT-based allowance in half
1970  * for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance
1971  * is below 1500 bytes after 6 * ~500 usec = 3ms.
1972  */
tcp_tso_autosize(const struct sock * sk,unsigned int mss_now,int min_tso_segs)1973 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
1974 			    int min_tso_segs)
1975 {
1976 	unsigned long bytes;
1977 	u32 r;
1978 
1979 	bytes = sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift);
1980 
1981 	r = tcp_min_rtt(tcp_sk(sk)) >> READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_rtt_log);
1982 	if (r < BITS_PER_TYPE(sk->sk_gso_max_size))
1983 		bytes += sk->sk_gso_max_size >> r;
1984 
1985 	bytes = min_t(unsigned long, bytes, sk->sk_gso_max_size);
1986 
1987 	return max_t(u32, bytes / mss_now, min_tso_segs);
1988 }
1989 
1990 /* Return the number of segments we want in the skb we are transmitting.
1991  * See if congestion control module wants to decide; otherwise, autosize.
1992  */
tcp_tso_segs(struct sock * sk,unsigned int mss_now)1993 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
1994 {
1995 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
1996 	u32 min_tso, tso_segs;
1997 
1998 	min_tso = ca_ops->min_tso_segs ?
1999 			ca_ops->min_tso_segs(sk) :
2000 			READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
2001 
2002 	tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
2003 	return min_t(u32, tso_segs, sk->sk_gso_max_segs);
2004 }
2005 
2006 /* Returns the portion of skb which can be sent right away */
tcp_mss_split_point(const struct sock * sk,const struct sk_buff * skb,unsigned int mss_now,unsigned int max_segs,int nonagle)2007 static unsigned int tcp_mss_split_point(const struct sock *sk,
2008 					const struct sk_buff *skb,
2009 					unsigned int mss_now,
2010 					unsigned int max_segs,
2011 					int nonagle)
2012 {
2013 	const struct tcp_sock *tp = tcp_sk(sk);
2014 	u32 partial, needed, window, max_len;
2015 
2016 	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
2017 	max_len = mss_now * max_segs;
2018 
2019 	if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
2020 		return max_len;
2021 
2022 	needed = min(skb->len, window);
2023 
2024 	if (max_len <= needed)
2025 		return max_len;
2026 
2027 	partial = needed % mss_now;
2028 	/* If last segment is not a full MSS, check if Nagle rules allow us
2029 	 * to include this last segment in this skb.
2030 	 * Otherwise, we'll split the skb at last MSS boundary
2031 	 */
2032 	if (tcp_nagle_check(partial != 0, tp, nonagle))
2033 		return needed - partial;
2034 
2035 	return needed;
2036 }
2037 
2038 /* Can at least one segment of SKB be sent right now, according to the
2039  * congestion window rules?  If so, return how many segments are allowed.
2040  */
tcp_cwnd_test(const struct tcp_sock * tp,const struct sk_buff * skb)2041 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
2042 					 const struct sk_buff *skb)
2043 {
2044 	u32 in_flight, cwnd, halfcwnd;
2045 
2046 	/* Don't be strict about the congestion window for the final FIN.  */
2047 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
2048 	    tcp_skb_pcount(skb) == 1)
2049 		return 1;
2050 
2051 	in_flight = tcp_packets_in_flight(tp);
2052 	cwnd = tcp_snd_cwnd(tp);
2053 	if (in_flight >= cwnd)
2054 		return 0;
2055 
2056 	/* For better scheduling, ensure we have at least
2057 	 * 2 GSO packets in flight.
2058 	 */
2059 	halfcwnd = max(cwnd >> 1, 1U);
2060 	return min(halfcwnd, cwnd - in_flight);
2061 }
2062 
2063 /* Initialize TSO state of a skb.
2064  * This must be invoked the first time we consider transmitting
2065  * SKB onto the wire.
2066  */
tcp_init_tso_segs(struct sk_buff * skb,unsigned int mss_now)2067 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
2068 {
2069 	int tso_segs = tcp_skb_pcount(skb);
2070 
2071 	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
2072 		tcp_set_skb_tso_segs(skb, mss_now);
2073 		tso_segs = tcp_skb_pcount(skb);
2074 	}
2075 	return tso_segs;
2076 }
2077 
2078 
2079 /* Return true if the Nagle test allows this packet to be
2080  * sent now.
2081  */
tcp_nagle_test(const struct tcp_sock * tp,const struct sk_buff * skb,unsigned int cur_mss,int nonagle)2082 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
2083 				  unsigned int cur_mss, int nonagle)
2084 {
2085 	/* Nagle rule does not apply to frames, which sit in the middle of the
2086 	 * write_queue (they have no chances to get new data).
2087 	 *
2088 	 * This is implemented in the callers, where they modify the 'nonagle'
2089 	 * argument based upon the location of SKB in the send queue.
2090 	 */
2091 	if (nonagle & TCP_NAGLE_PUSH)
2092 		return true;
2093 
2094 	/* Don't use the nagle rule for urgent data (or for the final FIN). */
2095 	if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
2096 		return true;
2097 
2098 	if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
2099 		return true;
2100 
2101 	return false;
2102 }
2103 
2104 /* Does at least the first segment of SKB fit into the send window? */
tcp_snd_wnd_test(const struct tcp_sock * tp,const struct sk_buff * skb,unsigned int cur_mss)2105 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
2106 			     const struct sk_buff *skb,
2107 			     unsigned int cur_mss)
2108 {
2109 	u32 end_seq = TCP_SKB_CB(skb)->end_seq;
2110 
2111 	if (skb->len > cur_mss)
2112 		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
2113 
2114 	return !after(end_seq, tcp_wnd_end(tp));
2115 }
2116 
2117 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
2118  * which is put after SKB on the list.  It is very much like
2119  * tcp_fragment() except that it may make several kinds of assumptions
2120  * in order to speed up the splitting operation.  In particular, we
2121  * know that all the data is in scatter-gather pages, and that the
2122  * packet has never been sent out before (and thus is not cloned).
2123  */
tso_fragment(struct sock * sk,struct sk_buff * skb,unsigned int len,unsigned int mss_now,gfp_t gfp)2124 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
2125 			unsigned int mss_now, gfp_t gfp)
2126 {
2127 	int nlen = skb->len - len;
2128 	struct sk_buff *buff;
2129 	u8 flags;
2130 
2131 	/* All of a TSO frame must be composed of paged data.  */
2132 	if (skb->len != skb->data_len)
2133 		return tcp_fragment(sk, TCP_FRAG_IN_WRITE_QUEUE,
2134 				    skb, len, mss_now, gfp);
2135 
2136 	buff = tcp_stream_alloc_skb(sk, 0, gfp, true);
2137 	if (unlikely(!buff))
2138 		return -ENOMEM;
2139 	skb_copy_decrypted(buff, skb);
2140 	mptcp_skb_ext_copy(buff, skb);
2141 
2142 	sk_wmem_queued_add(sk, buff->truesize);
2143 	sk_mem_charge(sk, buff->truesize);
2144 	buff->truesize += nlen;
2145 	skb->truesize -= nlen;
2146 
2147 	/* Correct the sequence numbers. */
2148 	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
2149 	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
2150 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
2151 
2152 	/* PSH and FIN should only be set in the second packet. */
2153 	flags = TCP_SKB_CB(skb)->tcp_flags;
2154 	TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
2155 	TCP_SKB_CB(buff)->tcp_flags = flags;
2156 
2157 	tcp_skb_fragment_eor(skb, buff);
2158 
2159 	skb_split(skb, buff, len);
2160 	tcp_fragment_tstamp(skb, buff);
2161 
2162 	/* Fix up tso_factor for both original and new SKB.  */
2163 	tcp_set_skb_tso_segs(skb, mss_now);
2164 	tcp_set_skb_tso_segs(buff, mss_now);
2165 
2166 	/* Link BUFF into the send queue. */
2167 	__skb_header_release(buff);
2168 	tcp_insert_write_queue_after(skb, buff, sk, TCP_FRAG_IN_WRITE_QUEUE);
2169 
2170 	return 0;
2171 }
2172 
2173 /* Try to defer sending, if possible, in order to minimize the amount
2174  * of TSO splitting we do.  View it as a kind of TSO Nagle test.
2175  *
2176  * This algorithm is from John Heffner.
2177  */
tcp_tso_should_defer(struct sock * sk,struct sk_buff * skb,bool * is_cwnd_limited,bool * is_rwnd_limited,u32 max_segs)2178 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
2179 				 bool *is_cwnd_limited,
2180 				 bool *is_rwnd_limited,
2181 				 u32 max_segs)
2182 {
2183 	const struct inet_connection_sock *icsk = inet_csk(sk);
2184 	u32 send_win, cong_win, limit, in_flight;
2185 	struct tcp_sock *tp = tcp_sk(sk);
2186 	struct sk_buff *head;
2187 	int win_divisor;
2188 	s64 delta;
2189 
2190 	if (icsk->icsk_ca_state >= TCP_CA_Recovery)
2191 		goto send_now;
2192 
2193 	/* Avoid bursty behavior by allowing defer
2194 	 * only if the last write was recent (1 ms).
2195 	 * Note that tp->tcp_wstamp_ns can be in the future if we have
2196 	 * packets waiting in a qdisc or device for EDT delivery.
2197 	 */
2198 	delta = tp->tcp_clock_cache - tp->tcp_wstamp_ns - NSEC_PER_MSEC;
2199 	if (delta > 0)
2200 		goto send_now;
2201 
2202 	in_flight = tcp_packets_in_flight(tp);
2203 
2204 	BUG_ON(tcp_skb_pcount(skb) <= 1);
2205 	BUG_ON(tcp_snd_cwnd(tp) <= in_flight);
2206 
2207 	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
2208 
2209 	/* From in_flight test above, we know that cwnd > in_flight.  */
2210 	cong_win = (tcp_snd_cwnd(tp) - in_flight) * tp->mss_cache;
2211 
2212 	limit = min(send_win, cong_win);
2213 
2214 	/* If a full-sized TSO skb can be sent, do it. */
2215 	if (limit >= max_segs * tp->mss_cache)
2216 		goto send_now;
2217 
2218 	/* Middle in queue won't get any more data, full sendable already? */
2219 	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
2220 		goto send_now;
2221 
2222 	win_divisor = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_win_divisor);
2223 	if (win_divisor) {
2224 		u32 chunk = min(tp->snd_wnd, tcp_snd_cwnd(tp) * tp->mss_cache);
2225 
2226 		/* If at least some fraction of a window is available,
2227 		 * just use it.
2228 		 */
2229 		chunk /= win_divisor;
2230 		if (limit >= chunk)
2231 			goto send_now;
2232 	} else {
2233 		/* Different approach, try not to defer past a single
2234 		 * ACK.  Receiver should ACK every other full sized
2235 		 * frame, so if we have space for more than 3 frames
2236 		 * then send now.
2237 		 */
2238 		if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
2239 			goto send_now;
2240 	}
2241 
2242 	/* TODO : use tsorted_sent_queue ? */
2243 	head = tcp_rtx_queue_head(sk);
2244 	if (!head)
2245 		goto send_now;
2246 	delta = tp->tcp_clock_cache - head->tstamp;
2247 	/* If next ACK is likely to come too late (half srtt), do not defer */
2248 	if ((s64)(delta - (u64)NSEC_PER_USEC * (tp->srtt_us >> 4)) < 0)
2249 		goto send_now;
2250 
2251 	/* Ok, it looks like it is advisable to defer.
2252 	 * Three cases are tracked :
2253 	 * 1) We are cwnd-limited
2254 	 * 2) We are rwnd-limited
2255 	 * 3) We are application limited.
2256 	 */
2257 	if (cong_win < send_win) {
2258 		if (cong_win <= skb->len) {
2259 			*is_cwnd_limited = true;
2260 			return true;
2261 		}
2262 	} else {
2263 		if (send_win <= skb->len) {
2264 			*is_rwnd_limited = true;
2265 			return true;
2266 		}
2267 	}
2268 
2269 	/* If this packet won't get more data, do not wait. */
2270 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) ||
2271 	    TCP_SKB_CB(skb)->eor)
2272 		goto send_now;
2273 
2274 	return true;
2275 
2276 send_now:
2277 	return false;
2278 }
2279 
tcp_mtu_check_reprobe(struct sock * sk)2280 static inline void tcp_mtu_check_reprobe(struct sock *sk)
2281 {
2282 	struct inet_connection_sock *icsk = inet_csk(sk);
2283 	struct tcp_sock *tp = tcp_sk(sk);
2284 	struct net *net = sock_net(sk);
2285 	u32 interval;
2286 	s32 delta;
2287 
2288 	interval = READ_ONCE(net->ipv4.sysctl_tcp_probe_interval);
2289 	delta = tcp_jiffies32 - icsk->icsk_mtup.probe_timestamp;
2290 	if (unlikely(delta >= interval * HZ)) {
2291 		int mss = tcp_current_mss(sk);
2292 
2293 		/* Update current search range */
2294 		icsk->icsk_mtup.probe_size = 0;
2295 		icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
2296 			sizeof(struct tcphdr) +
2297 			icsk->icsk_af_ops->net_header_len;
2298 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
2299 
2300 		/* Update probe time stamp */
2301 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
2302 	}
2303 }
2304 
tcp_can_coalesce_send_queue_head(struct sock * sk,int len)2305 static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
2306 {
2307 	struct sk_buff *skb, *next;
2308 
2309 	skb = tcp_send_head(sk);
2310 	tcp_for_write_queue_from_safe(skb, next, sk) {
2311 		if (len <= skb->len)
2312 			break;
2313 
2314 		if (unlikely(TCP_SKB_CB(skb)->eor) ||
2315 		    tcp_has_tx_tstamp(skb) ||
2316 		    !skb_pure_zcopy_same(skb, next))
2317 			return false;
2318 
2319 		len -= skb->len;
2320 	}
2321 
2322 	return true;
2323 }
2324 
2325 /* Create a new MTU probe if we are ready.
2326  * MTU probe is regularly attempting to increase the path MTU by
2327  * deliberately sending larger packets.  This discovers routing
2328  * changes resulting in larger path MTUs.
2329  *
2330  * Returns 0 if we should wait to probe (no cwnd available),
2331  *         1 if a probe was sent,
2332  *         -1 otherwise
2333  */
tcp_mtu_probe(struct sock * sk)2334 static int tcp_mtu_probe(struct sock *sk)
2335 {
2336 	struct inet_connection_sock *icsk = inet_csk(sk);
2337 	struct tcp_sock *tp = tcp_sk(sk);
2338 	struct sk_buff *skb, *nskb, *next;
2339 	struct net *net = sock_net(sk);
2340 	int probe_size;
2341 	int size_needed;
2342 	int copy, len;
2343 	int mss_now;
2344 	int interval;
2345 
2346 	/* Not currently probing/verifying,
2347 	 * not in recovery,
2348 	 * have enough cwnd, and
2349 	 * not SACKing (the variable headers throw things off)
2350 	 */
2351 	if (likely(!icsk->icsk_mtup.enabled ||
2352 		   icsk->icsk_mtup.probe_size ||
2353 		   inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
2354 		   tcp_snd_cwnd(tp) < 11 ||
2355 		   tp->rx_opt.num_sacks || tp->rx_opt.dsack))
2356 		return -1;
2357 
2358 	/* Use binary search for probe_size between tcp_mss_base,
2359 	 * and current mss_clamp. if (search_high - search_low)
2360 	 * smaller than a threshold, backoff from probing.
2361 	 */
2362 	mss_now = tcp_current_mss(sk);
2363 	probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
2364 				    icsk->icsk_mtup.search_low) >> 1);
2365 	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
2366 	interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
2367 	/* When misfortune happens, we are reprobing actively,
2368 	 * and then reprobe timer has expired. We stick with current
2369 	 * probing process by not resetting search range to its orignal.
2370 	 */
2371 	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
2372 	    interval < READ_ONCE(net->ipv4.sysctl_tcp_probe_threshold)) {
2373 		/* Check whether enough time has elaplased for
2374 		 * another round of probing.
2375 		 */
2376 		tcp_mtu_check_reprobe(sk);
2377 		return -1;
2378 	}
2379 
2380 	/* Have enough data in the send queue to probe? */
2381 	if (tp->write_seq - tp->snd_nxt < size_needed)
2382 		return -1;
2383 
2384 	if (tp->snd_wnd < size_needed)
2385 		return -1;
2386 	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
2387 		return 0;
2388 
2389 	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
2390 	if (tcp_packets_in_flight(tp) + 2 > tcp_snd_cwnd(tp)) {
2391 		if (!tcp_packets_in_flight(tp))
2392 			return -1;
2393 		else
2394 			return 0;
2395 	}
2396 
2397 	if (!tcp_can_coalesce_send_queue_head(sk, probe_size))
2398 		return -1;
2399 
2400 	/* We're allowed to probe.  Build it now. */
2401 	nskb = tcp_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
2402 	if (!nskb)
2403 		return -1;
2404 	sk_wmem_queued_add(sk, nskb->truesize);
2405 	sk_mem_charge(sk, nskb->truesize);
2406 
2407 	skb = tcp_send_head(sk);
2408 	skb_copy_decrypted(nskb, skb);
2409 	mptcp_skb_ext_copy(nskb, skb);
2410 
2411 	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
2412 	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
2413 	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
2414 
2415 	tcp_insert_write_queue_before(nskb, skb, sk);
2416 	tcp_highest_sack_replace(sk, skb, nskb);
2417 
2418 	len = 0;
2419 	tcp_for_write_queue_from_safe(skb, next, sk) {
2420 		copy = min_t(int, skb->len, probe_size - len);
2421 		skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
2422 
2423 		if (skb->len <= copy) {
2424 			/* We've eaten all the data from this skb.
2425 			 * Throw it away. */
2426 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2427 			/* If this is the last SKB we copy and eor is set
2428 			 * we need to propagate it to the new skb.
2429 			 */
2430 			TCP_SKB_CB(nskb)->eor = TCP_SKB_CB(skb)->eor;
2431 			tcp_skb_collapse_tstamp(nskb, skb);
2432 			tcp_unlink_write_queue(skb, sk);
2433 			tcp_wmem_free_skb(sk, skb);
2434 		} else {
2435 			TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2436 						   ~(TCPHDR_FIN|TCPHDR_PSH);
2437 			if (!skb_shinfo(skb)->nr_frags) {
2438 				skb_pull(skb, copy);
2439 			} else {
2440 				__pskb_trim_head(skb, copy);
2441 				tcp_set_skb_tso_segs(skb, mss_now);
2442 			}
2443 			TCP_SKB_CB(skb)->seq += copy;
2444 		}
2445 
2446 		len += copy;
2447 
2448 		if (len >= probe_size)
2449 			break;
2450 	}
2451 	tcp_init_tso_segs(nskb, nskb->len);
2452 
2453 	/* We're ready to send.  If this fails, the probe will
2454 	 * be resegmented into mss-sized pieces by tcp_write_xmit().
2455 	 */
2456 	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2457 		/* Decrement cwnd here because we are sending
2458 		 * effectively two packets. */
2459 		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - 1);
2460 		tcp_event_new_data_sent(sk, nskb);
2461 
2462 		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2463 		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2464 		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2465 
2466 		return 1;
2467 	}
2468 
2469 	return -1;
2470 }
2471 
tcp_pacing_check(struct sock * sk)2472 static bool tcp_pacing_check(struct sock *sk)
2473 {
2474 	struct tcp_sock *tp = tcp_sk(sk);
2475 
2476 	if (!tcp_needs_internal_pacing(sk))
2477 		return false;
2478 
2479 	if (tp->tcp_wstamp_ns <= tp->tcp_clock_cache)
2480 		return false;
2481 
2482 	if (!hrtimer_is_queued(&tp->pacing_timer)) {
2483 		hrtimer_start(&tp->pacing_timer,
2484 			      ns_to_ktime(tp->tcp_wstamp_ns),
2485 			      HRTIMER_MODE_ABS_PINNED_SOFT);
2486 		sock_hold(sk);
2487 	}
2488 	return true;
2489 }
2490 
2491 /* TCP Small Queues :
2492  * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2493  * (These limits are doubled for retransmits)
2494  * This allows for :
2495  *  - better RTT estimation and ACK scheduling
2496  *  - faster recovery
2497  *  - high rates
2498  * Alas, some drivers / subsystems require a fair amount
2499  * of queued bytes to ensure line rate.
2500  * One example is wifi aggregation (802.11 AMPDU)
2501  */
tcp_small_queue_check(struct sock * sk,const struct sk_buff * skb,unsigned int factor)2502 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
2503 				  unsigned int factor)
2504 {
2505 	unsigned long limit;
2506 
2507 	limit = max_t(unsigned long,
2508 		      2 * skb->truesize,
2509 		      sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift));
2510 	if (sk->sk_pacing_status == SK_PACING_NONE)
2511 		limit = min_t(unsigned long, limit,
2512 			      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes));
2513 	limit <<= factor;
2514 
2515 	if (static_branch_unlikely(&tcp_tx_delay_enabled) &&
2516 	    tcp_sk(sk)->tcp_tx_delay) {
2517 		u64 extra_bytes = (u64)sk->sk_pacing_rate * tcp_sk(sk)->tcp_tx_delay;
2518 
2519 		/* TSQ is based on skb truesize sum (sk_wmem_alloc), so we
2520 		 * approximate our needs assuming an ~100% skb->truesize overhead.
2521 		 * USEC_PER_SEC is approximated by 2^20.
2522 		 * do_div(extra_bytes, USEC_PER_SEC/2) is replaced by a right shift.
2523 		 */
2524 		extra_bytes >>= (20 - 1);
2525 		limit += extra_bytes;
2526 	}
2527 	if (refcount_read(&sk->sk_wmem_alloc) > limit) {
2528 		/* Always send skb if rtx queue is empty.
2529 		 * No need to wait for TX completion to call us back,
2530 		 * after softirq/tasklet schedule.
2531 		 * This helps when TX completions are delayed too much.
2532 		 */
2533 		if (tcp_rtx_queue_empty(sk))
2534 			return false;
2535 
2536 		set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2537 		/* It is possible TX completion already happened
2538 		 * before we set TSQ_THROTTLED, so we must
2539 		 * test again the condition.
2540 		 */
2541 		smp_mb__after_atomic();
2542 		if (refcount_read(&sk->sk_wmem_alloc) > limit)
2543 			return true;
2544 	}
2545 	return false;
2546 }
2547 
tcp_chrono_set(struct tcp_sock * tp,const enum tcp_chrono new)2548 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
2549 {
2550 	const u32 now = tcp_jiffies32;
2551 	enum tcp_chrono old = tp->chrono_type;
2552 
2553 	if (old > TCP_CHRONO_UNSPEC)
2554 		tp->chrono_stat[old - 1] += now - tp->chrono_start;
2555 	tp->chrono_start = now;
2556 	tp->chrono_type = new;
2557 }
2558 
tcp_chrono_start(struct sock * sk,const enum tcp_chrono type)2559 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
2560 {
2561 	struct tcp_sock *tp = tcp_sk(sk);
2562 
2563 	/* If there are multiple conditions worthy of tracking in a
2564 	 * chronograph then the highest priority enum takes precedence
2565 	 * over the other conditions. So that if something "more interesting"
2566 	 * starts happening, stop the previous chrono and start a new one.
2567 	 */
2568 	if (type > tp->chrono_type)
2569 		tcp_chrono_set(tp, type);
2570 }
2571 
tcp_chrono_stop(struct sock * sk,const enum tcp_chrono type)2572 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
2573 {
2574 	struct tcp_sock *tp = tcp_sk(sk);
2575 
2576 
2577 	/* There are multiple conditions worthy of tracking in a
2578 	 * chronograph, so that the highest priority enum takes
2579 	 * precedence over the other conditions (see tcp_chrono_start).
2580 	 * If a condition stops, we only stop chrono tracking if
2581 	 * it's the "most interesting" or current chrono we are
2582 	 * tracking and starts busy chrono if we have pending data.
2583 	 */
2584 	if (tcp_rtx_and_write_queues_empty(sk))
2585 		tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
2586 	else if (type == tp->chrono_type)
2587 		tcp_chrono_set(tp, TCP_CHRONO_BUSY);
2588 }
2589 
2590 /* This routine writes packets to the network.  It advances the
2591  * send_head.  This happens as incoming acks open up the remote
2592  * window for us.
2593  *
2594  * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2595  * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2596  * account rare use of URG, this is not a big flaw.
2597  *
2598  * Send at most one packet when push_one > 0. Temporarily ignore
2599  * cwnd limit to force at most one packet out when push_one == 2.
2600 
2601  * Returns true, if no segments are in flight and we have queued segments,
2602  * but cannot send anything now because of SWS or another problem.
2603  */
tcp_write_xmit(struct sock * sk,unsigned int mss_now,int nonagle,int push_one,gfp_t gfp)2604 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2605 			   int push_one, gfp_t gfp)
2606 {
2607 	struct tcp_sock *tp = tcp_sk(sk);
2608 	struct sk_buff *skb;
2609 	unsigned int tso_segs, sent_pkts;
2610 	int cwnd_quota;
2611 	int result;
2612 	bool is_cwnd_limited = false, is_rwnd_limited = false;
2613 	u32 max_segs;
2614 
2615 	sent_pkts = 0;
2616 
2617 	tcp_mstamp_refresh(tp);
2618 	if (!push_one) {
2619 		/* Do MTU probing. */
2620 		result = tcp_mtu_probe(sk);
2621 		if (!result) {
2622 			return false;
2623 		} else if (result > 0) {
2624 			sent_pkts = 1;
2625 		}
2626 	}
2627 
2628 	max_segs = tcp_tso_segs(sk, mss_now);
2629 	while ((skb = tcp_send_head(sk))) {
2630 		unsigned int limit;
2631 
2632 		if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2633 			/* "skb_mstamp_ns" is used as a start point for the retransmit timer */
2634 			tp->tcp_wstamp_ns = tp->tcp_clock_cache;
2635 			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
2636 			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
2637 			tcp_init_tso_segs(skb, mss_now);
2638 			goto repair; /* Skip network transmission */
2639 		}
2640 
2641 		if (tcp_pacing_check(sk))
2642 			break;
2643 
2644 		tso_segs = tcp_init_tso_segs(skb, mss_now);
2645 		BUG_ON(!tso_segs);
2646 
2647 		cwnd_quota = tcp_cwnd_test(tp, skb);
2648 		if (!cwnd_quota) {
2649 			if (push_one == 2)
2650 				/* Force out a loss probe pkt. */
2651 				cwnd_quota = 1;
2652 			else
2653 				break;
2654 		}
2655 
2656 		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
2657 			is_rwnd_limited = true;
2658 			break;
2659 		}
2660 
2661 		if (tso_segs == 1) {
2662 			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2663 						     (tcp_skb_is_last(sk, skb) ?
2664 						      nonagle : TCP_NAGLE_PUSH))))
2665 				break;
2666 		} else {
2667 			if (!push_one &&
2668 			    tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2669 						 &is_rwnd_limited, max_segs))
2670 				break;
2671 		}
2672 
2673 		limit = mss_now;
2674 		if (tso_segs > 1 && !tcp_urg_mode(tp))
2675 			limit = tcp_mss_split_point(sk, skb, mss_now,
2676 						    min_t(unsigned int,
2677 							  cwnd_quota,
2678 							  max_segs),
2679 						    nonagle);
2680 
2681 		if (skb->len > limit &&
2682 		    unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2683 			break;
2684 
2685 		if (tcp_small_queue_check(sk, skb, 0))
2686 			break;
2687 
2688 		/* Argh, we hit an empty skb(), presumably a thread
2689 		 * is sleeping in sendmsg()/sk_stream_wait_memory().
2690 		 * We do not want to send a pure-ack packet and have
2691 		 * a strange looking rtx queue with empty packet(s).
2692 		 */
2693 		if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq)
2694 			break;
2695 
2696 		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2697 			break;
2698 
2699 repair:
2700 		/* Advance the send_head.  This one is sent out.
2701 		 * This call will increment packets_out.
2702 		 */
2703 		tcp_event_new_data_sent(sk, skb);
2704 
2705 		tcp_minshall_update(tp, mss_now, skb);
2706 		sent_pkts += tcp_skb_pcount(skb);
2707 
2708 		if (push_one)
2709 			break;
2710 	}
2711 
2712 	if (is_rwnd_limited)
2713 		tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
2714 	else
2715 		tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
2716 
2717 	is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp));
2718 	if (likely(sent_pkts || is_cwnd_limited))
2719 		tcp_cwnd_validate(sk, is_cwnd_limited);
2720 
2721 	if (likely(sent_pkts)) {
2722 		if (tcp_in_cwnd_reduction(sk))
2723 			tp->prr_out += sent_pkts;
2724 
2725 		/* Send one loss probe per tail loss episode. */
2726 		if (push_one != 2)
2727 			tcp_schedule_loss_probe(sk, false);
2728 		return false;
2729 	}
2730 	return !tp->packets_out && !tcp_write_queue_empty(sk);
2731 }
2732 
tcp_schedule_loss_probe(struct sock * sk,bool advancing_rto)2733 bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto)
2734 {
2735 	struct inet_connection_sock *icsk = inet_csk(sk);
2736 	struct tcp_sock *tp = tcp_sk(sk);
2737 	u32 timeout, rto_delta_us;
2738 	int early_retrans;
2739 
2740 	/* Don't do any loss probe on a Fast Open connection before 3WHS
2741 	 * finishes.
2742 	 */
2743 	if (rcu_access_pointer(tp->fastopen_rsk))
2744 		return false;
2745 
2746 	early_retrans = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_early_retrans);
2747 	/* Schedule a loss probe in 2*RTT for SACK capable connections
2748 	 * not in loss recovery, that are either limited by cwnd or application.
2749 	 */
2750 	if ((early_retrans != 3 && early_retrans != 4) ||
2751 	    !tp->packets_out || !tcp_is_sack(tp) ||
2752 	    (icsk->icsk_ca_state != TCP_CA_Open &&
2753 	     icsk->icsk_ca_state != TCP_CA_CWR))
2754 		return false;
2755 
2756 	/* Probe timeout is 2*rtt. Add minimum RTO to account
2757 	 * for delayed ack when there's one outstanding packet. If no RTT
2758 	 * sample is available then probe after TCP_TIMEOUT_INIT.
2759 	 */
2760 	if (tp->srtt_us) {
2761 		timeout = usecs_to_jiffies(tp->srtt_us >> 2);
2762 		if (tp->packets_out == 1)
2763 			timeout += TCP_RTO_MIN;
2764 		else
2765 			timeout += TCP_TIMEOUT_MIN;
2766 	} else {
2767 		timeout = TCP_TIMEOUT_INIT;
2768 	}
2769 
2770 	/* If the RTO formula yields an earlier time, then use that time. */
2771 	rto_delta_us = advancing_rto ?
2772 			jiffies_to_usecs(inet_csk(sk)->icsk_rto) :
2773 			tcp_rto_delta_us(sk);  /* How far in future is RTO? */
2774 	if (rto_delta_us > 0)
2775 		timeout = min_t(u32, timeout, usecs_to_jiffies(rto_delta_us));
2776 
2777 	tcp_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout, TCP_RTO_MAX);
2778 	return true;
2779 }
2780 
2781 /* Thanks to skb fast clones, we can detect if a prior transmit of
2782  * a packet is still in a qdisc or driver queue.
2783  * In this case, there is very little point doing a retransmit !
2784  */
skb_still_in_host_queue(struct sock * sk,const struct sk_buff * skb)2785 static bool skb_still_in_host_queue(struct sock *sk,
2786 				    const struct sk_buff *skb)
2787 {
2788 	if (unlikely(skb_fclone_busy(sk, skb))) {
2789 		set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags);
2790 		smp_mb__after_atomic();
2791 		if (skb_fclone_busy(sk, skb)) {
2792 			NET_INC_STATS(sock_net(sk),
2793 				      LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2794 			return true;
2795 		}
2796 	}
2797 	return false;
2798 }
2799 
2800 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2801  * retransmit the last segment.
2802  */
tcp_send_loss_probe(struct sock * sk)2803 void tcp_send_loss_probe(struct sock *sk)
2804 {
2805 	struct tcp_sock *tp = tcp_sk(sk);
2806 	struct sk_buff *skb;
2807 	int pcount;
2808 	int mss = tcp_current_mss(sk);
2809 
2810 	/* At most one outstanding TLP */
2811 	if (tp->tlp_high_seq)
2812 		goto rearm_timer;
2813 
2814 	tp->tlp_retrans = 0;
2815 	skb = tcp_send_head(sk);
2816 	if (skb && tcp_snd_wnd_test(tp, skb, mss)) {
2817 		pcount = tp->packets_out;
2818 		tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2819 		if (tp->packets_out > pcount)
2820 			goto probe_sent;
2821 		goto rearm_timer;
2822 	}
2823 	skb = skb_rb_last(&sk->tcp_rtx_queue);
2824 	if (unlikely(!skb)) {
2825 		WARN_ONCE(tp->packets_out,
2826 			  "invalid inflight: %u state %u cwnd %u mss %d\n",
2827 			  tp->packets_out, sk->sk_state, tcp_snd_cwnd(tp), mss);
2828 		inet_csk(sk)->icsk_pending = 0;
2829 		return;
2830 	}
2831 
2832 	if (skb_still_in_host_queue(sk, skb))
2833 		goto rearm_timer;
2834 
2835 	pcount = tcp_skb_pcount(skb);
2836 	if (WARN_ON(!pcount))
2837 		goto rearm_timer;
2838 
2839 	if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2840 		if (unlikely(tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
2841 					  (pcount - 1) * mss, mss,
2842 					  GFP_ATOMIC)))
2843 			goto rearm_timer;
2844 		skb = skb_rb_next(skb);
2845 	}
2846 
2847 	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2848 		goto rearm_timer;
2849 
2850 	if (__tcp_retransmit_skb(sk, skb, 1))
2851 		goto rearm_timer;
2852 
2853 	tp->tlp_retrans = 1;
2854 
2855 probe_sent:
2856 	/* Record snd_nxt for loss detection. */
2857 	tp->tlp_high_seq = tp->snd_nxt;
2858 
2859 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2860 	/* Reset s.t. tcp_rearm_rto will restart timer from now */
2861 	inet_csk(sk)->icsk_pending = 0;
2862 rearm_timer:
2863 	tcp_rearm_rto(sk);
2864 }
2865 
2866 /* Push out any pending frames which were held back due to
2867  * TCP_CORK or attempt at coalescing tiny packets.
2868  * The socket must be locked by the caller.
2869  */
__tcp_push_pending_frames(struct sock * sk,unsigned int cur_mss,int nonagle)2870 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2871 			       int nonagle)
2872 {
2873 	/* If we are closed, the bytes will have to remain here.
2874 	 * In time closedown will finish, we empty the write queue and
2875 	 * all will be happy.
2876 	 */
2877 	if (unlikely(sk->sk_state == TCP_CLOSE))
2878 		return;
2879 
2880 	if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2881 			   sk_gfp_mask(sk, GFP_ATOMIC)))
2882 		tcp_check_probe_timer(sk);
2883 }
2884 
2885 /* Send _single_ skb sitting at the send head. This function requires
2886  * true push pending frames to setup probe timer etc.
2887  */
tcp_push_one(struct sock * sk,unsigned int mss_now)2888 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2889 {
2890 	struct sk_buff *skb = tcp_send_head(sk);
2891 
2892 	BUG_ON(!skb || skb->len < mss_now);
2893 
2894 	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2895 }
2896 
2897 /* This function returns the amount that we can raise the
2898  * usable window based on the following constraints
2899  *
2900  * 1. The window can never be shrunk once it is offered (RFC 793)
2901  * 2. We limit memory per socket
2902  *
2903  * RFC 1122:
2904  * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2905  *  RECV.NEXT + RCV.WIN fixed until:
2906  *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2907  *
2908  * i.e. don't raise the right edge of the window until you can raise
2909  * it at least MSS bytes.
2910  *
2911  * Unfortunately, the recommended algorithm breaks header prediction,
2912  * since header prediction assumes th->window stays fixed.
2913  *
2914  * Strictly speaking, keeping th->window fixed violates the receiver
2915  * side SWS prevention criteria. The problem is that under this rule
2916  * a stream of single byte packets will cause the right side of the
2917  * window to always advance by a single byte.
2918  *
2919  * Of course, if the sender implements sender side SWS prevention
2920  * then this will not be a problem.
2921  *
2922  * BSD seems to make the following compromise:
2923  *
2924  *	If the free space is less than the 1/4 of the maximum
2925  *	space available and the free space is less than 1/2 mss,
2926  *	then set the window to 0.
2927  *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2928  *	Otherwise, just prevent the window from shrinking
2929  *	and from being larger than the largest representable value.
2930  *
2931  * This prevents incremental opening of the window in the regime
2932  * where TCP is limited by the speed of the reader side taking
2933  * data out of the TCP receive queue. It does nothing about
2934  * those cases where the window is constrained on the sender side
2935  * because the pipeline is full.
2936  *
2937  * BSD also seems to "accidentally" limit itself to windows that are a
2938  * multiple of MSS, at least until the free space gets quite small.
2939  * This would appear to be a side effect of the mbuf implementation.
2940  * Combining these two algorithms results in the observed behavior
2941  * of having a fixed window size at almost all times.
2942  *
2943  * Below we obtain similar behavior by forcing the offered window to
2944  * a multiple of the mss when it is feasible to do so.
2945  *
2946  * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2947  * Regular options like TIMESTAMP are taken into account.
2948  */
__tcp_select_window(struct sock * sk)2949 u32 __tcp_select_window(struct sock *sk)
2950 {
2951 	struct inet_connection_sock *icsk = inet_csk(sk);
2952 	struct tcp_sock *tp = tcp_sk(sk);
2953 	/* MSS for the peer's data.  Previous versions used mss_clamp
2954 	 * here.  I don't know if the value based on our guesses
2955 	 * of peer's MSS is better for the performance.  It's more correct
2956 	 * but may be worse for the performance because of rcv_mss
2957 	 * fluctuations.  --SAW  1998/11/1
2958 	 */
2959 	int mss = icsk->icsk_ack.rcv_mss;
2960 	int free_space = tcp_space(sk);
2961 	int allowed_space = tcp_full_space(sk);
2962 	int full_space, window;
2963 
2964 	if (sk_is_mptcp(sk))
2965 		mptcp_space(sk, &free_space, &allowed_space);
2966 
2967 	full_space = min_t(int, tp->window_clamp, allowed_space);
2968 
2969 	if (unlikely(mss > full_space)) {
2970 		mss = full_space;
2971 		if (mss <= 0)
2972 			return 0;
2973 	}
2974 	if (free_space < (full_space >> 1)) {
2975 		icsk->icsk_ack.quick = 0;
2976 
2977 		if (tcp_under_memory_pressure(sk))
2978 			tcp_adjust_rcv_ssthresh(sk);
2979 
2980 		/* free_space might become our new window, make sure we don't
2981 		 * increase it due to wscale.
2982 		 */
2983 		free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2984 
2985 		/* if free space is less than mss estimate, or is below 1/16th
2986 		 * of the maximum allowed, try to move to zero-window, else
2987 		 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2988 		 * new incoming data is dropped due to memory limits.
2989 		 * With large window, mss test triggers way too late in order
2990 		 * to announce zero window in time before rmem limit kicks in.
2991 		 */
2992 		if (free_space < (allowed_space >> 4) || free_space < mss)
2993 			return 0;
2994 	}
2995 
2996 	if (free_space > tp->rcv_ssthresh)
2997 		free_space = tp->rcv_ssthresh;
2998 
2999 	/* Don't do rounding if we are using window scaling, since the
3000 	 * scaled window will not line up with the MSS boundary anyway.
3001 	 */
3002 	if (tp->rx_opt.rcv_wscale) {
3003 		window = free_space;
3004 
3005 		/* Advertise enough space so that it won't get scaled away.
3006 		 * Import case: prevent zero window announcement if
3007 		 * 1<<rcv_wscale > mss.
3008 		 */
3009 		window = ALIGN(window, (1 << tp->rx_opt.rcv_wscale));
3010 	} else {
3011 		window = tp->rcv_wnd;
3012 		/* Get the largest window that is a nice multiple of mss.
3013 		 * Window clamp already applied above.
3014 		 * If our current window offering is within 1 mss of the
3015 		 * free space we just keep it. This prevents the divide
3016 		 * and multiply from happening most of the time.
3017 		 * We also don't do any window rounding when the free space
3018 		 * is too small.
3019 		 */
3020 		if (window <= free_space - mss || window > free_space)
3021 			window = rounddown(free_space, mss);
3022 		else if (mss == full_space &&
3023 			 free_space > window + (full_space >> 1))
3024 			window = free_space;
3025 	}
3026 
3027 	return window;
3028 }
3029 
tcp_skb_collapse_tstamp(struct sk_buff * skb,const struct sk_buff * next_skb)3030 void tcp_skb_collapse_tstamp(struct sk_buff *skb,
3031 			     const struct sk_buff *next_skb)
3032 {
3033 	if (unlikely(tcp_has_tx_tstamp(next_skb))) {
3034 		const struct skb_shared_info *next_shinfo =
3035 			skb_shinfo(next_skb);
3036 		struct skb_shared_info *shinfo = skb_shinfo(skb);
3037 
3038 		shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP;
3039 		shinfo->tskey = next_shinfo->tskey;
3040 		TCP_SKB_CB(skb)->txstamp_ack |=
3041 			TCP_SKB_CB(next_skb)->txstamp_ack;
3042 	}
3043 }
3044 
3045 /* Collapses two adjacent SKB's during retransmission. */
tcp_collapse_retrans(struct sock * sk,struct sk_buff * skb)3046 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
3047 {
3048 	struct tcp_sock *tp = tcp_sk(sk);
3049 	struct sk_buff *next_skb = skb_rb_next(skb);
3050 	int next_skb_size;
3051 
3052 	next_skb_size = next_skb->len;
3053 
3054 	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
3055 
3056 	if (next_skb_size && !tcp_skb_shift(skb, next_skb, 1, next_skb_size))
3057 		return false;
3058 
3059 	tcp_highest_sack_replace(sk, next_skb, skb);
3060 
3061 	/* Update sequence range on original skb. */
3062 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
3063 
3064 	/* Merge over control information. This moves PSH/FIN etc. over */
3065 	TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
3066 
3067 	/* All done, get rid of second SKB and account for it so
3068 	 * packet counting does not break.
3069 	 */
3070 	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
3071 	TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor;
3072 
3073 	/* changed transmit queue under us so clear hints */
3074 	tcp_clear_retrans_hints_partial(tp);
3075 	if (next_skb == tp->retransmit_skb_hint)
3076 		tp->retransmit_skb_hint = skb;
3077 
3078 	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
3079 
3080 	tcp_skb_collapse_tstamp(skb, next_skb);
3081 
3082 	tcp_rtx_queue_unlink_and_free(next_skb, sk);
3083 	return true;
3084 }
3085 
3086 /* Check if coalescing SKBs is legal. */
tcp_can_collapse(const struct sock * sk,const struct sk_buff * skb)3087 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
3088 {
3089 	if (tcp_skb_pcount(skb) > 1)
3090 		return false;
3091 	if (skb_cloned(skb))
3092 		return false;
3093 	/* Some heuristics for collapsing over SACK'd could be invented */
3094 	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3095 		return false;
3096 
3097 	return true;
3098 }
3099 
3100 /* Collapse packets in the retransmit queue to make to create
3101  * less packets on the wire. This is only done on retransmission.
3102  */
tcp_retrans_try_collapse(struct sock * sk,struct sk_buff * to,int space)3103 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
3104 				     int space)
3105 {
3106 	struct tcp_sock *tp = tcp_sk(sk);
3107 	struct sk_buff *skb = to, *tmp;
3108 	bool first = true;
3109 
3110 	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retrans_collapse))
3111 		return;
3112 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
3113 		return;
3114 
3115 	skb_rbtree_walk_from_safe(skb, tmp) {
3116 		if (!tcp_can_collapse(sk, skb))
3117 			break;
3118 
3119 		if (!tcp_skb_can_collapse(to, skb))
3120 			break;
3121 
3122 		space -= skb->len;
3123 
3124 		if (first) {
3125 			first = false;
3126 			continue;
3127 		}
3128 
3129 		if (space < 0)
3130 			break;
3131 
3132 		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
3133 			break;
3134 
3135 		if (!tcp_collapse_retrans(sk, to))
3136 			break;
3137 	}
3138 }
3139 
3140 /* This retransmits one SKB.  Policy decisions and retransmit queue
3141  * state updates are done by the caller.  Returns non-zero if an
3142  * error occurred which prevented the send.
3143  */
__tcp_retransmit_skb(struct sock * sk,struct sk_buff * skb,int segs)3144 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
3145 {
3146 	struct inet_connection_sock *icsk = inet_csk(sk);
3147 	struct tcp_sock *tp = tcp_sk(sk);
3148 	unsigned int cur_mss;
3149 	int diff, len, err;
3150 	int avail_wnd;
3151 
3152 	/* Inconclusive MTU probe */
3153 	if (icsk->icsk_mtup.probe_size)
3154 		icsk->icsk_mtup.probe_size = 0;
3155 
3156 	if (skb_still_in_host_queue(sk, skb))
3157 		return -EBUSY;
3158 
3159 	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
3160 		if (unlikely(before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))) {
3161 			WARN_ON_ONCE(1);
3162 			return -EINVAL;
3163 		}
3164 		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3165 			return -ENOMEM;
3166 	}
3167 
3168 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
3169 		return -EHOSTUNREACH; /* Routing failure or similar. */
3170 
3171 	cur_mss = tcp_current_mss(sk);
3172 	avail_wnd = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3173 
3174 	/* If receiver has shrunk his window, and skb is out of
3175 	 * new window, do not retransmit it. The exception is the
3176 	 * case, when window is shrunk to zero. In this case
3177 	 * our retransmit of one segment serves as a zero window probe.
3178 	 */
3179 	if (avail_wnd <= 0) {
3180 		if (TCP_SKB_CB(skb)->seq != tp->snd_una)
3181 			return -EAGAIN;
3182 		avail_wnd = cur_mss;
3183 	}
3184 
3185 	len = cur_mss * segs;
3186 	if (len > avail_wnd) {
3187 		len = rounddown(avail_wnd, cur_mss);
3188 		if (!len)
3189 			len = avail_wnd;
3190 	}
3191 	if (skb->len > len) {
3192 		if (tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, len,
3193 				 cur_mss, GFP_ATOMIC))
3194 			return -ENOMEM; /* We'll try again later. */
3195 	} else {
3196 		if (skb_unclone_keeptruesize(skb, GFP_ATOMIC))
3197 			return -ENOMEM;
3198 
3199 		diff = tcp_skb_pcount(skb);
3200 		tcp_set_skb_tso_segs(skb, cur_mss);
3201 		diff -= tcp_skb_pcount(skb);
3202 		if (diff)
3203 			tcp_adjust_pcount(sk, skb, diff);
3204 		avail_wnd = min_t(int, avail_wnd, cur_mss);
3205 		if (skb->len < avail_wnd)
3206 			tcp_retrans_try_collapse(sk, skb, avail_wnd);
3207 	}
3208 
3209 	/* RFC3168, section 6.1.1.1. ECN fallback */
3210 	if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
3211 		tcp_ecn_clear_syn(sk, skb);
3212 
3213 	/* Update global and local TCP statistics. */
3214 	segs = tcp_skb_pcount(skb);
3215 	TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
3216 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
3217 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3218 	tp->total_retrans += segs;
3219 	tp->bytes_retrans += skb->len;
3220 
3221 	/* make sure skb->data is aligned on arches that require it
3222 	 * and check if ack-trimming & collapsing extended the headroom
3223 	 * beyond what csum_start can cover.
3224 	 */
3225 	if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
3226 		     skb_headroom(skb) >= 0xFFFF)) {
3227 		struct sk_buff *nskb;
3228 
3229 		tcp_skb_tsorted_save(skb) {
3230 			nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
3231 			if (nskb) {
3232 				nskb->dev = NULL;
3233 				err = tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC);
3234 			} else {
3235 				err = -ENOBUFS;
3236 			}
3237 		} tcp_skb_tsorted_restore(skb);
3238 
3239 		if (!err) {
3240 			tcp_update_skb_after_send(sk, skb, tp->tcp_wstamp_ns);
3241 			tcp_rate_skb_sent(sk, skb);
3242 		}
3243 	} else {
3244 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3245 	}
3246 
3247 	/* To avoid taking spuriously low RTT samples based on a timestamp
3248 	 * for a transmit that never happened, always mark EVER_RETRANS
3249 	 */
3250 	TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
3251 
3252 	if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RETRANS_CB_FLAG))
3253 		tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RETRANS_CB,
3254 				  TCP_SKB_CB(skb)->seq, segs, err);
3255 
3256 	if (likely(!err)) {
3257 		trace_tcp_retransmit_skb(sk, skb);
3258 	} else if (err != -EBUSY) {
3259 		NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL, segs);
3260 	}
3261 	return err;
3262 }
3263 
tcp_retransmit_skb(struct sock * sk,struct sk_buff * skb,int segs)3264 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
3265 {
3266 	struct tcp_sock *tp = tcp_sk(sk);
3267 	int err = __tcp_retransmit_skb(sk, skb, segs);
3268 
3269 	if (err == 0) {
3270 #if FASTRETRANS_DEBUG > 0
3271 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
3272 			net_dbg_ratelimited("retrans_out leaked\n");
3273 		}
3274 #endif
3275 		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
3276 		tp->retrans_out += tcp_skb_pcount(skb);
3277 	}
3278 
3279 	/* Save stamp of the first (attempted) retransmit. */
3280 	if (!tp->retrans_stamp)
3281 		tp->retrans_stamp = tcp_skb_timestamp(skb);
3282 
3283 	if (tp->undo_retrans < 0)
3284 		tp->undo_retrans = 0;
3285 	tp->undo_retrans += tcp_skb_pcount(skb);
3286 	return err;
3287 }
3288 
3289 /* This gets called after a retransmit timeout, and the initially
3290  * retransmitted data is acknowledged.  It tries to continue
3291  * resending the rest of the retransmit queue, until either
3292  * we've sent it all or the congestion window limit is reached.
3293  */
tcp_xmit_retransmit_queue(struct sock * sk)3294 void tcp_xmit_retransmit_queue(struct sock *sk)
3295 {
3296 	const struct inet_connection_sock *icsk = inet_csk(sk);
3297 	struct sk_buff *skb, *rtx_head, *hole = NULL;
3298 	struct tcp_sock *tp = tcp_sk(sk);
3299 	bool rearm_timer = false;
3300 	u32 max_segs;
3301 	int mib_idx;
3302 
3303 	if (!tp->packets_out)
3304 		return;
3305 
3306 	rtx_head = tcp_rtx_queue_head(sk);
3307 	skb = tp->retransmit_skb_hint ?: rtx_head;
3308 	max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
3309 	skb_rbtree_walk_from(skb) {
3310 		__u8 sacked;
3311 		int segs;
3312 
3313 		if (tcp_pacing_check(sk))
3314 			break;
3315 
3316 		/* we could do better than to assign each time */
3317 		if (!hole)
3318 			tp->retransmit_skb_hint = skb;
3319 
3320 		segs = tcp_snd_cwnd(tp) - tcp_packets_in_flight(tp);
3321 		if (segs <= 0)
3322 			break;
3323 		sacked = TCP_SKB_CB(skb)->sacked;
3324 		/* In case tcp_shift_skb_data() have aggregated large skbs,
3325 		 * we need to make sure not sending too bigs TSO packets
3326 		 */
3327 		segs = min_t(int, segs, max_segs);
3328 
3329 		if (tp->retrans_out >= tp->lost_out) {
3330 			break;
3331 		} else if (!(sacked & TCPCB_LOST)) {
3332 			if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
3333 				hole = skb;
3334 			continue;
3335 
3336 		} else {
3337 			if (icsk->icsk_ca_state != TCP_CA_Loss)
3338 				mib_idx = LINUX_MIB_TCPFASTRETRANS;
3339 			else
3340 				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
3341 		}
3342 
3343 		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
3344 			continue;
3345 
3346 		if (tcp_small_queue_check(sk, skb, 1))
3347 			break;
3348 
3349 		if (tcp_retransmit_skb(sk, skb, segs))
3350 			break;
3351 
3352 		NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb));
3353 
3354 		if (tcp_in_cwnd_reduction(sk))
3355 			tp->prr_out += tcp_skb_pcount(skb);
3356 
3357 		if (skb == rtx_head &&
3358 		    icsk->icsk_pending != ICSK_TIME_REO_TIMEOUT)
3359 			rearm_timer = true;
3360 
3361 	}
3362 	if (rearm_timer)
3363 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3364 				     inet_csk(sk)->icsk_rto,
3365 				     TCP_RTO_MAX);
3366 }
3367 
3368 /* We allow to exceed memory limits for FIN packets to expedite
3369  * connection tear down and (memory) recovery.
3370  * Otherwise tcp_send_fin() could be tempted to either delay FIN
3371  * or even be forced to close flow without any FIN.
3372  * In general, we want to allow one skb per socket to avoid hangs
3373  * with edge trigger epoll()
3374  */
sk_forced_mem_schedule(struct sock * sk,int size)3375 void sk_forced_mem_schedule(struct sock *sk, int size)
3376 {
3377 	int delta, amt;
3378 
3379 	delta = size - sk->sk_forward_alloc;
3380 	if (delta <= 0)
3381 		return;
3382 	amt = sk_mem_pages(delta);
3383 	sk->sk_forward_alloc += amt << PAGE_SHIFT;
3384 	sk_memory_allocated_add(sk, amt);
3385 
3386 	if (mem_cgroup_sockets_enabled && sk->sk_memcg)
3387 		mem_cgroup_charge_skmem(sk->sk_memcg, amt,
3388 					gfp_memcg_charge() | __GFP_NOFAIL);
3389 }
3390 
3391 /* Send a FIN. The caller locks the socket for us.
3392  * We should try to send a FIN packet really hard, but eventually give up.
3393  */
tcp_send_fin(struct sock * sk)3394 void tcp_send_fin(struct sock *sk)
3395 {
3396 	struct sk_buff *skb, *tskb, *tail = tcp_write_queue_tail(sk);
3397 	struct tcp_sock *tp = tcp_sk(sk);
3398 
3399 	/* Optimization, tack on the FIN if we have one skb in write queue and
3400 	 * this skb was not yet sent, or we are under memory pressure.
3401 	 * Note: in the latter case, FIN packet will be sent after a timeout,
3402 	 * as TCP stack thinks it has already been transmitted.
3403 	 */
3404 	tskb = tail;
3405 	if (!tskb && tcp_under_memory_pressure(sk))
3406 		tskb = skb_rb_last(&sk->tcp_rtx_queue);
3407 
3408 	if (tskb) {
3409 		TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
3410 		TCP_SKB_CB(tskb)->end_seq++;
3411 		tp->write_seq++;
3412 		if (!tail) {
3413 			/* This means tskb was already sent.
3414 			 * Pretend we included the FIN on previous transmit.
3415 			 * We need to set tp->snd_nxt to the value it would have
3416 			 * if FIN had been sent. This is because retransmit path
3417 			 * does not change tp->snd_nxt.
3418 			 */
3419 			WRITE_ONCE(tp->snd_nxt, tp->snd_nxt + 1);
3420 			return;
3421 		}
3422 	} else {
3423 		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
3424 		if (unlikely(!skb))
3425 			return;
3426 
3427 		INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
3428 		skb_reserve(skb, MAX_TCP_HEADER);
3429 		sk_forced_mem_schedule(sk, skb->truesize);
3430 		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
3431 		tcp_init_nondata_skb(skb, tp->write_seq,
3432 				     TCPHDR_ACK | TCPHDR_FIN);
3433 		tcp_queue_skb(sk, skb);
3434 	}
3435 	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
3436 }
3437 
3438 /* We get here when a process closes a file descriptor (either due to
3439  * an explicit close() or as a byproduct of exit()'ing) and there
3440  * was unread data in the receive queue.  This behavior is recommended
3441  * by RFC 2525, section 2.17.  -DaveM
3442  */
tcp_send_active_reset(struct sock * sk,gfp_t priority)3443 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
3444 {
3445 	struct sk_buff *skb;
3446 
3447 	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
3448 
3449 	/* NOTE: No TCP options attached and we never retransmit this. */
3450 	skb = alloc_skb(MAX_TCP_HEADER, priority);
3451 	if (!skb) {
3452 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3453 		return;
3454 	}
3455 
3456 	/* Reserve space for headers and prepare control bits. */
3457 	skb_reserve(skb, MAX_TCP_HEADER);
3458 	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
3459 			     TCPHDR_ACK | TCPHDR_RST);
3460 	tcp_mstamp_refresh(tcp_sk(sk));
3461 	/* Send it off. */
3462 	if (tcp_transmit_skb(sk, skb, 0, priority))
3463 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
3464 
3465 	/* skb of trace_tcp_send_reset() keeps the skb that caused RST,
3466 	 * skb here is different to the troublesome skb, so use NULL
3467 	 */
3468 	trace_tcp_send_reset(sk, NULL);
3469 }
3470 
3471 /* Send a crossed SYN-ACK during socket establishment.
3472  * WARNING: This routine must only be called when we have already sent
3473  * a SYN packet that crossed the incoming SYN that caused this routine
3474  * to get called. If this assumption fails then the initial rcv_wnd
3475  * and rcv_wscale values will not be correct.
3476  */
tcp_send_synack(struct sock * sk)3477 int tcp_send_synack(struct sock *sk)
3478 {
3479 	struct sk_buff *skb;
3480 
3481 	skb = tcp_rtx_queue_head(sk);
3482 	if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
3483 		pr_err("%s: wrong queue state\n", __func__);
3484 		return -EFAULT;
3485 	}
3486 	if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
3487 		if (skb_cloned(skb)) {
3488 			struct sk_buff *nskb;
3489 
3490 			tcp_skb_tsorted_save(skb) {
3491 				nskb = skb_copy(skb, GFP_ATOMIC);
3492 			} tcp_skb_tsorted_restore(skb);
3493 			if (!nskb)
3494 				return -ENOMEM;
3495 			INIT_LIST_HEAD(&nskb->tcp_tsorted_anchor);
3496 			tcp_highest_sack_replace(sk, skb, nskb);
3497 			tcp_rtx_queue_unlink_and_free(skb, sk);
3498 			__skb_header_release(nskb);
3499 			tcp_rbtree_insert(&sk->tcp_rtx_queue, nskb);
3500 			sk_wmem_queued_add(sk, nskb->truesize);
3501 			sk_mem_charge(sk, nskb->truesize);
3502 			skb = nskb;
3503 		}
3504 
3505 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
3506 		tcp_ecn_send_synack(sk, skb);
3507 	}
3508 	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3509 }
3510 
3511 /**
3512  * tcp_make_synack - Allocate one skb and build a SYNACK packet.
3513  * @sk: listener socket
3514  * @dst: dst entry attached to the SYNACK. It is consumed and caller
3515  *       should not use it again.
3516  * @req: request_sock pointer
3517  * @foc: cookie for tcp fast open
3518  * @synack_type: Type of synack to prepare
3519  * @syn_skb: SYN packet just received.  It could be NULL for rtx case.
3520  */
tcp_make_synack(const struct sock * sk,struct dst_entry * dst,struct request_sock * req,struct tcp_fastopen_cookie * foc,enum tcp_synack_type synack_type,struct sk_buff * syn_skb)3521 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3522 				struct request_sock *req,
3523 				struct tcp_fastopen_cookie *foc,
3524 				enum tcp_synack_type synack_type,
3525 				struct sk_buff *syn_skb)
3526 {
3527 	struct inet_request_sock *ireq = inet_rsk(req);
3528 	const struct tcp_sock *tp = tcp_sk(sk);
3529 	struct tcp_md5sig_key *md5 = NULL;
3530 	struct tcp_out_options opts;
3531 	struct sk_buff *skb;
3532 	int tcp_header_size;
3533 	struct tcphdr *th;
3534 	int mss;
3535 	u64 now;
3536 
3537 	skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3538 	if (unlikely(!skb)) {
3539 		dst_release(dst);
3540 		return NULL;
3541 	}
3542 	/* Reserve space for headers. */
3543 	skb_reserve(skb, MAX_TCP_HEADER);
3544 
3545 	switch (synack_type) {
3546 	case TCP_SYNACK_NORMAL:
3547 		skb_set_owner_w(skb, req_to_sk(req));
3548 		break;
3549 	case TCP_SYNACK_COOKIE:
3550 		/* Under synflood, we do not attach skb to a socket,
3551 		 * to avoid false sharing.
3552 		 */
3553 		break;
3554 	case TCP_SYNACK_FASTOPEN:
3555 		/* sk is a const pointer, because we want to express multiple
3556 		 * cpu might call us concurrently.
3557 		 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3558 		 */
3559 		skb_set_owner_w(skb, (struct sock *)sk);
3560 		break;
3561 	}
3562 	skb_dst_set(skb, dst);
3563 
3564 	mss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3565 
3566 	memset(&opts, 0, sizeof(opts));
3567 	now = tcp_clock_ns();
3568 #ifdef CONFIG_SYN_COOKIES
3569 	if (unlikely(synack_type == TCP_SYNACK_COOKIE && ireq->tstamp_ok))
3570 		skb_set_delivery_time(skb, cookie_init_timestamp(req, now),
3571 				      true);
3572 	else
3573 #endif
3574 	{
3575 		skb_set_delivery_time(skb, now, true);
3576 		if (!tcp_rsk(req)->snt_synack) /* Timestamp first SYNACK */
3577 			tcp_rsk(req)->snt_synack = tcp_skb_timestamp_us(skb);
3578 	}
3579 
3580 #ifdef CONFIG_TCP_MD5SIG
3581 	rcu_read_lock();
3582 	md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3583 #endif
3584 	skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3585 	/* bpf program will be interested in the tcp_flags */
3586 	TCP_SKB_CB(skb)->tcp_flags = TCPHDR_SYN | TCPHDR_ACK;
3587 	tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, md5,
3588 					     foc, synack_type,
3589 					     syn_skb) + sizeof(*th);
3590 
3591 	skb_push(skb, tcp_header_size);
3592 	skb_reset_transport_header(skb);
3593 
3594 	th = (struct tcphdr *)skb->data;
3595 	memset(th, 0, sizeof(struct tcphdr));
3596 	th->syn = 1;
3597 	th->ack = 1;
3598 	tcp_ecn_make_synack(req, th);
3599 	th->source = htons(ireq->ir_num);
3600 	th->dest = ireq->ir_rmt_port;
3601 	skb->mark = ireq->ir_mark;
3602 	skb->ip_summed = CHECKSUM_PARTIAL;
3603 	th->seq = htonl(tcp_rsk(req)->snt_isn);
3604 	/* XXX data is queued and acked as is. No buffer/window check */
3605 	th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3606 
3607 	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3608 	th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3609 	tcp_options_write(th, NULL, &opts);
3610 	th->doff = (tcp_header_size >> 2);
3611 	__TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
3612 
3613 #ifdef CONFIG_TCP_MD5SIG
3614 	/* Okay, we have all we need - do the md5 hash if needed */
3615 	if (md5)
3616 		tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3617 					       md5, req_to_sk(req), skb);
3618 	rcu_read_unlock();
3619 #endif
3620 
3621 	bpf_skops_write_hdr_opt((struct sock *)sk, skb, req, syn_skb,
3622 				synack_type, &opts);
3623 
3624 	skb_set_delivery_time(skb, now, true);
3625 	tcp_add_tx_delay(skb, tp);
3626 
3627 	return skb;
3628 }
3629 EXPORT_SYMBOL(tcp_make_synack);
3630 
tcp_ca_dst_init(struct sock * sk,const struct dst_entry * dst)3631 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3632 {
3633 	struct inet_connection_sock *icsk = inet_csk(sk);
3634 	const struct tcp_congestion_ops *ca;
3635 	u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3636 
3637 	if (ca_key == TCP_CA_UNSPEC)
3638 		return;
3639 
3640 	rcu_read_lock();
3641 	ca = tcp_ca_find_key(ca_key);
3642 	if (likely(ca && bpf_try_module_get(ca, ca->owner))) {
3643 		bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
3644 		icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3645 		icsk->icsk_ca_ops = ca;
3646 	}
3647 	rcu_read_unlock();
3648 }
3649 
3650 /* Do all connect socket setups that can be done AF independent. */
tcp_connect_init(struct sock * sk)3651 static void tcp_connect_init(struct sock *sk)
3652 {
3653 	const struct dst_entry *dst = __sk_dst_get(sk);
3654 	struct tcp_sock *tp = tcp_sk(sk);
3655 	__u8 rcv_wscale;
3656 	u32 rcv_wnd;
3657 
3658 	/* We'll fix this up when we get a response from the other end.
3659 	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3660 	 */
3661 	tp->tcp_header_len = sizeof(struct tcphdr);
3662 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_timestamps))
3663 		tp->tcp_header_len += TCPOLEN_TSTAMP_ALIGNED;
3664 
3665 #ifdef CONFIG_TCP_MD5SIG
3666 	if (tp->af_specific->md5_lookup(sk, sk))
3667 		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3668 #endif
3669 
3670 	/* If user gave his TCP_MAXSEG, record it to clamp */
3671 	if (tp->rx_opt.user_mss)
3672 		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3673 	tp->max_window = 0;
3674 	tcp_mtup_init(sk);
3675 	tcp_sync_mss(sk, dst_mtu(dst));
3676 
3677 	tcp_ca_dst_init(sk, dst);
3678 
3679 	if (!tp->window_clamp)
3680 		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3681 	tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst));
3682 
3683 	tcp_initialize_rcv_mss(sk);
3684 
3685 	/* limit the window selection if the user enforce a smaller rx buffer */
3686 	if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3687 	    (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3688 		tp->window_clamp = tcp_full_space(sk);
3689 
3690 	rcv_wnd = tcp_rwnd_init_bpf(sk);
3691 	if (rcv_wnd == 0)
3692 		rcv_wnd = dst_metric(dst, RTAX_INITRWND);
3693 
3694 	tcp_select_initial_window(sk, tcp_full_space(sk),
3695 				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3696 				  &tp->rcv_wnd,
3697 				  &tp->window_clamp,
3698 				  READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_window_scaling),
3699 				  &rcv_wscale,
3700 				  rcv_wnd);
3701 
3702 	tp->rx_opt.rcv_wscale = rcv_wscale;
3703 	tp->rcv_ssthresh = tp->rcv_wnd;
3704 
3705 	sk->sk_err = 0;
3706 	sock_reset_flag(sk, SOCK_DONE);
3707 	tp->snd_wnd = 0;
3708 	tcp_init_wl(tp, 0);
3709 	tcp_write_queue_purge(sk);
3710 	tp->snd_una = tp->write_seq;
3711 	tp->snd_sml = tp->write_seq;
3712 	tp->snd_up = tp->write_seq;
3713 	WRITE_ONCE(tp->snd_nxt, tp->write_seq);
3714 
3715 	if (likely(!tp->repair))
3716 		tp->rcv_nxt = 0;
3717 	else
3718 		tp->rcv_tstamp = tcp_jiffies32;
3719 	tp->rcv_wup = tp->rcv_nxt;
3720 	WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
3721 
3722 	inet_csk(sk)->icsk_rto = tcp_timeout_init(sk);
3723 	inet_csk(sk)->icsk_retransmits = 0;
3724 	tcp_clear_retrans(tp);
3725 }
3726 
tcp_connect_queue_skb(struct sock * sk,struct sk_buff * skb)3727 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3728 {
3729 	struct tcp_sock *tp = tcp_sk(sk);
3730 	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3731 
3732 	tcb->end_seq += skb->len;
3733 	__skb_header_release(skb);
3734 	sk_wmem_queued_add(sk, skb->truesize);
3735 	sk_mem_charge(sk, skb->truesize);
3736 	WRITE_ONCE(tp->write_seq, tcb->end_seq);
3737 	tp->packets_out += tcp_skb_pcount(skb);
3738 }
3739 
3740 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3741  * queue a data-only packet after the regular SYN, such that regular SYNs
3742  * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3743  * only the SYN sequence, the data are retransmitted in the first ACK.
3744  * If cookie is not cached or other error occurs, falls back to send a
3745  * regular SYN with Fast Open cookie request option.
3746  */
tcp_send_syn_data(struct sock * sk,struct sk_buff * syn)3747 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3748 {
3749 	struct inet_connection_sock *icsk = inet_csk(sk);
3750 	struct tcp_sock *tp = tcp_sk(sk);
3751 	struct tcp_fastopen_request *fo = tp->fastopen_req;
3752 	int space, err = 0;
3753 	struct sk_buff *syn_data;
3754 
3755 	tp->rx_opt.mss_clamp = tp->advmss;  /* If MSS is not cached */
3756 	if (!tcp_fastopen_cookie_check(sk, &tp->rx_opt.mss_clamp, &fo->cookie))
3757 		goto fallback;
3758 
3759 	/* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3760 	 * user-MSS. Reserve maximum option space for middleboxes that add
3761 	 * private TCP options. The cost is reduced data space in SYN :(
3762 	 */
3763 	tp->rx_opt.mss_clamp = tcp_mss_clamp(tp, tp->rx_opt.mss_clamp);
3764 	/* Sync mss_cache after updating the mss_clamp */
3765 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
3766 
3767 	space = __tcp_mtu_to_mss(sk, icsk->icsk_pmtu_cookie) -
3768 		MAX_TCP_OPTION_SPACE;
3769 
3770 	space = min_t(size_t, space, fo->size);
3771 
3772 	/* limit to order-0 allocations */
3773 	space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3774 
3775 	syn_data = tcp_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3776 	if (!syn_data)
3777 		goto fallback;
3778 	memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3779 	if (space) {
3780 		int copied = copy_from_iter(skb_put(syn_data, space), space,
3781 					    &fo->data->msg_iter);
3782 		if (unlikely(!copied)) {
3783 			tcp_skb_tsorted_anchor_cleanup(syn_data);
3784 			kfree_skb(syn_data);
3785 			goto fallback;
3786 		}
3787 		if (copied != space) {
3788 			skb_trim(syn_data, copied);
3789 			space = copied;
3790 		}
3791 		skb_zcopy_set(syn_data, fo->uarg, NULL);
3792 	}
3793 	/* No more data pending in inet_wait_for_connect() */
3794 	if (space == fo->size)
3795 		fo->data = NULL;
3796 	fo->copied = space;
3797 
3798 	tcp_connect_queue_skb(sk, syn_data);
3799 	if (syn_data->len)
3800 		tcp_chrono_start(sk, TCP_CHRONO_BUSY);
3801 
3802 	err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3803 
3804 	skb_set_delivery_time(syn, syn_data->skb_mstamp_ns, true);
3805 
3806 	/* Now full SYN+DATA was cloned and sent (or not),
3807 	 * remove the SYN from the original skb (syn_data)
3808 	 * we keep in write queue in case of a retransmit, as we
3809 	 * also have the SYN packet (with no data) in the same queue.
3810 	 */
3811 	TCP_SKB_CB(syn_data)->seq++;
3812 	TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3813 	if (!err) {
3814 		tp->syn_data = (fo->copied > 0);
3815 		tcp_rbtree_insert(&sk->tcp_rtx_queue, syn_data);
3816 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3817 		goto done;
3818 	}
3819 
3820 	/* data was not sent, put it in write_queue */
3821 	__skb_queue_tail(&sk->sk_write_queue, syn_data);
3822 	tp->packets_out -= tcp_skb_pcount(syn_data);
3823 
3824 fallback:
3825 	/* Send a regular SYN with Fast Open cookie request option */
3826 	if (fo->cookie.len > 0)
3827 		fo->cookie.len = 0;
3828 	err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3829 	if (err)
3830 		tp->syn_fastopen = 0;
3831 done:
3832 	fo->cookie.len = -1;  /* Exclude Fast Open option for SYN retries */
3833 	return err;
3834 }
3835 
3836 /* Build a SYN and send it off. */
tcp_connect(struct sock * sk)3837 int tcp_connect(struct sock *sk)
3838 {
3839 	struct tcp_sock *tp = tcp_sk(sk);
3840 	struct sk_buff *buff;
3841 	int err;
3842 
3843 	tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_CONNECT_CB, 0, NULL);
3844 
3845 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
3846 		return -EHOSTUNREACH; /* Routing failure or similar. */
3847 
3848 	tcp_connect_init(sk);
3849 
3850 	if (unlikely(tp->repair)) {
3851 		tcp_finish_connect(sk, NULL);
3852 		return 0;
3853 	}
3854 
3855 	buff = tcp_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3856 	if (unlikely(!buff))
3857 		return -ENOBUFS;
3858 
3859 	tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3860 	tcp_mstamp_refresh(tp);
3861 	tp->retrans_stamp = tcp_time_stamp(tp);
3862 	tcp_connect_queue_skb(sk, buff);
3863 	tcp_ecn_send_syn(sk, buff);
3864 	tcp_rbtree_insert(&sk->tcp_rtx_queue, buff);
3865 
3866 	/* Send off SYN; include data in Fast Open. */
3867 	err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3868 	      tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3869 	if (err == -ECONNREFUSED)
3870 		return err;
3871 
3872 	/* We change tp->snd_nxt after the tcp_transmit_skb() call
3873 	 * in order to make this packet get counted in tcpOutSegs.
3874 	 */
3875 	WRITE_ONCE(tp->snd_nxt, tp->write_seq);
3876 	tp->pushed_seq = tp->write_seq;
3877 	buff = tcp_send_head(sk);
3878 	if (unlikely(buff)) {
3879 		WRITE_ONCE(tp->snd_nxt, TCP_SKB_CB(buff)->seq);
3880 		tp->pushed_seq	= TCP_SKB_CB(buff)->seq;
3881 	}
3882 	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3883 
3884 	/* Timer for repeating the SYN until an answer. */
3885 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3886 				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3887 	return 0;
3888 }
3889 EXPORT_SYMBOL(tcp_connect);
3890 
3891 /* Send out a delayed ack, the caller does the policy checking
3892  * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
3893  * for details.
3894  */
tcp_send_delayed_ack(struct sock * sk)3895 void tcp_send_delayed_ack(struct sock *sk)
3896 {
3897 	struct inet_connection_sock *icsk = inet_csk(sk);
3898 	int ato = icsk->icsk_ack.ato;
3899 	unsigned long timeout;
3900 
3901 	if (ato > TCP_DELACK_MIN) {
3902 		const struct tcp_sock *tp = tcp_sk(sk);
3903 		int max_ato = HZ / 2;
3904 
3905 		if (inet_csk_in_pingpong_mode(sk) ||
3906 		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3907 			max_ato = TCP_DELACK_MAX;
3908 
3909 		/* Slow path, intersegment interval is "high". */
3910 
3911 		/* If some rtt estimate is known, use it to bound delayed ack.
3912 		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3913 		 * directly.
3914 		 */
3915 		if (tp->srtt_us) {
3916 			int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3917 					TCP_DELACK_MIN);
3918 
3919 			if (rtt < max_ato)
3920 				max_ato = rtt;
3921 		}
3922 
3923 		ato = min(ato, max_ato);
3924 	}
3925 
3926 	ato = min_t(u32, ato, inet_csk(sk)->icsk_delack_max);
3927 
3928 	/* Stay within the limit we were given */
3929 	timeout = jiffies + ato;
3930 
3931 	/* Use new timeout only if there wasn't a older one earlier. */
3932 	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3933 		/* If delack timer is about to expire, send ACK now. */
3934 		if (time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3935 			tcp_send_ack(sk);
3936 			return;
3937 		}
3938 
3939 		if (!time_before(timeout, icsk->icsk_ack.timeout))
3940 			timeout = icsk->icsk_ack.timeout;
3941 	}
3942 	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3943 	icsk->icsk_ack.timeout = timeout;
3944 	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3945 }
3946 
3947 /* This routine sends an ack and also updates the window. */
__tcp_send_ack(struct sock * sk,u32 rcv_nxt)3948 void __tcp_send_ack(struct sock *sk, u32 rcv_nxt)
3949 {
3950 	struct sk_buff *buff;
3951 
3952 	/* If we have been reset, we may not send again. */
3953 	if (sk->sk_state == TCP_CLOSE)
3954 		return;
3955 
3956 	/* We are not putting this on the write queue, so
3957 	 * tcp_transmit_skb() will set the ownership to this
3958 	 * sock.
3959 	 */
3960 	buff = alloc_skb(MAX_TCP_HEADER,
3961 			 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
3962 	if (unlikely(!buff)) {
3963 		struct inet_connection_sock *icsk = inet_csk(sk);
3964 		unsigned long delay;
3965 
3966 		delay = TCP_DELACK_MAX << icsk->icsk_ack.retry;
3967 		if (delay < TCP_RTO_MAX)
3968 			icsk->icsk_ack.retry++;
3969 		inet_csk_schedule_ack(sk);
3970 		icsk->icsk_ack.ato = TCP_ATO_MIN;
3971 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, delay, TCP_RTO_MAX);
3972 		return;
3973 	}
3974 
3975 	/* Reserve space for headers and prepare control bits. */
3976 	skb_reserve(buff, MAX_TCP_HEADER);
3977 	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3978 
3979 	/* We do not want pure acks influencing TCP Small Queues or fq/pacing
3980 	 * too much.
3981 	 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3982 	 */
3983 	skb_set_tcp_pure_ack(buff);
3984 
3985 	/* Send it off, this clears delayed acks for us. */
3986 	__tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0, rcv_nxt);
3987 }
3988 EXPORT_SYMBOL_GPL(__tcp_send_ack);
3989 
tcp_send_ack(struct sock * sk)3990 void tcp_send_ack(struct sock *sk)
3991 {
3992 	__tcp_send_ack(sk, tcp_sk(sk)->rcv_nxt);
3993 }
3994 
3995 /* This routine sends a packet with an out of date sequence
3996  * number. It assumes the other end will try to ack it.
3997  *
3998  * Question: what should we make while urgent mode?
3999  * 4.4BSD forces sending single byte of data. We cannot send
4000  * out of window data, because we have SND.NXT==SND.MAX...
4001  *
4002  * Current solution: to send TWO zero-length segments in urgent mode:
4003  * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
4004  * out-of-date with SND.UNA-1 to probe window.
4005  */
tcp_xmit_probe_skb(struct sock * sk,int urgent,int mib)4006 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
4007 {
4008 	struct tcp_sock *tp = tcp_sk(sk);
4009 	struct sk_buff *skb;
4010 
4011 	/* We don't queue it, tcp_transmit_skb() sets ownership. */
4012 	skb = alloc_skb(MAX_TCP_HEADER,
4013 			sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
4014 	if (!skb)
4015 		return -1;
4016 
4017 	/* Reserve space for headers and set control bits. */
4018 	skb_reserve(skb, MAX_TCP_HEADER);
4019 	/* Use a previous sequence.  This should cause the other
4020 	 * end to send an ack.  Don't queue or clone SKB, just
4021 	 * send it.
4022 	 */
4023 	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
4024 	NET_INC_STATS(sock_net(sk), mib);
4025 	return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0);
4026 }
4027 
4028 /* Called from setsockopt( ... TCP_REPAIR ) */
tcp_send_window_probe(struct sock * sk)4029 void tcp_send_window_probe(struct sock *sk)
4030 {
4031 	if (sk->sk_state == TCP_ESTABLISHED) {
4032 		tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
4033 		tcp_mstamp_refresh(tcp_sk(sk));
4034 		tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
4035 	}
4036 }
4037 
4038 /* Initiate keepalive or window probe from timer. */
tcp_write_wakeup(struct sock * sk,int mib)4039 int tcp_write_wakeup(struct sock *sk, int mib)
4040 {
4041 	struct tcp_sock *tp = tcp_sk(sk);
4042 	struct sk_buff *skb;
4043 
4044 	if (sk->sk_state == TCP_CLOSE)
4045 		return -1;
4046 
4047 	skb = tcp_send_head(sk);
4048 	if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
4049 		int err;
4050 		unsigned int mss = tcp_current_mss(sk);
4051 		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
4052 
4053 		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
4054 			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
4055 
4056 		/* We are probing the opening of a window
4057 		 * but the window size is != 0
4058 		 * must have been a result SWS avoidance ( sender )
4059 		 */
4060 		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
4061 		    skb->len > mss) {
4062 			seg_size = min(seg_size, mss);
4063 			TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
4064 			if (tcp_fragment(sk, TCP_FRAG_IN_WRITE_QUEUE,
4065 					 skb, seg_size, mss, GFP_ATOMIC))
4066 				return -1;
4067 		} else if (!tcp_skb_pcount(skb))
4068 			tcp_set_skb_tso_segs(skb, mss);
4069 
4070 		TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
4071 		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
4072 		if (!err)
4073 			tcp_event_new_data_sent(sk, skb);
4074 		return err;
4075 	} else {
4076 		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
4077 			tcp_xmit_probe_skb(sk, 1, mib);
4078 		return tcp_xmit_probe_skb(sk, 0, mib);
4079 	}
4080 }
4081 
4082 /* A window probe timeout has occurred.  If window is not closed send
4083  * a partial packet else a zero probe.
4084  */
tcp_send_probe0(struct sock * sk)4085 void tcp_send_probe0(struct sock *sk)
4086 {
4087 	struct inet_connection_sock *icsk = inet_csk(sk);
4088 	struct tcp_sock *tp = tcp_sk(sk);
4089 	struct net *net = sock_net(sk);
4090 	unsigned long timeout;
4091 	int err;
4092 
4093 	err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
4094 
4095 	if (tp->packets_out || tcp_write_queue_empty(sk)) {
4096 		/* Cancel probe timer, if it is not required. */
4097 		icsk->icsk_probes_out = 0;
4098 		icsk->icsk_backoff = 0;
4099 		icsk->icsk_probes_tstamp = 0;
4100 		return;
4101 	}
4102 
4103 	icsk->icsk_probes_out++;
4104 	if (err <= 0) {
4105 		if (icsk->icsk_backoff < READ_ONCE(net->ipv4.sysctl_tcp_retries2))
4106 			icsk->icsk_backoff++;
4107 		timeout = tcp_probe0_when(sk, TCP_RTO_MAX);
4108 	} else {
4109 		/* If packet was not sent due to local congestion,
4110 		 * Let senders fight for local resources conservatively.
4111 		 */
4112 		timeout = TCP_RESOURCE_PROBE_INTERVAL;
4113 	}
4114 
4115 	timeout = tcp_clamp_probe0_to_user_timeout(sk, timeout);
4116 	tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, timeout, TCP_RTO_MAX);
4117 }
4118 
tcp_rtx_synack(const struct sock * sk,struct request_sock * req)4119 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
4120 {
4121 	const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
4122 	struct flowi fl;
4123 	int res;
4124 
4125 	/* Paired with WRITE_ONCE() in sock_setsockopt() */
4126 	if (READ_ONCE(sk->sk_txrehash) == SOCK_TXREHASH_ENABLED)
4127 		tcp_rsk(req)->txhash = net_tx_rndhash();
4128 	res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL,
4129 				  NULL);
4130 	if (!res) {
4131 		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
4132 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
4133 		if (unlikely(tcp_passive_fastopen(sk)))
4134 			tcp_sk(sk)->total_retrans++;
4135 		trace_tcp_retransmit_synack(sk, req);
4136 	}
4137 	return res;
4138 }
4139 EXPORT_SYMBOL(tcp_rtx_synack);
4140