1 /*
2  *		INETPEER - A storage for permanent information about peers
3  *
4  *  This source is covered by the GNU GPL, the same as all kernel sources.
5  *
6  *  Authors:	Andrey V. Savochkin <saw@msu.ru>
7  */
8 
9 #include <linux/cache.h>
10 #include <linux/module.h>
11 #include <linux/types.h>
12 #include <linux/slab.h>
13 #include <linux/interrupt.h>
14 #include <linux/spinlock.h>
15 #include <linux/random.h>
16 #include <linux/timer.h>
17 #include <linux/time.h>
18 #include <linux/kernel.h>
19 #include <linux/mm.h>
20 #include <linux/net.h>
21 #include <linux/workqueue.h>
22 #include <net/ip.h>
23 #include <net/inetpeer.h>
24 #include <net/secure_seq.h>
25 
26 /*
27  *  Theory of operations.
28  *  We keep one entry for each peer IP address.  The nodes contains long-living
29  *  information about the peer which doesn't depend on routes.
30  *
31  *  Nodes are removed only when reference counter goes to 0.
32  *  When it's happened the node may be removed when a sufficient amount of
33  *  time has been passed since its last use.  The less-recently-used entry can
34  *  also be removed if the pool is overloaded i.e. if the total amount of
35  *  entries is greater-or-equal than the threshold.
36  *
37  *  Node pool is organised as an RB tree.
38  *  Such an implementation has been chosen not just for fun.  It's a way to
39  *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge
40  *  amount of long living nodes in a single hash slot would significantly delay
41  *  lookups performed with disabled BHs.
42  *
43  *  Serialisation issues.
44  *  1.  Nodes may appear in the tree only with the pool lock held.
45  *  2.  Nodes may disappear from the tree only with the pool lock held
46  *      AND reference count being 0.
47  *  3.  Global variable peer_total is modified under the pool lock.
48  *  4.  struct inet_peer fields modification:
49  *		rb_node: pool lock
50  *		refcnt: atomically against modifications on other CPU;
51  *		   usually under some other lock to prevent node disappearing
52  *		daddr: unchangeable
53  */
54 
55 static struct kmem_cache *peer_cachep __ro_after_init;
56 
inet_peer_base_init(struct inet_peer_base * bp)57 void inet_peer_base_init(struct inet_peer_base *bp)
58 {
59 	bp->rb_root = RB_ROOT;
60 	seqlock_init(&bp->lock);
61 	bp->total = 0;
62 }
63 EXPORT_SYMBOL_GPL(inet_peer_base_init);
64 
65 #define PEER_MAX_GC 32
66 
67 /* Exported for sysctl_net_ipv4.  */
68 int inet_peer_threshold __read_mostly;	/* start to throw entries more
69 					 * aggressively at this stage */
70 int inet_peer_minttl __read_mostly = 120 * HZ;	/* TTL under high load: 120 sec */
71 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;	/* usual time to live: 10 min */
72 
73 /* Called from ip_output.c:ip_init  */
inet_initpeers(void)74 void __init inet_initpeers(void)
75 {
76 	u64 nr_entries;
77 
78 	 /* 1% of physical memory */
79 	nr_entries = div64_ul((u64)totalram_pages() << PAGE_SHIFT,
80 			      100 * L1_CACHE_ALIGN(sizeof(struct inet_peer)));
81 
82 	inet_peer_threshold = clamp_val(nr_entries, 4096, 65536 + 128);
83 
84 	peer_cachep = kmem_cache_create("inet_peer_cache",
85 			sizeof(struct inet_peer),
86 			0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
87 			NULL);
88 }
89 
90 /* Called with rcu_read_lock() or base->lock held */
lookup(const struct inetpeer_addr * daddr,struct inet_peer_base * base,unsigned int seq,struct inet_peer * gc_stack[],unsigned int * gc_cnt,struct rb_node ** parent_p,struct rb_node *** pp_p)91 static struct inet_peer *lookup(const struct inetpeer_addr *daddr,
92 				struct inet_peer_base *base,
93 				unsigned int seq,
94 				struct inet_peer *gc_stack[],
95 				unsigned int *gc_cnt,
96 				struct rb_node **parent_p,
97 				struct rb_node ***pp_p)
98 {
99 	struct rb_node **pp, *parent, *next;
100 	struct inet_peer *p;
101 
102 	pp = &base->rb_root.rb_node;
103 	parent = NULL;
104 	while (1) {
105 		int cmp;
106 
107 		next = rcu_dereference_raw(*pp);
108 		if (!next)
109 			break;
110 		parent = next;
111 		p = rb_entry(parent, struct inet_peer, rb_node);
112 		cmp = inetpeer_addr_cmp(daddr, &p->daddr);
113 		if (cmp == 0) {
114 			if (!refcount_inc_not_zero(&p->refcnt))
115 				break;
116 			return p;
117 		}
118 		if (gc_stack) {
119 			if (*gc_cnt < PEER_MAX_GC)
120 				gc_stack[(*gc_cnt)++] = p;
121 		} else if (unlikely(read_seqretry(&base->lock, seq))) {
122 			break;
123 		}
124 		if (cmp == -1)
125 			pp = &next->rb_left;
126 		else
127 			pp = &next->rb_right;
128 	}
129 	*parent_p = parent;
130 	*pp_p = pp;
131 	return NULL;
132 }
133 
inetpeer_free_rcu(struct rcu_head * head)134 static void inetpeer_free_rcu(struct rcu_head *head)
135 {
136 	kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
137 }
138 
139 /* perform garbage collect on all items stacked during a lookup */
inet_peer_gc(struct inet_peer_base * base,struct inet_peer * gc_stack[],unsigned int gc_cnt)140 static void inet_peer_gc(struct inet_peer_base *base,
141 			 struct inet_peer *gc_stack[],
142 			 unsigned int gc_cnt)
143 {
144 	int peer_threshold, peer_maxttl, peer_minttl;
145 	struct inet_peer *p;
146 	__u32 delta, ttl;
147 	int i;
148 
149 	peer_threshold = READ_ONCE(inet_peer_threshold);
150 	peer_maxttl = READ_ONCE(inet_peer_maxttl);
151 	peer_minttl = READ_ONCE(inet_peer_minttl);
152 
153 	if (base->total >= peer_threshold)
154 		ttl = 0; /* be aggressive */
155 	else
156 		ttl = peer_maxttl - (peer_maxttl - peer_minttl) / HZ *
157 			base->total / peer_threshold * HZ;
158 	for (i = 0; i < gc_cnt; i++) {
159 		p = gc_stack[i];
160 
161 		/* The READ_ONCE() pairs with the WRITE_ONCE()
162 		 * in inet_putpeer()
163 		 */
164 		delta = (__u32)jiffies - READ_ONCE(p->dtime);
165 
166 		if (delta < ttl || !refcount_dec_if_one(&p->refcnt))
167 			gc_stack[i] = NULL;
168 	}
169 	for (i = 0; i < gc_cnt; i++) {
170 		p = gc_stack[i];
171 		if (p) {
172 			rb_erase(&p->rb_node, &base->rb_root);
173 			base->total--;
174 			call_rcu(&p->rcu, inetpeer_free_rcu);
175 		}
176 	}
177 }
178 
inet_getpeer(struct inet_peer_base * base,const struct inetpeer_addr * daddr,int create)179 struct inet_peer *inet_getpeer(struct inet_peer_base *base,
180 			       const struct inetpeer_addr *daddr,
181 			       int create)
182 {
183 	struct inet_peer *p, *gc_stack[PEER_MAX_GC];
184 	struct rb_node **pp, *parent;
185 	unsigned int gc_cnt, seq;
186 	int invalidated;
187 
188 	/* Attempt a lockless lookup first.
189 	 * Because of a concurrent writer, we might not find an existing entry.
190 	 */
191 	rcu_read_lock();
192 	seq = read_seqbegin(&base->lock);
193 	p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);
194 	invalidated = read_seqretry(&base->lock, seq);
195 	rcu_read_unlock();
196 
197 	if (p)
198 		return p;
199 
200 	/* If no writer did a change during our lookup, we can return early. */
201 	if (!create && !invalidated)
202 		return NULL;
203 
204 	/* retry an exact lookup, taking the lock before.
205 	 * At least, nodes should be hot in our cache.
206 	 */
207 	parent = NULL;
208 	write_seqlock_bh(&base->lock);
209 
210 	gc_cnt = 0;
211 	p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);
212 	if (!p && create) {
213 		p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
214 		if (p) {
215 			p->daddr = *daddr;
216 			p->dtime = (__u32)jiffies;
217 			refcount_set(&p->refcnt, 2);
218 			atomic_set(&p->rid, 0);
219 			p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
220 			p->rate_tokens = 0;
221 			p->n_redirects = 0;
222 			/* 60*HZ is arbitrary, but chosen enough high so that the first
223 			 * calculation of tokens is at its maximum.
224 			 */
225 			p->rate_last = jiffies - 60*HZ;
226 
227 			rb_link_node(&p->rb_node, parent, pp);
228 			rb_insert_color(&p->rb_node, &base->rb_root);
229 			base->total++;
230 		}
231 	}
232 	if (gc_cnt)
233 		inet_peer_gc(base, gc_stack, gc_cnt);
234 	write_sequnlock_bh(&base->lock);
235 
236 	return p;
237 }
238 EXPORT_SYMBOL_GPL(inet_getpeer);
239 
inet_putpeer(struct inet_peer * p)240 void inet_putpeer(struct inet_peer *p)
241 {
242 	/* The WRITE_ONCE() pairs with itself (we run lockless)
243 	 * and the READ_ONCE() in inet_peer_gc()
244 	 */
245 	WRITE_ONCE(p->dtime, (__u32)jiffies);
246 
247 	if (refcount_dec_and_test(&p->refcnt))
248 		call_rcu(&p->rcu, inetpeer_free_rcu);
249 }
250 EXPORT_SYMBOL_GPL(inet_putpeer);
251 
252 /*
253  *	Check transmit rate limitation for given message.
254  *	The rate information is held in the inet_peer entries now.
255  *	This function is generic and could be used for other purposes
256  *	too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
257  *
258  *	Note that the same inet_peer fields are modified by functions in
259  *	route.c too, but these work for packet destinations while xrlim_allow
260  *	works for icmp destinations. This means the rate limiting information
261  *	for one "ip object" is shared - and these ICMPs are twice limited:
262  *	by source and by destination.
263  *
264  *	RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
265  *			  SHOULD allow setting of rate limits
266  *
267  * 	Shared between ICMPv4 and ICMPv6.
268  */
269 #define XRLIM_BURST_FACTOR 6
inet_peer_xrlim_allow(struct inet_peer * peer,int timeout)270 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
271 {
272 	unsigned long now, token;
273 	bool rc = false;
274 
275 	if (!peer)
276 		return true;
277 
278 	token = peer->rate_tokens;
279 	now = jiffies;
280 	token += now - peer->rate_last;
281 	peer->rate_last = now;
282 	if (token > XRLIM_BURST_FACTOR * timeout)
283 		token = XRLIM_BURST_FACTOR * timeout;
284 	if (token >= timeout) {
285 		token -= timeout;
286 		rc = true;
287 	}
288 	peer->rate_tokens = token;
289 	return rc;
290 }
291 EXPORT_SYMBOL(inet_peer_xrlim_allow);
292 
inetpeer_invalidate_tree(struct inet_peer_base * base)293 void inetpeer_invalidate_tree(struct inet_peer_base *base)
294 {
295 	struct rb_node *p = rb_first(&base->rb_root);
296 
297 	while (p) {
298 		struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
299 
300 		p = rb_next(p);
301 		rb_erase(&peer->rb_node, &base->rb_root);
302 		inet_putpeer(peer);
303 		cond_resched();
304 	}
305 
306 	base->total = 0;
307 }
308 EXPORT_SYMBOL(inetpeer_invalidate_tree);
309