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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/module.h>
10#include <linux/types.h>
11#include <linux/slab.h>
12#include <linux/interrupt.h>
13#include <linux/spinlock.h>
14#include <linux/random.h>
15#include <linux/timer.h>
16#include <linux/time.h>
17#include <linux/kernel.h>
18#include <linux/mm.h>
19#include <linux/net.h>
20#include <linux/workqueue.h>
21#include <net/ip.h>
22#include <net/inetpeer.h>
23#include <net/secure_seq.h>
24
25/*
26 * Theory of operations.
27 * We keep one entry for each peer IP address. The nodes contains long-living
28 * information about the peer which doesn't depend on routes.
29 * At this moment this information consists only of ID field for the next
30 * outgoing IP packet. This field is incremented with each packet as encoded
31 * in inet_getid() function (include/net/inetpeer.h).
32 * At the moment of writing this notes identifier of IP packets is generated
33 * to be unpredictable using this code only for packets subjected
34 * (actually or potentially) to defragmentation. I.e. DF packets less than
35 * PMTU in size when local fragmentation is disabled use a constant ID and do
36 * not use this code (see ip_select_ident() in include/net/ip.h).
37 *
38 * Route cache entries hold references to our nodes.
39 * New cache entries get references via lookup by destination IP address in
40 * the avl tree. The reference is grabbed only when it's needed i.e. only
41 * when we try to output IP packet which needs an unpredictable ID (see
42 * __ip_select_ident() in net/ipv4/route.c).
43 * Nodes are removed only when reference counter goes to 0.
44 * When it's happened the node may be removed when a sufficient amount of
45 * time has been passed since its last use. The less-recently-used entry can
46 * also be removed if the pool is overloaded i.e. if the total amount of
47 * entries is greater-or-equal than the threshold.
48 *
49 * Node pool is organised as an AVL tree.
50 * Such an implementation has been chosen not just for fun. It's a way to
51 * prevent easy and efficient DoS attacks by creating hash collisions. A huge
52 * amount of long living nodes in a single hash slot would significantly delay
53 * lookups performed with disabled BHs.
54 *
55 * Serialisation issues.
56 * 1. Nodes may appear in the tree only with the pool lock held.
57 * 2. Nodes may disappear from the tree only with the pool lock held
58 * AND reference count being 0.
59 * 3. Global variable peer_total is modified under the pool lock.
60 * 4. struct inet_peer fields modification:
61 * avl_left, avl_right, avl_parent, avl_height: pool lock
62 * refcnt: atomically against modifications on other CPU;
63 * usually under some other lock to prevent node disappearing
64 * daddr: unchangeable
65 * ip_id_count: atomic value (no lock needed)
66 */
67
68static struct kmem_cache *peer_cachep __read_mostly;
69
70static LIST_HEAD(gc_list);
71static const int gc_delay = 60 * HZ;
72static struct delayed_work gc_work;
73static DEFINE_SPINLOCK(gc_lock);
74
75#define node_height(x) x->avl_height
76
77#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
78#define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
79static const struct inet_peer peer_fake_node = {
80 .avl_left = peer_avl_empty_rcu,
81 .avl_right = peer_avl_empty_rcu,
82 .avl_height = 0
83};
84
85void inet_peer_base_init(struct inet_peer_base *bp)
86{
87 bp->root = peer_avl_empty_rcu;
88 seqlock_init(&bp->lock);
89 bp->flush_seq = ~0U;
90 bp->total = 0;
91}
92EXPORT_SYMBOL_GPL(inet_peer_base_init);
93
94static atomic_t v4_seq = ATOMIC_INIT(0);
95static atomic_t v6_seq = ATOMIC_INIT(0);
96
97static atomic_t *inetpeer_seq_ptr(int family)
98{
99 return (family == AF_INET ? &v4_seq : &v6_seq);
100}
101
102static inline void flush_check(struct inet_peer_base *base, int family)
103{
104 atomic_t *fp = inetpeer_seq_ptr(family);
105
106 if (unlikely(base->flush_seq != atomic_read(fp))) {
107 inetpeer_invalidate_tree(base);
108 base->flush_seq = atomic_read(fp);
109 }
110}
111
112#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
113
114/* Exported for sysctl_net_ipv4. */
115int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
116 * aggressively at this stage */
117int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
118int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
119
120static void inetpeer_gc_worker(struct work_struct *work)
121{
122 struct inet_peer *p, *n, *c;
123 LIST_HEAD(list);
124
125 spin_lock_bh(&gc_lock);
126 list_replace_init(&gc_list, &list);
127 spin_unlock_bh(&gc_lock);
128
129 if (list_empty(&list))
130 return;
131
132 list_for_each_entry_safe(p, n, &list, gc_list) {
133
134 if (need_resched())
135 cond_resched();
136
137 c = rcu_dereference_protected(p->avl_left, 1);
138 if (c != peer_avl_empty) {
139 list_add_tail(&c->gc_list, &list);
140 p->avl_left = peer_avl_empty_rcu;
141 }
142
143 c = rcu_dereference_protected(p->avl_right, 1);
144 if (c != peer_avl_empty) {
145 list_add_tail(&c->gc_list, &list);
146 p->avl_right = peer_avl_empty_rcu;
147 }
148
149 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
150
151 if (!atomic_read(&p->refcnt)) {
152 list_del(&p->gc_list);
153 kmem_cache_free(peer_cachep, p);
154 }
155 }
156
157 if (list_empty(&list))
158 return;
159
160 spin_lock_bh(&gc_lock);
161 list_splice(&list, &gc_list);
162 spin_unlock_bh(&gc_lock);
163
164 schedule_delayed_work(&gc_work, gc_delay);
165}
166
167/* Called from ip_output.c:ip_init */
168void __init inet_initpeers(void)
169{
170 struct sysinfo si;
171
172 /* Use the straight interface to information about memory. */
173 si_meminfo(&si);
174 /* The values below were suggested by Alexey Kuznetsov
175 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
176 * myself. --SAW
177 */
178 if (si.totalram <= (32768*1024)/PAGE_SIZE)
179 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
180 if (si.totalram <= (16384*1024)/PAGE_SIZE)
181 inet_peer_threshold >>= 1; /* about 512KB */
182 if (si.totalram <= (8192*1024)/PAGE_SIZE)
183 inet_peer_threshold >>= 2; /* about 128KB */
184
185 peer_cachep = kmem_cache_create("inet_peer_cache",
186 sizeof(struct inet_peer),
187 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
188 NULL);
189
190 INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker);
191}
192
193static int addr_compare(const struct inetpeer_addr *a,
194 const struct inetpeer_addr *b)
195{
196 int i, n = (a->family == AF_INET ? 1 : 4);
197
198 for (i = 0; i < n; i++) {
199 if (a->addr.a6[i] == b->addr.a6[i])
200 continue;
201 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i])
202 return -1;
203 return 1;
204 }
205
206 return 0;
207}
208
209#define rcu_deref_locked(X, BASE) \
210 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
211
212/*
213 * Called with local BH disabled and the pool lock held.
214 */
215#define lookup(_daddr, _stack, _base) \
216({ \
217 struct inet_peer *u; \
218 struct inet_peer __rcu **v; \
219 \
220 stackptr = _stack; \
221 *stackptr++ = &_base->root; \
222 for (u = rcu_deref_locked(_base->root, _base); \
223 u != peer_avl_empty;) { \
224 int cmp = addr_compare(_daddr, &u->daddr); \
225 if (cmp == 0) \
226 break; \
227 if (cmp == -1) \
228 v = &u->avl_left; \
229 else \
230 v = &u->avl_right; \
231 *stackptr++ = v; \
232 u = rcu_deref_locked(*v, _base); \
233 } \
234 u; \
235})
236
237/*
238 * Called with rcu_read_lock()
239 * Because we hold no lock against a writer, its quite possible we fall
240 * in an endless loop.
241 * But every pointer we follow is guaranteed to be valid thanks to RCU.
242 * We exit from this function if number of links exceeds PEER_MAXDEPTH
243 */
244static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
245 struct inet_peer_base *base)
246{
247 struct inet_peer *u = rcu_dereference(base->root);
248 int count = 0;
249
250 while (u != peer_avl_empty) {
251 int cmp = addr_compare(daddr, &u->daddr);
252 if (cmp == 0) {
253 /* Before taking a reference, check if this entry was
254 * deleted (refcnt=-1)
255 */
256 if (!atomic_add_unless(&u->refcnt, 1, -1))
257 u = NULL;
258 return u;
259 }
260 if (cmp == -1)
261 u = rcu_dereference(u->avl_left);
262 else
263 u = rcu_dereference(u->avl_right);
264 if (unlikely(++count == PEER_MAXDEPTH))
265 break;
266 }
267 return NULL;
268}
269
270/* Called with local BH disabled and the pool lock held. */
271#define lookup_rightempty(start, base) \
272({ \
273 struct inet_peer *u; \
274 struct inet_peer __rcu **v; \
275 *stackptr++ = &start->avl_left; \
276 v = &start->avl_left; \
277 for (u = rcu_deref_locked(*v, base); \
278 u->avl_right != peer_avl_empty_rcu;) { \
279 v = &u->avl_right; \
280 *stackptr++ = v; \
281 u = rcu_deref_locked(*v, base); \
282 } \
283 u; \
284})
285
286/* Called with local BH disabled and the pool lock held.
287 * Variable names are the proof of operation correctness.
288 * Look into mm/map_avl.c for more detail description of the ideas.
289 */
290static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
291 struct inet_peer __rcu ***stackend,
292 struct inet_peer_base *base)
293{
294 struct inet_peer __rcu **nodep;
295 struct inet_peer *node, *l, *r;
296 int lh, rh;
297
298 while (stackend > stack) {
299 nodep = *--stackend;
300 node = rcu_deref_locked(*nodep, base);
301 l = rcu_deref_locked(node->avl_left, base);
302 r = rcu_deref_locked(node->avl_right, base);
303 lh = node_height(l);
304 rh = node_height(r);
305 if (lh > rh + 1) { /* l: RH+2 */
306 struct inet_peer *ll, *lr, *lrl, *lrr;
307 int lrh;
308 ll = rcu_deref_locked(l->avl_left, base);
309 lr = rcu_deref_locked(l->avl_right, base);
310 lrh = node_height(lr);
311 if (lrh <= node_height(ll)) { /* ll: RH+1 */
312 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */
313 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
314 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
315 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */
316 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */
317 l->avl_height = node->avl_height + 1;
318 RCU_INIT_POINTER(*nodep, l);
319 } else { /* ll: RH, lr: RH+1 */
320 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
321 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
322 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */
323 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
324 node->avl_height = rh + 1; /* node: RH+1 */
325 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */
326 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */
327 l->avl_height = rh + 1; /* l: RH+1 */
328 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */
329 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */
330 lr->avl_height = rh + 2;
331 RCU_INIT_POINTER(*nodep, lr);
332 }
333 } else if (rh > lh + 1) { /* r: LH+2 */
334 struct inet_peer *rr, *rl, *rlr, *rll;
335 int rlh;
336 rr = rcu_deref_locked(r->avl_right, base);
337 rl = rcu_deref_locked(r->avl_left, base);
338 rlh = node_height(rl);
339 if (rlh <= node_height(rr)) { /* rr: LH+1 */
340 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */
341 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
342 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
343 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */
344 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */
345 r->avl_height = node->avl_height + 1;
346 RCU_INIT_POINTER(*nodep, r);
347 } else { /* rr: RH, rl: RH+1 */
348 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
349 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
350 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
351 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
352 node->avl_height = lh + 1; /* node: LH+1 */
353 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */
354 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */
355 r->avl_height = lh + 1; /* r: LH+1 */
356 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */
357 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */
358 rl->avl_height = lh + 2;
359 RCU_INIT_POINTER(*nodep, rl);
360 }
361 } else {
362 node->avl_height = (lh > rh ? lh : rh) + 1;
363 }
364 }
365}
366
367/* Called with local BH disabled and the pool lock held. */
368#define link_to_pool(n, base) \
369do { \
370 n->avl_height = 1; \
371 n->avl_left = peer_avl_empty_rcu; \
372 n->avl_right = peer_avl_empty_rcu; \
373 /* lockless readers can catch us now */ \
374 rcu_assign_pointer(**--stackptr, n); \
375 peer_avl_rebalance(stack, stackptr, base); \
376} while (0)
377
378static void inetpeer_free_rcu(struct rcu_head *head)
379{
380 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
381}
382
383static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
384 struct inet_peer __rcu **stack[PEER_MAXDEPTH])
385{
386 struct inet_peer __rcu ***stackptr, ***delp;
387
388 if (lookup(&p->daddr, stack, base) != p)
389 BUG();
390 delp = stackptr - 1; /* *delp[0] == p */
391 if (p->avl_left == peer_avl_empty_rcu) {
392 *delp[0] = p->avl_right;
393 --stackptr;
394 } else {
395 /* look for a node to insert instead of p */
396 struct inet_peer *t;
397 t = lookup_rightempty(p, base);
398 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
399 **--stackptr = t->avl_left;
400 /* t is removed, t->daddr > x->daddr for any
401 * x in p->avl_left subtree.
402 * Put t in the old place of p. */
403 RCU_INIT_POINTER(*delp[0], t);
404 t->avl_left = p->avl_left;
405 t->avl_right = p->avl_right;
406 t->avl_height = p->avl_height;
407 BUG_ON(delp[1] != &p->avl_left);
408 delp[1] = &t->avl_left; /* was &p->avl_left */
409 }
410 peer_avl_rebalance(stack, stackptr, base);
411 base->total--;
412 call_rcu(&p->rcu, inetpeer_free_rcu);
413}
414
415/* perform garbage collect on all items stacked during a lookup */
416static int inet_peer_gc(struct inet_peer_base *base,
417 struct inet_peer __rcu **stack[PEER_MAXDEPTH],
418 struct inet_peer __rcu ***stackptr)
419{
420 struct inet_peer *p, *gchead = NULL;
421 __u32 delta, ttl;
422 int cnt = 0;
423
424 if (base->total >= inet_peer_threshold)
425 ttl = 0; /* be aggressive */
426 else
427 ttl = inet_peer_maxttl
428 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
429 base->total / inet_peer_threshold * HZ;
430 stackptr--; /* last stack slot is peer_avl_empty */
431 while (stackptr > stack) {
432 stackptr--;
433 p = rcu_deref_locked(**stackptr, base);
434 if (atomic_read(&p->refcnt) == 0) {
435 smp_rmb();
436 delta = (__u32)jiffies - p->dtime;
437 if (delta >= ttl &&
438 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
439 p->gc_next = gchead;
440 gchead = p;
441 }
442 }
443 }
444 while ((p = gchead) != NULL) {
445 gchead = p->gc_next;
446 cnt++;
447 unlink_from_pool(p, base, stack);
448 }
449 return cnt;
450}
451
452struct inet_peer *inet_getpeer(struct inet_peer_base *base,
453 const struct inetpeer_addr *daddr,
454 int create)
455{
456 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
457 struct inet_peer *p;
458 unsigned int sequence;
459 int invalidated, gccnt = 0;
460
461 flush_check(base, daddr->family);
462
463 /* Attempt a lockless lookup first.
464 * Because of a concurrent writer, we might not find an existing entry.
465 */
466 rcu_read_lock();
467 sequence = read_seqbegin(&base->lock);
468 p = lookup_rcu(daddr, base);
469 invalidated = read_seqretry(&base->lock, sequence);
470 rcu_read_unlock();
471
472 if (p)
473 return p;
474
475 /* If no writer did a change during our lookup, we can return early. */
476 if (!create && !invalidated)
477 return NULL;
478
479 /* retry an exact lookup, taking the lock before.
480 * At least, nodes should be hot in our cache.
481 */
482 write_seqlock_bh(&base->lock);
483relookup:
484 p = lookup(daddr, stack, base);
485 if (p != peer_avl_empty) {
486 atomic_inc(&p->refcnt);
487 write_sequnlock_bh(&base->lock);
488 return p;
489 }
490 if (!gccnt) {
491 gccnt = inet_peer_gc(base, stack, stackptr);
492 if (gccnt && create)
493 goto relookup;
494 }
495 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
496 if (p) {
497 p->daddr = *daddr;
498 atomic_set(&p->refcnt, 1);
499 atomic_set(&p->rid, 0);
500 atomic_set(&p->ip_id_count,
501 (daddr->family == AF_INET) ?
502 secure_ip_id(daddr->addr.a4) :
503 secure_ipv6_id(daddr->addr.a6));
504 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
505 p->rate_tokens = 0;
506 /* 60*HZ is arbitrary, but chosen enough high so that the first
507 * calculation of tokens is at its maximum.
508 */
509 p->rate_last = jiffies - 60*HZ;
510 INIT_LIST_HEAD(&p->gc_list);
511
512 /* Link the node. */
513 link_to_pool(p, base);
514 base->total++;
515 }
516 write_sequnlock_bh(&base->lock);
517
518 return p;
519}
520EXPORT_SYMBOL_GPL(inet_getpeer);
521
522void inet_putpeer(struct inet_peer *p)
523{
524 p->dtime = (__u32)jiffies;
525 smp_mb__before_atomic_dec();
526 atomic_dec(&p->refcnt);
527}
528EXPORT_SYMBOL_GPL(inet_putpeer);
529
530/*
531 * Check transmit rate limitation for given message.
532 * The rate information is held in the inet_peer entries now.
533 * This function is generic and could be used for other purposes
534 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
535 *
536 * Note that the same inet_peer fields are modified by functions in
537 * route.c too, but these work for packet destinations while xrlim_allow
538 * works for icmp destinations. This means the rate limiting information
539 * for one "ip object" is shared - and these ICMPs are twice limited:
540 * by source and by destination.
541 *
542 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
543 * SHOULD allow setting of rate limits
544 *
545 * Shared between ICMPv4 and ICMPv6.
546 */
547#define XRLIM_BURST_FACTOR 6
548bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
549{
550 unsigned long now, token;
551 bool rc = false;
552
553 if (!peer)
554 return true;
555
556 token = peer->rate_tokens;
557 now = jiffies;
558 token += now - peer->rate_last;
559 peer->rate_last = now;
560 if (token > XRLIM_BURST_FACTOR * timeout)
561 token = XRLIM_BURST_FACTOR * timeout;
562 if (token >= timeout) {
563 token -= timeout;
564 rc = true;
565 }
566 peer->rate_tokens = token;
567 return rc;
568}
569EXPORT_SYMBOL(inet_peer_xrlim_allow);
570
571static void inetpeer_inval_rcu(struct rcu_head *head)
572{
573 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
574
575 spin_lock_bh(&gc_lock);
576 list_add_tail(&p->gc_list, &gc_list);
577 spin_unlock_bh(&gc_lock);
578
579 schedule_delayed_work(&gc_work, gc_delay);
580}
581
582void inetpeer_invalidate_tree(struct inet_peer_base *base)
583{
584 struct inet_peer *root;
585
586 write_seqlock_bh(&base->lock);
587
588 root = rcu_deref_locked(base->root, base);
589 if (root != peer_avl_empty) {
590 base->root = peer_avl_empty_rcu;
591 base->total = 0;
592 call_rcu(&root->gc_rcu, inetpeer_inval_rcu);
593 }
594
595 write_sequnlock_bh(&base->lock);
596}
597EXPORT_SYMBOL(inetpeer_invalidate_tree);
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
55static struct kmem_cache *peer_cachep __ro_after_init;
56
57void 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}
63EXPORT_SYMBOL_GPL(inet_peer_base_init);
64
65#define PEER_MAX_GC 32
66
67/* Exported for sysctl_net_ipv4. */
68int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
69 * aggressively at this stage */
70int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
71int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
72
73/* Called from ip_output.c:ip_init */
74void __init inet_initpeers(void)
75{
76 struct sysinfo si;
77
78 /* Use the straight interface to information about memory. */
79 si_meminfo(&si);
80 /* The values below were suggested by Alexey Kuznetsov
81 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
82 * myself. --SAW
83 */
84 if (si.totalram <= (32768*1024)/PAGE_SIZE)
85 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
86 if (si.totalram <= (16384*1024)/PAGE_SIZE)
87 inet_peer_threshold >>= 1; /* about 512KB */
88 if (si.totalram <= (8192*1024)/PAGE_SIZE)
89 inet_peer_threshold >>= 2; /* about 128KB */
90
91 peer_cachep = kmem_cache_create("inet_peer_cache",
92 sizeof(struct inet_peer),
93 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
94 NULL);
95}
96
97/* Called with rcu_read_lock() or base->lock held */
98static struct inet_peer *lookup(const struct inetpeer_addr *daddr,
99 struct inet_peer_base *base,
100 unsigned int seq,
101 struct inet_peer *gc_stack[],
102 unsigned int *gc_cnt,
103 struct rb_node **parent_p,
104 struct rb_node ***pp_p)
105{
106 struct rb_node **pp, *parent, *next;
107 struct inet_peer *p;
108
109 pp = &base->rb_root.rb_node;
110 parent = NULL;
111 while (1) {
112 int cmp;
113
114 next = rcu_dereference_raw(*pp);
115 if (!next)
116 break;
117 parent = next;
118 p = rb_entry(parent, struct inet_peer, rb_node);
119 cmp = inetpeer_addr_cmp(daddr, &p->daddr);
120 if (cmp == 0) {
121 if (!refcount_inc_not_zero(&p->refcnt))
122 break;
123 return p;
124 }
125 if (gc_stack) {
126 if (*gc_cnt < PEER_MAX_GC)
127 gc_stack[(*gc_cnt)++] = p;
128 } else if (unlikely(read_seqretry(&base->lock, seq))) {
129 break;
130 }
131 if (cmp == -1)
132 pp = &next->rb_left;
133 else
134 pp = &next->rb_right;
135 }
136 *parent_p = parent;
137 *pp_p = pp;
138 return NULL;
139}
140
141static void inetpeer_free_rcu(struct rcu_head *head)
142{
143 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
144}
145
146/* perform garbage collect on all items stacked during a lookup */
147static void inet_peer_gc(struct inet_peer_base *base,
148 struct inet_peer *gc_stack[],
149 unsigned int gc_cnt)
150{
151 struct inet_peer *p;
152 __u32 delta, ttl;
153 int i;
154
155 if (base->total >= inet_peer_threshold)
156 ttl = 0; /* be aggressive */
157 else
158 ttl = inet_peer_maxttl
159 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
160 base->total / inet_peer_threshold * HZ;
161 for (i = 0; i < gc_cnt; i++) {
162 p = gc_stack[i];
163 delta = (__u32)jiffies - p->dtime;
164 if (delta < ttl || !refcount_dec_if_one(&p->refcnt))
165 gc_stack[i] = NULL;
166 }
167 for (i = 0; i < gc_cnt; i++) {
168 p = gc_stack[i];
169 if (p) {
170 rb_erase(&p->rb_node, &base->rb_root);
171 base->total--;
172 call_rcu(&p->rcu, inetpeer_free_rcu);
173 }
174 }
175}
176
177struct inet_peer *inet_getpeer(struct inet_peer_base *base,
178 const struct inetpeer_addr *daddr,
179 int create)
180{
181 struct inet_peer *p, *gc_stack[PEER_MAX_GC];
182 struct rb_node **pp, *parent;
183 unsigned int gc_cnt, seq;
184 int invalidated;
185
186 /* Attempt a lockless lookup first.
187 * Because of a concurrent writer, we might not find an existing entry.
188 */
189 rcu_read_lock();
190 seq = read_seqbegin(&base->lock);
191 p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);
192 invalidated = read_seqretry(&base->lock, seq);
193 rcu_read_unlock();
194
195 if (p)
196 return p;
197
198 /* If no writer did a change during our lookup, we can return early. */
199 if (!create && !invalidated)
200 return NULL;
201
202 /* retry an exact lookup, taking the lock before.
203 * At least, nodes should be hot in our cache.
204 */
205 parent = NULL;
206 write_seqlock_bh(&base->lock);
207
208 gc_cnt = 0;
209 p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);
210 if (!p && create) {
211 p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
212 if (p) {
213 p->daddr = *daddr;
214 p->dtime = (__u32)jiffies;
215 refcount_set(&p->refcnt, 2);
216 atomic_set(&p->rid, 0);
217 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
218 p->rate_tokens = 0;
219 p->n_redirects = 0;
220 /* 60*HZ is arbitrary, but chosen enough high so that the first
221 * calculation of tokens is at its maximum.
222 */
223 p->rate_last = jiffies - 60*HZ;
224
225 rb_link_node(&p->rb_node, parent, pp);
226 rb_insert_color(&p->rb_node, &base->rb_root);
227 base->total++;
228 }
229 }
230 if (gc_cnt)
231 inet_peer_gc(base, gc_stack, gc_cnt);
232 write_sequnlock_bh(&base->lock);
233
234 return p;
235}
236EXPORT_SYMBOL_GPL(inet_getpeer);
237
238void inet_putpeer(struct inet_peer *p)
239{
240 p->dtime = (__u32)jiffies;
241
242 if (refcount_dec_and_test(&p->refcnt))
243 call_rcu(&p->rcu, inetpeer_free_rcu);
244}
245EXPORT_SYMBOL_GPL(inet_putpeer);
246
247/*
248 * Check transmit rate limitation for given message.
249 * The rate information is held in the inet_peer entries now.
250 * This function is generic and could be used for other purposes
251 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
252 *
253 * Note that the same inet_peer fields are modified by functions in
254 * route.c too, but these work for packet destinations while xrlim_allow
255 * works for icmp destinations. This means the rate limiting information
256 * for one "ip object" is shared - and these ICMPs are twice limited:
257 * by source and by destination.
258 *
259 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
260 * SHOULD allow setting of rate limits
261 *
262 * Shared between ICMPv4 and ICMPv6.
263 */
264#define XRLIM_BURST_FACTOR 6
265bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
266{
267 unsigned long now, token;
268 bool rc = false;
269
270 if (!peer)
271 return true;
272
273 token = peer->rate_tokens;
274 now = jiffies;
275 token += now - peer->rate_last;
276 peer->rate_last = now;
277 if (token > XRLIM_BURST_FACTOR * timeout)
278 token = XRLIM_BURST_FACTOR * timeout;
279 if (token >= timeout) {
280 token -= timeout;
281 rc = true;
282 }
283 peer->rate_tokens = token;
284 return rc;
285}
286EXPORT_SYMBOL(inet_peer_xrlim_allow);
287
288void inetpeer_invalidate_tree(struct inet_peer_base *base)
289{
290 struct rb_node *p = rb_first(&base->rb_root);
291
292 while (p) {
293 struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
294
295 p = rb_next(p);
296 rb_erase(&peer->rb_node, &base->rb_root);
297 inet_putpeer(peer);
298 cond_resched();
299 }
300
301 base->total = 0;
302}
303EXPORT_SYMBOL(inetpeer_invalidate_tree);