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
68 static struct kmem_cache *peer_cachep __read_mostly;
69
70 static LIST_HEAD(gc_list);
71 static const int gc_delay = 60 * HZ;
72 static struct delayed_work gc_work;
73 static 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)
79 static 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
85 struct inet_peer_base {
86 struct inet_peer __rcu *root;
87 seqlock_t lock;
88 int total;
89 };
90
91 static struct inet_peer_base v4_peers = {
92 .root = peer_avl_empty_rcu,
93 .lock = __SEQLOCK_UNLOCKED(v4_peers.lock),
94 .total = 0,
95 };
96
97 static struct inet_peer_base v6_peers = {
98 .root = peer_avl_empty_rcu,
99 .lock = __SEQLOCK_UNLOCKED(v6_peers.lock),
100 .total = 0,
101 };
102
103 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
104
105 /* Exported for sysctl_net_ipv4. */
106 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
107 * aggressively at this stage */
108 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
109 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
110
inetpeer_gc_worker(struct work_struct * work)111 static void inetpeer_gc_worker(struct work_struct *work)
112 {
113 struct inet_peer *p, *n;
114 LIST_HEAD(list);
115
116 spin_lock_bh(&gc_lock);
117 list_replace_init(&gc_list, &list);
118 spin_unlock_bh(&gc_lock);
119
120 if (list_empty(&list))
121 return;
122
123 list_for_each_entry_safe(p, n, &list, gc_list) {
124
125 if(need_resched())
126 cond_resched();
127
128 if (p->avl_left != peer_avl_empty) {
129 list_add_tail(&p->avl_left->gc_list, &list);
130 p->avl_left = peer_avl_empty;
131 }
132
133 if (p->avl_right != peer_avl_empty) {
134 list_add_tail(&p->avl_right->gc_list, &list);
135 p->avl_right = peer_avl_empty;
136 }
137
138 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
139
140 if (!atomic_read(&p->refcnt)) {
141 list_del(&p->gc_list);
142 kmem_cache_free(peer_cachep, p);
143 }
144 }
145
146 if (list_empty(&list))
147 return;
148
149 spin_lock_bh(&gc_lock);
150 list_splice(&list, &gc_list);
151 spin_unlock_bh(&gc_lock);
152
153 schedule_delayed_work(&gc_work, gc_delay);
154 }
155
156 /* Called from ip_output.c:ip_init */
inet_initpeers(void)157 void __init inet_initpeers(void)
158 {
159 struct sysinfo si;
160
161 /* Use the straight interface to information about memory. */
162 si_meminfo(&si);
163 /* The values below were suggested by Alexey Kuznetsov
164 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
165 * myself. --SAW
166 */
167 if (si.totalram <= (32768*1024)/PAGE_SIZE)
168 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
169 if (si.totalram <= (16384*1024)/PAGE_SIZE)
170 inet_peer_threshold >>= 1; /* about 512KB */
171 if (si.totalram <= (8192*1024)/PAGE_SIZE)
172 inet_peer_threshold >>= 2; /* about 128KB */
173
174 peer_cachep = kmem_cache_create("inet_peer_cache",
175 sizeof(struct inet_peer),
176 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
177 NULL);
178
179 INIT_DELAYED_WORK_DEFERRABLE(&gc_work, inetpeer_gc_worker);
180 }
181
addr_compare(const struct inetpeer_addr * a,const struct inetpeer_addr * b)182 static int addr_compare(const struct inetpeer_addr *a,
183 const struct inetpeer_addr *b)
184 {
185 int i, n = (a->family == AF_INET ? 1 : 4);
186
187 for (i = 0; i < n; i++) {
188 if (a->addr.a6[i] == b->addr.a6[i])
189 continue;
190 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i])
191 return -1;
192 return 1;
193 }
194
195 return 0;
196 }
197
198 #define rcu_deref_locked(X, BASE) \
199 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
200
201 /*
202 * Called with local BH disabled and the pool lock held.
203 */
204 #define lookup(_daddr, _stack, _base) \
205 ({ \
206 struct inet_peer *u; \
207 struct inet_peer __rcu **v; \
208 \
209 stackptr = _stack; \
210 *stackptr++ = &_base->root; \
211 for (u = rcu_deref_locked(_base->root, _base); \
212 u != peer_avl_empty; ) { \
213 int cmp = addr_compare(_daddr, &u->daddr); \
214 if (cmp == 0) \
215 break; \
216 if (cmp == -1) \
217 v = &u->avl_left; \
218 else \
219 v = &u->avl_right; \
220 *stackptr++ = v; \
221 u = rcu_deref_locked(*v, _base); \
222 } \
223 u; \
224 })
225
226 /*
227 * Called with rcu_read_lock()
228 * Because we hold no lock against a writer, its quite possible we fall
229 * in an endless loop.
230 * But every pointer we follow is guaranteed to be valid thanks to RCU.
231 * We exit from this function if number of links exceeds PEER_MAXDEPTH
232 */
lookup_rcu(const struct inetpeer_addr * daddr,struct inet_peer_base * base)233 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
234 struct inet_peer_base *base)
235 {
236 struct inet_peer *u = rcu_dereference(base->root);
237 int count = 0;
238
239 while (u != peer_avl_empty) {
240 int cmp = addr_compare(daddr, &u->daddr);
241 if (cmp == 0) {
242 /* Before taking a reference, check if this entry was
243 * deleted (refcnt=-1)
244 */
245 if (!atomic_add_unless(&u->refcnt, 1, -1))
246 u = NULL;
247 return u;
248 }
249 if (cmp == -1)
250 u = rcu_dereference(u->avl_left);
251 else
252 u = rcu_dereference(u->avl_right);
253 if (unlikely(++count == PEER_MAXDEPTH))
254 break;
255 }
256 return NULL;
257 }
258
259 /* Called with local BH disabled and the pool lock held. */
260 #define lookup_rightempty(start, base) \
261 ({ \
262 struct inet_peer *u; \
263 struct inet_peer __rcu **v; \
264 *stackptr++ = &start->avl_left; \
265 v = &start->avl_left; \
266 for (u = rcu_deref_locked(*v, base); \
267 u->avl_right != peer_avl_empty_rcu; ) { \
268 v = &u->avl_right; \
269 *stackptr++ = v; \
270 u = rcu_deref_locked(*v, base); \
271 } \
272 u; \
273 })
274
275 /* Called with local BH disabled and the pool lock held.
276 * Variable names are the proof of operation correctness.
277 * Look into mm/map_avl.c for more detail description of the ideas.
278 */
peer_avl_rebalance(struct inet_peer __rcu ** stack[],struct inet_peer __rcu *** stackend,struct inet_peer_base * base)279 static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
280 struct inet_peer __rcu ***stackend,
281 struct inet_peer_base *base)
282 {
283 struct inet_peer __rcu **nodep;
284 struct inet_peer *node, *l, *r;
285 int lh, rh;
286
287 while (stackend > stack) {
288 nodep = *--stackend;
289 node = rcu_deref_locked(*nodep, base);
290 l = rcu_deref_locked(node->avl_left, base);
291 r = rcu_deref_locked(node->avl_right, base);
292 lh = node_height(l);
293 rh = node_height(r);
294 if (lh > rh + 1) { /* l: RH+2 */
295 struct inet_peer *ll, *lr, *lrl, *lrr;
296 int lrh;
297 ll = rcu_deref_locked(l->avl_left, base);
298 lr = rcu_deref_locked(l->avl_right, base);
299 lrh = node_height(lr);
300 if (lrh <= node_height(ll)) { /* ll: RH+1 */
301 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */
302 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
303 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
304 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */
305 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */
306 l->avl_height = node->avl_height + 1;
307 RCU_INIT_POINTER(*nodep, l);
308 } else { /* ll: RH, lr: RH+1 */
309 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
310 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
311 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */
312 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
313 node->avl_height = rh + 1; /* node: RH+1 */
314 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */
315 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */
316 l->avl_height = rh + 1; /* l: RH+1 */
317 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */
318 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */
319 lr->avl_height = rh + 2;
320 RCU_INIT_POINTER(*nodep, lr);
321 }
322 } else if (rh > lh + 1) { /* r: LH+2 */
323 struct inet_peer *rr, *rl, *rlr, *rll;
324 int rlh;
325 rr = rcu_deref_locked(r->avl_right, base);
326 rl = rcu_deref_locked(r->avl_left, base);
327 rlh = node_height(rl);
328 if (rlh <= node_height(rr)) { /* rr: LH+1 */
329 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */
330 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
331 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
332 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */
333 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */
334 r->avl_height = node->avl_height + 1;
335 RCU_INIT_POINTER(*nodep, r);
336 } else { /* rr: RH, rl: RH+1 */
337 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
338 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
339 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
340 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
341 node->avl_height = lh + 1; /* node: LH+1 */
342 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */
343 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */
344 r->avl_height = lh + 1; /* r: LH+1 */
345 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */
346 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */
347 rl->avl_height = lh + 2;
348 RCU_INIT_POINTER(*nodep, rl);
349 }
350 } else {
351 node->avl_height = (lh > rh ? lh : rh) + 1;
352 }
353 }
354 }
355
356 /* Called with local BH disabled and the pool lock held. */
357 #define link_to_pool(n, base) \
358 do { \
359 n->avl_height = 1; \
360 n->avl_left = peer_avl_empty_rcu; \
361 n->avl_right = peer_avl_empty_rcu; \
362 /* lockless readers can catch us now */ \
363 rcu_assign_pointer(**--stackptr, n); \
364 peer_avl_rebalance(stack, stackptr, base); \
365 } while (0)
366
inetpeer_free_rcu(struct rcu_head * head)367 static void inetpeer_free_rcu(struct rcu_head *head)
368 {
369 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
370 }
371
unlink_from_pool(struct inet_peer * p,struct inet_peer_base * base,struct inet_peer __rcu ** stack[PEER_MAXDEPTH])372 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
373 struct inet_peer __rcu **stack[PEER_MAXDEPTH])
374 {
375 struct inet_peer __rcu ***stackptr, ***delp;
376
377 if (lookup(&p->daddr, stack, base) != p)
378 BUG();
379 delp = stackptr - 1; /* *delp[0] == p */
380 if (p->avl_left == peer_avl_empty_rcu) {
381 *delp[0] = p->avl_right;
382 --stackptr;
383 } else {
384 /* look for a node to insert instead of p */
385 struct inet_peer *t;
386 t = lookup_rightempty(p, base);
387 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
388 **--stackptr = t->avl_left;
389 /* t is removed, t->daddr > x->daddr for any
390 * x in p->avl_left subtree.
391 * Put t in the old place of p. */
392 RCU_INIT_POINTER(*delp[0], t);
393 t->avl_left = p->avl_left;
394 t->avl_right = p->avl_right;
395 t->avl_height = p->avl_height;
396 BUG_ON(delp[1] != &p->avl_left);
397 delp[1] = &t->avl_left; /* was &p->avl_left */
398 }
399 peer_avl_rebalance(stack, stackptr, base);
400 base->total--;
401 call_rcu(&p->rcu, inetpeer_free_rcu);
402 }
403
family_to_base(int family)404 static struct inet_peer_base *family_to_base(int family)
405 {
406 return family == AF_INET ? &v4_peers : &v6_peers;
407 }
408
409 /* perform garbage collect on all items stacked during a lookup */
inet_peer_gc(struct inet_peer_base * base,struct inet_peer __rcu ** stack[PEER_MAXDEPTH],struct inet_peer __rcu *** stackptr)410 static int inet_peer_gc(struct inet_peer_base *base,
411 struct inet_peer __rcu **stack[PEER_MAXDEPTH],
412 struct inet_peer __rcu ***stackptr)
413 {
414 struct inet_peer *p, *gchead = NULL;
415 __u32 delta, ttl;
416 int cnt = 0;
417
418 if (base->total >= inet_peer_threshold)
419 ttl = 0; /* be aggressive */
420 else
421 ttl = inet_peer_maxttl
422 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
423 base->total / inet_peer_threshold * HZ;
424 stackptr--; /* last stack slot is peer_avl_empty */
425 while (stackptr > stack) {
426 stackptr--;
427 p = rcu_deref_locked(**stackptr, base);
428 if (atomic_read(&p->refcnt) == 0) {
429 smp_rmb();
430 delta = (__u32)jiffies - p->dtime;
431 if (delta >= ttl &&
432 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
433 p->gc_next = gchead;
434 gchead = p;
435 }
436 }
437 }
438 while ((p = gchead) != NULL) {
439 gchead = p->gc_next;
440 cnt++;
441 unlink_from_pool(p, base, stack);
442 }
443 return cnt;
444 }
445
inet_getpeer(const struct inetpeer_addr * daddr,int create)446 struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create)
447 {
448 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
449 struct inet_peer_base *base = family_to_base(daddr->family);
450 struct inet_peer *p;
451 unsigned int sequence;
452 int invalidated, gccnt = 0;
453
454 /* Attempt a lockless lookup first.
455 * Because of a concurrent writer, we might not find an existing entry.
456 */
457 rcu_read_lock();
458 sequence = read_seqbegin(&base->lock);
459 p = lookup_rcu(daddr, base);
460 invalidated = read_seqretry(&base->lock, sequence);
461 rcu_read_unlock();
462
463 if (p)
464 return p;
465
466 /* If no writer did a change during our lookup, we can return early. */
467 if (!create && !invalidated)
468 return NULL;
469
470 /* retry an exact lookup, taking the lock before.
471 * At least, nodes should be hot in our cache.
472 */
473 write_seqlock_bh(&base->lock);
474 relookup:
475 p = lookup(daddr, stack, base);
476 if (p != peer_avl_empty) {
477 atomic_inc(&p->refcnt);
478 write_sequnlock_bh(&base->lock);
479 return p;
480 }
481 if (!gccnt) {
482 gccnt = inet_peer_gc(base, stack, stackptr);
483 if (gccnt && create)
484 goto relookup;
485 }
486 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
487 if (p) {
488 p->daddr = *daddr;
489 atomic_set(&p->refcnt, 1);
490 atomic_set(&p->rid, 0);
491 atomic_set(&p->ip_id_count,
492 (daddr->family == AF_INET) ?
493 secure_ip_id(daddr->addr.a4) :
494 secure_ipv6_id(daddr->addr.a6));
495 p->tcp_ts_stamp = 0;
496 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
497 p->rate_tokens = 0;
498 p->rate_last = 0;
499 p->pmtu_expires = 0;
500 p->pmtu_orig = 0;
501 memset(&p->redirect_learned, 0, sizeof(p->redirect_learned));
502 INIT_LIST_HEAD(&p->gc_list);
503
504 /* Link the node. */
505 link_to_pool(p, base);
506 base->total++;
507 }
508 write_sequnlock_bh(&base->lock);
509
510 return p;
511 }
512 EXPORT_SYMBOL_GPL(inet_getpeer);
513
inet_putpeer(struct inet_peer * p)514 void inet_putpeer(struct inet_peer *p)
515 {
516 p->dtime = (__u32)jiffies;
517 smp_mb__before_atomic_dec();
518 atomic_dec(&p->refcnt);
519 }
520 EXPORT_SYMBOL_GPL(inet_putpeer);
521
522 /*
523 * Check transmit rate limitation for given message.
524 * The rate information is held in the inet_peer entries now.
525 * This function is generic and could be used for other purposes
526 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
527 *
528 * Note that the same inet_peer fields are modified by functions in
529 * route.c too, but these work for packet destinations while xrlim_allow
530 * works for icmp destinations. This means the rate limiting information
531 * for one "ip object" is shared - and these ICMPs are twice limited:
532 * by source and by destination.
533 *
534 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
535 * SHOULD allow setting of rate limits
536 *
537 * Shared between ICMPv4 and ICMPv6.
538 */
539 #define XRLIM_BURST_FACTOR 6
inet_peer_xrlim_allow(struct inet_peer * peer,int timeout)540 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
541 {
542 unsigned long now, token;
543 bool rc = false;
544
545 if (!peer)
546 return true;
547
548 token = peer->rate_tokens;
549 now = jiffies;
550 token += now - peer->rate_last;
551 peer->rate_last = now;
552 if (token > XRLIM_BURST_FACTOR * timeout)
553 token = XRLIM_BURST_FACTOR * timeout;
554 if (token >= timeout) {
555 token -= timeout;
556 rc = true;
557 }
558 peer->rate_tokens = token;
559 return rc;
560 }
561 EXPORT_SYMBOL(inet_peer_xrlim_allow);
562
inetpeer_inval_rcu(struct rcu_head * head)563 static void inetpeer_inval_rcu(struct rcu_head *head)
564 {
565 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
566
567 spin_lock_bh(&gc_lock);
568 list_add_tail(&p->gc_list, &gc_list);
569 spin_unlock_bh(&gc_lock);
570
571 schedule_delayed_work(&gc_work, gc_delay);
572 }
573
inetpeer_invalidate_tree(int family)574 void inetpeer_invalidate_tree(int family)
575 {
576 struct inet_peer *old, *new, *prev;
577 struct inet_peer_base *base = family_to_base(family);
578
579 write_seqlock_bh(&base->lock);
580
581 old = base->root;
582 if (old == peer_avl_empty_rcu)
583 goto out;
584
585 new = peer_avl_empty_rcu;
586
587 prev = cmpxchg(&base->root, old, new);
588 if (prev == old) {
589 base->total = 0;
590 call_rcu(&prev->gc_rcu, inetpeer_inval_rcu);
591 }
592
593 out:
594 write_sequnlock_bh(&base->lock);
595 }
596 EXPORT_SYMBOL(inetpeer_invalidate_tree);
597