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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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 *
Linus Torvalds1da177e2005-04-16 15:20:36 -07006 * 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>
Linus Torvalds1da177e2005-04-16 15:20:36 -070015#include <linux/timer.h>
16#include <linux/time.h>
17#include <linux/kernel.h>
18#include <linux/mm.h>
19#include <linux/net.h>
Arnaldo Carvalho de Melo20380732005-08-16 02:18:02 -030020#include <net/ip.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070021#include <net/inetpeer.h>
22
23/*
24 * Theory of operations.
25 * We keep one entry for each peer IP address. The nodes contains long-living
26 * information about the peer which doesn't depend on routes.
27 * At this moment this information consists only of ID field for the next
28 * outgoing IP packet. This field is incremented with each packet as encoded
29 * in inet_getid() function (include/net/inetpeer.h).
30 * At the moment of writing this notes identifier of IP packets is generated
31 * to be unpredictable using this code only for packets subjected
32 * (actually or potentially) to defragmentation. I.e. DF packets less than
33 * PMTU in size uses a constant ID and do not use this code (see
34 * ip_select_ident() in include/net/ip.h).
35 *
36 * Route cache entries hold references to our nodes.
37 * New cache entries get references via lookup by destination IP address in
38 * the avl tree. The reference is grabbed only when it's needed i.e. only
39 * when we try to output IP packet which needs an unpredictable ID (see
40 * __ip_select_ident() in net/ipv4/route.c).
41 * Nodes are removed only when reference counter goes to 0.
42 * When it's happened the node may be removed when a sufficient amount of
43 * time has been passed since its last use. The less-recently-used entry can
44 * also be removed if the pool is overloaded i.e. if the total amount of
45 * entries is greater-or-equal than the threshold.
46 *
47 * Node pool is organised as an AVL tree.
48 * Such an implementation has been chosen not just for fun. It's a way to
49 * prevent easy and efficient DoS attacks by creating hash collisions. A huge
50 * amount of long living nodes in a single hash slot would significantly delay
51 * lookups performed with disabled BHs.
52 *
53 * Serialisation issues.
54 * 1. Nodes may appear in the tree only with the pool write lock held.
55 * 2. Nodes may disappear from the tree only with the pool write lock held
56 * AND reference count being 0.
57 * 3. Nodes appears and disappears from unused node list only under
58 * "inet_peer_unused_lock".
59 * 4. Global variable peer_total is modified under the pool lock.
60 * 5. struct inet_peer fields modification:
61 * avl_left, avl_right, avl_parent, avl_height: pool lock
Pavel Emelyanovd71209d2007-11-12 21:27:28 -080062 * unused: unused node list lock
Linus Torvalds1da177e2005-04-16 15:20:36 -070063 * refcnt: atomically against modifications on other CPU;
64 * usually under some other lock to prevent node disappearing
65 * dtime: unused node list lock
66 * v4daddr: unchangeable
67 * ip_id_count: idlock
68 */
69
70/* Exported for inet_getid inline function. */
71DEFINE_SPINLOCK(inet_peer_idlock);
72
Christoph Lametere18b8902006-12-06 20:33:20 -080073static struct kmem_cache *peer_cachep __read_mostly;
Linus Torvalds1da177e2005-04-16 15:20:36 -070074
75#define node_height(x) x->avl_height
76static struct inet_peer peer_fake_node = {
77 .avl_left = &peer_fake_node,
78 .avl_right = &peer_fake_node,
79 .avl_height = 0
80};
81#define peer_avl_empty (&peer_fake_node)
82static struct inet_peer *peer_root = peer_avl_empty;
83static DEFINE_RWLOCK(peer_pool_lock);
84#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
85
Herbert Xu7466d902006-07-09 18:18:00 -070086static int peer_total;
Linus Torvalds1da177e2005-04-16 15:20:36 -070087/* Exported for sysctl_net_ipv4. */
Eric Dumazet243bbca2007-03-06 20:23:10 -080088int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
Linus Torvalds1da177e2005-04-16 15:20:36 -070089 * aggressively at this stage */
Eric Dumazet243bbca2007-03-06 20:23:10 -080090int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
91int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
92int inet_peer_gc_mintime __read_mostly = 10 * HZ;
93int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -070094
Pavel Emelyanovd71209d2007-11-12 21:27:28 -080095static LIST_HEAD(unused_peers);
Eric Dumazet4663afe2006-10-12 21:21:06 -070096static DEFINE_SPINLOCK(inet_peer_unused_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
98static void peer_check_expire(unsigned long dummy);
Ingo Molnar8d06afa2005-09-09 13:10:40 -070099static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101
102/* Called from ip_output.c:ip_init */
103void __init inet_initpeers(void)
104{
105 struct sysinfo si;
106
107 /* Use the straight interface to information about memory. */
108 si_meminfo(&si);
109 /* The values below were suggested by Alexey Kuznetsov
110 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
111 * myself. --SAW
112 */
113 if (si.totalram <= (32768*1024)/PAGE_SIZE)
114 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
115 if (si.totalram <= (16384*1024)/PAGE_SIZE)
116 inet_peer_threshold >>= 1; /* about 512KB */
117 if (si.totalram <= (8192*1024)/PAGE_SIZE)
118 inet_peer_threshold >>= 2; /* about 128KB */
119
120 peer_cachep = kmem_cache_create("inet_peer_cache",
121 sizeof(struct inet_peer),
Alexey Dobriyane5d679f2006-08-26 19:25:52 -0700122 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
Paul Mundt20c2df82007-07-20 10:11:58 +0900123 NULL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124
Linus Torvalds1da177e2005-04-16 15:20:36 -0700125 /* All the timers, started at system startup tend
126 to synchronize. Perturb it a bit.
127 */
128 peer_periodic_timer.expires = jiffies
129 + net_random() % inet_peer_gc_maxtime
130 + inet_peer_gc_maxtime;
131 add_timer(&peer_periodic_timer);
132}
133
134/* Called with or without local BH being disabled. */
135static void unlink_from_unused(struct inet_peer *p)
136{
137 spin_lock_bh(&inet_peer_unused_lock);
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800138 list_del_init(&p->unused);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139 spin_unlock_bh(&inet_peer_unused_lock);
140}
141
Eric Dumazet243bbca2007-03-06 20:23:10 -0800142/*
143 * Called with local BH disabled and the pool lock held.
144 * _stack is known to be NULL or not at compile time,
145 * so compiler will optimize the if (_stack) tests.
146 */
Jianjun Kongd9319102008-11-03 00:23:42 -0800147#define lookup(_daddr, _stack) \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148({ \
149 struct inet_peer *u, **v; \
Patrick McHardyfc7b9382007-07-20 19:39:17 -0700150 if (_stack != NULL) { \
Eric Dumazet243bbca2007-03-06 20:23:10 -0800151 stackptr = _stack; \
152 *stackptr++ = &peer_root; \
153 } \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700154 for (u = peer_root; u != peer_avl_empty; ) { \
Eric Dumazet243bbca2007-03-06 20:23:10 -0800155 if (_daddr == u->v4daddr) \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700156 break; \
Eric Dumazet243bbca2007-03-06 20:23:10 -0800157 if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700158 v = &u->avl_left; \
159 else \
160 v = &u->avl_right; \
Patrick McHardyfc7b9382007-07-20 19:39:17 -0700161 if (_stack != NULL) \
Eric Dumazet243bbca2007-03-06 20:23:10 -0800162 *stackptr++ = v; \
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163 u = *v; \
164 } \
165 u; \
166})
167
168/* Called with local BH disabled and the pool write lock held. */
169#define lookup_rightempty(start) \
170({ \
171 struct inet_peer *u, **v; \
172 *stackptr++ = &start->avl_left; \
173 v = &start->avl_left; \
174 for (u = *v; u->avl_right != peer_avl_empty; ) { \
175 v = &u->avl_right; \
176 *stackptr++ = v; \
177 u = *v; \
178 } \
179 u; \
180})
181
182/* Called with local BH disabled and the pool write lock held.
183 * Variable names are the proof of operation correctness.
184 * Look into mm/map_avl.c for more detail description of the ideas. */
185static void peer_avl_rebalance(struct inet_peer **stack[],
186 struct inet_peer ***stackend)
187{
188 struct inet_peer **nodep, *node, *l, *r;
189 int lh, rh;
190
191 while (stackend > stack) {
192 nodep = *--stackend;
193 node = *nodep;
194 l = node->avl_left;
195 r = node->avl_right;
196 lh = node_height(l);
197 rh = node_height(r);
198 if (lh > rh + 1) { /* l: RH+2 */
199 struct inet_peer *ll, *lr, *lrl, *lrr;
200 int lrh;
201 ll = l->avl_left;
202 lr = l->avl_right;
203 lrh = node_height(lr);
204 if (lrh <= node_height(ll)) { /* ll: RH+1 */
205 node->avl_left = lr; /* lr: RH or RH+1 */
206 node->avl_right = r; /* r: RH */
207 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
208 l->avl_left = ll; /* ll: RH+1 */
209 l->avl_right = node; /* node: RH+1 or RH+2 */
210 l->avl_height = node->avl_height + 1;
211 *nodep = l;
212 } else { /* ll: RH, lr: RH+1 */
213 lrl = lr->avl_left; /* lrl: RH or RH-1 */
214 lrr = lr->avl_right; /* lrr: RH or RH-1 */
215 node->avl_left = lrr; /* lrr: RH or RH-1 */
216 node->avl_right = r; /* r: RH */
217 node->avl_height = rh + 1; /* node: RH+1 */
218 l->avl_left = ll; /* ll: RH */
219 l->avl_right = lrl; /* lrl: RH or RH-1 */
220 l->avl_height = rh + 1; /* l: RH+1 */
221 lr->avl_left = l; /* l: RH+1 */
222 lr->avl_right = node; /* node: RH+1 */
223 lr->avl_height = rh + 2;
224 *nodep = lr;
225 }
226 } else if (rh > lh + 1) { /* r: LH+2 */
227 struct inet_peer *rr, *rl, *rlr, *rll;
228 int rlh;
229 rr = r->avl_right;
230 rl = r->avl_left;
231 rlh = node_height(rl);
232 if (rlh <= node_height(rr)) { /* rr: LH+1 */
233 node->avl_right = rl; /* rl: LH or LH+1 */
234 node->avl_left = l; /* l: LH */
235 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
236 r->avl_right = rr; /* rr: LH+1 */
237 r->avl_left = node; /* node: LH+1 or LH+2 */
238 r->avl_height = node->avl_height + 1;
239 *nodep = r;
240 } else { /* rr: RH, rl: RH+1 */
241 rlr = rl->avl_right; /* rlr: LH or LH-1 */
242 rll = rl->avl_left; /* rll: LH or LH-1 */
243 node->avl_right = rll; /* rll: LH or LH-1 */
244 node->avl_left = l; /* l: LH */
245 node->avl_height = lh + 1; /* node: LH+1 */
246 r->avl_right = rr; /* rr: LH */
247 r->avl_left = rlr; /* rlr: LH or LH-1 */
248 r->avl_height = lh + 1; /* r: LH+1 */
249 rl->avl_right = r; /* r: LH+1 */
250 rl->avl_left = node; /* node: LH+1 */
251 rl->avl_height = lh + 2;
252 *nodep = rl;
253 }
254 } else {
255 node->avl_height = (lh > rh ? lh : rh) + 1;
256 }
257 }
258}
259
260/* Called with local BH disabled and the pool write lock held. */
261#define link_to_pool(n) \
262do { \
263 n->avl_height = 1; \
264 n->avl_left = peer_avl_empty; \
265 n->avl_right = peer_avl_empty; \
266 **--stackptr = n; \
267 peer_avl_rebalance(stack, stackptr); \
268} while(0)
269
270/* May be called with local BH enabled. */
271static void unlink_from_pool(struct inet_peer *p)
272{
273 int do_free;
274
275 do_free = 0;
276
277 write_lock_bh(&peer_pool_lock);
278 /* Check the reference counter. It was artificially incremented by 1
279 * in cleanup() function to prevent sudden disappearing. If the
280 * reference count is still 1 then the node is referenced only as `p'
281 * here and from the pool. So under the exclusive pool lock it's safe
282 * to remove the node and free it later. */
283 if (atomic_read(&p->refcnt) == 1) {
284 struct inet_peer **stack[PEER_MAXDEPTH];
285 struct inet_peer ***stackptr, ***delp;
Eric Dumazet243bbca2007-03-06 20:23:10 -0800286 if (lookup(p->v4daddr, stack) != p)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700287 BUG();
288 delp = stackptr - 1; /* *delp[0] == p */
289 if (p->avl_left == peer_avl_empty) {
290 *delp[0] = p->avl_right;
291 --stackptr;
292 } else {
293 /* look for a node to insert instead of p */
294 struct inet_peer *t;
295 t = lookup_rightempty(p);
Kris Katterjohn09a62662006-01-08 22:24:28 -0800296 BUG_ON(*stackptr[-1] != t);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700297 **--stackptr = t->avl_left;
298 /* t is removed, t->v4daddr > x->v4daddr for any
299 * x in p->avl_left subtree.
300 * Put t in the old place of p. */
301 *delp[0] = t;
302 t->avl_left = p->avl_left;
303 t->avl_right = p->avl_right;
304 t->avl_height = p->avl_height;
Kris Katterjohn09a62662006-01-08 22:24:28 -0800305 BUG_ON(delp[1] != &p->avl_left);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700306 delp[1] = &t->avl_left; /* was &p->avl_left */
307 }
308 peer_avl_rebalance(stack, stackptr);
309 peer_total--;
310 do_free = 1;
311 }
312 write_unlock_bh(&peer_pool_lock);
313
314 if (do_free)
315 kmem_cache_free(peer_cachep, p);
316 else
317 /* The node is used again. Decrease the reference counter
318 * back. The loop "cleanup -> unlink_from_unused
319 * -> unlink_from_pool -> putpeer -> link_to_unused
320 * -> cleanup (for the same node)"
321 * doesn't really exist because the entry will have a
322 * recent deletion time and will not be cleaned again soon. */
323 inet_putpeer(p);
324}
325
326/* May be called with local BH enabled. */
327static int cleanup_once(unsigned long ttl)
328{
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800329 struct inet_peer *p = NULL;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330
331 /* Remove the first entry from the list of unused nodes. */
332 spin_lock_bh(&inet_peer_unused_lock);
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800333 if (!list_empty(&unused_peers)) {
334 __u32 delta;
335
336 p = list_first_entry(&unused_peers, struct inet_peer, unused);
337 delta = (__u32)jiffies - p->dtime;
338
Eric Dumazet4663afe2006-10-12 21:21:06 -0700339 if (delta < ttl) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700340 /* Do not prune fresh entries. */
341 spin_unlock_bh(&inet_peer_unused_lock);
342 return -1;
343 }
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800344
345 list_del_init(&p->unused);
346
Linus Torvalds1da177e2005-04-16 15:20:36 -0700347 /* Grab an extra reference to prevent node disappearing
348 * before unlink_from_pool() call. */
349 atomic_inc(&p->refcnt);
350 }
351 spin_unlock_bh(&inet_peer_unused_lock);
352
353 if (p == NULL)
354 /* It means that the total number of USED entries has
355 * grown over inet_peer_threshold. It shouldn't really
356 * happen because of entry limits in route cache. */
357 return -1;
358
359 unlink_from_pool(p);
360 return 0;
361}
362
363/* Called with or without local BH being disabled. */
Al Viro53576d92006-09-26 22:18:43 -0700364struct inet_peer *inet_getpeer(__be32 daddr, int create)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700365{
366 struct inet_peer *p, *n;
367 struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
368
369 /* Look up for the address quickly. */
370 read_lock_bh(&peer_pool_lock);
Eric Dumazet243bbca2007-03-06 20:23:10 -0800371 p = lookup(daddr, NULL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700372 if (p != peer_avl_empty)
373 atomic_inc(&p->refcnt);
374 read_unlock_bh(&peer_pool_lock);
375
376 if (p != peer_avl_empty) {
377 /* The existing node has been found. */
378 /* Remove the entry from unused list if it was there. */
379 unlink_from_unused(p);
380 return p;
381 }
382
383 if (!create)
384 return NULL;
385
386 /* Allocate the space outside the locked region. */
387 n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
388 if (n == NULL)
389 return NULL;
390 n->v4daddr = daddr;
391 atomic_set(&n->refcnt, 1);
Herbert Xu89cee8b2005-12-13 23:14:27 -0800392 atomic_set(&n->rid, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700393 n->ip_id_count = secure_ip_id(daddr);
394 n->tcp_ts_stamp = 0;
395
396 write_lock_bh(&peer_pool_lock);
397 /* Check if an entry has suddenly appeared. */
Eric Dumazet243bbca2007-03-06 20:23:10 -0800398 p = lookup(daddr, stack);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700399 if (p != peer_avl_empty)
400 goto out_free;
401
402 /* Link the node. */
403 link_to_pool(n);
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800404 INIT_LIST_HEAD(&n->unused);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700405 peer_total++;
406 write_unlock_bh(&peer_pool_lock);
407
408 if (peer_total >= inet_peer_threshold)
409 /* Remove one less-recently-used entry. */
410 cleanup_once(0);
411
412 return n;
413
414out_free:
415 /* The appropriate node is already in the pool. */
416 atomic_inc(&p->refcnt);
417 write_unlock_bh(&peer_pool_lock);
418 /* Remove the entry from unused list if it was there. */
419 unlink_from_unused(p);
420 /* Free preallocated the preallocated node. */
421 kmem_cache_free(peer_cachep, n);
422 return p;
423}
424
425/* Called with local BH disabled. */
426static void peer_check_expire(unsigned long dummy)
427{
Eric Dumazet4663afe2006-10-12 21:21:06 -0700428 unsigned long now = jiffies;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700429 int ttl;
430
431 if (peer_total >= inet_peer_threshold)
432 ttl = inet_peer_minttl;
433 else
434 ttl = inet_peer_maxttl
435 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
436 peer_total / inet_peer_threshold * HZ;
Eric Dumazet4663afe2006-10-12 21:21:06 -0700437 while (!cleanup_once(ttl)) {
438 if (jiffies != now)
439 break;
440 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700441
442 /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
443 * interval depending on the total number of entries (more entries,
444 * less interval). */
Dave Johnson1344a412005-08-23 10:10:15 -0700445 if (peer_total >= inet_peer_threshold)
446 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
447 else
448 peer_periodic_timer.expires = jiffies
449 + inet_peer_gc_maxtime
450 - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
451 peer_total / inet_peer_threshold * HZ;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700452 add_timer(&peer_periodic_timer);
453}
Eric Dumazet4663afe2006-10-12 21:21:06 -0700454
455void inet_putpeer(struct inet_peer *p)
456{
457 spin_lock_bh(&inet_peer_unused_lock);
458 if (atomic_dec_and_test(&p->refcnt)) {
Pavel Emelyanovd71209d2007-11-12 21:27:28 -0800459 list_add_tail(&p->unused, &unused_peers);
Eric Dumazet4663afe2006-10-12 21:21:06 -0700460 p->dtime = (__u32)jiffies;
461 }
462 spin_unlock_bh(&inet_peer_unused_lock);
463}