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1da177e4 LT |
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 | * Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $ | |
7 | * | |
8 | * Authors: Andrey V. Savochkin <saw@msu.ru> | |
9 | */ | |
10 | ||
11 | #include <linux/module.h> | |
12 | #include <linux/types.h> | |
13 | #include <linux/slab.h> | |
14 | #include <linux/interrupt.h> | |
15 | #include <linux/spinlock.h> | |
16 | #include <linux/random.h> | |
1da177e4 LT |
17 | #include <linux/timer.h> |
18 | #include <linux/time.h> | |
19 | #include <linux/kernel.h> | |
20 | #include <linux/mm.h> | |
21 | #include <linux/net.h> | |
20380731 | 22 | #include <net/ip.h> |
1da177e4 LT |
23 | #include <net/inetpeer.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 uses a constant ID and do not use this code (see | |
36 | * 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 write lock held. | |
57 | * 2. Nodes may disappear from the tree only with the pool write lock held | |
58 | * AND reference count being 0. | |
59 | * 3. Nodes appears and disappears from unused node list only under | |
60 | * "inet_peer_unused_lock". | |
61 | * 4. Global variable peer_total is modified under the pool lock. | |
62 | * 5. struct inet_peer fields modification: | |
63 | * avl_left, avl_right, avl_parent, avl_height: pool lock | |
64 | * unused_next, unused_prevp: unused node list lock | |
65 | * refcnt: atomically against modifications on other CPU; | |
66 | * usually under some other lock to prevent node disappearing | |
67 | * dtime: unused node list lock | |
68 | * v4daddr: unchangeable | |
69 | * ip_id_count: idlock | |
70 | */ | |
71 | ||
72 | /* Exported for inet_getid inline function. */ | |
73 | DEFINE_SPINLOCK(inet_peer_idlock); | |
74 | ||
e18b890b | 75 | static struct kmem_cache *peer_cachep __read_mostly; |
1da177e4 LT |
76 | |
77 | #define node_height(x) x->avl_height | |
78 | static struct inet_peer peer_fake_node = { | |
79 | .avl_left = &peer_fake_node, | |
80 | .avl_right = &peer_fake_node, | |
81 | .avl_height = 0 | |
82 | }; | |
83 | #define peer_avl_empty (&peer_fake_node) | |
84 | static struct inet_peer *peer_root = peer_avl_empty; | |
85 | static DEFINE_RWLOCK(peer_pool_lock); | |
86 | #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ | |
87 | ||
7466d90f | 88 | static int peer_total; |
1da177e4 LT |
89 | /* Exported for sysctl_net_ipv4. */ |
90 | int inet_peer_threshold = 65536 + 128; /* start to throw entries more | |
91 | * aggressively at this stage */ | |
92 | int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */ | |
93 | int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */ | |
94 | ||
95 | static struct inet_peer *inet_peer_unused_head; | |
4663afe2 ED |
96 | static struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head; |
97 | static DEFINE_SPINLOCK(inet_peer_unused_lock); | |
1da177e4 LT |
98 | |
99 | static void peer_check_expire(unsigned long dummy); | |
8d06afab | 100 | static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0); |
1da177e4 LT |
101 | |
102 | /* Exported for sysctl_net_ipv4. */ | |
103 | int inet_peer_gc_mintime = 10 * HZ, | |
104 | inet_peer_gc_maxtime = 120 * HZ; | |
105 | ||
106 | /* Called from ip_output.c:ip_init */ | |
107 | void __init inet_initpeers(void) | |
108 | { | |
109 | struct sysinfo si; | |
110 | ||
111 | /* Use the straight interface to information about memory. */ | |
112 | si_meminfo(&si); | |
113 | /* The values below were suggested by Alexey Kuznetsov | |
114 | * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values | |
115 | * myself. --SAW | |
116 | */ | |
117 | if (si.totalram <= (32768*1024)/PAGE_SIZE) | |
118 | inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ | |
119 | if (si.totalram <= (16384*1024)/PAGE_SIZE) | |
120 | inet_peer_threshold >>= 1; /* about 512KB */ | |
121 | if (si.totalram <= (8192*1024)/PAGE_SIZE) | |
122 | inet_peer_threshold >>= 2; /* about 128KB */ | |
123 | ||
124 | peer_cachep = kmem_cache_create("inet_peer_cache", | |
125 | sizeof(struct inet_peer), | |
e5d679f3 | 126 | 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, |
1da177e4 LT |
127 | NULL, NULL); |
128 | ||
1da177e4 LT |
129 | /* All the timers, started at system startup tend |
130 | to synchronize. Perturb it a bit. | |
131 | */ | |
132 | peer_periodic_timer.expires = jiffies | |
133 | + net_random() % inet_peer_gc_maxtime | |
134 | + inet_peer_gc_maxtime; | |
135 | add_timer(&peer_periodic_timer); | |
136 | } | |
137 | ||
138 | /* Called with or without local BH being disabled. */ | |
139 | static void unlink_from_unused(struct inet_peer *p) | |
140 | { | |
141 | spin_lock_bh(&inet_peer_unused_lock); | |
142 | if (p->unused_prevp != NULL) { | |
143 | /* On unused list. */ | |
144 | *p->unused_prevp = p->unused_next; | |
145 | if (p->unused_next != NULL) | |
146 | p->unused_next->unused_prevp = p->unused_prevp; | |
147 | else | |
148 | inet_peer_unused_tailp = p->unused_prevp; | |
149 | p->unused_prevp = NULL; /* mark it as removed */ | |
150 | } | |
151 | spin_unlock_bh(&inet_peer_unused_lock); | |
152 | } | |
153 | ||
154 | /* Called with local BH disabled and the pool lock held. */ | |
155 | #define lookup(daddr) \ | |
156 | ({ \ | |
157 | struct inet_peer *u, **v; \ | |
158 | stackptr = stack; \ | |
159 | *stackptr++ = &peer_root; \ | |
160 | for (u = peer_root; u != peer_avl_empty; ) { \ | |
161 | if (daddr == u->v4daddr) \ | |
162 | break; \ | |
53576d9b | 163 | if ((__force __u32)daddr < (__force __u32)u->v4daddr) \ |
1da177e4 LT |
164 | v = &u->avl_left; \ |
165 | else \ | |
166 | v = &u->avl_right; \ | |
167 | *stackptr++ = v; \ | |
168 | u = *v; \ | |
169 | } \ | |
170 | u; \ | |
171 | }) | |
172 | ||
173 | /* Called with local BH disabled and the pool write lock held. */ | |
174 | #define lookup_rightempty(start) \ | |
175 | ({ \ | |
176 | struct inet_peer *u, **v; \ | |
177 | *stackptr++ = &start->avl_left; \ | |
178 | v = &start->avl_left; \ | |
179 | for (u = *v; u->avl_right != peer_avl_empty; ) { \ | |
180 | v = &u->avl_right; \ | |
181 | *stackptr++ = v; \ | |
182 | u = *v; \ | |
183 | } \ | |
184 | u; \ | |
185 | }) | |
186 | ||
187 | /* Called with local BH disabled and the pool write lock held. | |
188 | * Variable names are the proof of operation correctness. | |
189 | * Look into mm/map_avl.c for more detail description of the ideas. */ | |
190 | static void peer_avl_rebalance(struct inet_peer **stack[], | |
191 | struct inet_peer ***stackend) | |
192 | { | |
193 | struct inet_peer **nodep, *node, *l, *r; | |
194 | int lh, rh; | |
195 | ||
196 | while (stackend > stack) { | |
197 | nodep = *--stackend; | |
198 | node = *nodep; | |
199 | l = node->avl_left; | |
200 | r = node->avl_right; | |
201 | lh = node_height(l); | |
202 | rh = node_height(r); | |
203 | if (lh > rh + 1) { /* l: RH+2 */ | |
204 | struct inet_peer *ll, *lr, *lrl, *lrr; | |
205 | int lrh; | |
206 | ll = l->avl_left; | |
207 | lr = l->avl_right; | |
208 | lrh = node_height(lr); | |
209 | if (lrh <= node_height(ll)) { /* ll: RH+1 */ | |
210 | node->avl_left = lr; /* lr: RH or RH+1 */ | |
211 | node->avl_right = r; /* r: RH */ | |
212 | node->avl_height = lrh + 1; /* RH+1 or RH+2 */ | |
213 | l->avl_left = ll; /* ll: RH+1 */ | |
214 | l->avl_right = node; /* node: RH+1 or RH+2 */ | |
215 | l->avl_height = node->avl_height + 1; | |
216 | *nodep = l; | |
217 | } else { /* ll: RH, lr: RH+1 */ | |
218 | lrl = lr->avl_left; /* lrl: RH or RH-1 */ | |
219 | lrr = lr->avl_right; /* lrr: RH or RH-1 */ | |
220 | node->avl_left = lrr; /* lrr: RH or RH-1 */ | |
221 | node->avl_right = r; /* r: RH */ | |
222 | node->avl_height = rh + 1; /* node: RH+1 */ | |
223 | l->avl_left = ll; /* ll: RH */ | |
224 | l->avl_right = lrl; /* lrl: RH or RH-1 */ | |
225 | l->avl_height = rh + 1; /* l: RH+1 */ | |
226 | lr->avl_left = l; /* l: RH+1 */ | |
227 | lr->avl_right = node; /* node: RH+1 */ | |
228 | lr->avl_height = rh + 2; | |
229 | *nodep = lr; | |
230 | } | |
231 | } else if (rh > lh + 1) { /* r: LH+2 */ | |
232 | struct inet_peer *rr, *rl, *rlr, *rll; | |
233 | int rlh; | |
234 | rr = r->avl_right; | |
235 | rl = r->avl_left; | |
236 | rlh = node_height(rl); | |
237 | if (rlh <= node_height(rr)) { /* rr: LH+1 */ | |
238 | node->avl_right = rl; /* rl: LH or LH+1 */ | |
239 | node->avl_left = l; /* l: LH */ | |
240 | node->avl_height = rlh + 1; /* LH+1 or LH+2 */ | |
241 | r->avl_right = rr; /* rr: LH+1 */ | |
242 | r->avl_left = node; /* node: LH+1 or LH+2 */ | |
243 | r->avl_height = node->avl_height + 1; | |
244 | *nodep = r; | |
245 | } else { /* rr: RH, rl: RH+1 */ | |
246 | rlr = rl->avl_right; /* rlr: LH or LH-1 */ | |
247 | rll = rl->avl_left; /* rll: LH or LH-1 */ | |
248 | node->avl_right = rll; /* rll: LH or LH-1 */ | |
249 | node->avl_left = l; /* l: LH */ | |
250 | node->avl_height = lh + 1; /* node: LH+1 */ | |
251 | r->avl_right = rr; /* rr: LH */ | |
252 | r->avl_left = rlr; /* rlr: LH or LH-1 */ | |
253 | r->avl_height = lh + 1; /* r: LH+1 */ | |
254 | rl->avl_right = r; /* r: LH+1 */ | |
255 | rl->avl_left = node; /* node: LH+1 */ | |
256 | rl->avl_height = lh + 2; | |
257 | *nodep = rl; | |
258 | } | |
259 | } else { | |
260 | node->avl_height = (lh > rh ? lh : rh) + 1; | |
261 | } | |
262 | } | |
263 | } | |
264 | ||
265 | /* Called with local BH disabled and the pool write lock held. */ | |
266 | #define link_to_pool(n) \ | |
267 | do { \ | |
268 | n->avl_height = 1; \ | |
269 | n->avl_left = peer_avl_empty; \ | |
270 | n->avl_right = peer_avl_empty; \ | |
271 | **--stackptr = n; \ | |
272 | peer_avl_rebalance(stack, stackptr); \ | |
273 | } while(0) | |
274 | ||
275 | /* May be called with local BH enabled. */ | |
276 | static void unlink_from_pool(struct inet_peer *p) | |
277 | { | |
278 | int do_free; | |
279 | ||
280 | do_free = 0; | |
281 | ||
282 | write_lock_bh(&peer_pool_lock); | |
283 | /* Check the reference counter. It was artificially incremented by 1 | |
284 | * in cleanup() function to prevent sudden disappearing. If the | |
285 | * reference count is still 1 then the node is referenced only as `p' | |
286 | * here and from the pool. So under the exclusive pool lock it's safe | |
287 | * to remove the node and free it later. */ | |
288 | if (atomic_read(&p->refcnt) == 1) { | |
289 | struct inet_peer **stack[PEER_MAXDEPTH]; | |
290 | struct inet_peer ***stackptr, ***delp; | |
291 | if (lookup(p->v4daddr) != p) | |
292 | BUG(); | |
293 | delp = stackptr - 1; /* *delp[0] == p */ | |
294 | if (p->avl_left == peer_avl_empty) { | |
295 | *delp[0] = p->avl_right; | |
296 | --stackptr; | |
297 | } else { | |
298 | /* look for a node to insert instead of p */ | |
299 | struct inet_peer *t; | |
300 | t = lookup_rightempty(p); | |
09a62660 | 301 | BUG_ON(*stackptr[-1] != t); |
1da177e4 LT |
302 | **--stackptr = t->avl_left; |
303 | /* t is removed, t->v4daddr > x->v4daddr for any | |
304 | * x in p->avl_left subtree. | |
305 | * Put t in the old place of p. */ | |
306 | *delp[0] = t; | |
307 | t->avl_left = p->avl_left; | |
308 | t->avl_right = p->avl_right; | |
309 | t->avl_height = p->avl_height; | |
09a62660 | 310 | BUG_ON(delp[1] != &p->avl_left); |
1da177e4 LT |
311 | delp[1] = &t->avl_left; /* was &p->avl_left */ |
312 | } | |
313 | peer_avl_rebalance(stack, stackptr); | |
314 | peer_total--; | |
315 | do_free = 1; | |
316 | } | |
317 | write_unlock_bh(&peer_pool_lock); | |
318 | ||
319 | if (do_free) | |
320 | kmem_cache_free(peer_cachep, p); | |
321 | else | |
322 | /* The node is used again. Decrease the reference counter | |
323 | * back. The loop "cleanup -> unlink_from_unused | |
324 | * -> unlink_from_pool -> putpeer -> link_to_unused | |
325 | * -> cleanup (for the same node)" | |
326 | * doesn't really exist because the entry will have a | |
327 | * recent deletion time and will not be cleaned again soon. */ | |
328 | inet_putpeer(p); | |
329 | } | |
330 | ||
331 | /* May be called with local BH enabled. */ | |
332 | static int cleanup_once(unsigned long ttl) | |
333 | { | |
334 | struct inet_peer *p; | |
335 | ||
336 | /* Remove the first entry from the list of unused nodes. */ | |
337 | spin_lock_bh(&inet_peer_unused_lock); | |
338 | p = inet_peer_unused_head; | |
339 | if (p != NULL) { | |
4663afe2 ED |
340 | __u32 delta = (__u32)jiffies - p->dtime; |
341 | if (delta < ttl) { | |
1da177e4 LT |
342 | /* Do not prune fresh entries. */ |
343 | spin_unlock_bh(&inet_peer_unused_lock); | |
344 | return -1; | |
345 | } | |
346 | inet_peer_unused_head = p->unused_next; | |
347 | if (p->unused_next != NULL) | |
348 | p->unused_next->unused_prevp = p->unused_prevp; | |
349 | else | |
350 | inet_peer_unused_tailp = p->unused_prevp; | |
351 | p->unused_prevp = NULL; /* mark as not on the list */ | |
352 | /* Grab an extra reference to prevent node disappearing | |
353 | * before unlink_from_pool() call. */ | |
354 | atomic_inc(&p->refcnt); | |
355 | } | |
356 | spin_unlock_bh(&inet_peer_unused_lock); | |
357 | ||
358 | if (p == NULL) | |
359 | /* It means that the total number of USED entries has | |
360 | * grown over inet_peer_threshold. It shouldn't really | |
361 | * happen because of entry limits in route cache. */ | |
362 | return -1; | |
363 | ||
364 | unlink_from_pool(p); | |
365 | return 0; | |
366 | } | |
367 | ||
368 | /* Called with or without local BH being disabled. */ | |
53576d9b | 369 | struct inet_peer *inet_getpeer(__be32 daddr, int create) |
1da177e4 LT |
370 | { |
371 | struct inet_peer *p, *n; | |
372 | struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; | |
373 | ||
374 | /* Look up for the address quickly. */ | |
375 | read_lock_bh(&peer_pool_lock); | |
376 | p = lookup(daddr); | |
377 | if (p != peer_avl_empty) | |
378 | atomic_inc(&p->refcnt); | |
379 | read_unlock_bh(&peer_pool_lock); | |
380 | ||
381 | if (p != peer_avl_empty) { | |
382 | /* The existing node has been found. */ | |
383 | /* Remove the entry from unused list if it was there. */ | |
384 | unlink_from_unused(p); | |
385 | return p; | |
386 | } | |
387 | ||
388 | if (!create) | |
389 | return NULL; | |
390 | ||
391 | /* Allocate the space outside the locked region. */ | |
392 | n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); | |
393 | if (n == NULL) | |
394 | return NULL; | |
395 | n->v4daddr = daddr; | |
396 | atomic_set(&n->refcnt, 1); | |
89cee8b1 | 397 | atomic_set(&n->rid, 0); |
1da177e4 LT |
398 | n->ip_id_count = secure_ip_id(daddr); |
399 | n->tcp_ts_stamp = 0; | |
400 | ||
401 | write_lock_bh(&peer_pool_lock); | |
402 | /* Check if an entry has suddenly appeared. */ | |
403 | p = lookup(daddr); | |
404 | if (p != peer_avl_empty) | |
405 | goto out_free; | |
406 | ||
407 | /* Link the node. */ | |
408 | link_to_pool(n); | |
409 | n->unused_prevp = NULL; /* not on the list */ | |
410 | peer_total++; | |
411 | write_unlock_bh(&peer_pool_lock); | |
412 | ||
413 | if (peer_total >= inet_peer_threshold) | |
414 | /* Remove one less-recently-used entry. */ | |
415 | cleanup_once(0); | |
416 | ||
417 | return n; | |
418 | ||
419 | out_free: | |
420 | /* The appropriate node is already in the pool. */ | |
421 | atomic_inc(&p->refcnt); | |
422 | write_unlock_bh(&peer_pool_lock); | |
423 | /* Remove the entry from unused list if it was there. */ | |
424 | unlink_from_unused(p); | |
425 | /* Free preallocated the preallocated node. */ | |
426 | kmem_cache_free(peer_cachep, n); | |
427 | return p; | |
428 | } | |
429 | ||
430 | /* Called with local BH disabled. */ | |
431 | static void peer_check_expire(unsigned long dummy) | |
432 | { | |
4663afe2 | 433 | unsigned long now = jiffies; |
1da177e4 LT |
434 | int ttl; |
435 | ||
436 | if (peer_total >= inet_peer_threshold) | |
437 | ttl = inet_peer_minttl; | |
438 | else | |
439 | ttl = inet_peer_maxttl | |
440 | - (inet_peer_maxttl - inet_peer_minttl) / HZ * | |
441 | peer_total / inet_peer_threshold * HZ; | |
4663afe2 ED |
442 | while (!cleanup_once(ttl)) { |
443 | if (jiffies != now) | |
444 | break; | |
445 | } | |
1da177e4 LT |
446 | |
447 | /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime | |
448 | * interval depending on the total number of entries (more entries, | |
449 | * less interval). */ | |
1344a416 DJ |
450 | if (peer_total >= inet_peer_threshold) |
451 | peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime; | |
452 | else | |
453 | peer_periodic_timer.expires = jiffies | |
454 | + inet_peer_gc_maxtime | |
455 | - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * | |
456 | peer_total / inet_peer_threshold * HZ; | |
1da177e4 LT |
457 | add_timer(&peer_periodic_timer); |
458 | } | |
4663afe2 ED |
459 | |
460 | void inet_putpeer(struct inet_peer *p) | |
461 | { | |
462 | spin_lock_bh(&inet_peer_unused_lock); | |
463 | if (atomic_dec_and_test(&p->refcnt)) { | |
464 | p->unused_prevp = inet_peer_unused_tailp; | |
465 | p->unused_next = NULL; | |
466 | *inet_peer_unused_tailp = p; | |
467 | inet_peer_unused_tailp = &p->unused_next; | |
468 | p->dtime = (__u32)jiffies; | |
469 | } | |
470 | spin_unlock_bh(&inet_peer_unused_lock); | |
471 | } |