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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> | |
17 | #include <linux/sched.h> | |
18 | #include <linux/timer.h> | |
19 | #include <linux/time.h> | |
20 | #include <linux/kernel.h> | |
21 | #include <linux/mm.h> | |
22 | #include <linux/net.h> | |
20380731 | 23 | #include <net/ip.h> |
1da177e4 LT |
24 | #include <net/inetpeer.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 | * At this moment this information consists only of ID field for the next | |
31 | * outgoing IP packet. This field is incremented with each packet as encoded | |
32 | * in inet_getid() function (include/net/inetpeer.h). | |
33 | * At the moment of writing this notes identifier of IP packets is generated | |
34 | * to be unpredictable using this code only for packets subjected | |
35 | * (actually or potentially) to defragmentation. I.e. DF packets less than | |
36 | * PMTU in size uses a constant ID and do not use this code (see | |
37 | * ip_select_ident() in include/net/ip.h). | |
38 | * | |
39 | * Route cache entries hold references to our nodes. | |
40 | * New cache entries get references via lookup by destination IP address in | |
41 | * the avl tree. The reference is grabbed only when it's needed i.e. only | |
42 | * when we try to output IP packet which needs an unpredictable ID (see | |
43 | * __ip_select_ident() in net/ipv4/route.c). | |
44 | * Nodes are removed only when reference counter goes to 0. | |
45 | * When it's happened the node may be removed when a sufficient amount of | |
46 | * time has been passed since its last use. The less-recently-used entry can | |
47 | * also be removed if the pool is overloaded i.e. if the total amount of | |
48 | * entries is greater-or-equal than the threshold. | |
49 | * | |
50 | * Node pool is organised as an AVL tree. | |
51 | * Such an implementation has been chosen not just for fun. It's a way to | |
52 | * prevent easy and efficient DoS attacks by creating hash collisions. A huge | |
53 | * amount of long living nodes in a single hash slot would significantly delay | |
54 | * lookups performed with disabled BHs. | |
55 | * | |
56 | * Serialisation issues. | |
57 | * 1. Nodes may appear in the tree only with the pool write lock held. | |
58 | * 2. Nodes may disappear from the tree only with the pool write lock held | |
59 | * AND reference count being 0. | |
60 | * 3. Nodes appears and disappears from unused node list only under | |
61 | * "inet_peer_unused_lock". | |
62 | * 4. Global variable peer_total is modified under the pool lock. | |
63 | * 5. struct inet_peer fields modification: | |
64 | * avl_left, avl_right, avl_parent, avl_height: pool lock | |
65 | * unused_next, unused_prevp: unused node list lock | |
66 | * refcnt: atomically against modifications on other CPU; | |
67 | * usually under some other lock to prevent node disappearing | |
68 | * dtime: unused node list lock | |
69 | * v4daddr: unchangeable | |
70 | * ip_id_count: idlock | |
71 | */ | |
72 | ||
73 | /* Exported for inet_getid inline function. */ | |
74 | DEFINE_SPINLOCK(inet_peer_idlock); | |
75 | ||
ba89966c | 76 | static kmem_cache_t *peer_cachep __read_mostly; |
1da177e4 LT |
77 | |
78 | #define node_height(x) x->avl_height | |
79 | static struct inet_peer peer_fake_node = { | |
80 | .avl_left = &peer_fake_node, | |
81 | .avl_right = &peer_fake_node, | |
82 | .avl_height = 0 | |
83 | }; | |
84 | #define peer_avl_empty (&peer_fake_node) | |
85 | static struct inet_peer *peer_root = peer_avl_empty; | |
86 | static DEFINE_RWLOCK(peer_pool_lock); | |
87 | #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ | |
88 | ||
89 | static volatile int peer_total; | |
90 | /* Exported for sysctl_net_ipv4. */ | |
91 | int inet_peer_threshold = 65536 + 128; /* start to throw entries more | |
92 | * aggressively at this stage */ | |
93 | int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */ | |
94 | int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */ | |
95 | ||
96 | static struct inet_peer *inet_peer_unused_head; | |
97 | /* Exported for inet_putpeer inline function. */ | |
98 | struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head; | |
99 | DEFINE_SPINLOCK(inet_peer_unused_lock); | |
100 | #define PEER_MAX_CLEANUP_WORK 30 | |
101 | ||
102 | static void peer_check_expire(unsigned long dummy); | |
8d06afab | 103 | static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0); |
1da177e4 LT |
104 | |
105 | /* Exported for sysctl_net_ipv4. */ | |
106 | int inet_peer_gc_mintime = 10 * HZ, | |
107 | inet_peer_gc_maxtime = 120 * HZ; | |
108 | ||
109 | /* Called from ip_output.c:ip_init */ | |
110 | void __init inet_initpeers(void) | |
111 | { | |
112 | struct sysinfo si; | |
113 | ||
114 | /* Use the straight interface to information about memory. */ | |
115 | si_meminfo(&si); | |
116 | /* The values below were suggested by Alexey Kuznetsov | |
117 | * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values | |
118 | * myself. --SAW | |
119 | */ | |
120 | if (si.totalram <= (32768*1024)/PAGE_SIZE) | |
121 | inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ | |
122 | if (si.totalram <= (16384*1024)/PAGE_SIZE) | |
123 | inet_peer_threshold >>= 1; /* about 512KB */ | |
124 | if (si.totalram <= (8192*1024)/PAGE_SIZE) | |
125 | inet_peer_threshold >>= 2; /* about 128KB */ | |
126 | ||
127 | peer_cachep = kmem_cache_create("inet_peer_cache", | |
128 | sizeof(struct inet_peer), | |
129 | 0, SLAB_HWCACHE_ALIGN, | |
130 | NULL, NULL); | |
131 | ||
132 | if (!peer_cachep) | |
133 | panic("cannot create inet_peer_cache"); | |
134 | ||
135 | /* All the timers, started at system startup tend | |
136 | to synchronize. Perturb it a bit. | |
137 | */ | |
138 | peer_periodic_timer.expires = jiffies | |
139 | + net_random() % inet_peer_gc_maxtime | |
140 | + inet_peer_gc_maxtime; | |
141 | add_timer(&peer_periodic_timer); | |
142 | } | |
143 | ||
144 | /* Called with or without local BH being disabled. */ | |
145 | static void unlink_from_unused(struct inet_peer *p) | |
146 | { | |
147 | spin_lock_bh(&inet_peer_unused_lock); | |
148 | if (p->unused_prevp != NULL) { | |
149 | /* On unused list. */ | |
150 | *p->unused_prevp = p->unused_next; | |
151 | if (p->unused_next != NULL) | |
152 | p->unused_next->unused_prevp = p->unused_prevp; | |
153 | else | |
154 | inet_peer_unused_tailp = p->unused_prevp; | |
155 | p->unused_prevp = NULL; /* mark it as removed */ | |
156 | } | |
157 | spin_unlock_bh(&inet_peer_unused_lock); | |
158 | } | |
159 | ||
160 | /* Called with local BH disabled and the pool lock held. */ | |
161 | #define lookup(daddr) \ | |
162 | ({ \ | |
163 | struct inet_peer *u, **v; \ | |
164 | stackptr = stack; \ | |
165 | *stackptr++ = &peer_root; \ | |
166 | for (u = peer_root; u != peer_avl_empty; ) { \ | |
167 | if (daddr == u->v4daddr) \ | |
168 | break; \ | |
169 | if (daddr < u->v4daddr) \ | |
170 | v = &u->avl_left; \ | |
171 | else \ | |
172 | v = &u->avl_right; \ | |
173 | *stackptr++ = v; \ | |
174 | u = *v; \ | |
175 | } \ | |
176 | u; \ | |
177 | }) | |
178 | ||
179 | /* Called with local BH disabled and the pool write lock held. */ | |
180 | #define lookup_rightempty(start) \ | |
181 | ({ \ | |
182 | struct inet_peer *u, **v; \ | |
183 | *stackptr++ = &start->avl_left; \ | |
184 | v = &start->avl_left; \ | |
185 | for (u = *v; u->avl_right != peer_avl_empty; ) { \ | |
186 | v = &u->avl_right; \ | |
187 | *stackptr++ = v; \ | |
188 | u = *v; \ | |
189 | } \ | |
190 | u; \ | |
191 | }) | |
192 | ||
193 | /* Called with local BH disabled and the pool write lock held. | |
194 | * Variable names are the proof of operation correctness. | |
195 | * Look into mm/map_avl.c for more detail description of the ideas. */ | |
196 | static void peer_avl_rebalance(struct inet_peer **stack[], | |
197 | struct inet_peer ***stackend) | |
198 | { | |
199 | struct inet_peer **nodep, *node, *l, *r; | |
200 | int lh, rh; | |
201 | ||
202 | while (stackend > stack) { | |
203 | nodep = *--stackend; | |
204 | node = *nodep; | |
205 | l = node->avl_left; | |
206 | r = node->avl_right; | |
207 | lh = node_height(l); | |
208 | rh = node_height(r); | |
209 | if (lh > rh + 1) { /* l: RH+2 */ | |
210 | struct inet_peer *ll, *lr, *lrl, *lrr; | |
211 | int lrh; | |
212 | ll = l->avl_left; | |
213 | lr = l->avl_right; | |
214 | lrh = node_height(lr); | |
215 | if (lrh <= node_height(ll)) { /* ll: RH+1 */ | |
216 | node->avl_left = lr; /* lr: RH or RH+1 */ | |
217 | node->avl_right = r; /* r: RH */ | |
218 | node->avl_height = lrh + 1; /* RH+1 or RH+2 */ | |
219 | l->avl_left = ll; /* ll: RH+1 */ | |
220 | l->avl_right = node; /* node: RH+1 or RH+2 */ | |
221 | l->avl_height = node->avl_height + 1; | |
222 | *nodep = l; | |
223 | } else { /* ll: RH, lr: RH+1 */ | |
224 | lrl = lr->avl_left; /* lrl: RH or RH-1 */ | |
225 | lrr = lr->avl_right; /* lrr: RH or RH-1 */ | |
226 | node->avl_left = lrr; /* lrr: RH or RH-1 */ | |
227 | node->avl_right = r; /* r: RH */ | |
228 | node->avl_height = rh + 1; /* node: RH+1 */ | |
229 | l->avl_left = ll; /* ll: RH */ | |
230 | l->avl_right = lrl; /* lrl: RH or RH-1 */ | |
231 | l->avl_height = rh + 1; /* l: RH+1 */ | |
232 | lr->avl_left = l; /* l: RH+1 */ | |
233 | lr->avl_right = node; /* node: RH+1 */ | |
234 | lr->avl_height = rh + 2; | |
235 | *nodep = lr; | |
236 | } | |
237 | } else if (rh > lh + 1) { /* r: LH+2 */ | |
238 | struct inet_peer *rr, *rl, *rlr, *rll; | |
239 | int rlh; | |
240 | rr = r->avl_right; | |
241 | rl = r->avl_left; | |
242 | rlh = node_height(rl); | |
243 | if (rlh <= node_height(rr)) { /* rr: LH+1 */ | |
244 | node->avl_right = rl; /* rl: LH or LH+1 */ | |
245 | node->avl_left = l; /* l: LH */ | |
246 | node->avl_height = rlh + 1; /* LH+1 or LH+2 */ | |
247 | r->avl_right = rr; /* rr: LH+1 */ | |
248 | r->avl_left = node; /* node: LH+1 or LH+2 */ | |
249 | r->avl_height = node->avl_height + 1; | |
250 | *nodep = r; | |
251 | } else { /* rr: RH, rl: RH+1 */ | |
252 | rlr = rl->avl_right; /* rlr: LH or LH-1 */ | |
253 | rll = rl->avl_left; /* rll: LH or LH-1 */ | |
254 | node->avl_right = rll; /* rll: LH or LH-1 */ | |
255 | node->avl_left = l; /* l: LH */ | |
256 | node->avl_height = lh + 1; /* node: LH+1 */ | |
257 | r->avl_right = rr; /* rr: LH */ | |
258 | r->avl_left = rlr; /* rlr: LH or LH-1 */ | |
259 | r->avl_height = lh + 1; /* r: LH+1 */ | |
260 | rl->avl_right = r; /* r: LH+1 */ | |
261 | rl->avl_left = node; /* node: LH+1 */ | |
262 | rl->avl_height = lh + 2; | |
263 | *nodep = rl; | |
264 | } | |
265 | } else { | |
266 | node->avl_height = (lh > rh ? lh : rh) + 1; | |
267 | } | |
268 | } | |
269 | } | |
270 | ||
271 | /* Called with local BH disabled and the pool write lock held. */ | |
272 | #define link_to_pool(n) \ | |
273 | do { \ | |
274 | n->avl_height = 1; \ | |
275 | n->avl_left = peer_avl_empty; \ | |
276 | n->avl_right = peer_avl_empty; \ | |
277 | **--stackptr = n; \ | |
278 | peer_avl_rebalance(stack, stackptr); \ | |
279 | } while(0) | |
280 | ||
281 | /* May be called with local BH enabled. */ | |
282 | static void unlink_from_pool(struct inet_peer *p) | |
283 | { | |
284 | int do_free; | |
285 | ||
286 | do_free = 0; | |
287 | ||
288 | write_lock_bh(&peer_pool_lock); | |
289 | /* Check the reference counter. It was artificially incremented by 1 | |
290 | * in cleanup() function to prevent sudden disappearing. If the | |
291 | * reference count is still 1 then the node is referenced only as `p' | |
292 | * here and from the pool. So under the exclusive pool lock it's safe | |
293 | * to remove the node and free it later. */ | |
294 | if (atomic_read(&p->refcnt) == 1) { | |
295 | struct inet_peer **stack[PEER_MAXDEPTH]; | |
296 | struct inet_peer ***stackptr, ***delp; | |
297 | if (lookup(p->v4daddr) != p) | |
298 | BUG(); | |
299 | delp = stackptr - 1; /* *delp[0] == p */ | |
300 | if (p->avl_left == peer_avl_empty) { | |
301 | *delp[0] = p->avl_right; | |
302 | --stackptr; | |
303 | } else { | |
304 | /* look for a node to insert instead of p */ | |
305 | struct inet_peer *t; | |
306 | t = lookup_rightempty(p); | |
307 | if (*stackptr[-1] != t) | |
308 | BUG(); | |
309 | **--stackptr = t->avl_left; | |
310 | /* t is removed, t->v4daddr > x->v4daddr for any | |
311 | * x in p->avl_left subtree. | |
312 | * Put t in the old place of p. */ | |
313 | *delp[0] = t; | |
314 | t->avl_left = p->avl_left; | |
315 | t->avl_right = p->avl_right; | |
316 | t->avl_height = p->avl_height; | |
317 | if (delp[1] != &p->avl_left) | |
318 | BUG(); | |
319 | delp[1] = &t->avl_left; /* was &p->avl_left */ | |
320 | } | |
321 | peer_avl_rebalance(stack, stackptr); | |
322 | peer_total--; | |
323 | do_free = 1; | |
324 | } | |
325 | write_unlock_bh(&peer_pool_lock); | |
326 | ||
327 | if (do_free) | |
328 | kmem_cache_free(peer_cachep, p); | |
329 | else | |
330 | /* The node is used again. Decrease the reference counter | |
331 | * back. The loop "cleanup -> unlink_from_unused | |
332 | * -> unlink_from_pool -> putpeer -> link_to_unused | |
333 | * -> cleanup (for the same node)" | |
334 | * doesn't really exist because the entry will have a | |
335 | * recent deletion time and will not be cleaned again soon. */ | |
336 | inet_putpeer(p); | |
337 | } | |
338 | ||
339 | /* May be called with local BH enabled. */ | |
340 | static int cleanup_once(unsigned long ttl) | |
341 | { | |
342 | struct inet_peer *p; | |
343 | ||
344 | /* Remove the first entry from the list of unused nodes. */ | |
345 | spin_lock_bh(&inet_peer_unused_lock); | |
346 | p = inet_peer_unused_head; | |
347 | if (p != NULL) { | |
348 | if (time_after(p->dtime + ttl, jiffies)) { | |
349 | /* Do not prune fresh entries. */ | |
350 | spin_unlock_bh(&inet_peer_unused_lock); | |
351 | return -1; | |
352 | } | |
353 | inet_peer_unused_head = p->unused_next; | |
354 | if (p->unused_next != NULL) | |
355 | p->unused_next->unused_prevp = p->unused_prevp; | |
356 | else | |
357 | inet_peer_unused_tailp = p->unused_prevp; | |
358 | p->unused_prevp = NULL; /* mark as not on the list */ | |
359 | /* Grab an extra reference to prevent node disappearing | |
360 | * before unlink_from_pool() call. */ | |
361 | atomic_inc(&p->refcnt); | |
362 | } | |
363 | spin_unlock_bh(&inet_peer_unused_lock); | |
364 | ||
365 | if (p == NULL) | |
366 | /* It means that the total number of USED entries has | |
367 | * grown over inet_peer_threshold. It shouldn't really | |
368 | * happen because of entry limits in route cache. */ | |
369 | return -1; | |
370 | ||
371 | unlink_from_pool(p); | |
372 | return 0; | |
373 | } | |
374 | ||
375 | /* Called with or without local BH being disabled. */ | |
376 | struct inet_peer *inet_getpeer(__u32 daddr, int create) | |
377 | { | |
378 | struct inet_peer *p, *n; | |
379 | struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; | |
380 | ||
381 | /* Look up for the address quickly. */ | |
382 | read_lock_bh(&peer_pool_lock); | |
383 | p = lookup(daddr); | |
384 | if (p != peer_avl_empty) | |
385 | atomic_inc(&p->refcnt); | |
386 | read_unlock_bh(&peer_pool_lock); | |
387 | ||
388 | if (p != peer_avl_empty) { | |
389 | /* The existing node has been found. */ | |
390 | /* Remove the entry from unused list if it was there. */ | |
391 | unlink_from_unused(p); | |
392 | return p; | |
393 | } | |
394 | ||
395 | if (!create) | |
396 | return NULL; | |
397 | ||
398 | /* Allocate the space outside the locked region. */ | |
399 | n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); | |
400 | if (n == NULL) | |
401 | return NULL; | |
402 | n->v4daddr = daddr; | |
403 | atomic_set(&n->refcnt, 1); | |
404 | n->ip_id_count = secure_ip_id(daddr); | |
405 | n->tcp_ts_stamp = 0; | |
406 | ||
407 | write_lock_bh(&peer_pool_lock); | |
408 | /* Check if an entry has suddenly appeared. */ | |
409 | p = lookup(daddr); | |
410 | if (p != peer_avl_empty) | |
411 | goto out_free; | |
412 | ||
413 | /* Link the node. */ | |
414 | link_to_pool(n); | |
415 | n->unused_prevp = NULL; /* not on the list */ | |
416 | peer_total++; | |
417 | write_unlock_bh(&peer_pool_lock); | |
418 | ||
419 | if (peer_total >= inet_peer_threshold) | |
420 | /* Remove one less-recently-used entry. */ | |
421 | cleanup_once(0); | |
422 | ||
423 | return n; | |
424 | ||
425 | out_free: | |
426 | /* The appropriate node is already in the pool. */ | |
427 | atomic_inc(&p->refcnt); | |
428 | write_unlock_bh(&peer_pool_lock); | |
429 | /* Remove the entry from unused list if it was there. */ | |
430 | unlink_from_unused(p); | |
431 | /* Free preallocated the preallocated node. */ | |
432 | kmem_cache_free(peer_cachep, n); | |
433 | return p; | |
434 | } | |
435 | ||
436 | /* Called with local BH disabled. */ | |
437 | static void peer_check_expire(unsigned long dummy) | |
438 | { | |
439 | int i; | |
440 | int ttl; | |
441 | ||
442 | if (peer_total >= inet_peer_threshold) | |
443 | ttl = inet_peer_minttl; | |
444 | else | |
445 | ttl = inet_peer_maxttl | |
446 | - (inet_peer_maxttl - inet_peer_minttl) / HZ * | |
447 | peer_total / inet_peer_threshold * HZ; | |
448 | for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++); | |
449 | ||
450 | /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime | |
451 | * interval depending on the total number of entries (more entries, | |
452 | * less interval). */ | |
1344a416 DJ |
453 | if (peer_total >= inet_peer_threshold) |
454 | peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime; | |
455 | else | |
456 | peer_periodic_timer.expires = jiffies | |
457 | + inet_peer_gc_maxtime | |
458 | - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * | |
459 | peer_total / inet_peer_threshold * HZ; | |
1da177e4 LT |
460 | add_timer(&peer_periodic_timer); |
461 | } |