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