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 * 30 * Nodes are removed only when reference counter goes to 0. 31 * When it's happened the node may be removed when a sufficient amount of 32 * time has been passed since its last use. The less-recently-used entry can 33 * also be removed if the pool is overloaded i.e. if the total amount of 34 * entries is greater-or-equal than the threshold. 35 * 36 * Node pool is organised as an AVL tree. 37 * Such an implementation has been chosen not just for fun. It's a way to 38 * prevent easy and efficient DoS attacks by creating hash collisions. A huge 39 * amount of long living nodes in a single hash slot would significantly delay 40 * lookups performed with disabled BHs. 41 * 42 * Serialisation issues. 43 * 1. Nodes may appear in the tree only with the pool lock held. 44 * 2. Nodes may disappear from the tree only with the pool lock held 45 * AND reference count being 0. 46 * 3. Global variable peer_total is modified under the pool lock. 47 * 4. struct inet_peer fields modification: 48 * avl_left, avl_right, avl_parent, avl_height: pool lock 49 * refcnt: atomically against modifications on other CPU; 50 * usually under some other lock to prevent node disappearing 51 * daddr: unchangeable 52 */ 53 54 static struct kmem_cache *peer_cachep __read_mostly; 55 56 static LIST_HEAD(gc_list); 57 static const int gc_delay = 60 * HZ; 58 static struct delayed_work gc_work; 59 static DEFINE_SPINLOCK(gc_lock); 60 61 #define node_height(x) x->avl_height 62 63 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node) 64 #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node) 65 static const struct inet_peer peer_fake_node = { 66 .avl_left = peer_avl_empty_rcu, 67 .avl_right = peer_avl_empty_rcu, 68 .avl_height = 0 69 }; 70 71 void inet_peer_base_init(struct inet_peer_base *bp) 72 { 73 bp->root = peer_avl_empty_rcu; 74 seqlock_init(&bp->lock); 75 bp->total = 0; 76 } 77 EXPORT_SYMBOL_GPL(inet_peer_base_init); 78 79 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 80 81 /* Exported for sysctl_net_ipv4. */ 82 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more 83 * aggressively at this stage */ 84 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ 85 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ 86 87 static void inetpeer_gc_worker(struct work_struct *work) 88 { 89 struct inet_peer *p, *n, *c; 90 struct list_head list; 91 92 spin_lock_bh(&gc_lock); 93 list_replace_init(&gc_list, &list); 94 spin_unlock_bh(&gc_lock); 95 96 if (list_empty(&list)) 97 return; 98 99 list_for_each_entry_safe(p, n, &list, gc_list) { 100 101 if (need_resched()) 102 cond_resched(); 103 104 c = rcu_dereference_protected(p->avl_left, 1); 105 if (c != peer_avl_empty) { 106 list_add_tail(&c->gc_list, &list); 107 p->avl_left = peer_avl_empty_rcu; 108 } 109 110 c = rcu_dereference_protected(p->avl_right, 1); 111 if (c != peer_avl_empty) { 112 list_add_tail(&c->gc_list, &list); 113 p->avl_right = peer_avl_empty_rcu; 114 } 115 116 n = list_entry(p->gc_list.next, struct inet_peer, gc_list); 117 118 if (refcount_read(&p->refcnt) == 1) { 119 list_del(&p->gc_list); 120 kmem_cache_free(peer_cachep, p); 121 } 122 } 123 124 if (list_empty(&list)) 125 return; 126 127 spin_lock_bh(&gc_lock); 128 list_splice(&list, &gc_list); 129 spin_unlock_bh(&gc_lock); 130 131 schedule_delayed_work(&gc_work, gc_delay); 132 } 133 134 /* Called from ip_output.c:ip_init */ 135 void __init inet_initpeers(void) 136 { 137 struct sysinfo si; 138 139 /* Use the straight interface to information about memory. */ 140 si_meminfo(&si); 141 /* The values below were suggested by Alexey Kuznetsov 142 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 143 * myself. --SAW 144 */ 145 if (si.totalram <= (32768*1024)/PAGE_SIZE) 146 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 147 if (si.totalram <= (16384*1024)/PAGE_SIZE) 148 inet_peer_threshold >>= 1; /* about 512KB */ 149 if (si.totalram <= (8192*1024)/PAGE_SIZE) 150 inet_peer_threshold >>= 2; /* about 128KB */ 151 152 peer_cachep = kmem_cache_create("inet_peer_cache", 153 sizeof(struct inet_peer), 154 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, 155 NULL); 156 157 INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker); 158 } 159 160 #define rcu_deref_locked(X, BASE) \ 161 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock)) 162 163 /* 164 * Called with local BH disabled and the pool lock held. 165 */ 166 #define lookup(_daddr, _stack, _base) \ 167 ({ \ 168 struct inet_peer *u; \ 169 struct inet_peer __rcu **v; \ 170 \ 171 stackptr = _stack; \ 172 *stackptr++ = &_base->root; \ 173 for (u = rcu_deref_locked(_base->root, _base); \ 174 u != peer_avl_empty;) { \ 175 int cmp = inetpeer_addr_cmp(_daddr, &u->daddr); \ 176 if (cmp == 0) \ 177 break; \ 178 if (cmp == -1) \ 179 v = &u->avl_left; \ 180 else \ 181 v = &u->avl_right; \ 182 *stackptr++ = v; \ 183 u = rcu_deref_locked(*v, _base); \ 184 } \ 185 u; \ 186 }) 187 188 /* 189 * Called with rcu_read_lock() 190 * Because we hold no lock against a writer, its quite possible we fall 191 * in an endless loop. 192 * But every pointer we follow is guaranteed to be valid thanks to RCU. 193 * We exit from this function if number of links exceeds PEER_MAXDEPTH 194 */ 195 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr, 196 struct inet_peer_base *base) 197 { 198 struct inet_peer *u = rcu_dereference(base->root); 199 int count = 0; 200 201 while (u != peer_avl_empty) { 202 int cmp = inetpeer_addr_cmp(daddr, &u->daddr); 203 if (cmp == 0) { 204 /* Before taking a reference, check if this entry was 205 * deleted (refcnt=0) 206 */ 207 if (!refcount_inc_not_zero(&u->refcnt)) { 208 u = NULL; 209 } 210 return u; 211 } 212 if (cmp == -1) 213 u = rcu_dereference(u->avl_left); 214 else 215 u = rcu_dereference(u->avl_right); 216 if (unlikely(++count == PEER_MAXDEPTH)) 217 break; 218 } 219 return NULL; 220 } 221 222 /* Called with local BH disabled and the pool lock held. */ 223 #define lookup_rightempty(start, base) \ 224 ({ \ 225 struct inet_peer *u; \ 226 struct inet_peer __rcu **v; \ 227 *stackptr++ = &start->avl_left; \ 228 v = &start->avl_left; \ 229 for (u = rcu_deref_locked(*v, base); \ 230 u->avl_right != peer_avl_empty_rcu;) { \ 231 v = &u->avl_right; \ 232 *stackptr++ = v; \ 233 u = rcu_deref_locked(*v, base); \ 234 } \ 235 u; \ 236 }) 237 238 /* Called with local BH disabled and the pool lock held. 239 * Variable names are the proof of operation correctness. 240 * Look into mm/map_avl.c for more detail description of the ideas. 241 */ 242 static void peer_avl_rebalance(struct inet_peer __rcu **stack[], 243 struct inet_peer __rcu ***stackend, 244 struct inet_peer_base *base) 245 { 246 struct inet_peer __rcu **nodep; 247 struct inet_peer *node, *l, *r; 248 int lh, rh; 249 250 while (stackend > stack) { 251 nodep = *--stackend; 252 node = rcu_deref_locked(*nodep, base); 253 l = rcu_deref_locked(node->avl_left, base); 254 r = rcu_deref_locked(node->avl_right, base); 255 lh = node_height(l); 256 rh = node_height(r); 257 if (lh > rh + 1) { /* l: RH+2 */ 258 struct inet_peer *ll, *lr, *lrl, *lrr; 259 int lrh; 260 ll = rcu_deref_locked(l->avl_left, base); 261 lr = rcu_deref_locked(l->avl_right, base); 262 lrh = node_height(lr); 263 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 264 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ 265 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 266 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 267 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ 268 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ 269 l->avl_height = node->avl_height + 1; 270 RCU_INIT_POINTER(*nodep, l); 271 } else { /* ll: RH, lr: RH+1 */ 272 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */ 273 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */ 274 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ 275 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 276 node->avl_height = rh + 1; /* node: RH+1 */ 277 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ 278 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ 279 l->avl_height = rh + 1; /* l: RH+1 */ 280 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ 281 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ 282 lr->avl_height = rh + 2; 283 RCU_INIT_POINTER(*nodep, lr); 284 } 285 } else if (rh > lh + 1) { /* r: LH+2 */ 286 struct inet_peer *rr, *rl, *rlr, *rll; 287 int rlh; 288 rr = rcu_deref_locked(r->avl_right, base); 289 rl = rcu_deref_locked(r->avl_left, base); 290 rlh = node_height(rl); 291 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 292 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ 293 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 294 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 295 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ 296 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ 297 r->avl_height = node->avl_height + 1; 298 RCU_INIT_POINTER(*nodep, r); 299 } else { /* rr: RH, rl: RH+1 */ 300 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */ 301 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */ 302 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ 303 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 304 node->avl_height = lh + 1; /* node: LH+1 */ 305 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ 306 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ 307 r->avl_height = lh + 1; /* r: LH+1 */ 308 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ 309 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ 310 rl->avl_height = lh + 2; 311 RCU_INIT_POINTER(*nodep, rl); 312 } 313 } else { 314 node->avl_height = (lh > rh ? lh : rh) + 1; 315 } 316 } 317 } 318 319 /* Called with local BH disabled and the pool lock held. */ 320 #define link_to_pool(n, base) \ 321 do { \ 322 n->avl_height = 1; \ 323 n->avl_left = peer_avl_empty_rcu; \ 324 n->avl_right = peer_avl_empty_rcu; \ 325 /* lockless readers can catch us now */ \ 326 rcu_assign_pointer(**--stackptr, n); \ 327 peer_avl_rebalance(stack, stackptr, base); \ 328 } while (0) 329 330 static void inetpeer_free_rcu(struct rcu_head *head) 331 { 332 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); 333 } 334 335 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base, 336 struct inet_peer __rcu **stack[PEER_MAXDEPTH]) 337 { 338 struct inet_peer __rcu ***stackptr, ***delp; 339 340 if (lookup(&p->daddr, stack, base) != p) 341 BUG(); 342 delp = stackptr - 1; /* *delp[0] == p */ 343 if (p->avl_left == peer_avl_empty_rcu) { 344 *delp[0] = p->avl_right; 345 --stackptr; 346 } else { 347 /* look for a node to insert instead of p */ 348 struct inet_peer *t; 349 t = lookup_rightempty(p, base); 350 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t); 351 **--stackptr = t->avl_left; 352 /* t is removed, t->daddr > x->daddr for any 353 * x in p->avl_left subtree. 354 * Put t in the old place of p. */ 355 RCU_INIT_POINTER(*delp[0], t); 356 t->avl_left = p->avl_left; 357 t->avl_right = p->avl_right; 358 t->avl_height = p->avl_height; 359 BUG_ON(delp[1] != &p->avl_left); 360 delp[1] = &t->avl_left; /* was &p->avl_left */ 361 } 362 peer_avl_rebalance(stack, stackptr, base); 363 base->total--; 364 call_rcu(&p->rcu, inetpeer_free_rcu); 365 } 366 367 /* perform garbage collect on all items stacked during a lookup */ 368 static int inet_peer_gc(struct inet_peer_base *base, 369 struct inet_peer __rcu **stack[PEER_MAXDEPTH], 370 struct inet_peer __rcu ***stackptr) 371 { 372 struct inet_peer *p, *gchead = NULL; 373 __u32 delta, ttl; 374 int cnt = 0; 375 376 if (base->total >= inet_peer_threshold) 377 ttl = 0; /* be aggressive */ 378 else 379 ttl = inet_peer_maxttl 380 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 381 base->total / inet_peer_threshold * HZ; 382 stackptr--; /* last stack slot is peer_avl_empty */ 383 while (stackptr > stack) { 384 stackptr--; 385 p = rcu_deref_locked(**stackptr, base); 386 if (refcount_read(&p->refcnt) == 1) { 387 smp_rmb(); 388 delta = (__u32)jiffies - p->dtime; 389 if (delta >= ttl && refcount_dec_if_one(&p->refcnt)) { 390 p->gc_next = gchead; 391 gchead = p; 392 } 393 } 394 } 395 while ((p = gchead) != NULL) { 396 gchead = p->gc_next; 397 cnt++; 398 unlink_from_pool(p, base, stack); 399 } 400 return cnt; 401 } 402 403 struct inet_peer *inet_getpeer(struct inet_peer_base *base, 404 const struct inetpeer_addr *daddr, 405 int create) 406 { 407 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; 408 struct inet_peer *p; 409 unsigned int sequence; 410 int invalidated, gccnt = 0; 411 412 /* Attempt a lockless lookup first. 413 * Because of a concurrent writer, we might not find an existing entry. 414 */ 415 rcu_read_lock(); 416 sequence = read_seqbegin(&base->lock); 417 p = lookup_rcu(daddr, base); 418 invalidated = read_seqretry(&base->lock, sequence); 419 rcu_read_unlock(); 420 421 if (p) 422 return p; 423 424 /* If no writer did a change during our lookup, we can return early. */ 425 if (!create && !invalidated) 426 return NULL; 427 428 /* retry an exact lookup, taking the lock before. 429 * At least, nodes should be hot in our cache. 430 */ 431 write_seqlock_bh(&base->lock); 432 relookup: 433 p = lookup(daddr, stack, base); 434 if (p != peer_avl_empty) { 435 refcount_inc(&p->refcnt); 436 write_sequnlock_bh(&base->lock); 437 return p; 438 } 439 if (!gccnt) { 440 gccnt = inet_peer_gc(base, stack, stackptr); 441 if (gccnt && create) 442 goto relookup; 443 } 444 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; 445 if (p) { 446 p->daddr = *daddr; 447 refcount_set(&p->refcnt, 2); 448 atomic_set(&p->rid, 0); 449 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; 450 p->rate_tokens = 0; 451 /* 60*HZ is arbitrary, but chosen enough high so that the first 452 * calculation of tokens is at its maximum. 453 */ 454 p->rate_last = jiffies - 60*HZ; 455 INIT_LIST_HEAD(&p->gc_list); 456 457 /* Link the node. */ 458 link_to_pool(p, base); 459 base->total++; 460 } 461 write_sequnlock_bh(&base->lock); 462 463 return p; 464 } 465 EXPORT_SYMBOL_GPL(inet_getpeer); 466 467 void inet_putpeer(struct inet_peer *p) 468 { 469 p->dtime = (__u32)jiffies; 470 smp_mb__before_atomic(); 471 refcount_dec(&p->refcnt); 472 } 473 EXPORT_SYMBOL_GPL(inet_putpeer); 474 475 /* 476 * Check transmit rate limitation for given message. 477 * The rate information is held in the inet_peer entries now. 478 * This function is generic and could be used for other purposes 479 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. 480 * 481 * Note that the same inet_peer fields are modified by functions in 482 * route.c too, but these work for packet destinations while xrlim_allow 483 * works for icmp destinations. This means the rate limiting information 484 * for one "ip object" is shared - and these ICMPs are twice limited: 485 * by source and by destination. 486 * 487 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate 488 * SHOULD allow setting of rate limits 489 * 490 * Shared between ICMPv4 and ICMPv6. 491 */ 492 #define XRLIM_BURST_FACTOR 6 493 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 494 { 495 unsigned long now, token; 496 bool rc = false; 497 498 if (!peer) 499 return true; 500 501 token = peer->rate_tokens; 502 now = jiffies; 503 token += now - peer->rate_last; 504 peer->rate_last = now; 505 if (token > XRLIM_BURST_FACTOR * timeout) 506 token = XRLIM_BURST_FACTOR * timeout; 507 if (token >= timeout) { 508 token -= timeout; 509 rc = true; 510 } 511 peer->rate_tokens = token; 512 return rc; 513 } 514 EXPORT_SYMBOL(inet_peer_xrlim_allow); 515 516 static void inetpeer_inval_rcu(struct rcu_head *head) 517 { 518 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu); 519 520 spin_lock_bh(&gc_lock); 521 list_add_tail(&p->gc_list, &gc_list); 522 spin_unlock_bh(&gc_lock); 523 524 schedule_delayed_work(&gc_work, gc_delay); 525 } 526 527 void inetpeer_invalidate_tree(struct inet_peer_base *base) 528 { 529 struct inet_peer *root; 530 531 write_seqlock_bh(&base->lock); 532 533 root = rcu_deref_locked(base->root, base); 534 if (root != peer_avl_empty) { 535 base->root = peer_avl_empty_rcu; 536 base->total = 0; 537 call_rcu(&root->gc_rcu, inetpeer_inval_rcu); 538 } 539 540 write_sequnlock_bh(&base->lock); 541 } 542 EXPORT_SYMBOL(inetpeer_invalidate_tree); 543