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->flush_seq = ~0U; 76 bp->total = 0; 77 } 78 EXPORT_SYMBOL_GPL(inet_peer_base_init); 79 80 static atomic_t v4_seq = ATOMIC_INIT(0); 81 static atomic_t v6_seq = ATOMIC_INIT(0); 82 83 static atomic_t *inetpeer_seq_ptr(int family) 84 { 85 return (family == AF_INET ? &v4_seq : &v6_seq); 86 } 87 88 static inline void flush_check(struct inet_peer_base *base, int family) 89 { 90 atomic_t *fp = inetpeer_seq_ptr(family); 91 92 if (unlikely(base->flush_seq != atomic_read(fp))) { 93 inetpeer_invalidate_tree(base); 94 base->flush_seq = atomic_read(fp); 95 } 96 } 97 98 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 99 100 /* Exported for sysctl_net_ipv4. */ 101 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more 102 * aggressively at this stage */ 103 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ 104 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ 105 106 static void inetpeer_gc_worker(struct work_struct *work) 107 { 108 struct inet_peer *p, *n, *c; 109 struct list_head list; 110 111 spin_lock_bh(&gc_lock); 112 list_replace_init(&gc_list, &list); 113 spin_unlock_bh(&gc_lock); 114 115 if (list_empty(&list)) 116 return; 117 118 list_for_each_entry_safe(p, n, &list, gc_list) { 119 120 if (need_resched()) 121 cond_resched(); 122 123 c = rcu_dereference_protected(p->avl_left, 1); 124 if (c != peer_avl_empty) { 125 list_add_tail(&c->gc_list, &list); 126 p->avl_left = peer_avl_empty_rcu; 127 } 128 129 c = rcu_dereference_protected(p->avl_right, 1); 130 if (c != peer_avl_empty) { 131 list_add_tail(&c->gc_list, &list); 132 p->avl_right = peer_avl_empty_rcu; 133 } 134 135 n = list_entry(p->gc_list.next, struct inet_peer, gc_list); 136 137 if (!atomic_read(&p->refcnt)) { 138 list_del(&p->gc_list); 139 kmem_cache_free(peer_cachep, p); 140 } 141 } 142 143 if (list_empty(&list)) 144 return; 145 146 spin_lock_bh(&gc_lock); 147 list_splice(&list, &gc_list); 148 spin_unlock_bh(&gc_lock); 149 150 schedule_delayed_work(&gc_work, gc_delay); 151 } 152 153 /* Called from ip_output.c:ip_init */ 154 void __init inet_initpeers(void) 155 { 156 struct sysinfo si; 157 158 /* Use the straight interface to information about memory. */ 159 si_meminfo(&si); 160 /* The values below were suggested by Alexey Kuznetsov 161 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 162 * myself. --SAW 163 */ 164 if (si.totalram <= (32768*1024)/PAGE_SIZE) 165 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 166 if (si.totalram <= (16384*1024)/PAGE_SIZE) 167 inet_peer_threshold >>= 1; /* about 512KB */ 168 if (si.totalram <= (8192*1024)/PAGE_SIZE) 169 inet_peer_threshold >>= 2; /* about 128KB */ 170 171 peer_cachep = kmem_cache_create("inet_peer_cache", 172 sizeof(struct inet_peer), 173 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, 174 NULL); 175 176 INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker); 177 } 178 179 static int addr_compare(const struct inetpeer_addr *a, 180 const struct inetpeer_addr *b) 181 { 182 int i, n = (a->family == AF_INET ? 1 : 4); 183 184 for (i = 0; i < n; i++) { 185 if (a->addr.a6[i] == b->addr.a6[i]) 186 continue; 187 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i]) 188 return -1; 189 return 1; 190 } 191 192 return 0; 193 } 194 195 #define rcu_deref_locked(X, BASE) \ 196 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock)) 197 198 /* 199 * Called with local BH disabled and the pool lock held. 200 */ 201 #define lookup(_daddr, _stack, _base) \ 202 ({ \ 203 struct inet_peer *u; \ 204 struct inet_peer __rcu **v; \ 205 \ 206 stackptr = _stack; \ 207 *stackptr++ = &_base->root; \ 208 for (u = rcu_deref_locked(_base->root, _base); \ 209 u != peer_avl_empty;) { \ 210 int cmp = addr_compare(_daddr, &u->daddr); \ 211 if (cmp == 0) \ 212 break; \ 213 if (cmp == -1) \ 214 v = &u->avl_left; \ 215 else \ 216 v = &u->avl_right; \ 217 *stackptr++ = v; \ 218 u = rcu_deref_locked(*v, _base); \ 219 } \ 220 u; \ 221 }) 222 223 /* 224 * Called with rcu_read_lock() 225 * Because we hold no lock against a writer, its quite possible we fall 226 * in an endless loop. 227 * But every pointer we follow is guaranteed to be valid thanks to RCU. 228 * We exit from this function if number of links exceeds PEER_MAXDEPTH 229 */ 230 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr, 231 struct inet_peer_base *base) 232 { 233 struct inet_peer *u = rcu_dereference(base->root); 234 int count = 0; 235 236 while (u != peer_avl_empty) { 237 int cmp = addr_compare(daddr, &u->daddr); 238 if (cmp == 0) { 239 /* Before taking a reference, check if this entry was 240 * deleted (refcnt=-1) 241 */ 242 if (!atomic_add_unless(&u->refcnt, 1, -1)) 243 u = NULL; 244 return u; 245 } 246 if (cmp == -1) 247 u = rcu_dereference(u->avl_left); 248 else 249 u = rcu_dereference(u->avl_right); 250 if (unlikely(++count == PEER_MAXDEPTH)) 251 break; 252 } 253 return NULL; 254 } 255 256 /* Called with local BH disabled and the pool lock held. */ 257 #define lookup_rightempty(start, base) \ 258 ({ \ 259 struct inet_peer *u; \ 260 struct inet_peer __rcu **v; \ 261 *stackptr++ = &start->avl_left; \ 262 v = &start->avl_left; \ 263 for (u = rcu_deref_locked(*v, base); \ 264 u->avl_right != peer_avl_empty_rcu;) { \ 265 v = &u->avl_right; \ 266 *stackptr++ = v; \ 267 u = rcu_deref_locked(*v, base); \ 268 } \ 269 u; \ 270 }) 271 272 /* Called with local BH disabled and the pool lock held. 273 * Variable names are the proof of operation correctness. 274 * Look into mm/map_avl.c for more detail description of the ideas. 275 */ 276 static void peer_avl_rebalance(struct inet_peer __rcu **stack[], 277 struct inet_peer __rcu ***stackend, 278 struct inet_peer_base *base) 279 { 280 struct inet_peer __rcu **nodep; 281 struct inet_peer *node, *l, *r; 282 int lh, rh; 283 284 while (stackend > stack) { 285 nodep = *--stackend; 286 node = rcu_deref_locked(*nodep, base); 287 l = rcu_deref_locked(node->avl_left, base); 288 r = rcu_deref_locked(node->avl_right, base); 289 lh = node_height(l); 290 rh = node_height(r); 291 if (lh > rh + 1) { /* l: RH+2 */ 292 struct inet_peer *ll, *lr, *lrl, *lrr; 293 int lrh; 294 ll = rcu_deref_locked(l->avl_left, base); 295 lr = rcu_deref_locked(l->avl_right, base); 296 lrh = node_height(lr); 297 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 298 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ 299 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 300 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 301 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ 302 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ 303 l->avl_height = node->avl_height + 1; 304 RCU_INIT_POINTER(*nodep, l); 305 } else { /* ll: RH, lr: RH+1 */ 306 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */ 307 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */ 308 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ 309 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 310 node->avl_height = rh + 1; /* node: RH+1 */ 311 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ 312 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ 313 l->avl_height = rh + 1; /* l: RH+1 */ 314 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ 315 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ 316 lr->avl_height = rh + 2; 317 RCU_INIT_POINTER(*nodep, lr); 318 } 319 } else if (rh > lh + 1) { /* r: LH+2 */ 320 struct inet_peer *rr, *rl, *rlr, *rll; 321 int rlh; 322 rr = rcu_deref_locked(r->avl_right, base); 323 rl = rcu_deref_locked(r->avl_left, base); 324 rlh = node_height(rl); 325 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 326 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ 327 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 328 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 329 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ 330 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ 331 r->avl_height = node->avl_height + 1; 332 RCU_INIT_POINTER(*nodep, r); 333 } else { /* rr: RH, rl: RH+1 */ 334 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */ 335 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */ 336 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ 337 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 338 node->avl_height = lh + 1; /* node: LH+1 */ 339 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ 340 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ 341 r->avl_height = lh + 1; /* r: LH+1 */ 342 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ 343 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ 344 rl->avl_height = lh + 2; 345 RCU_INIT_POINTER(*nodep, rl); 346 } 347 } else { 348 node->avl_height = (lh > rh ? lh : rh) + 1; 349 } 350 } 351 } 352 353 /* Called with local BH disabled and the pool lock held. */ 354 #define link_to_pool(n, base) \ 355 do { \ 356 n->avl_height = 1; \ 357 n->avl_left = peer_avl_empty_rcu; \ 358 n->avl_right = peer_avl_empty_rcu; \ 359 /* lockless readers can catch us now */ \ 360 rcu_assign_pointer(**--stackptr, n); \ 361 peer_avl_rebalance(stack, stackptr, base); \ 362 } while (0) 363 364 static void inetpeer_free_rcu(struct rcu_head *head) 365 { 366 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); 367 } 368 369 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base, 370 struct inet_peer __rcu **stack[PEER_MAXDEPTH]) 371 { 372 struct inet_peer __rcu ***stackptr, ***delp; 373 374 if (lookup(&p->daddr, stack, base) != p) 375 BUG(); 376 delp = stackptr - 1; /* *delp[0] == p */ 377 if (p->avl_left == peer_avl_empty_rcu) { 378 *delp[0] = p->avl_right; 379 --stackptr; 380 } else { 381 /* look for a node to insert instead of p */ 382 struct inet_peer *t; 383 t = lookup_rightempty(p, base); 384 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t); 385 **--stackptr = t->avl_left; 386 /* t is removed, t->daddr > x->daddr for any 387 * x in p->avl_left subtree. 388 * Put t in the old place of p. */ 389 RCU_INIT_POINTER(*delp[0], t); 390 t->avl_left = p->avl_left; 391 t->avl_right = p->avl_right; 392 t->avl_height = p->avl_height; 393 BUG_ON(delp[1] != &p->avl_left); 394 delp[1] = &t->avl_left; /* was &p->avl_left */ 395 } 396 peer_avl_rebalance(stack, stackptr, base); 397 base->total--; 398 call_rcu(&p->rcu, inetpeer_free_rcu); 399 } 400 401 /* perform garbage collect on all items stacked during a lookup */ 402 static int inet_peer_gc(struct inet_peer_base *base, 403 struct inet_peer __rcu **stack[PEER_MAXDEPTH], 404 struct inet_peer __rcu ***stackptr) 405 { 406 struct inet_peer *p, *gchead = NULL; 407 __u32 delta, ttl; 408 int cnt = 0; 409 410 if (base->total >= inet_peer_threshold) 411 ttl = 0; /* be aggressive */ 412 else 413 ttl = inet_peer_maxttl 414 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 415 base->total / inet_peer_threshold * HZ; 416 stackptr--; /* last stack slot is peer_avl_empty */ 417 while (stackptr > stack) { 418 stackptr--; 419 p = rcu_deref_locked(**stackptr, base); 420 if (atomic_read(&p->refcnt) == 0) { 421 smp_rmb(); 422 delta = (__u32)jiffies - p->dtime; 423 if (delta >= ttl && 424 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) { 425 p->gc_next = gchead; 426 gchead = p; 427 } 428 } 429 } 430 while ((p = gchead) != NULL) { 431 gchead = p->gc_next; 432 cnt++; 433 unlink_from_pool(p, base, stack); 434 } 435 return cnt; 436 } 437 438 struct inet_peer *inet_getpeer(struct inet_peer_base *base, 439 const struct inetpeer_addr *daddr, 440 int create) 441 { 442 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; 443 struct inet_peer *p; 444 unsigned int sequence; 445 int invalidated, gccnt = 0; 446 447 flush_check(base, daddr->family); 448 449 /* Attempt a lockless lookup first. 450 * Because of a concurrent writer, we might not find an existing entry. 451 */ 452 rcu_read_lock(); 453 sequence = read_seqbegin(&base->lock); 454 p = lookup_rcu(daddr, base); 455 invalidated = read_seqretry(&base->lock, sequence); 456 rcu_read_unlock(); 457 458 if (p) 459 return p; 460 461 /* If no writer did a change during our lookup, we can return early. */ 462 if (!create && !invalidated) 463 return NULL; 464 465 /* retry an exact lookup, taking the lock before. 466 * At least, nodes should be hot in our cache. 467 */ 468 write_seqlock_bh(&base->lock); 469 relookup: 470 p = lookup(daddr, stack, base); 471 if (p != peer_avl_empty) { 472 atomic_inc(&p->refcnt); 473 write_sequnlock_bh(&base->lock); 474 return p; 475 } 476 if (!gccnt) { 477 gccnt = inet_peer_gc(base, stack, stackptr); 478 if (gccnt && create) 479 goto relookup; 480 } 481 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; 482 if (p) { 483 p->daddr = *daddr; 484 atomic_set(&p->refcnt, 1); 485 atomic_set(&p->rid, 0); 486 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; 487 p->rate_tokens = 0; 488 /* 60*HZ is arbitrary, but chosen enough high so that the first 489 * calculation of tokens is at its maximum. 490 */ 491 p->rate_last = jiffies - 60*HZ; 492 INIT_LIST_HEAD(&p->gc_list); 493 494 /* Link the node. */ 495 link_to_pool(p, base); 496 base->total++; 497 } 498 write_sequnlock_bh(&base->lock); 499 500 return p; 501 } 502 EXPORT_SYMBOL_GPL(inet_getpeer); 503 504 void inet_putpeer(struct inet_peer *p) 505 { 506 p->dtime = (__u32)jiffies; 507 smp_mb__before_atomic(); 508 atomic_dec(&p->refcnt); 509 } 510 EXPORT_SYMBOL_GPL(inet_putpeer); 511 512 /* 513 * Check transmit rate limitation for given message. 514 * The rate information is held in the inet_peer entries now. 515 * This function is generic and could be used for other purposes 516 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. 517 * 518 * Note that the same inet_peer fields are modified by functions in 519 * route.c too, but these work for packet destinations while xrlim_allow 520 * works for icmp destinations. This means the rate limiting information 521 * for one "ip object" is shared - and these ICMPs are twice limited: 522 * by source and by destination. 523 * 524 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate 525 * SHOULD allow setting of rate limits 526 * 527 * Shared between ICMPv4 and ICMPv6. 528 */ 529 #define XRLIM_BURST_FACTOR 6 530 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 531 { 532 unsigned long now, token; 533 bool rc = false; 534 535 if (!peer) 536 return true; 537 538 token = peer->rate_tokens; 539 now = jiffies; 540 token += now - peer->rate_last; 541 peer->rate_last = now; 542 if (token > XRLIM_BURST_FACTOR * timeout) 543 token = XRLIM_BURST_FACTOR * timeout; 544 if (token >= timeout) { 545 token -= timeout; 546 rc = true; 547 } 548 peer->rate_tokens = token; 549 return rc; 550 } 551 EXPORT_SYMBOL(inet_peer_xrlim_allow); 552 553 static void inetpeer_inval_rcu(struct rcu_head *head) 554 { 555 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu); 556 557 spin_lock_bh(&gc_lock); 558 list_add_tail(&p->gc_list, &gc_list); 559 spin_unlock_bh(&gc_lock); 560 561 schedule_delayed_work(&gc_work, gc_delay); 562 } 563 564 void inetpeer_invalidate_tree(struct inet_peer_base *base) 565 { 566 struct inet_peer *root; 567 568 write_seqlock_bh(&base->lock); 569 570 root = rcu_deref_locked(base->root, base); 571 if (root != peer_avl_empty) { 572 base->root = peer_avl_empty_rcu; 573 base->total = 0; 574 call_rcu(&root->gc_rcu, inetpeer_inval_rcu); 575 } 576 577 write_sequnlock_bh(&base->lock); 578 } 579 EXPORT_SYMBOL(inetpeer_invalidate_tree); 580