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 * 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 lock held. 57 * 2. Nodes may disappear from the tree only with the pool lock held 58 * AND reference count being 0. 59 * 3. Global variable peer_total is modified under the pool lock. 60 * 4. struct inet_peer fields modification: 61 * avl_left, avl_right, avl_parent, avl_height: pool lock 62 * refcnt: atomically against modifications on other CPU; 63 * usually under some other lock to prevent node disappearing 64 * daddr: unchangeable 65 * ip_id_count: atomic value (no lock needed) 66 */ 67 68 static struct kmem_cache *peer_cachep __read_mostly; 69 70 static LIST_HEAD(gc_list); 71 static const int gc_delay = 60 * HZ; 72 static struct delayed_work gc_work; 73 static DEFINE_SPINLOCK(gc_lock); 74 75 #define node_height(x) x->avl_height 76 77 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node) 78 #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node) 79 static const struct inet_peer peer_fake_node = { 80 .avl_left = peer_avl_empty_rcu, 81 .avl_right = peer_avl_empty_rcu, 82 .avl_height = 0 83 }; 84 85 void inet_peer_base_init(struct inet_peer_base *bp) 86 { 87 bp->root = peer_avl_empty_rcu; 88 seqlock_init(&bp->lock); 89 bp->flush_seq = ~0U; 90 bp->total = 0; 91 } 92 EXPORT_SYMBOL_GPL(inet_peer_base_init); 93 94 static atomic_t v4_seq = ATOMIC_INIT(0); 95 static atomic_t v6_seq = ATOMIC_INIT(0); 96 97 static atomic_t *inetpeer_seq_ptr(int family) 98 { 99 return (family == AF_INET ? &v4_seq : &v6_seq); 100 } 101 102 static inline void flush_check(struct inet_peer_base *base, int family) 103 { 104 atomic_t *fp = inetpeer_seq_ptr(family); 105 106 if (unlikely(base->flush_seq != atomic_read(fp))) { 107 inetpeer_invalidate_tree(base); 108 base->flush_seq = atomic_read(fp); 109 } 110 } 111 112 void inetpeer_invalidate_family(int family) 113 { 114 atomic_t *fp = inetpeer_seq_ptr(family); 115 116 atomic_inc(fp); 117 } 118 119 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 120 121 /* Exported for sysctl_net_ipv4. */ 122 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more 123 * aggressively at this stage */ 124 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ 125 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ 126 127 static void inetpeer_gc_worker(struct work_struct *work) 128 { 129 struct inet_peer *p, *n, *c; 130 LIST_HEAD(list); 131 132 spin_lock_bh(&gc_lock); 133 list_replace_init(&gc_list, &list); 134 spin_unlock_bh(&gc_lock); 135 136 if (list_empty(&list)) 137 return; 138 139 list_for_each_entry_safe(p, n, &list, gc_list) { 140 141 if (need_resched()) 142 cond_resched(); 143 144 c = rcu_dereference_protected(p->avl_left, 1); 145 if (c != peer_avl_empty) { 146 list_add_tail(&c->gc_list, &list); 147 p->avl_left = peer_avl_empty_rcu; 148 } 149 150 c = rcu_dereference_protected(p->avl_right, 1); 151 if (c != peer_avl_empty) { 152 list_add_tail(&c->gc_list, &list); 153 p->avl_right = peer_avl_empty_rcu; 154 } 155 156 n = list_entry(p->gc_list.next, struct inet_peer, gc_list); 157 158 if (!atomic_read(&p->refcnt)) { 159 list_del(&p->gc_list); 160 kmem_cache_free(peer_cachep, p); 161 } 162 } 163 164 if (list_empty(&list)) 165 return; 166 167 spin_lock_bh(&gc_lock); 168 list_splice(&list, &gc_list); 169 spin_unlock_bh(&gc_lock); 170 171 schedule_delayed_work(&gc_work, gc_delay); 172 } 173 174 /* Called from ip_output.c:ip_init */ 175 void __init inet_initpeers(void) 176 { 177 struct sysinfo si; 178 179 /* Use the straight interface to information about memory. */ 180 si_meminfo(&si); 181 /* The values below were suggested by Alexey Kuznetsov 182 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 183 * myself. --SAW 184 */ 185 if (si.totalram <= (32768*1024)/PAGE_SIZE) 186 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 187 if (si.totalram <= (16384*1024)/PAGE_SIZE) 188 inet_peer_threshold >>= 1; /* about 512KB */ 189 if (si.totalram <= (8192*1024)/PAGE_SIZE) 190 inet_peer_threshold >>= 2; /* about 128KB */ 191 192 peer_cachep = kmem_cache_create("inet_peer_cache", 193 sizeof(struct inet_peer), 194 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, 195 NULL); 196 197 INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker); 198 } 199 200 static int addr_compare(const struct inetpeer_addr *a, 201 const struct inetpeer_addr *b) 202 { 203 int i, n = (a->family == AF_INET ? 1 : 4); 204 205 for (i = 0; i < n; i++) { 206 if (a->addr.a6[i] == b->addr.a6[i]) 207 continue; 208 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i]) 209 return -1; 210 return 1; 211 } 212 213 return 0; 214 } 215 216 #define rcu_deref_locked(X, BASE) \ 217 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock)) 218 219 /* 220 * Called with local BH disabled and the pool lock held. 221 */ 222 #define lookup(_daddr, _stack, _base) \ 223 ({ \ 224 struct inet_peer *u; \ 225 struct inet_peer __rcu **v; \ 226 \ 227 stackptr = _stack; \ 228 *stackptr++ = &_base->root; \ 229 for (u = rcu_deref_locked(_base->root, _base); \ 230 u != peer_avl_empty; ) { \ 231 int cmp = addr_compare(_daddr, &u->daddr); \ 232 if (cmp == 0) \ 233 break; \ 234 if (cmp == -1) \ 235 v = &u->avl_left; \ 236 else \ 237 v = &u->avl_right; \ 238 *stackptr++ = v; \ 239 u = rcu_deref_locked(*v, _base); \ 240 } \ 241 u; \ 242 }) 243 244 /* 245 * Called with rcu_read_lock() 246 * Because we hold no lock against a writer, its quite possible we fall 247 * in an endless loop. 248 * But every pointer we follow is guaranteed to be valid thanks to RCU. 249 * We exit from this function if number of links exceeds PEER_MAXDEPTH 250 */ 251 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr, 252 struct inet_peer_base *base) 253 { 254 struct inet_peer *u = rcu_dereference(base->root); 255 int count = 0; 256 257 while (u != peer_avl_empty) { 258 int cmp = addr_compare(daddr, &u->daddr); 259 if (cmp == 0) { 260 /* Before taking a reference, check if this entry was 261 * deleted (refcnt=-1) 262 */ 263 if (!atomic_add_unless(&u->refcnt, 1, -1)) 264 u = NULL; 265 return u; 266 } 267 if (cmp == -1) 268 u = rcu_dereference(u->avl_left); 269 else 270 u = rcu_dereference(u->avl_right); 271 if (unlikely(++count == PEER_MAXDEPTH)) 272 break; 273 } 274 return NULL; 275 } 276 277 /* Called with local BH disabled and the pool lock held. */ 278 #define lookup_rightempty(start, base) \ 279 ({ \ 280 struct inet_peer *u; \ 281 struct inet_peer __rcu **v; \ 282 *stackptr++ = &start->avl_left; \ 283 v = &start->avl_left; \ 284 for (u = rcu_deref_locked(*v, base); \ 285 u->avl_right != peer_avl_empty_rcu; ) { \ 286 v = &u->avl_right; \ 287 *stackptr++ = v; \ 288 u = rcu_deref_locked(*v, base); \ 289 } \ 290 u; \ 291 }) 292 293 /* Called with local BH disabled and the pool lock held. 294 * Variable names are the proof of operation correctness. 295 * Look into mm/map_avl.c for more detail description of the ideas. 296 */ 297 static void peer_avl_rebalance(struct inet_peer __rcu **stack[], 298 struct inet_peer __rcu ***stackend, 299 struct inet_peer_base *base) 300 { 301 struct inet_peer __rcu **nodep; 302 struct inet_peer *node, *l, *r; 303 int lh, rh; 304 305 while (stackend > stack) { 306 nodep = *--stackend; 307 node = rcu_deref_locked(*nodep, base); 308 l = rcu_deref_locked(node->avl_left, base); 309 r = rcu_deref_locked(node->avl_right, base); 310 lh = node_height(l); 311 rh = node_height(r); 312 if (lh > rh + 1) { /* l: RH+2 */ 313 struct inet_peer *ll, *lr, *lrl, *lrr; 314 int lrh; 315 ll = rcu_deref_locked(l->avl_left, base); 316 lr = rcu_deref_locked(l->avl_right, base); 317 lrh = node_height(lr); 318 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 319 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ 320 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 321 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 322 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ 323 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ 324 l->avl_height = node->avl_height + 1; 325 RCU_INIT_POINTER(*nodep, l); 326 } else { /* ll: RH, lr: RH+1 */ 327 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */ 328 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */ 329 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ 330 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 331 node->avl_height = rh + 1; /* node: RH+1 */ 332 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ 333 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ 334 l->avl_height = rh + 1; /* l: RH+1 */ 335 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ 336 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ 337 lr->avl_height = rh + 2; 338 RCU_INIT_POINTER(*nodep, lr); 339 } 340 } else if (rh > lh + 1) { /* r: LH+2 */ 341 struct inet_peer *rr, *rl, *rlr, *rll; 342 int rlh; 343 rr = rcu_deref_locked(r->avl_right, base); 344 rl = rcu_deref_locked(r->avl_left, base); 345 rlh = node_height(rl); 346 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 347 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ 348 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 349 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 350 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ 351 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ 352 r->avl_height = node->avl_height + 1; 353 RCU_INIT_POINTER(*nodep, r); 354 } else { /* rr: RH, rl: RH+1 */ 355 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */ 356 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */ 357 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ 358 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 359 node->avl_height = lh + 1; /* node: LH+1 */ 360 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ 361 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ 362 r->avl_height = lh + 1; /* r: LH+1 */ 363 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ 364 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ 365 rl->avl_height = lh + 2; 366 RCU_INIT_POINTER(*nodep, rl); 367 } 368 } else { 369 node->avl_height = (lh > rh ? lh : rh) + 1; 370 } 371 } 372 } 373 374 /* Called with local BH disabled and the pool lock held. */ 375 #define link_to_pool(n, base) \ 376 do { \ 377 n->avl_height = 1; \ 378 n->avl_left = peer_avl_empty_rcu; \ 379 n->avl_right = peer_avl_empty_rcu; \ 380 /* lockless readers can catch us now */ \ 381 rcu_assign_pointer(**--stackptr, n); \ 382 peer_avl_rebalance(stack, stackptr, base); \ 383 } while (0) 384 385 static void inetpeer_free_rcu(struct rcu_head *head) 386 { 387 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); 388 } 389 390 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base, 391 struct inet_peer __rcu **stack[PEER_MAXDEPTH]) 392 { 393 struct inet_peer __rcu ***stackptr, ***delp; 394 395 if (lookup(&p->daddr, stack, base) != p) 396 BUG(); 397 delp = stackptr - 1; /* *delp[0] == p */ 398 if (p->avl_left == peer_avl_empty_rcu) { 399 *delp[0] = p->avl_right; 400 --stackptr; 401 } else { 402 /* look for a node to insert instead of p */ 403 struct inet_peer *t; 404 t = lookup_rightempty(p, base); 405 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t); 406 **--stackptr = t->avl_left; 407 /* t is removed, t->daddr > x->daddr for any 408 * x in p->avl_left subtree. 409 * Put t in the old place of p. */ 410 RCU_INIT_POINTER(*delp[0], t); 411 t->avl_left = p->avl_left; 412 t->avl_right = p->avl_right; 413 t->avl_height = p->avl_height; 414 BUG_ON(delp[1] != &p->avl_left); 415 delp[1] = &t->avl_left; /* was &p->avl_left */ 416 } 417 peer_avl_rebalance(stack, stackptr, base); 418 base->total--; 419 call_rcu(&p->rcu, inetpeer_free_rcu); 420 } 421 422 /* perform garbage collect on all items stacked during a lookup */ 423 static int inet_peer_gc(struct inet_peer_base *base, 424 struct inet_peer __rcu **stack[PEER_MAXDEPTH], 425 struct inet_peer __rcu ***stackptr) 426 { 427 struct inet_peer *p, *gchead = NULL; 428 __u32 delta, ttl; 429 int cnt = 0; 430 431 if (base->total >= inet_peer_threshold) 432 ttl = 0; /* be aggressive */ 433 else 434 ttl = inet_peer_maxttl 435 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 436 base->total / inet_peer_threshold * HZ; 437 stackptr--; /* last stack slot is peer_avl_empty */ 438 while (stackptr > stack) { 439 stackptr--; 440 p = rcu_deref_locked(**stackptr, base); 441 if (atomic_read(&p->refcnt) == 0) { 442 smp_rmb(); 443 delta = (__u32)jiffies - p->dtime; 444 if (delta >= ttl && 445 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) { 446 p->gc_next = gchead; 447 gchead = p; 448 } 449 } 450 } 451 while ((p = gchead) != NULL) { 452 gchead = p->gc_next; 453 cnt++; 454 unlink_from_pool(p, base, stack); 455 } 456 return cnt; 457 } 458 459 struct inet_peer *inet_getpeer(struct inet_peer_base *base, 460 const struct inetpeer_addr *daddr, 461 int create) 462 { 463 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; 464 struct inet_peer *p; 465 unsigned int sequence; 466 int invalidated, gccnt = 0; 467 468 flush_check(base, daddr->family); 469 470 /* Attempt a lockless lookup first. 471 * Because of a concurrent writer, we might not find an existing entry. 472 */ 473 rcu_read_lock(); 474 sequence = read_seqbegin(&base->lock); 475 p = lookup_rcu(daddr, base); 476 invalidated = read_seqretry(&base->lock, sequence); 477 rcu_read_unlock(); 478 479 if (p) 480 return p; 481 482 /* If no writer did a change during our lookup, we can return early. */ 483 if (!create && !invalidated) 484 return NULL; 485 486 /* retry an exact lookup, taking the lock before. 487 * At least, nodes should be hot in our cache. 488 */ 489 write_seqlock_bh(&base->lock); 490 relookup: 491 p = lookup(daddr, stack, base); 492 if (p != peer_avl_empty) { 493 atomic_inc(&p->refcnt); 494 write_sequnlock_bh(&base->lock); 495 return p; 496 } 497 if (!gccnt) { 498 gccnt = inet_peer_gc(base, stack, stackptr); 499 if (gccnt && create) 500 goto relookup; 501 } 502 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; 503 if (p) { 504 p->daddr = *daddr; 505 atomic_set(&p->refcnt, 1); 506 atomic_set(&p->rid, 0); 507 atomic_set(&p->ip_id_count, 508 (daddr->family == AF_INET) ? 509 secure_ip_id(daddr->addr.a4) : 510 secure_ipv6_id(daddr->addr.a6)); 511 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; 512 p->rate_tokens = 0; 513 /* 60*HZ is arbitrary, but chosen enough high so that the first 514 * calculation of tokens is at its maximum. 515 */ 516 p->rate_last = jiffies - 60*HZ; 517 INIT_LIST_HEAD(&p->gc_list); 518 519 /* Link the node. */ 520 link_to_pool(p, base); 521 base->total++; 522 } 523 write_sequnlock_bh(&base->lock); 524 525 return p; 526 } 527 EXPORT_SYMBOL_GPL(inet_getpeer); 528 529 void inet_putpeer(struct inet_peer *p) 530 { 531 p->dtime = (__u32)jiffies; 532 smp_mb__before_atomic_dec(); 533 atomic_dec(&p->refcnt); 534 } 535 EXPORT_SYMBOL_GPL(inet_putpeer); 536 537 /* 538 * Check transmit rate limitation for given message. 539 * The rate information is held in the inet_peer entries now. 540 * This function is generic and could be used for other purposes 541 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. 542 * 543 * Note that the same inet_peer fields are modified by functions in 544 * route.c too, but these work for packet destinations while xrlim_allow 545 * works for icmp destinations. This means the rate limiting information 546 * for one "ip object" is shared - and these ICMPs are twice limited: 547 * by source and by destination. 548 * 549 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate 550 * SHOULD allow setting of rate limits 551 * 552 * Shared between ICMPv4 and ICMPv6. 553 */ 554 #define XRLIM_BURST_FACTOR 6 555 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 556 { 557 unsigned long now, token; 558 bool rc = false; 559 560 if (!peer) 561 return true; 562 563 token = peer->rate_tokens; 564 now = jiffies; 565 token += now - peer->rate_last; 566 peer->rate_last = now; 567 if (token > XRLIM_BURST_FACTOR * timeout) 568 token = XRLIM_BURST_FACTOR * timeout; 569 if (token >= timeout) { 570 token -= timeout; 571 rc = true; 572 } 573 peer->rate_tokens = token; 574 return rc; 575 } 576 EXPORT_SYMBOL(inet_peer_xrlim_allow); 577 578 static void inetpeer_inval_rcu(struct rcu_head *head) 579 { 580 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu); 581 582 spin_lock_bh(&gc_lock); 583 list_add_tail(&p->gc_list, &gc_list); 584 spin_unlock_bh(&gc_lock); 585 586 schedule_delayed_work(&gc_work, gc_delay); 587 } 588 589 void inetpeer_invalidate_tree(struct inet_peer_base *base) 590 { 591 struct inet_peer *root; 592 593 write_seqlock_bh(&base->lock); 594 595 root = rcu_deref_locked(base->root, base); 596 if (root != peer_avl_empty) { 597 base->root = peer_avl_empty_rcu; 598 base->total = 0; 599 call_rcu(&root->gc_rcu, inetpeer_inval_rcu); 600 } 601 602 write_sequnlock_bh(&base->lock); 603 } 604 EXPORT_SYMBOL(inetpeer_invalidate_tree); 605