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 struct inet_peer_base { 86 struct inet_peer __rcu *root; 87 seqlock_t lock; 88 int total; 89 }; 90 91 static struct inet_peer_base v4_peers = { 92 .root = peer_avl_empty_rcu, 93 .lock = __SEQLOCK_UNLOCKED(v4_peers.lock), 94 .total = 0, 95 }; 96 97 static struct inet_peer_base v6_peers = { 98 .root = peer_avl_empty_rcu, 99 .lock = __SEQLOCK_UNLOCKED(v6_peers.lock), 100 .total = 0, 101 }; 102 103 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 104 105 /* Exported for sysctl_net_ipv4. */ 106 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more 107 * aggressively at this stage */ 108 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ 109 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ 110 111 static void inetpeer_gc_worker(struct work_struct *work) 112 { 113 struct inet_peer *p, *n; 114 LIST_HEAD(list); 115 116 spin_lock_bh(&gc_lock); 117 list_replace_init(&gc_list, &list); 118 spin_unlock_bh(&gc_lock); 119 120 if (list_empty(&list)) 121 return; 122 123 list_for_each_entry_safe(p, n, &list, gc_list) { 124 125 if(need_resched()) 126 cond_resched(); 127 128 if (p->avl_left != peer_avl_empty) { 129 list_add_tail(&p->avl_left->gc_list, &list); 130 p->avl_left = peer_avl_empty; 131 } 132 133 if (p->avl_right != peer_avl_empty) { 134 list_add_tail(&p->avl_right->gc_list, &list); 135 p->avl_right = peer_avl_empty; 136 } 137 138 n = list_entry(p->gc_list.next, struct inet_peer, gc_list); 139 140 if (!atomic_read(&p->refcnt)) { 141 list_del(&p->gc_list); 142 kmem_cache_free(peer_cachep, p); 143 } 144 } 145 146 if (list_empty(&list)) 147 return; 148 149 spin_lock_bh(&gc_lock); 150 list_splice(&list, &gc_list); 151 spin_unlock_bh(&gc_lock); 152 153 schedule_delayed_work(&gc_work, gc_delay); 154 } 155 156 /* Called from ip_output.c:ip_init */ 157 void __init inet_initpeers(void) 158 { 159 struct sysinfo si; 160 161 /* Use the straight interface to information about memory. */ 162 si_meminfo(&si); 163 /* The values below were suggested by Alexey Kuznetsov 164 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 165 * myself. --SAW 166 */ 167 if (si.totalram <= (32768*1024)/PAGE_SIZE) 168 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 169 if (si.totalram <= (16384*1024)/PAGE_SIZE) 170 inet_peer_threshold >>= 1; /* about 512KB */ 171 if (si.totalram <= (8192*1024)/PAGE_SIZE) 172 inet_peer_threshold >>= 2; /* about 128KB */ 173 174 peer_cachep = kmem_cache_create("inet_peer_cache", 175 sizeof(struct inet_peer), 176 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, 177 NULL); 178 179 INIT_DELAYED_WORK_DEFERRABLE(&gc_work, inetpeer_gc_worker); 180 } 181 182 static int addr_compare(const struct inetpeer_addr *a, 183 const struct inetpeer_addr *b) 184 { 185 int i, n = (a->family == AF_INET ? 1 : 4); 186 187 for (i = 0; i < n; i++) { 188 if (a->addr.a6[i] == b->addr.a6[i]) 189 continue; 190 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i]) 191 return -1; 192 return 1; 193 } 194 195 return 0; 196 } 197 198 #define rcu_deref_locked(X, BASE) \ 199 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock)) 200 201 /* 202 * Called with local BH disabled and the pool lock held. 203 */ 204 #define lookup(_daddr, _stack, _base) \ 205 ({ \ 206 struct inet_peer *u; \ 207 struct inet_peer __rcu **v; \ 208 \ 209 stackptr = _stack; \ 210 *stackptr++ = &_base->root; \ 211 for (u = rcu_deref_locked(_base->root, _base); \ 212 u != peer_avl_empty; ) { \ 213 int cmp = addr_compare(_daddr, &u->daddr); \ 214 if (cmp == 0) \ 215 break; \ 216 if (cmp == -1) \ 217 v = &u->avl_left; \ 218 else \ 219 v = &u->avl_right; \ 220 *stackptr++ = v; \ 221 u = rcu_deref_locked(*v, _base); \ 222 } \ 223 u; \ 224 }) 225 226 /* 227 * Called with rcu_read_lock() 228 * Because we hold no lock against a writer, its quite possible we fall 229 * in an endless loop. 230 * But every pointer we follow is guaranteed to be valid thanks to RCU. 231 * We exit from this function if number of links exceeds PEER_MAXDEPTH 232 */ 233 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr, 234 struct inet_peer_base *base) 235 { 236 struct inet_peer *u = rcu_dereference(base->root); 237 int count = 0; 238 239 while (u != peer_avl_empty) { 240 int cmp = addr_compare(daddr, &u->daddr); 241 if (cmp == 0) { 242 /* Before taking a reference, check if this entry was 243 * deleted (refcnt=-1) 244 */ 245 if (!atomic_add_unless(&u->refcnt, 1, -1)) 246 u = NULL; 247 return u; 248 } 249 if (cmp == -1) 250 u = rcu_dereference(u->avl_left); 251 else 252 u = rcu_dereference(u->avl_right); 253 if (unlikely(++count == PEER_MAXDEPTH)) 254 break; 255 } 256 return NULL; 257 } 258 259 /* Called with local BH disabled and the pool lock held. */ 260 #define lookup_rightempty(start, base) \ 261 ({ \ 262 struct inet_peer *u; \ 263 struct inet_peer __rcu **v; \ 264 *stackptr++ = &start->avl_left; \ 265 v = &start->avl_left; \ 266 for (u = rcu_deref_locked(*v, base); \ 267 u->avl_right != peer_avl_empty_rcu; ) { \ 268 v = &u->avl_right; \ 269 *stackptr++ = v; \ 270 u = rcu_deref_locked(*v, base); \ 271 } \ 272 u; \ 273 }) 274 275 /* Called with local BH disabled and the pool lock held. 276 * Variable names are the proof of operation correctness. 277 * Look into mm/map_avl.c for more detail description of the ideas. 278 */ 279 static void peer_avl_rebalance(struct inet_peer __rcu **stack[], 280 struct inet_peer __rcu ***stackend, 281 struct inet_peer_base *base) 282 { 283 struct inet_peer __rcu **nodep; 284 struct inet_peer *node, *l, *r; 285 int lh, rh; 286 287 while (stackend > stack) { 288 nodep = *--stackend; 289 node = rcu_deref_locked(*nodep, base); 290 l = rcu_deref_locked(node->avl_left, base); 291 r = rcu_deref_locked(node->avl_right, base); 292 lh = node_height(l); 293 rh = node_height(r); 294 if (lh > rh + 1) { /* l: RH+2 */ 295 struct inet_peer *ll, *lr, *lrl, *lrr; 296 int lrh; 297 ll = rcu_deref_locked(l->avl_left, base); 298 lr = rcu_deref_locked(l->avl_right, base); 299 lrh = node_height(lr); 300 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 301 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ 302 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 303 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 304 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ 305 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ 306 l->avl_height = node->avl_height + 1; 307 RCU_INIT_POINTER(*nodep, l); 308 } else { /* ll: RH, lr: RH+1 */ 309 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */ 310 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */ 311 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ 312 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 313 node->avl_height = rh + 1; /* node: RH+1 */ 314 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ 315 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ 316 l->avl_height = rh + 1; /* l: RH+1 */ 317 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ 318 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ 319 lr->avl_height = rh + 2; 320 RCU_INIT_POINTER(*nodep, lr); 321 } 322 } else if (rh > lh + 1) { /* r: LH+2 */ 323 struct inet_peer *rr, *rl, *rlr, *rll; 324 int rlh; 325 rr = rcu_deref_locked(r->avl_right, base); 326 rl = rcu_deref_locked(r->avl_left, base); 327 rlh = node_height(rl); 328 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 329 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ 330 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 331 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 332 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ 333 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ 334 r->avl_height = node->avl_height + 1; 335 RCU_INIT_POINTER(*nodep, r); 336 } else { /* rr: RH, rl: RH+1 */ 337 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */ 338 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */ 339 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ 340 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 341 node->avl_height = lh + 1; /* node: LH+1 */ 342 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ 343 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ 344 r->avl_height = lh + 1; /* r: LH+1 */ 345 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ 346 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ 347 rl->avl_height = lh + 2; 348 RCU_INIT_POINTER(*nodep, rl); 349 } 350 } else { 351 node->avl_height = (lh > rh ? lh : rh) + 1; 352 } 353 } 354 } 355 356 /* Called with local BH disabled and the pool lock held. */ 357 #define link_to_pool(n, base) \ 358 do { \ 359 n->avl_height = 1; \ 360 n->avl_left = peer_avl_empty_rcu; \ 361 n->avl_right = peer_avl_empty_rcu; \ 362 /* lockless readers can catch us now */ \ 363 rcu_assign_pointer(**--stackptr, n); \ 364 peer_avl_rebalance(stack, stackptr, base); \ 365 } while (0) 366 367 static void inetpeer_free_rcu(struct rcu_head *head) 368 { 369 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); 370 } 371 372 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base, 373 struct inet_peer __rcu **stack[PEER_MAXDEPTH]) 374 { 375 struct inet_peer __rcu ***stackptr, ***delp; 376 377 if (lookup(&p->daddr, stack, base) != p) 378 BUG(); 379 delp = stackptr - 1; /* *delp[0] == p */ 380 if (p->avl_left == peer_avl_empty_rcu) { 381 *delp[0] = p->avl_right; 382 --stackptr; 383 } else { 384 /* look for a node to insert instead of p */ 385 struct inet_peer *t; 386 t = lookup_rightempty(p, base); 387 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t); 388 **--stackptr = t->avl_left; 389 /* t is removed, t->daddr > x->daddr for any 390 * x in p->avl_left subtree. 391 * Put t in the old place of p. */ 392 RCU_INIT_POINTER(*delp[0], t); 393 t->avl_left = p->avl_left; 394 t->avl_right = p->avl_right; 395 t->avl_height = p->avl_height; 396 BUG_ON(delp[1] != &p->avl_left); 397 delp[1] = &t->avl_left; /* was &p->avl_left */ 398 } 399 peer_avl_rebalance(stack, stackptr, base); 400 base->total--; 401 call_rcu(&p->rcu, inetpeer_free_rcu); 402 } 403 404 static struct inet_peer_base *family_to_base(int family) 405 { 406 return family == AF_INET ? &v4_peers : &v6_peers; 407 } 408 409 /* perform garbage collect on all items stacked during a lookup */ 410 static int inet_peer_gc(struct inet_peer_base *base, 411 struct inet_peer __rcu **stack[PEER_MAXDEPTH], 412 struct inet_peer __rcu ***stackptr) 413 { 414 struct inet_peer *p, *gchead = NULL; 415 __u32 delta, ttl; 416 int cnt = 0; 417 418 if (base->total >= inet_peer_threshold) 419 ttl = 0; /* be aggressive */ 420 else 421 ttl = inet_peer_maxttl 422 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 423 base->total / inet_peer_threshold * HZ; 424 stackptr--; /* last stack slot is peer_avl_empty */ 425 while (stackptr > stack) { 426 stackptr--; 427 p = rcu_deref_locked(**stackptr, base); 428 if (atomic_read(&p->refcnt) == 0) { 429 smp_rmb(); 430 delta = (__u32)jiffies - p->dtime; 431 if (delta >= ttl && 432 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) { 433 p->gc_next = gchead; 434 gchead = p; 435 } 436 } 437 } 438 while ((p = gchead) != NULL) { 439 gchead = p->gc_next; 440 cnt++; 441 unlink_from_pool(p, base, stack); 442 } 443 return cnt; 444 } 445 446 struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create) 447 { 448 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; 449 struct inet_peer_base *base = family_to_base(daddr->family); 450 struct inet_peer *p; 451 unsigned int sequence; 452 int invalidated, gccnt = 0; 453 454 /* Attempt a lockless lookup first. 455 * Because of a concurrent writer, we might not find an existing entry. 456 */ 457 rcu_read_lock(); 458 sequence = read_seqbegin(&base->lock); 459 p = lookup_rcu(daddr, base); 460 invalidated = read_seqretry(&base->lock, sequence); 461 rcu_read_unlock(); 462 463 if (p) 464 return p; 465 466 /* If no writer did a change during our lookup, we can return early. */ 467 if (!create && !invalidated) 468 return NULL; 469 470 /* retry an exact lookup, taking the lock before. 471 * At least, nodes should be hot in our cache. 472 */ 473 write_seqlock_bh(&base->lock); 474 relookup: 475 p = lookup(daddr, stack, base); 476 if (p != peer_avl_empty) { 477 atomic_inc(&p->refcnt); 478 write_sequnlock_bh(&base->lock); 479 return p; 480 } 481 if (!gccnt) { 482 gccnt = inet_peer_gc(base, stack, stackptr); 483 if (gccnt && create) 484 goto relookup; 485 } 486 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; 487 if (p) { 488 p->daddr = *daddr; 489 atomic_set(&p->refcnt, 1); 490 atomic_set(&p->rid, 0); 491 atomic_set(&p->ip_id_count, 492 (daddr->family == AF_INET) ? 493 secure_ip_id(daddr->addr.a4) : 494 secure_ipv6_id(daddr->addr.a6)); 495 p->tcp_ts_stamp = 0; 496 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; 497 p->rate_tokens = 0; 498 p->rate_last = 0; 499 p->pmtu_expires = 0; 500 p->pmtu_orig = 0; 501 memset(&p->redirect_learned, 0, sizeof(p->redirect_learned)); 502 INIT_LIST_HEAD(&p->gc_list); 503 504 /* Link the node. */ 505 link_to_pool(p, base); 506 base->total++; 507 } 508 write_sequnlock_bh(&base->lock); 509 510 return p; 511 } 512 EXPORT_SYMBOL_GPL(inet_getpeer); 513 514 void inet_putpeer(struct inet_peer *p) 515 { 516 p->dtime = (__u32)jiffies; 517 smp_mb__before_atomic_dec(); 518 atomic_dec(&p->refcnt); 519 } 520 EXPORT_SYMBOL_GPL(inet_putpeer); 521 522 /* 523 * Check transmit rate limitation for given message. 524 * The rate information is held in the inet_peer entries now. 525 * This function is generic and could be used for other purposes 526 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. 527 * 528 * Note that the same inet_peer fields are modified by functions in 529 * route.c too, but these work for packet destinations while xrlim_allow 530 * works for icmp destinations. This means the rate limiting information 531 * for one "ip object" is shared - and these ICMPs are twice limited: 532 * by source and by destination. 533 * 534 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate 535 * SHOULD allow setting of rate limits 536 * 537 * Shared between ICMPv4 and ICMPv6. 538 */ 539 #define XRLIM_BURST_FACTOR 6 540 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 541 { 542 unsigned long now, token; 543 bool rc = false; 544 545 if (!peer) 546 return true; 547 548 token = peer->rate_tokens; 549 now = jiffies; 550 token += now - peer->rate_last; 551 peer->rate_last = now; 552 if (token > XRLIM_BURST_FACTOR * timeout) 553 token = XRLIM_BURST_FACTOR * timeout; 554 if (token >= timeout) { 555 token -= timeout; 556 rc = true; 557 } 558 peer->rate_tokens = token; 559 return rc; 560 } 561 EXPORT_SYMBOL(inet_peer_xrlim_allow); 562 563 void inetpeer_invalidate_tree(int family) 564 { 565 struct inet_peer *old, *new, *prev; 566 struct inet_peer_base *base = family_to_base(family); 567 568 write_seqlock_bh(&base->lock); 569 570 old = base->root; 571 if (old == peer_avl_empty_rcu) 572 goto out; 573 574 new = peer_avl_empty_rcu; 575 576 prev = cmpxchg(&base->root, old, new); 577 if (prev == old) { 578 base->total = 0; 579 spin_lock(&gc_lock); 580 list_add_tail(&prev->gc_list, &gc_list); 581 spin_unlock(&gc_lock); 582 schedule_delayed_work(&gc_work, gc_delay); 583 } 584 585 out: 586 write_sequnlock_bh(&base->lock); 587 } 588 EXPORT_SYMBOL(inetpeer_invalidate_tree); 589