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 (!atomic_read(&p->refcnt)) { 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 static int addr_compare(const struct inetpeer_addr *a, 161 const struct inetpeer_addr *b) 162 { 163 int i, n = (a->family == AF_INET ? 1 : 4); 164 165 for (i = 0; i < n; i++) { 166 if (a->addr.a6[i] == b->addr.a6[i]) 167 continue; 168 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i]) 169 return -1; 170 return 1; 171 } 172 173 return 0; 174 } 175 176 #define rcu_deref_locked(X, BASE) \ 177 rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock)) 178 179 /* 180 * Called with local BH disabled and the pool lock held. 181 */ 182 #define lookup(_daddr, _stack, _base) \ 183 ({ \ 184 struct inet_peer *u; \ 185 struct inet_peer __rcu **v; \ 186 \ 187 stackptr = _stack; \ 188 *stackptr++ = &_base->root; \ 189 for (u = rcu_deref_locked(_base->root, _base); \ 190 u != peer_avl_empty;) { \ 191 int cmp = addr_compare(_daddr, &u->daddr); \ 192 if (cmp == 0) \ 193 break; \ 194 if (cmp == -1) \ 195 v = &u->avl_left; \ 196 else \ 197 v = &u->avl_right; \ 198 *stackptr++ = v; \ 199 u = rcu_deref_locked(*v, _base); \ 200 } \ 201 u; \ 202 }) 203 204 /* 205 * Called with rcu_read_lock() 206 * Because we hold no lock against a writer, its quite possible we fall 207 * in an endless loop. 208 * But every pointer we follow is guaranteed to be valid thanks to RCU. 209 * We exit from this function if number of links exceeds PEER_MAXDEPTH 210 */ 211 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr, 212 struct inet_peer_base *base) 213 { 214 struct inet_peer *u = rcu_dereference(base->root); 215 int count = 0; 216 217 while (u != peer_avl_empty) { 218 int cmp = addr_compare(daddr, &u->daddr); 219 if (cmp == 0) { 220 /* Before taking a reference, check if this entry was 221 * deleted (refcnt=-1) 222 */ 223 if (!atomic_add_unless(&u->refcnt, 1, -1)) 224 u = NULL; 225 return u; 226 } 227 if (cmp == -1) 228 u = rcu_dereference(u->avl_left); 229 else 230 u = rcu_dereference(u->avl_right); 231 if (unlikely(++count == PEER_MAXDEPTH)) 232 break; 233 } 234 return NULL; 235 } 236 237 /* Called with local BH disabled and the pool lock held. */ 238 #define lookup_rightempty(start, base) \ 239 ({ \ 240 struct inet_peer *u; \ 241 struct inet_peer __rcu **v; \ 242 *stackptr++ = &start->avl_left; \ 243 v = &start->avl_left; \ 244 for (u = rcu_deref_locked(*v, base); \ 245 u->avl_right != peer_avl_empty_rcu;) { \ 246 v = &u->avl_right; \ 247 *stackptr++ = v; \ 248 u = rcu_deref_locked(*v, base); \ 249 } \ 250 u; \ 251 }) 252 253 /* Called with local BH disabled and the pool lock held. 254 * Variable names are the proof of operation correctness. 255 * Look into mm/map_avl.c for more detail description of the ideas. 256 */ 257 static void peer_avl_rebalance(struct inet_peer __rcu **stack[], 258 struct inet_peer __rcu ***stackend, 259 struct inet_peer_base *base) 260 { 261 struct inet_peer __rcu **nodep; 262 struct inet_peer *node, *l, *r; 263 int lh, rh; 264 265 while (stackend > stack) { 266 nodep = *--stackend; 267 node = rcu_deref_locked(*nodep, base); 268 l = rcu_deref_locked(node->avl_left, base); 269 r = rcu_deref_locked(node->avl_right, base); 270 lh = node_height(l); 271 rh = node_height(r); 272 if (lh > rh + 1) { /* l: RH+2 */ 273 struct inet_peer *ll, *lr, *lrl, *lrr; 274 int lrh; 275 ll = rcu_deref_locked(l->avl_left, base); 276 lr = rcu_deref_locked(l->avl_right, base); 277 lrh = node_height(lr); 278 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 279 RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ 280 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 281 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 282 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ 283 RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ 284 l->avl_height = node->avl_height + 1; 285 RCU_INIT_POINTER(*nodep, l); 286 } else { /* ll: RH, lr: RH+1 */ 287 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */ 288 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */ 289 RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ 290 RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ 291 node->avl_height = rh + 1; /* node: RH+1 */ 292 RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ 293 RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ 294 l->avl_height = rh + 1; /* l: RH+1 */ 295 RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ 296 RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ 297 lr->avl_height = rh + 2; 298 RCU_INIT_POINTER(*nodep, lr); 299 } 300 } else if (rh > lh + 1) { /* r: LH+2 */ 301 struct inet_peer *rr, *rl, *rlr, *rll; 302 int rlh; 303 rr = rcu_deref_locked(r->avl_right, base); 304 rl = rcu_deref_locked(r->avl_left, base); 305 rlh = node_height(rl); 306 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 307 RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ 308 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 309 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 310 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ 311 RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ 312 r->avl_height = node->avl_height + 1; 313 RCU_INIT_POINTER(*nodep, r); 314 } else { /* rr: RH, rl: RH+1 */ 315 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */ 316 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */ 317 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ 318 RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ 319 node->avl_height = lh + 1; /* node: LH+1 */ 320 RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ 321 RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ 322 r->avl_height = lh + 1; /* r: LH+1 */ 323 RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ 324 RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ 325 rl->avl_height = lh + 2; 326 RCU_INIT_POINTER(*nodep, rl); 327 } 328 } else { 329 node->avl_height = (lh > rh ? lh : rh) + 1; 330 } 331 } 332 } 333 334 /* Called with local BH disabled and the pool lock held. */ 335 #define link_to_pool(n, base) \ 336 do { \ 337 n->avl_height = 1; \ 338 n->avl_left = peer_avl_empty_rcu; \ 339 n->avl_right = peer_avl_empty_rcu; \ 340 /* lockless readers can catch us now */ \ 341 rcu_assign_pointer(**--stackptr, n); \ 342 peer_avl_rebalance(stack, stackptr, base); \ 343 } while (0) 344 345 static void inetpeer_free_rcu(struct rcu_head *head) 346 { 347 kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); 348 } 349 350 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base, 351 struct inet_peer __rcu **stack[PEER_MAXDEPTH]) 352 { 353 struct inet_peer __rcu ***stackptr, ***delp; 354 355 if (lookup(&p->daddr, stack, base) != p) 356 BUG(); 357 delp = stackptr - 1; /* *delp[0] == p */ 358 if (p->avl_left == peer_avl_empty_rcu) { 359 *delp[0] = p->avl_right; 360 --stackptr; 361 } else { 362 /* look for a node to insert instead of p */ 363 struct inet_peer *t; 364 t = lookup_rightempty(p, base); 365 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t); 366 **--stackptr = t->avl_left; 367 /* t is removed, t->daddr > x->daddr for any 368 * x in p->avl_left subtree. 369 * Put t in the old place of p. */ 370 RCU_INIT_POINTER(*delp[0], t); 371 t->avl_left = p->avl_left; 372 t->avl_right = p->avl_right; 373 t->avl_height = p->avl_height; 374 BUG_ON(delp[1] != &p->avl_left); 375 delp[1] = &t->avl_left; /* was &p->avl_left */ 376 } 377 peer_avl_rebalance(stack, stackptr, base); 378 base->total--; 379 call_rcu(&p->rcu, inetpeer_free_rcu); 380 } 381 382 /* perform garbage collect on all items stacked during a lookup */ 383 static int inet_peer_gc(struct inet_peer_base *base, 384 struct inet_peer __rcu **stack[PEER_MAXDEPTH], 385 struct inet_peer __rcu ***stackptr) 386 { 387 struct inet_peer *p, *gchead = NULL; 388 __u32 delta, ttl; 389 int cnt = 0; 390 391 if (base->total >= inet_peer_threshold) 392 ttl = 0; /* be aggressive */ 393 else 394 ttl = inet_peer_maxttl 395 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 396 base->total / inet_peer_threshold * HZ; 397 stackptr--; /* last stack slot is peer_avl_empty */ 398 while (stackptr > stack) { 399 stackptr--; 400 p = rcu_deref_locked(**stackptr, base); 401 if (atomic_read(&p->refcnt) == 0) { 402 smp_rmb(); 403 delta = (__u32)jiffies - p->dtime; 404 if (delta >= ttl && 405 atomic_cmpxchg(&p->refcnt, 0, -1) == 0) { 406 p->gc_next = gchead; 407 gchead = p; 408 } 409 } 410 } 411 while ((p = gchead) != NULL) { 412 gchead = p->gc_next; 413 cnt++; 414 unlink_from_pool(p, base, stack); 415 } 416 return cnt; 417 } 418 419 struct inet_peer *inet_getpeer(struct inet_peer_base *base, 420 const struct inetpeer_addr *daddr, 421 int create) 422 { 423 struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; 424 struct inet_peer *p; 425 unsigned int sequence; 426 int invalidated, gccnt = 0; 427 428 /* Attempt a lockless lookup first. 429 * Because of a concurrent writer, we might not find an existing entry. 430 */ 431 rcu_read_lock(); 432 sequence = read_seqbegin(&base->lock); 433 p = lookup_rcu(daddr, base); 434 invalidated = read_seqretry(&base->lock, sequence); 435 rcu_read_unlock(); 436 437 if (p) 438 return p; 439 440 /* If no writer did a change during our lookup, we can return early. */ 441 if (!create && !invalidated) 442 return NULL; 443 444 /* retry an exact lookup, taking the lock before. 445 * At least, nodes should be hot in our cache. 446 */ 447 write_seqlock_bh(&base->lock); 448 relookup: 449 p = lookup(daddr, stack, base); 450 if (p != peer_avl_empty) { 451 atomic_inc(&p->refcnt); 452 write_sequnlock_bh(&base->lock); 453 return p; 454 } 455 if (!gccnt) { 456 gccnt = inet_peer_gc(base, stack, stackptr); 457 if (gccnt && create) 458 goto relookup; 459 } 460 p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; 461 if (p) { 462 p->daddr = *daddr; 463 atomic_set(&p->refcnt, 1); 464 atomic_set(&p->rid, 0); 465 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; 466 p->rate_tokens = 0; 467 /* 60*HZ is arbitrary, but chosen enough high so that the first 468 * calculation of tokens is at its maximum. 469 */ 470 p->rate_last = jiffies - 60*HZ; 471 INIT_LIST_HEAD(&p->gc_list); 472 473 /* Link the node. */ 474 link_to_pool(p, base); 475 base->total++; 476 } 477 write_sequnlock_bh(&base->lock); 478 479 return p; 480 } 481 EXPORT_SYMBOL_GPL(inet_getpeer); 482 483 void inet_putpeer(struct inet_peer *p) 484 { 485 p->dtime = (__u32)jiffies; 486 smp_mb__before_atomic(); 487 atomic_dec(&p->refcnt); 488 } 489 EXPORT_SYMBOL_GPL(inet_putpeer); 490 491 /* 492 * Check transmit rate limitation for given message. 493 * The rate information is held in the inet_peer entries now. 494 * This function is generic and could be used for other purposes 495 * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. 496 * 497 * Note that the same inet_peer fields are modified by functions in 498 * route.c too, but these work for packet destinations while xrlim_allow 499 * works for icmp destinations. This means the rate limiting information 500 * for one "ip object" is shared - and these ICMPs are twice limited: 501 * by source and by destination. 502 * 503 * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate 504 * SHOULD allow setting of rate limits 505 * 506 * Shared between ICMPv4 and ICMPv6. 507 */ 508 #define XRLIM_BURST_FACTOR 6 509 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) 510 { 511 unsigned long now, token; 512 bool rc = false; 513 514 if (!peer) 515 return true; 516 517 token = peer->rate_tokens; 518 now = jiffies; 519 token += now - peer->rate_last; 520 peer->rate_last = now; 521 if (token > XRLIM_BURST_FACTOR * timeout) 522 token = XRLIM_BURST_FACTOR * timeout; 523 if (token >= timeout) { 524 token -= timeout; 525 rc = true; 526 } 527 peer->rate_tokens = token; 528 return rc; 529 } 530 EXPORT_SYMBOL(inet_peer_xrlim_allow); 531 532 static void inetpeer_inval_rcu(struct rcu_head *head) 533 { 534 struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu); 535 536 spin_lock_bh(&gc_lock); 537 list_add_tail(&p->gc_list, &gc_list); 538 spin_unlock_bh(&gc_lock); 539 540 schedule_delayed_work(&gc_work, gc_delay); 541 } 542 543 void inetpeer_invalidate_tree(struct inet_peer_base *base) 544 { 545 struct inet_peer *root; 546 547 write_seqlock_bh(&base->lock); 548 549 root = rcu_deref_locked(base->root, base); 550 if (root != peer_avl_empty) { 551 base->root = peer_avl_empty_rcu; 552 base->total = 0; 553 call_rcu(&root->gc_rcu, inetpeer_inval_rcu); 554 } 555 556 write_sequnlock_bh(&base->lock); 557 } 558 EXPORT_SYMBOL(inetpeer_invalidate_tree); 559