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 * Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $ 7 * 8 * Authors: Andrey V. Savochkin <saw@msu.ru> 9 */ 10 11 #include <linux/module.h> 12 #include <linux/types.h> 13 #include <linux/slab.h> 14 #include <linux/interrupt.h> 15 #include <linux/spinlock.h> 16 #include <linux/random.h> 17 #include <linux/timer.h> 18 #include <linux/time.h> 19 #include <linux/kernel.h> 20 #include <linux/mm.h> 21 #include <linux/net.h> 22 #include <net/ip.h> 23 #include <net/inetpeer.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 write lock held. 57 * 2. Nodes may disappear from the tree only with the pool write lock held 58 * AND reference count being 0. 59 * 3. Nodes appears and disappears from unused node list only under 60 * "inet_peer_unused_lock". 61 * 4. Global variable peer_total is modified under the pool lock. 62 * 5. struct inet_peer fields modification: 63 * avl_left, avl_right, avl_parent, avl_height: pool lock 64 * unused_next, unused_prevp: unused node list lock 65 * refcnt: atomically against modifications on other CPU; 66 * usually under some other lock to prevent node disappearing 67 * dtime: unused node list lock 68 * v4daddr: unchangeable 69 * ip_id_count: idlock 70 */ 71 72 /* Exported for inet_getid inline function. */ 73 DEFINE_SPINLOCK(inet_peer_idlock); 74 75 static struct kmem_cache *peer_cachep __read_mostly; 76 77 #define node_height(x) x->avl_height 78 static struct inet_peer peer_fake_node = { 79 .avl_left = &peer_fake_node, 80 .avl_right = &peer_fake_node, 81 .avl_height = 0 82 }; 83 #define peer_avl_empty (&peer_fake_node) 84 static struct inet_peer *peer_root = peer_avl_empty; 85 static DEFINE_RWLOCK(peer_pool_lock); 86 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 87 88 static int peer_total; 89 /* Exported for sysctl_net_ipv4. */ 90 int inet_peer_threshold = 65536 + 128; /* start to throw entries more 91 * aggressively at this stage */ 92 int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */ 93 int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */ 94 95 static struct inet_peer *inet_peer_unused_head; 96 static struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head; 97 static DEFINE_SPINLOCK(inet_peer_unused_lock); 98 99 static void peer_check_expire(unsigned long dummy); 100 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0); 101 102 /* Exported for sysctl_net_ipv4. */ 103 int inet_peer_gc_mintime = 10 * HZ, 104 inet_peer_gc_maxtime = 120 * HZ; 105 106 /* Called from ip_output.c:ip_init */ 107 void __init inet_initpeers(void) 108 { 109 struct sysinfo si; 110 111 /* Use the straight interface to information about memory. */ 112 si_meminfo(&si); 113 /* The values below were suggested by Alexey Kuznetsov 114 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 115 * myself. --SAW 116 */ 117 if (si.totalram <= (32768*1024)/PAGE_SIZE) 118 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 119 if (si.totalram <= (16384*1024)/PAGE_SIZE) 120 inet_peer_threshold >>= 1; /* about 512KB */ 121 if (si.totalram <= (8192*1024)/PAGE_SIZE) 122 inet_peer_threshold >>= 2; /* about 128KB */ 123 124 peer_cachep = kmem_cache_create("inet_peer_cache", 125 sizeof(struct inet_peer), 126 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, 127 NULL, NULL); 128 129 /* All the timers, started at system startup tend 130 to synchronize. Perturb it a bit. 131 */ 132 peer_periodic_timer.expires = jiffies 133 + net_random() % inet_peer_gc_maxtime 134 + inet_peer_gc_maxtime; 135 add_timer(&peer_periodic_timer); 136 } 137 138 /* Called with or without local BH being disabled. */ 139 static void unlink_from_unused(struct inet_peer *p) 140 { 141 spin_lock_bh(&inet_peer_unused_lock); 142 if (p->unused_prevp != NULL) { 143 /* On unused list. */ 144 *p->unused_prevp = p->unused_next; 145 if (p->unused_next != NULL) 146 p->unused_next->unused_prevp = p->unused_prevp; 147 else 148 inet_peer_unused_tailp = p->unused_prevp; 149 p->unused_prevp = NULL; /* mark it as removed */ 150 } 151 spin_unlock_bh(&inet_peer_unused_lock); 152 } 153 154 /* Called with local BH disabled and the pool lock held. */ 155 #define lookup(daddr) \ 156 ({ \ 157 struct inet_peer *u, **v; \ 158 stackptr = stack; \ 159 *stackptr++ = &peer_root; \ 160 for (u = peer_root; u != peer_avl_empty; ) { \ 161 if (daddr == u->v4daddr) \ 162 break; \ 163 if ((__force __u32)daddr < (__force __u32)u->v4daddr) \ 164 v = &u->avl_left; \ 165 else \ 166 v = &u->avl_right; \ 167 *stackptr++ = v; \ 168 u = *v; \ 169 } \ 170 u; \ 171 }) 172 173 /* Called with local BH disabled and the pool write lock held. */ 174 #define lookup_rightempty(start) \ 175 ({ \ 176 struct inet_peer *u, **v; \ 177 *stackptr++ = &start->avl_left; \ 178 v = &start->avl_left; \ 179 for (u = *v; u->avl_right != peer_avl_empty; ) { \ 180 v = &u->avl_right; \ 181 *stackptr++ = v; \ 182 u = *v; \ 183 } \ 184 u; \ 185 }) 186 187 /* Called with local BH disabled and the pool write lock held. 188 * Variable names are the proof of operation correctness. 189 * Look into mm/map_avl.c for more detail description of the ideas. */ 190 static void peer_avl_rebalance(struct inet_peer **stack[], 191 struct inet_peer ***stackend) 192 { 193 struct inet_peer **nodep, *node, *l, *r; 194 int lh, rh; 195 196 while (stackend > stack) { 197 nodep = *--stackend; 198 node = *nodep; 199 l = node->avl_left; 200 r = node->avl_right; 201 lh = node_height(l); 202 rh = node_height(r); 203 if (lh > rh + 1) { /* l: RH+2 */ 204 struct inet_peer *ll, *lr, *lrl, *lrr; 205 int lrh; 206 ll = l->avl_left; 207 lr = l->avl_right; 208 lrh = node_height(lr); 209 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 210 node->avl_left = lr; /* lr: RH or RH+1 */ 211 node->avl_right = r; /* r: RH */ 212 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 213 l->avl_left = ll; /* ll: RH+1 */ 214 l->avl_right = node; /* node: RH+1 or RH+2 */ 215 l->avl_height = node->avl_height + 1; 216 *nodep = l; 217 } else { /* ll: RH, lr: RH+1 */ 218 lrl = lr->avl_left; /* lrl: RH or RH-1 */ 219 lrr = lr->avl_right; /* lrr: RH or RH-1 */ 220 node->avl_left = lrr; /* lrr: RH or RH-1 */ 221 node->avl_right = r; /* r: RH */ 222 node->avl_height = rh + 1; /* node: RH+1 */ 223 l->avl_left = ll; /* ll: RH */ 224 l->avl_right = lrl; /* lrl: RH or RH-1 */ 225 l->avl_height = rh + 1; /* l: RH+1 */ 226 lr->avl_left = l; /* l: RH+1 */ 227 lr->avl_right = node; /* node: RH+1 */ 228 lr->avl_height = rh + 2; 229 *nodep = lr; 230 } 231 } else if (rh > lh + 1) { /* r: LH+2 */ 232 struct inet_peer *rr, *rl, *rlr, *rll; 233 int rlh; 234 rr = r->avl_right; 235 rl = r->avl_left; 236 rlh = node_height(rl); 237 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 238 node->avl_right = rl; /* rl: LH or LH+1 */ 239 node->avl_left = l; /* l: LH */ 240 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 241 r->avl_right = rr; /* rr: LH+1 */ 242 r->avl_left = node; /* node: LH+1 or LH+2 */ 243 r->avl_height = node->avl_height + 1; 244 *nodep = r; 245 } else { /* rr: RH, rl: RH+1 */ 246 rlr = rl->avl_right; /* rlr: LH or LH-1 */ 247 rll = rl->avl_left; /* rll: LH or LH-1 */ 248 node->avl_right = rll; /* rll: LH or LH-1 */ 249 node->avl_left = l; /* l: LH */ 250 node->avl_height = lh + 1; /* node: LH+1 */ 251 r->avl_right = rr; /* rr: LH */ 252 r->avl_left = rlr; /* rlr: LH or LH-1 */ 253 r->avl_height = lh + 1; /* r: LH+1 */ 254 rl->avl_right = r; /* r: LH+1 */ 255 rl->avl_left = node; /* node: LH+1 */ 256 rl->avl_height = lh + 2; 257 *nodep = rl; 258 } 259 } else { 260 node->avl_height = (lh > rh ? lh : rh) + 1; 261 } 262 } 263 } 264 265 /* Called with local BH disabled and the pool write lock held. */ 266 #define link_to_pool(n) \ 267 do { \ 268 n->avl_height = 1; \ 269 n->avl_left = peer_avl_empty; \ 270 n->avl_right = peer_avl_empty; \ 271 **--stackptr = n; \ 272 peer_avl_rebalance(stack, stackptr); \ 273 } while(0) 274 275 /* May be called with local BH enabled. */ 276 static void unlink_from_pool(struct inet_peer *p) 277 { 278 int do_free; 279 280 do_free = 0; 281 282 write_lock_bh(&peer_pool_lock); 283 /* Check the reference counter. It was artificially incremented by 1 284 * in cleanup() function to prevent sudden disappearing. If the 285 * reference count is still 1 then the node is referenced only as `p' 286 * here and from the pool. So under the exclusive pool lock it's safe 287 * to remove the node and free it later. */ 288 if (atomic_read(&p->refcnt) == 1) { 289 struct inet_peer **stack[PEER_MAXDEPTH]; 290 struct inet_peer ***stackptr, ***delp; 291 if (lookup(p->v4daddr) != p) 292 BUG(); 293 delp = stackptr - 1; /* *delp[0] == p */ 294 if (p->avl_left == peer_avl_empty) { 295 *delp[0] = p->avl_right; 296 --stackptr; 297 } else { 298 /* look for a node to insert instead of p */ 299 struct inet_peer *t; 300 t = lookup_rightempty(p); 301 BUG_ON(*stackptr[-1] != t); 302 **--stackptr = t->avl_left; 303 /* t is removed, t->v4daddr > x->v4daddr for any 304 * x in p->avl_left subtree. 305 * Put t in the old place of p. */ 306 *delp[0] = t; 307 t->avl_left = p->avl_left; 308 t->avl_right = p->avl_right; 309 t->avl_height = p->avl_height; 310 BUG_ON(delp[1] != &p->avl_left); 311 delp[1] = &t->avl_left; /* was &p->avl_left */ 312 } 313 peer_avl_rebalance(stack, stackptr); 314 peer_total--; 315 do_free = 1; 316 } 317 write_unlock_bh(&peer_pool_lock); 318 319 if (do_free) 320 kmem_cache_free(peer_cachep, p); 321 else 322 /* The node is used again. Decrease the reference counter 323 * back. The loop "cleanup -> unlink_from_unused 324 * -> unlink_from_pool -> putpeer -> link_to_unused 325 * -> cleanup (for the same node)" 326 * doesn't really exist because the entry will have a 327 * recent deletion time and will not be cleaned again soon. */ 328 inet_putpeer(p); 329 } 330 331 /* May be called with local BH enabled. */ 332 static int cleanup_once(unsigned long ttl) 333 { 334 struct inet_peer *p; 335 336 /* Remove the first entry from the list of unused nodes. */ 337 spin_lock_bh(&inet_peer_unused_lock); 338 p = inet_peer_unused_head; 339 if (p != NULL) { 340 __u32 delta = (__u32)jiffies - p->dtime; 341 if (delta < ttl) { 342 /* Do not prune fresh entries. */ 343 spin_unlock_bh(&inet_peer_unused_lock); 344 return -1; 345 } 346 inet_peer_unused_head = p->unused_next; 347 if (p->unused_next != NULL) 348 p->unused_next->unused_prevp = p->unused_prevp; 349 else 350 inet_peer_unused_tailp = p->unused_prevp; 351 p->unused_prevp = NULL; /* mark as not on the list */ 352 /* Grab an extra reference to prevent node disappearing 353 * before unlink_from_pool() call. */ 354 atomic_inc(&p->refcnt); 355 } 356 spin_unlock_bh(&inet_peer_unused_lock); 357 358 if (p == NULL) 359 /* It means that the total number of USED entries has 360 * grown over inet_peer_threshold. It shouldn't really 361 * happen because of entry limits in route cache. */ 362 return -1; 363 364 unlink_from_pool(p); 365 return 0; 366 } 367 368 /* Called with or without local BH being disabled. */ 369 struct inet_peer *inet_getpeer(__be32 daddr, int create) 370 { 371 struct inet_peer *p, *n; 372 struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; 373 374 /* Look up for the address quickly. */ 375 read_lock_bh(&peer_pool_lock); 376 p = lookup(daddr); 377 if (p != peer_avl_empty) 378 atomic_inc(&p->refcnt); 379 read_unlock_bh(&peer_pool_lock); 380 381 if (p != peer_avl_empty) { 382 /* The existing node has been found. */ 383 /* Remove the entry from unused list if it was there. */ 384 unlink_from_unused(p); 385 return p; 386 } 387 388 if (!create) 389 return NULL; 390 391 /* Allocate the space outside the locked region. */ 392 n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); 393 if (n == NULL) 394 return NULL; 395 n->v4daddr = daddr; 396 atomic_set(&n->refcnt, 1); 397 atomic_set(&n->rid, 0); 398 n->ip_id_count = secure_ip_id(daddr); 399 n->tcp_ts_stamp = 0; 400 401 write_lock_bh(&peer_pool_lock); 402 /* Check if an entry has suddenly appeared. */ 403 p = lookup(daddr); 404 if (p != peer_avl_empty) 405 goto out_free; 406 407 /* Link the node. */ 408 link_to_pool(n); 409 n->unused_prevp = NULL; /* not on the list */ 410 peer_total++; 411 write_unlock_bh(&peer_pool_lock); 412 413 if (peer_total >= inet_peer_threshold) 414 /* Remove one less-recently-used entry. */ 415 cleanup_once(0); 416 417 return n; 418 419 out_free: 420 /* The appropriate node is already in the pool. */ 421 atomic_inc(&p->refcnt); 422 write_unlock_bh(&peer_pool_lock); 423 /* Remove the entry from unused list if it was there. */ 424 unlink_from_unused(p); 425 /* Free preallocated the preallocated node. */ 426 kmem_cache_free(peer_cachep, n); 427 return p; 428 } 429 430 /* Called with local BH disabled. */ 431 static void peer_check_expire(unsigned long dummy) 432 { 433 unsigned long now = jiffies; 434 int ttl; 435 436 if (peer_total >= inet_peer_threshold) 437 ttl = inet_peer_minttl; 438 else 439 ttl = inet_peer_maxttl 440 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 441 peer_total / inet_peer_threshold * HZ; 442 while (!cleanup_once(ttl)) { 443 if (jiffies != now) 444 break; 445 } 446 447 /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime 448 * interval depending on the total number of entries (more entries, 449 * less interval). */ 450 if (peer_total >= inet_peer_threshold) 451 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime; 452 else 453 peer_periodic_timer.expires = jiffies 454 + inet_peer_gc_maxtime 455 - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * 456 peer_total / inet_peer_threshold * HZ; 457 add_timer(&peer_periodic_timer); 458 } 459 460 void inet_putpeer(struct inet_peer *p) 461 { 462 spin_lock_bh(&inet_peer_unused_lock); 463 if (atomic_dec_and_test(&p->refcnt)) { 464 p->unused_prevp = inet_peer_unused_tailp; 465 p->unused_next = NULL; 466 *inet_peer_unused_tailp = p; 467 inet_peer_unused_tailp = &p->unused_next; 468 p->dtime = (__u32)jiffies; 469 } 470 spin_unlock_bh(&inet_peer_unused_lock); 471 } 472