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/sched.h> 18 #include <linux/timer.h> 19 #include <linux/time.h> 20 #include <linux/kernel.h> 21 #include <linux/mm.h> 22 #include <linux/net.h> 23 #include <net/ip.h> 24 #include <net/inetpeer.h> 25 26 /* 27 * Theory of operations. 28 * We keep one entry for each peer IP address. The nodes contains long-living 29 * information about the peer which doesn't depend on routes. 30 * At this moment this information consists only of ID field for the next 31 * outgoing IP packet. This field is incremented with each packet as encoded 32 * in inet_getid() function (include/net/inetpeer.h). 33 * At the moment of writing this notes identifier of IP packets is generated 34 * to be unpredictable using this code only for packets subjected 35 * (actually or potentially) to defragmentation. I.e. DF packets less than 36 * PMTU in size uses a constant ID and do not use this code (see 37 * ip_select_ident() in include/net/ip.h). 38 * 39 * Route cache entries hold references to our nodes. 40 * New cache entries get references via lookup by destination IP address in 41 * the avl tree. The reference is grabbed only when it's needed i.e. only 42 * when we try to output IP packet which needs an unpredictable ID (see 43 * __ip_select_ident() in net/ipv4/route.c). 44 * Nodes are removed only when reference counter goes to 0. 45 * When it's happened the node may be removed when a sufficient amount of 46 * time has been passed since its last use. The less-recently-used entry can 47 * also be removed if the pool is overloaded i.e. if the total amount of 48 * entries is greater-or-equal than the threshold. 49 * 50 * Node pool is organised as an AVL tree. 51 * Such an implementation has been chosen not just for fun. It's a way to 52 * prevent easy and efficient DoS attacks by creating hash collisions. A huge 53 * amount of long living nodes in a single hash slot would significantly delay 54 * lookups performed with disabled BHs. 55 * 56 * Serialisation issues. 57 * 1. Nodes may appear in the tree only with the pool write lock held. 58 * 2. Nodes may disappear from the tree only with the pool write lock held 59 * AND reference count being 0. 60 * 3. Nodes appears and disappears from unused node list only under 61 * "inet_peer_unused_lock". 62 * 4. Global variable peer_total is modified under the pool lock. 63 * 5. struct inet_peer fields modification: 64 * avl_left, avl_right, avl_parent, avl_height: pool lock 65 * unused_next, unused_prevp: unused node list lock 66 * refcnt: atomically against modifications on other CPU; 67 * usually under some other lock to prevent node disappearing 68 * dtime: unused node list lock 69 * v4daddr: unchangeable 70 * ip_id_count: idlock 71 */ 72 73 /* Exported for inet_getid inline function. */ 74 DEFINE_SPINLOCK(inet_peer_idlock); 75 76 static kmem_cache_t *peer_cachep __read_mostly; 77 78 #define node_height(x) x->avl_height 79 static struct inet_peer peer_fake_node = { 80 .avl_left = &peer_fake_node, 81 .avl_right = &peer_fake_node, 82 .avl_height = 0 83 }; 84 #define peer_avl_empty (&peer_fake_node) 85 static struct inet_peer *peer_root = peer_avl_empty; 86 static DEFINE_RWLOCK(peer_pool_lock); 87 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 88 89 static volatile int peer_total; 90 /* Exported for sysctl_net_ipv4. */ 91 int inet_peer_threshold = 65536 + 128; /* start to throw entries more 92 * aggressively at this stage */ 93 int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */ 94 int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */ 95 96 static struct inet_peer *inet_peer_unused_head; 97 /* Exported for inet_putpeer inline function. */ 98 struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head; 99 DEFINE_SPINLOCK(inet_peer_unused_lock); 100 #define PEER_MAX_CLEANUP_WORK 30 101 102 static void peer_check_expire(unsigned long dummy); 103 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0); 104 105 /* Exported for sysctl_net_ipv4. */ 106 int inet_peer_gc_mintime = 10 * HZ, 107 inet_peer_gc_maxtime = 120 * HZ; 108 109 /* Called from ip_output.c:ip_init */ 110 void __init inet_initpeers(void) 111 { 112 struct sysinfo si; 113 114 /* Use the straight interface to information about memory. */ 115 si_meminfo(&si); 116 /* The values below were suggested by Alexey Kuznetsov 117 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 118 * myself. --SAW 119 */ 120 if (si.totalram <= (32768*1024)/PAGE_SIZE) 121 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 122 if (si.totalram <= (16384*1024)/PAGE_SIZE) 123 inet_peer_threshold >>= 1; /* about 512KB */ 124 if (si.totalram <= (8192*1024)/PAGE_SIZE) 125 inet_peer_threshold >>= 2; /* about 128KB */ 126 127 peer_cachep = kmem_cache_create("inet_peer_cache", 128 sizeof(struct inet_peer), 129 0, SLAB_HWCACHE_ALIGN, 130 NULL, NULL); 131 132 if (!peer_cachep) 133 panic("cannot create inet_peer_cache"); 134 135 /* All the timers, started at system startup tend 136 to synchronize. Perturb it a bit. 137 */ 138 peer_periodic_timer.expires = jiffies 139 + net_random() % inet_peer_gc_maxtime 140 + inet_peer_gc_maxtime; 141 add_timer(&peer_periodic_timer); 142 } 143 144 /* Called with or without local BH being disabled. */ 145 static void unlink_from_unused(struct inet_peer *p) 146 { 147 spin_lock_bh(&inet_peer_unused_lock); 148 if (p->unused_prevp != NULL) { 149 /* On unused list. */ 150 *p->unused_prevp = p->unused_next; 151 if (p->unused_next != NULL) 152 p->unused_next->unused_prevp = p->unused_prevp; 153 else 154 inet_peer_unused_tailp = p->unused_prevp; 155 p->unused_prevp = NULL; /* mark it as removed */ 156 } 157 spin_unlock_bh(&inet_peer_unused_lock); 158 } 159 160 /* Called with local BH disabled and the pool lock held. */ 161 #define lookup(daddr) \ 162 ({ \ 163 struct inet_peer *u, **v; \ 164 stackptr = stack; \ 165 *stackptr++ = &peer_root; \ 166 for (u = peer_root; u != peer_avl_empty; ) { \ 167 if (daddr == u->v4daddr) \ 168 break; \ 169 if (daddr < u->v4daddr) \ 170 v = &u->avl_left; \ 171 else \ 172 v = &u->avl_right; \ 173 *stackptr++ = v; \ 174 u = *v; \ 175 } \ 176 u; \ 177 }) 178 179 /* Called with local BH disabled and the pool write lock held. */ 180 #define lookup_rightempty(start) \ 181 ({ \ 182 struct inet_peer *u, **v; \ 183 *stackptr++ = &start->avl_left; \ 184 v = &start->avl_left; \ 185 for (u = *v; u->avl_right != peer_avl_empty; ) { \ 186 v = &u->avl_right; \ 187 *stackptr++ = v; \ 188 u = *v; \ 189 } \ 190 u; \ 191 }) 192 193 /* Called with local BH disabled and the pool write lock held. 194 * Variable names are the proof of operation correctness. 195 * Look into mm/map_avl.c for more detail description of the ideas. */ 196 static void peer_avl_rebalance(struct inet_peer **stack[], 197 struct inet_peer ***stackend) 198 { 199 struct inet_peer **nodep, *node, *l, *r; 200 int lh, rh; 201 202 while (stackend > stack) { 203 nodep = *--stackend; 204 node = *nodep; 205 l = node->avl_left; 206 r = node->avl_right; 207 lh = node_height(l); 208 rh = node_height(r); 209 if (lh > rh + 1) { /* l: RH+2 */ 210 struct inet_peer *ll, *lr, *lrl, *lrr; 211 int lrh; 212 ll = l->avl_left; 213 lr = l->avl_right; 214 lrh = node_height(lr); 215 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 216 node->avl_left = lr; /* lr: RH or RH+1 */ 217 node->avl_right = r; /* r: RH */ 218 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 219 l->avl_left = ll; /* ll: RH+1 */ 220 l->avl_right = node; /* node: RH+1 or RH+2 */ 221 l->avl_height = node->avl_height + 1; 222 *nodep = l; 223 } else { /* ll: RH, lr: RH+1 */ 224 lrl = lr->avl_left; /* lrl: RH or RH-1 */ 225 lrr = lr->avl_right; /* lrr: RH or RH-1 */ 226 node->avl_left = lrr; /* lrr: RH or RH-1 */ 227 node->avl_right = r; /* r: RH */ 228 node->avl_height = rh + 1; /* node: RH+1 */ 229 l->avl_left = ll; /* ll: RH */ 230 l->avl_right = lrl; /* lrl: RH or RH-1 */ 231 l->avl_height = rh + 1; /* l: RH+1 */ 232 lr->avl_left = l; /* l: RH+1 */ 233 lr->avl_right = node; /* node: RH+1 */ 234 lr->avl_height = rh + 2; 235 *nodep = lr; 236 } 237 } else if (rh > lh + 1) { /* r: LH+2 */ 238 struct inet_peer *rr, *rl, *rlr, *rll; 239 int rlh; 240 rr = r->avl_right; 241 rl = r->avl_left; 242 rlh = node_height(rl); 243 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 244 node->avl_right = rl; /* rl: LH or LH+1 */ 245 node->avl_left = l; /* l: LH */ 246 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 247 r->avl_right = rr; /* rr: LH+1 */ 248 r->avl_left = node; /* node: LH+1 or LH+2 */ 249 r->avl_height = node->avl_height + 1; 250 *nodep = r; 251 } else { /* rr: RH, rl: RH+1 */ 252 rlr = rl->avl_right; /* rlr: LH or LH-1 */ 253 rll = rl->avl_left; /* rll: LH or LH-1 */ 254 node->avl_right = rll; /* rll: LH or LH-1 */ 255 node->avl_left = l; /* l: LH */ 256 node->avl_height = lh + 1; /* node: LH+1 */ 257 r->avl_right = rr; /* rr: LH */ 258 r->avl_left = rlr; /* rlr: LH or LH-1 */ 259 r->avl_height = lh + 1; /* r: LH+1 */ 260 rl->avl_right = r; /* r: LH+1 */ 261 rl->avl_left = node; /* node: LH+1 */ 262 rl->avl_height = lh + 2; 263 *nodep = rl; 264 } 265 } else { 266 node->avl_height = (lh > rh ? lh : rh) + 1; 267 } 268 } 269 } 270 271 /* Called with local BH disabled and the pool write lock held. */ 272 #define link_to_pool(n) \ 273 do { \ 274 n->avl_height = 1; \ 275 n->avl_left = peer_avl_empty; \ 276 n->avl_right = peer_avl_empty; \ 277 **--stackptr = n; \ 278 peer_avl_rebalance(stack, stackptr); \ 279 } while(0) 280 281 /* May be called with local BH enabled. */ 282 static void unlink_from_pool(struct inet_peer *p) 283 { 284 int do_free; 285 286 do_free = 0; 287 288 write_lock_bh(&peer_pool_lock); 289 /* Check the reference counter. It was artificially incremented by 1 290 * in cleanup() function to prevent sudden disappearing. If the 291 * reference count is still 1 then the node is referenced only as `p' 292 * here and from the pool. So under the exclusive pool lock it's safe 293 * to remove the node and free it later. */ 294 if (atomic_read(&p->refcnt) == 1) { 295 struct inet_peer **stack[PEER_MAXDEPTH]; 296 struct inet_peer ***stackptr, ***delp; 297 if (lookup(p->v4daddr) != p) 298 BUG(); 299 delp = stackptr - 1; /* *delp[0] == p */ 300 if (p->avl_left == peer_avl_empty) { 301 *delp[0] = p->avl_right; 302 --stackptr; 303 } else { 304 /* look for a node to insert instead of p */ 305 struct inet_peer *t; 306 t = lookup_rightempty(p); 307 BUG_ON(*stackptr[-1] != t); 308 **--stackptr = t->avl_left; 309 /* t is removed, t->v4daddr > x->v4daddr for any 310 * x in p->avl_left subtree. 311 * Put t in the old place of p. */ 312 *delp[0] = t; 313 t->avl_left = p->avl_left; 314 t->avl_right = p->avl_right; 315 t->avl_height = p->avl_height; 316 BUG_ON(delp[1] != &p->avl_left); 317 delp[1] = &t->avl_left; /* was &p->avl_left */ 318 } 319 peer_avl_rebalance(stack, stackptr); 320 peer_total--; 321 do_free = 1; 322 } 323 write_unlock_bh(&peer_pool_lock); 324 325 if (do_free) 326 kmem_cache_free(peer_cachep, p); 327 else 328 /* The node is used again. Decrease the reference counter 329 * back. The loop "cleanup -> unlink_from_unused 330 * -> unlink_from_pool -> putpeer -> link_to_unused 331 * -> cleanup (for the same node)" 332 * doesn't really exist because the entry will have a 333 * recent deletion time and will not be cleaned again soon. */ 334 inet_putpeer(p); 335 } 336 337 /* May be called with local BH enabled. */ 338 static int cleanup_once(unsigned long ttl) 339 { 340 struct inet_peer *p; 341 342 /* Remove the first entry from the list of unused nodes. */ 343 spin_lock_bh(&inet_peer_unused_lock); 344 p = inet_peer_unused_head; 345 if (p != NULL) { 346 if (time_after(p->dtime + ttl, jiffies)) { 347 /* Do not prune fresh entries. */ 348 spin_unlock_bh(&inet_peer_unused_lock); 349 return -1; 350 } 351 inet_peer_unused_head = p->unused_next; 352 if (p->unused_next != NULL) 353 p->unused_next->unused_prevp = p->unused_prevp; 354 else 355 inet_peer_unused_tailp = p->unused_prevp; 356 p->unused_prevp = NULL; /* mark as not on the list */ 357 /* Grab an extra reference to prevent node disappearing 358 * before unlink_from_pool() call. */ 359 atomic_inc(&p->refcnt); 360 } 361 spin_unlock_bh(&inet_peer_unused_lock); 362 363 if (p == NULL) 364 /* It means that the total number of USED entries has 365 * grown over inet_peer_threshold. It shouldn't really 366 * happen because of entry limits in route cache. */ 367 return -1; 368 369 unlink_from_pool(p); 370 return 0; 371 } 372 373 /* Called with or without local BH being disabled. */ 374 struct inet_peer *inet_getpeer(__u32 daddr, int create) 375 { 376 struct inet_peer *p, *n; 377 struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; 378 379 /* Look up for the address quickly. */ 380 read_lock_bh(&peer_pool_lock); 381 p = lookup(daddr); 382 if (p != peer_avl_empty) 383 atomic_inc(&p->refcnt); 384 read_unlock_bh(&peer_pool_lock); 385 386 if (p != peer_avl_empty) { 387 /* The existing node has been found. */ 388 /* Remove the entry from unused list if it was there. */ 389 unlink_from_unused(p); 390 return p; 391 } 392 393 if (!create) 394 return NULL; 395 396 /* Allocate the space outside the locked region. */ 397 n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); 398 if (n == NULL) 399 return NULL; 400 n->v4daddr = daddr; 401 atomic_set(&n->refcnt, 1); 402 atomic_set(&n->rid, 0); 403 n->ip_id_count = secure_ip_id(daddr); 404 n->tcp_ts_stamp = 0; 405 406 write_lock_bh(&peer_pool_lock); 407 /* Check if an entry has suddenly appeared. */ 408 p = lookup(daddr); 409 if (p != peer_avl_empty) 410 goto out_free; 411 412 /* Link the node. */ 413 link_to_pool(n); 414 n->unused_prevp = NULL; /* not on the list */ 415 peer_total++; 416 write_unlock_bh(&peer_pool_lock); 417 418 if (peer_total >= inet_peer_threshold) 419 /* Remove one less-recently-used entry. */ 420 cleanup_once(0); 421 422 return n; 423 424 out_free: 425 /* The appropriate node is already in the pool. */ 426 atomic_inc(&p->refcnt); 427 write_unlock_bh(&peer_pool_lock); 428 /* Remove the entry from unused list if it was there. */ 429 unlink_from_unused(p); 430 /* Free preallocated the preallocated node. */ 431 kmem_cache_free(peer_cachep, n); 432 return p; 433 } 434 435 /* Called with local BH disabled. */ 436 static void peer_check_expire(unsigned long dummy) 437 { 438 int i; 439 int ttl; 440 441 if (peer_total >= inet_peer_threshold) 442 ttl = inet_peer_minttl; 443 else 444 ttl = inet_peer_maxttl 445 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 446 peer_total / inet_peer_threshold * HZ; 447 for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++); 448 449 /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime 450 * interval depending on the total number of entries (more entries, 451 * less interval). */ 452 if (peer_total >= inet_peer_threshold) 453 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime; 454 else 455 peer_periodic_timer.expires = jiffies 456 + inet_peer_gc_maxtime 457 - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * 458 peer_total / inet_peer_threshold * HZ; 459 add_timer(&peer_periodic_timer); 460 } 461