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 <net/ip.h> 21 #include <net/inetpeer.h> 22 23 /* 24 * Theory of operations. 25 * We keep one entry for each peer IP address. The nodes contains long-living 26 * information about the peer which doesn't depend on routes. 27 * At this moment this information consists only of ID field for the next 28 * outgoing IP packet. This field is incremented with each packet as encoded 29 * in inet_getid() function (include/net/inetpeer.h). 30 * At the moment of writing this notes identifier of IP packets is generated 31 * to be unpredictable using this code only for packets subjected 32 * (actually or potentially) to defragmentation. I.e. DF packets less than 33 * PMTU in size uses a constant ID and do not use this code (see 34 * ip_select_ident() in include/net/ip.h). 35 * 36 * Route cache entries hold references to our nodes. 37 * New cache entries get references via lookup by destination IP address in 38 * the avl tree. The reference is grabbed only when it's needed i.e. only 39 * when we try to output IP packet which needs an unpredictable ID (see 40 * __ip_select_ident() in net/ipv4/route.c). 41 * Nodes are removed only when reference counter goes to 0. 42 * When it's happened the node may be removed when a sufficient amount of 43 * time has been passed since its last use. The less-recently-used entry can 44 * also be removed if the pool is overloaded i.e. if the total amount of 45 * entries is greater-or-equal than the threshold. 46 * 47 * Node pool is organised as an AVL tree. 48 * Such an implementation has been chosen not just for fun. It's a way to 49 * prevent easy and efficient DoS attacks by creating hash collisions. A huge 50 * amount of long living nodes in a single hash slot would significantly delay 51 * lookups performed with disabled BHs. 52 * 53 * Serialisation issues. 54 * 1. Nodes may appear in the tree only with the pool write lock held. 55 * 2. Nodes may disappear from the tree only with the pool write lock held 56 * AND reference count being 0. 57 * 3. Nodes appears and disappears from unused node list only under 58 * "inet_peer_unused_lock". 59 * 4. Global variable peer_total is modified under the pool lock. 60 * 5. struct inet_peer fields modification: 61 * avl_left, avl_right, avl_parent, avl_height: pool lock 62 * unused: unused node list lock 63 * refcnt: atomically against modifications on other CPU; 64 * usually under some other lock to prevent node disappearing 65 * dtime: unused node list lock 66 * v4daddr: unchangeable 67 * ip_id_count: idlock 68 */ 69 70 /* Exported for inet_getid inline function. */ 71 DEFINE_SPINLOCK(inet_peer_idlock); 72 73 static struct kmem_cache *peer_cachep __read_mostly; 74 75 #define node_height(x) x->avl_height 76 static struct inet_peer peer_fake_node = { 77 .avl_left = &peer_fake_node, 78 .avl_right = &peer_fake_node, 79 .avl_height = 0 80 }; 81 #define peer_avl_empty (&peer_fake_node) 82 static struct inet_peer *peer_root = peer_avl_empty; 83 static DEFINE_RWLOCK(peer_pool_lock); 84 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ 85 86 static int peer_total; 87 /* Exported for sysctl_net_ipv4. */ 88 int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more 89 * aggressively at this stage */ 90 int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */ 91 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */ 92 int inet_peer_gc_mintime __read_mostly = 10 * HZ; 93 int inet_peer_gc_maxtime __read_mostly = 120 * HZ; 94 95 static LIST_HEAD(unused_peers); 96 static DEFINE_SPINLOCK(inet_peer_unused_lock); 97 98 static void peer_check_expire(unsigned long dummy); 99 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0); 100 101 102 /* Called from ip_output.c:ip_init */ 103 void __init inet_initpeers(void) 104 { 105 struct sysinfo si; 106 107 /* Use the straight interface to information about memory. */ 108 si_meminfo(&si); 109 /* The values below were suggested by Alexey Kuznetsov 110 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values 111 * myself. --SAW 112 */ 113 if (si.totalram <= (32768*1024)/PAGE_SIZE) 114 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */ 115 if (si.totalram <= (16384*1024)/PAGE_SIZE) 116 inet_peer_threshold >>= 1; /* about 512KB */ 117 if (si.totalram <= (8192*1024)/PAGE_SIZE) 118 inet_peer_threshold >>= 2; /* about 128KB */ 119 120 peer_cachep = kmem_cache_create("inet_peer_cache", 121 sizeof(struct inet_peer), 122 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, 123 NULL); 124 125 /* All the timers, started at system startup tend 126 to synchronize. Perturb it a bit. 127 */ 128 peer_periodic_timer.expires = jiffies 129 + net_random() % inet_peer_gc_maxtime 130 + inet_peer_gc_maxtime; 131 add_timer(&peer_periodic_timer); 132 } 133 134 /* Called with or without local BH being disabled. */ 135 static void unlink_from_unused(struct inet_peer *p) 136 { 137 spin_lock_bh(&inet_peer_unused_lock); 138 list_del_init(&p->unused); 139 spin_unlock_bh(&inet_peer_unused_lock); 140 } 141 142 /* 143 * Called with local BH disabled and the pool lock held. 144 * _stack is known to be NULL or not at compile time, 145 * so compiler will optimize the if (_stack) tests. 146 */ 147 #define lookup(_daddr,_stack) \ 148 ({ \ 149 struct inet_peer *u, **v; \ 150 if (_stack != NULL) { \ 151 stackptr = _stack; \ 152 *stackptr++ = &peer_root; \ 153 } \ 154 for (u = peer_root; u != peer_avl_empty; ) { \ 155 if (_daddr == u->v4daddr) \ 156 break; \ 157 if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \ 158 v = &u->avl_left; \ 159 else \ 160 v = &u->avl_right; \ 161 if (_stack != NULL) \ 162 *stackptr++ = v; \ 163 u = *v; \ 164 } \ 165 u; \ 166 }) 167 168 /* Called with local BH disabled and the pool write lock held. */ 169 #define lookup_rightempty(start) \ 170 ({ \ 171 struct inet_peer *u, **v; \ 172 *stackptr++ = &start->avl_left; \ 173 v = &start->avl_left; \ 174 for (u = *v; u->avl_right != peer_avl_empty; ) { \ 175 v = &u->avl_right; \ 176 *stackptr++ = v; \ 177 u = *v; \ 178 } \ 179 u; \ 180 }) 181 182 /* Called with local BH disabled and the pool write lock held. 183 * Variable names are the proof of operation correctness. 184 * Look into mm/map_avl.c for more detail description of the ideas. */ 185 static void peer_avl_rebalance(struct inet_peer **stack[], 186 struct inet_peer ***stackend) 187 { 188 struct inet_peer **nodep, *node, *l, *r; 189 int lh, rh; 190 191 while (stackend > stack) { 192 nodep = *--stackend; 193 node = *nodep; 194 l = node->avl_left; 195 r = node->avl_right; 196 lh = node_height(l); 197 rh = node_height(r); 198 if (lh > rh + 1) { /* l: RH+2 */ 199 struct inet_peer *ll, *lr, *lrl, *lrr; 200 int lrh; 201 ll = l->avl_left; 202 lr = l->avl_right; 203 lrh = node_height(lr); 204 if (lrh <= node_height(ll)) { /* ll: RH+1 */ 205 node->avl_left = lr; /* lr: RH or RH+1 */ 206 node->avl_right = r; /* r: RH */ 207 node->avl_height = lrh + 1; /* RH+1 or RH+2 */ 208 l->avl_left = ll; /* ll: RH+1 */ 209 l->avl_right = node; /* node: RH+1 or RH+2 */ 210 l->avl_height = node->avl_height + 1; 211 *nodep = l; 212 } else { /* ll: RH, lr: RH+1 */ 213 lrl = lr->avl_left; /* lrl: RH or RH-1 */ 214 lrr = lr->avl_right; /* lrr: RH or RH-1 */ 215 node->avl_left = lrr; /* lrr: RH or RH-1 */ 216 node->avl_right = r; /* r: RH */ 217 node->avl_height = rh + 1; /* node: RH+1 */ 218 l->avl_left = ll; /* ll: RH */ 219 l->avl_right = lrl; /* lrl: RH or RH-1 */ 220 l->avl_height = rh + 1; /* l: RH+1 */ 221 lr->avl_left = l; /* l: RH+1 */ 222 lr->avl_right = node; /* node: RH+1 */ 223 lr->avl_height = rh + 2; 224 *nodep = lr; 225 } 226 } else if (rh > lh + 1) { /* r: LH+2 */ 227 struct inet_peer *rr, *rl, *rlr, *rll; 228 int rlh; 229 rr = r->avl_right; 230 rl = r->avl_left; 231 rlh = node_height(rl); 232 if (rlh <= node_height(rr)) { /* rr: LH+1 */ 233 node->avl_right = rl; /* rl: LH or LH+1 */ 234 node->avl_left = l; /* l: LH */ 235 node->avl_height = rlh + 1; /* LH+1 or LH+2 */ 236 r->avl_right = rr; /* rr: LH+1 */ 237 r->avl_left = node; /* node: LH+1 or LH+2 */ 238 r->avl_height = node->avl_height + 1; 239 *nodep = r; 240 } else { /* rr: RH, rl: RH+1 */ 241 rlr = rl->avl_right; /* rlr: LH or LH-1 */ 242 rll = rl->avl_left; /* rll: LH or LH-1 */ 243 node->avl_right = rll; /* rll: LH or LH-1 */ 244 node->avl_left = l; /* l: LH */ 245 node->avl_height = lh + 1; /* node: LH+1 */ 246 r->avl_right = rr; /* rr: LH */ 247 r->avl_left = rlr; /* rlr: LH or LH-1 */ 248 r->avl_height = lh + 1; /* r: LH+1 */ 249 rl->avl_right = r; /* r: LH+1 */ 250 rl->avl_left = node; /* node: LH+1 */ 251 rl->avl_height = lh + 2; 252 *nodep = rl; 253 } 254 } else { 255 node->avl_height = (lh > rh ? lh : rh) + 1; 256 } 257 } 258 } 259 260 /* Called with local BH disabled and the pool write lock held. */ 261 #define link_to_pool(n) \ 262 do { \ 263 n->avl_height = 1; \ 264 n->avl_left = peer_avl_empty; \ 265 n->avl_right = peer_avl_empty; \ 266 **--stackptr = n; \ 267 peer_avl_rebalance(stack, stackptr); \ 268 } while(0) 269 270 /* May be called with local BH enabled. */ 271 static void unlink_from_pool(struct inet_peer *p) 272 { 273 int do_free; 274 275 do_free = 0; 276 277 write_lock_bh(&peer_pool_lock); 278 /* Check the reference counter. It was artificially incremented by 1 279 * in cleanup() function to prevent sudden disappearing. If the 280 * reference count is still 1 then the node is referenced only as `p' 281 * here and from the pool. So under the exclusive pool lock it's safe 282 * to remove the node and free it later. */ 283 if (atomic_read(&p->refcnt) == 1) { 284 struct inet_peer **stack[PEER_MAXDEPTH]; 285 struct inet_peer ***stackptr, ***delp; 286 if (lookup(p->v4daddr, stack) != p) 287 BUG(); 288 delp = stackptr - 1; /* *delp[0] == p */ 289 if (p->avl_left == peer_avl_empty) { 290 *delp[0] = p->avl_right; 291 --stackptr; 292 } else { 293 /* look for a node to insert instead of p */ 294 struct inet_peer *t; 295 t = lookup_rightempty(p); 296 BUG_ON(*stackptr[-1] != t); 297 **--stackptr = t->avl_left; 298 /* t is removed, t->v4daddr > x->v4daddr for any 299 * x in p->avl_left subtree. 300 * Put t in the old place of p. */ 301 *delp[0] = t; 302 t->avl_left = p->avl_left; 303 t->avl_right = p->avl_right; 304 t->avl_height = p->avl_height; 305 BUG_ON(delp[1] != &p->avl_left); 306 delp[1] = &t->avl_left; /* was &p->avl_left */ 307 } 308 peer_avl_rebalance(stack, stackptr); 309 peer_total--; 310 do_free = 1; 311 } 312 write_unlock_bh(&peer_pool_lock); 313 314 if (do_free) 315 kmem_cache_free(peer_cachep, p); 316 else 317 /* The node is used again. Decrease the reference counter 318 * back. The loop "cleanup -> unlink_from_unused 319 * -> unlink_from_pool -> putpeer -> link_to_unused 320 * -> cleanup (for the same node)" 321 * doesn't really exist because the entry will have a 322 * recent deletion time and will not be cleaned again soon. */ 323 inet_putpeer(p); 324 } 325 326 /* May be called with local BH enabled. */ 327 static int cleanup_once(unsigned long ttl) 328 { 329 struct inet_peer *p = NULL; 330 331 /* Remove the first entry from the list of unused nodes. */ 332 spin_lock_bh(&inet_peer_unused_lock); 333 if (!list_empty(&unused_peers)) { 334 __u32 delta; 335 336 p = list_first_entry(&unused_peers, struct inet_peer, unused); 337 delta = (__u32)jiffies - p->dtime; 338 339 if (delta < ttl) { 340 /* Do not prune fresh entries. */ 341 spin_unlock_bh(&inet_peer_unused_lock); 342 return -1; 343 } 344 345 list_del_init(&p->unused); 346 347 /* Grab an extra reference to prevent node disappearing 348 * before unlink_from_pool() call. */ 349 atomic_inc(&p->refcnt); 350 } 351 spin_unlock_bh(&inet_peer_unused_lock); 352 353 if (p == NULL) 354 /* It means that the total number of USED entries has 355 * grown over inet_peer_threshold. It shouldn't really 356 * happen because of entry limits in route cache. */ 357 return -1; 358 359 unlink_from_pool(p); 360 return 0; 361 } 362 363 /* Called with or without local BH being disabled. */ 364 struct inet_peer *inet_getpeer(__be32 daddr, int create) 365 { 366 struct inet_peer *p, *n; 367 struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; 368 369 /* Look up for the address quickly. */ 370 read_lock_bh(&peer_pool_lock); 371 p = lookup(daddr, NULL); 372 if (p != peer_avl_empty) 373 atomic_inc(&p->refcnt); 374 read_unlock_bh(&peer_pool_lock); 375 376 if (p != peer_avl_empty) { 377 /* The existing node has been found. */ 378 /* Remove the entry from unused list if it was there. */ 379 unlink_from_unused(p); 380 return p; 381 } 382 383 if (!create) 384 return NULL; 385 386 /* Allocate the space outside the locked region. */ 387 n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); 388 if (n == NULL) 389 return NULL; 390 n->v4daddr = daddr; 391 atomic_set(&n->refcnt, 1); 392 atomic_set(&n->rid, 0); 393 n->ip_id_count = secure_ip_id(daddr); 394 n->tcp_ts_stamp = 0; 395 396 write_lock_bh(&peer_pool_lock); 397 /* Check if an entry has suddenly appeared. */ 398 p = lookup(daddr, stack); 399 if (p != peer_avl_empty) 400 goto out_free; 401 402 /* Link the node. */ 403 link_to_pool(n); 404 INIT_LIST_HEAD(&n->unused); 405 peer_total++; 406 write_unlock_bh(&peer_pool_lock); 407 408 if (peer_total >= inet_peer_threshold) 409 /* Remove one less-recently-used entry. */ 410 cleanup_once(0); 411 412 return n; 413 414 out_free: 415 /* The appropriate node is already in the pool. */ 416 atomic_inc(&p->refcnt); 417 write_unlock_bh(&peer_pool_lock); 418 /* Remove the entry from unused list if it was there. */ 419 unlink_from_unused(p); 420 /* Free preallocated the preallocated node. */ 421 kmem_cache_free(peer_cachep, n); 422 return p; 423 } 424 425 /* Called with local BH disabled. */ 426 static void peer_check_expire(unsigned long dummy) 427 { 428 unsigned long now = jiffies; 429 int ttl; 430 431 if (peer_total >= inet_peer_threshold) 432 ttl = inet_peer_minttl; 433 else 434 ttl = inet_peer_maxttl 435 - (inet_peer_maxttl - inet_peer_minttl) / HZ * 436 peer_total / inet_peer_threshold * HZ; 437 while (!cleanup_once(ttl)) { 438 if (jiffies != now) 439 break; 440 } 441 442 /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime 443 * interval depending on the total number of entries (more entries, 444 * less interval). */ 445 if (peer_total >= inet_peer_threshold) 446 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime; 447 else 448 peer_periodic_timer.expires = jiffies 449 + inet_peer_gc_maxtime 450 - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * 451 peer_total / inet_peer_threshold * HZ; 452 add_timer(&peer_periodic_timer); 453 } 454 455 void inet_putpeer(struct inet_peer *p) 456 { 457 spin_lock_bh(&inet_peer_unused_lock); 458 if (atomic_dec_and_test(&p->refcnt)) { 459 list_add_tail(&p->unused, &unused_peers); 460 p->dtime = (__u32)jiffies; 461 } 462 spin_unlock_bh(&inet_peer_unused_lock); 463 } 464