net/ipv4/inetpeer.c

   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);