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 <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 static struct kmem_cache *peer_cachep __read_mostly;
  71
  72 #define node_height(x) x->avl_height
  73
  74 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
  75 static const struct inet_peer peer_fake_node = {
  76         .avl_left       = peer_avl_empty,
  77         .avl_right      = peer_avl_empty,
  78         .avl_height     = 0
  79 };
  80
  81 static struct {
  82         struct inet_peer *root;
  83         rwlock_t        lock;
  84         int             total;
  85 } peers = {
  86         .root           = peer_avl_empty,
  87         .lock           = __RW_LOCK_UNLOCKED(peers.lock),
  88         .total          = 0,
  89 };
  90 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
  91
  92 /* Exported for sysctl_net_ipv4.  */
  93 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
  94                                          * aggressively at this stage */
  95 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
  96 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
  97 int inet_peer_gc_mintime __read_mostly = 10 * HZ;
  98 int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
  99
 100 static struct {
 101         struct list_head        list;
 102         spinlock_t              lock;
 103 } unused_peers = {
 104         .list                   = LIST_HEAD_INIT(unused_peers.list),
 105         .lock                   = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
 106 };
 107
 108 static void peer_check_expire(unsigned long dummy);
 109 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
 110
 111
 112 /* Called from ip_output.c:ip_init  */
 113 void __init inet_initpeers(void)
 114 {
 115         struct sysinfo si;
 116
 117         /* Use the straight interface to information about memory. */
 118         si_meminfo(&si);
 119         /* The values below were suggested by Alexey Kuznetsov
 120          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 121          * myself.  --SAW
 122          */
 123         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 124                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 125         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 126                 inet_peer_threshold >>= 1; /* about 512KB */
 127         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 128                 inet_peer_threshold >>= 2; /* about 128KB */
 129
 130         peer_cachep = kmem_cache_create("inet_peer_cache",
 131                         sizeof(struct inet_peer),
 132                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
 133                         NULL);
 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         if (!list_empty(&p->unused)) {
 148                 spin_lock_bh(&unused_peers.lock);
 149                 list_del_init(&p->unused);
 150                 spin_unlock_bh(&unused_peers.lock);
 151         }
 152 }
 153
 154 /*
 155  * Called with local BH disabled and the pool lock held.
 156  * _stack is known to be NULL or not at compile time,
 157  * so compiler will optimize the if (_stack) tests.
 158  */
 159 #define lookup(_daddr, _stack)                                  \
 160 ({                                                              \
 161         struct inet_peer *u, **v;                               \
 162         if (_stack != NULL) {                                   \
 163                 stackptr = _stack;                              \
 164                 *stackptr++ = &peers.root;                      \
 165         }                                                       \
 166         for (u = peers.root; u != peer_avl_empty; ) {           \
 167                 if (_daddr == u->v4daddr)                       \
 168                         break;                                  \
 169                 if ((__force __u32)_daddr < (__force __u32)u->v4daddr)  \
 170                         v = &u->avl_left;                       \
 171                 else                                            \
 172                         v = &u->avl_right;                      \
 173                 if (_stack != NULL)                             \
 174                         *stackptr++ = v;                        \
 175                 u = *v;                                         \
 176         }                                                       \
 177         u;                                                      \
 178 })
 179
 180 /* Called with local BH disabled and the pool write lock held. */
 181 #define lookup_rightempty(start)                                \
 182 ({                                                              \
 183         struct inet_peer *u, **v;                               \
 184         *stackptr++ = &start->avl_left;                         \
 185         v = &start->avl_left;                                   \
 186         for (u = *v; u->avl_right != peer_avl_empty; ) {        \
 187                 v = &u->avl_right;                              \
 188                 *stackptr++ = v;                                \
 189                 u = *v;                                         \
 190         }                                                       \
 191         u;                                                      \
 192 })
 193
 194 /* Called with local BH disabled and the pool write lock held.
 195  * Variable names are the proof of operation correctness.
 196  * Look into mm/map_avl.c for more detail description of the ideas.  */
 197 static void peer_avl_rebalance(struct inet_peer **stack[],
 198                 struct inet_peer ***stackend)
 199 {
 200         struct inet_peer **nodep, *node, *l, *r;
 201         int lh, rh;
 202
 203         while (stackend > stack) {
 204                 nodep = *--stackend;
 205                 node = *nodep;
 206                 l = node->avl_left;
 207                 r = node->avl_right;
 208                 lh = node_height(l);
 209                 rh = node_height(r);
 210                 if (lh > rh + 1) { /* l: RH+2 */
 211                         struct inet_peer *ll, *lr, *lrl, *lrr;
 212                         int lrh;
 213                         ll = l->avl_left;
 214                         lr = l->avl_right;
 215                         lrh = node_height(lr);
 216                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 217                                 node->avl_left = lr;    /* lr: RH or RH+1 */
 218                                 node->avl_right = r;    /* r: RH */
 219                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 220                                 l->avl_left = ll;       /* ll: RH+1 */
 221                                 l->avl_right = node;    /* node: RH+1 or RH+2 */
 222                                 l->avl_height = node->avl_height + 1;
 223                                 *nodep = l;
 224                         } else { /* ll: RH, lr: RH+1 */
 225                                 lrl = lr->avl_left;     /* lrl: RH or RH-1 */
 226                                 lrr = lr->avl_right;    /* lrr: RH or RH-1 */
 227                                 node->avl_left = lrr;   /* lrr: RH or RH-1 */
 228                                 node->avl_right = r;    /* r: RH */
 229                                 node->avl_height = rh + 1; /* node: RH+1 */
 230                                 l->avl_left = ll;       /* ll: RH */
 231                                 l->avl_right = lrl;     /* lrl: RH or RH-1 */
 232                                 l->avl_height = rh + 1; /* l: RH+1 */
 233                                 lr->avl_left = l;       /* l: RH+1 */
 234                                 lr->avl_right = node;   /* node: RH+1 */
 235                                 lr->avl_height = rh + 2;
 236                                 *nodep = lr;
 237                         }
 238                 } else if (rh > lh + 1) { /* r: LH+2 */
 239                         struct inet_peer *rr, *rl, *rlr, *rll;
 240                         int rlh;
 241                         rr = r->avl_right;
 242                         rl = r->avl_left;
 243                         rlh = node_height(rl);
 244                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 245                                 node->avl_right = rl;   /* rl: LH or LH+1 */
 246                                 node->avl_left = l;     /* l: LH */
 247                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 248                                 r->avl_right = rr;      /* rr: LH+1 */
 249                                 r->avl_left = node;     /* node: LH+1 or LH+2 */
 250                                 r->avl_height = node->avl_height + 1;
 251                                 *nodep = r;
 252                         } else { /* rr: RH, rl: RH+1 */
 253                                 rlr = rl->avl_right;    /* rlr: LH or LH-1 */
 254                                 rll = rl->avl_left;     /* rll: LH or LH-1 */
 255                                 node->avl_right = rll;  /* rll: LH or LH-1 */
 256                                 node->avl_left = l;     /* l: LH */
 257                                 node->avl_height = lh + 1; /* node: LH+1 */
 258                                 r->avl_right = rr;      /* rr: LH */
 259                                 r->avl_left = rlr;      /* rlr: LH or LH-1 */
 260                                 r->avl_height = lh + 1; /* r: LH+1 */
 261                                 rl->avl_right = r;      /* r: LH+1 */
 262                                 rl->avl_left = node;    /* node: LH+1 */
 263                                 rl->avl_height = lh + 2;
 264                                 *nodep = rl;
 265                         }
 266                 } else {
 267                         node->avl_height = (lh > rh ? lh : rh) + 1;
 268                 }
 269         }
 270 }
 271
 272 /* Called with local BH disabled and the pool write lock held. */
 273 #define link_to_pool(n)                                         \
 274 do {                                                            \
 275         n->avl_height = 1;                                      \
 276         n->avl_left = peer_avl_empty;                           \
 277         n->avl_right = peer_avl_empty;                          \
 278         **--stackptr = n;                                       \
 279         peer_avl_rebalance(stack, stackptr);                    \
 280 } while (0)
 281
 282 /* May be called with local BH enabled. */
 283 static void unlink_from_pool(struct inet_peer *p)
 284 {
 285         int do_free;
 286
 287         do_free = 0;
 288
 289         write_lock_bh(&peers.lock);
 290         /* Check the reference counter.  It was artificially incremented by 1
 291          * in cleanup() function to prevent sudden disappearing.  If the
 292          * reference count is still 1 then the node is referenced only as `p'
 293          * here and from the pool.  So under the exclusive pool lock it's safe
 294          * to remove the node and free it later. */
 295         if (atomic_read(&p->refcnt) == 1) {
 296                 struct inet_peer **stack[PEER_MAXDEPTH];
 297                 struct inet_peer ***stackptr, ***delp;
 298                 if (lookup(p->v4daddr, stack) != p)
 299                         BUG();
 300                 delp = stackptr - 1; /* *delp[0] == p */
 301                 if (p->avl_left == peer_avl_empty) {
 302                         *delp[0] = p->avl_right;
 303                         --stackptr;
 304                 } else {
 305                         /* look for a node to insert instead of p */
 306                         struct inet_peer *t;
 307                         t = lookup_rightempty(p);
 308                         BUG_ON(*stackptr[-1] != t);
 309                         **--stackptr = t->avl_left;
 310                         /* t is removed, t->v4daddr > x->v4daddr for any
 311                          * x in p->avl_left subtree.
 312                          * Put t in the old place of p. */
 313                         *delp[0] = t;
 314                         t->avl_left = p->avl_left;
 315                         t->avl_right = p->avl_right;
 316                         t->avl_height = p->avl_height;
 317                         BUG_ON(delp[1] != &p->avl_left);
 318                         delp[1] = &t->avl_left; /* was &p->avl_left */
 319                 }
 320                 peer_avl_rebalance(stack, stackptr);
 321                 peers.total--;
 322                 do_free = 1;
 323         }
 324         write_unlock_bh(&peers.lock);
 325
 326         if (do_free)
 327                 kmem_cache_free(peer_cachep, p);
 328         else
 329                 /* The node is used again.  Decrease the reference counter
 330                  * back.  The loop "cleanup -> unlink_from_unused
 331                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 332                  *   -> cleanup (for the same node)"
 333                  * doesn't really exist because the entry will have a
 334                  * recent deletion time and will not be cleaned again soon. */
 335                 inet_putpeer(p);
 336 }
 337
 338 /* May be called with local BH enabled. */
 339 static int cleanup_once(unsigned long ttl)
 340 {
 341         struct inet_peer *p = NULL;
 342
 343         /* Remove the first entry from the list of unused nodes. */
 344         spin_lock_bh(&unused_peers.lock);
 345         if (!list_empty(&unused_peers.list)) {
 346                 __u32 delta;
 347
 348                 p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
 349                 delta = (__u32)jiffies - p->dtime;
 350
 351                 if (delta < ttl) {
 352                         /* Do not prune fresh entries. */
 353                         spin_unlock_bh(&unused_peers.lock);
 354                         return -1;
 355                 }
 356
 357                 list_del_init(&p->unused);
 358
 359                 /* Grab an extra reference to prevent node disappearing
 360                  * before unlink_from_pool() call. */
 361                 atomic_inc(&p->refcnt);
 362         }
 363         spin_unlock_bh(&unused_peers.lock);
 364
 365         if (p == NULL)
 366                 /* It means that the total number of USED entries has
 367                  * grown over inet_peer_threshold.  It shouldn't really
 368                  * happen because of entry limits in route cache. */
 369                 return -1;
 370
 371         unlink_from_pool(p);
 372         return 0;
 373 }
 374
 375 /* Called with or without local BH being disabled. */
 376 struct inet_peer *inet_getpeer(__be32 daddr, int create)
 377 {
 378         struct inet_peer *p, *n;
 379         struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
 380
 381         /* Look up for the address quickly. */
 382         read_lock_bh(&peers.lock);
 383         p = lookup(daddr, NULL);
 384         if (p != peer_avl_empty)
 385                 atomic_inc(&p->refcnt);
 386         read_unlock_bh(&peers.lock);
 387
 388         if (p != peer_avl_empty) {
 389                 /* The existing node has been found. */
 390                 /* Remove the entry from unused list if it was there. */
 391                 unlink_from_unused(p);
 392                 return p;
 393         }
 394
 395         if (!create)
 396                 return NULL;
 397
 398         /* Allocate the space outside the locked region. */
 399         n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
 400         if (n == NULL)
 401                 return NULL;
 402         n->v4daddr = daddr;
 403         atomic_set(&n->refcnt, 1);
 404         atomic_set(&n->rid, 0);
 405         atomic_set(&n->ip_id_count, secure_ip_id(daddr));
 406         n->tcp_ts_stamp = 0;
 407
 408         write_lock_bh(&peers.lock);
 409         /* Check if an entry has suddenly appeared. */
 410         p = lookup(daddr, stack);
 411         if (p != peer_avl_empty)
 412                 goto out_free;
 413
 414         /* Link the node. */
 415         link_to_pool(n);
 416         INIT_LIST_HEAD(&n->unused);
 417         peers.total++;
 418         write_unlock_bh(&peers.lock);
 419
 420         if (peers.total >= inet_peer_threshold)
 421                 /* Remove one less-recently-used entry. */
 422                 cleanup_once(0);
 423
 424         return n;
 425
 426 out_free:
 427         /* The appropriate node is already in the pool. */
 428         atomic_inc(&p->refcnt);
 429         write_unlock_bh(&peers.lock);
 430         /* Remove the entry from unused list if it was there. */
 431         unlink_from_unused(p);
 432         /* Free preallocated the preallocated node. */
 433         kmem_cache_free(peer_cachep, n);
 434         return p;
 435 }
 436
 437 /* Called with local BH disabled. */
 438 static void peer_check_expire(unsigned long dummy)
 439 {
 440         unsigned long now = jiffies;
 441         int ttl;
 442
 443         if (peers.total >= inet_peer_threshold)
 444                 ttl = inet_peer_minttl;
 445         else
 446                 ttl = inet_peer_maxttl
 447                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 448                                         peers.total / inet_peer_threshold * HZ;
 449         while (!cleanup_once(ttl)) {
 450                 if (jiffies != now)
 451                         break;
 452         }
 453
 454         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 455          * interval depending on the total number of entries (more entries,
 456          * less interval). */
 457         if (peers.total >= inet_peer_threshold)
 458                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
 459         else
 460                 peer_periodic_timer.expires = jiffies
 461                         + inet_peer_gc_maxtime
 462                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
 463                                 peers.total / inet_peer_threshold * HZ;
 464         add_timer(&peer_periodic_timer);
 465 }
 466
 467 void inet_putpeer(struct inet_peer *p)
 468 {
 469         local_bh_disable();
 470
 471         if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
 472                 list_add_tail(&p->unused, &unused_peers.list);
 473                 p->dtime = (__u32)jiffies;
 474                 spin_unlock(&unused_peers.lock);
 475         }
 476
 477         local_bh_enable();
 478 }