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  *  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/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 kmem_cache_t *peer_cachep;
  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 volatile 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 /* Exported for inet_putpeer inline function.  */
  97 struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
  98 DEFINE_SPINLOCK(inet_peer_unused_lock);
  99 #define PEER_MAX_CLEANUP_WORK 30
 100
 101 static void peer_check_expire(unsigned long dummy);
 102 static struct timer_list peer_periodic_timer =
 103         TIMER_INITIALIZER(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                         if (*stackptr[-1] != t)
 308                                 BUG();
 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                         if (delp[1] != &p->avl_left)
 318                                 BUG();
 319                         delp[1] = &t->avl_left; /* was &p->avl_left */
 320                 }
 321                 peer_avl_rebalance(stack, stackptr);
 322                 peer_total--;
 323                 do_free = 1;
 324         }
 325         write_unlock_bh(&peer_pool_lock);
 326
 327         if (do_free)
 328                 kmem_cache_free(peer_cachep, p);
 329         else
 330                 /* The node is used again.  Decrease the reference counter
 331                  * back.  The loop "cleanup -> unlink_from_unused
 332                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 333                  *   -> cleanup (for the same node)"
 334                  * doesn't really exist because the entry will have a
 335                  * recent deletion time and will not be cleaned again soon. */
 336                 inet_putpeer(p);
 337 }
 338
 339 /* May be called with local BH enabled. */
 340 static int cleanup_once(unsigned long ttl)
 341 {
 342         struct inet_peer *p;
 343
 344         /* Remove the first entry from the list of unused nodes. */
 345         spin_lock_bh(&inet_peer_unused_lock);
 346         p = inet_peer_unused_head;
 347         if (p != NULL) {
 348                 if (time_after(p->dtime + ttl, jiffies)) {
 349                         /* Do not prune fresh entries. */
 350                         spin_unlock_bh(&inet_peer_unused_lock);
 351                         return -1;
 352                 }
 353                 inet_peer_unused_head = p->unused_next;
 354                 if (p->unused_next != NULL)
 355                         p->unused_next->unused_prevp = p->unused_prevp;
 356                 else
 357                         inet_peer_unused_tailp = p->unused_prevp;
 358                 p->unused_prevp = NULL; /* mark as not on the list */
 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(&inet_peer_unused_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(__u32 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(&peer_pool_lock);
 383         p = lookup(daddr);
 384         if (p != peer_avl_empty)
 385                 atomic_inc(&p->refcnt);
 386         read_unlock_bh(&peer_pool_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         n->ip_id_count = secure_ip_id(daddr);
 405         n->tcp_ts_stamp = 0;
 406
 407         write_lock_bh(&peer_pool_lock);
 408         /* Check if an entry has suddenly appeared. */
 409         p = lookup(daddr);
 410         if (p != peer_avl_empty)
 411                 goto out_free;
 412
 413         /* Link the node. */
 414         link_to_pool(n);
 415         n->unused_prevp = NULL; /* not on the list */
 416         peer_total++;
 417         write_unlock_bh(&peer_pool_lock);
 418
 419         if (peer_total >= inet_peer_threshold)
 420                 /* Remove one less-recently-used entry. */
 421                 cleanup_once(0);
 422
 423         return n;
 424
 425 out_free:
 426         /* The appropriate node is already in the pool. */
 427         atomic_inc(&p->refcnt);
 428         write_unlock_bh(&peer_pool_lock);
 429         /* Remove the entry from unused list if it was there. */
 430         unlink_from_unused(p);
 431         /* Free preallocated the preallocated node. */
 432         kmem_cache_free(peer_cachep, n);
 433         return p;
 434 }
 435
 436 /* Called with local BH disabled. */
 437 static void peer_check_expire(unsigned long dummy)
 438 {
 439         int i;
 440         int ttl;
 441
 442         if (peer_total >= inet_peer_threshold)
 443                 ttl = inet_peer_minttl;
 444         else
 445                 ttl = inet_peer_maxttl
 446                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 447                                         peer_total / inet_peer_threshold * HZ;
 448         for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++);
 449
 450         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 451          * interval depending on the total number of entries (more entries,
 452          * less interval). */
 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 EXPORT_SYMBOL(inet_peer_idlock);