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/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 struct kmem_cache *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 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 static struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
  98 static DEFINE_SPINLOCK(inet_peer_unused_lock);
  99
 100 static void peer_check_expire(unsigned long dummy);
 101 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
 102
 103 /* Exported for sysctl_net_ipv4.  */
 104 int inet_peer_gc_mintime = 10 * HZ,
 105     inet_peer_gc_maxtime = 120 * HZ;
 106
 107 /* Called from ip_output.c:ip_init  */
 108 void __init inet_initpeers(void)
 109 {
 110         struct sysinfo si;
 111
 112         /* Use the straight interface to information about memory. */
 113         si_meminfo(&si);
 114         /* The values below were suggested by Alexey Kuznetsov
 115          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 116          * myself.  --SAW
 117          */
 118         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 119                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 120         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 121                 inet_peer_threshold >>= 1; /* about 512KB */
 122         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 123                 inet_peer_threshold >>= 2; /* about 128KB */
 124
 125         peer_cachep = kmem_cache_create("inet_peer_cache",
 126                         sizeof(struct inet_peer),
 127                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
 128                         NULL, NULL);
 129
 130         /* All the timers, started at system startup tend
 131            to synchronize. Perturb it a bit.
 132          */
 133         peer_periodic_timer.expires = jiffies
 134                 + net_random() % inet_peer_gc_maxtime
 135                 + inet_peer_gc_maxtime;
 136         add_timer(&peer_periodic_timer);
 137 }
 138
 139 /* Called with or without local BH being disabled. */
 140 static void unlink_from_unused(struct inet_peer *p)
 141 {
 142         spin_lock_bh(&inet_peer_unused_lock);
 143         if (p->unused_prevp != NULL) {
 144                 /* On unused list. */
 145                 *p->unused_prevp = p->unused_next;
 146                 if (p->unused_next != NULL)
 147                         p->unused_next->unused_prevp = p->unused_prevp;
 148                 else
 149                         inet_peer_unused_tailp = p->unused_prevp;
 150                 p->unused_prevp = NULL; /* mark it as removed */
 151         }
 152         spin_unlock_bh(&inet_peer_unused_lock);
 153 }
 154
 155 /* Called with local BH disabled and the pool lock held. */
 156 #define lookup(daddr)                                           \
 157 ({                                                              \
 158         struct inet_peer *u, **v;                               \
 159         stackptr = stack;                                       \
 160         *stackptr++ = &peer_root;                               \
 161         for (u = peer_root; u != peer_avl_empty; ) {            \
 162                 if (daddr == u->v4daddr)                        \
 163                         break;                                  \
 164                 if ((__force __u32)daddr < (__force __u32)u->v4daddr)   \
 165                         v = &u->avl_left;                       \
 166                 else                                            \
 167                         v = &u->avl_right;                      \
 168                 *stackptr++ = v;                                \
 169                 u = *v;                                         \
 170         }                                                       \
 171         u;                                                      \
 172 })
 173
 174 /* Called with local BH disabled and the pool write lock held. */
 175 #define lookup_rightempty(start)                                \
 176 ({                                                              \
 177         struct inet_peer *u, **v;                               \
 178         *stackptr++ = &start->avl_left;                         \
 179         v = &start->avl_left;                                   \
 180         for (u = *v; u->avl_right != peer_avl_empty; ) {        \
 181                 v = &u->avl_right;                              \
 182                 *stackptr++ = v;                                \
 183                 u = *v;                                         \
 184         }                                                       \
 185         u;                                                      \
 186 })
 187
 188 /* Called with local BH disabled and the pool write lock held.
 189  * Variable names are the proof of operation correctness.
 190  * Look into mm/map_avl.c for more detail description of the ideas.  */
 191 static void peer_avl_rebalance(struct inet_peer **stack[],
 192                 struct inet_peer ***stackend)
 193 {
 194         struct inet_peer **nodep, *node, *l, *r;
 195         int lh, rh;
 196
 197         while (stackend > stack) {
 198                 nodep = *--stackend;
 199                 node = *nodep;
 200                 l = node->avl_left;
 201                 r = node->avl_right;
 202                 lh = node_height(l);
 203                 rh = node_height(r);
 204                 if (lh > rh + 1) { /* l: RH+2 */
 205                         struct inet_peer *ll, *lr, *lrl, *lrr;
 206                         int lrh;
 207                         ll = l->avl_left;
 208                         lr = l->avl_right;
 209                         lrh = node_height(lr);
 210                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 211                                 node->avl_left = lr;    /* lr: RH or RH+1 */
 212                                 node->avl_right = r;    /* r: RH */
 213                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 214                                 l->avl_left = ll;       /* ll: RH+1 */
 215                                 l->avl_right = node;    /* node: RH+1 or RH+2 */
 216                                 l->avl_height = node->avl_height + 1;
 217                                 *nodep = l;
 218                         } else { /* ll: RH, lr: RH+1 */
 219                                 lrl = lr->avl_left;     /* lrl: RH or RH-1 */
 220                                 lrr = lr->avl_right;    /* lrr: RH or RH-1 */
 221                                 node->avl_left = lrr;   /* lrr: RH or RH-1 */
 222                                 node->avl_right = r;    /* r: RH */
 223                                 node->avl_height = rh + 1; /* node: RH+1 */
 224                                 l->avl_left = ll;       /* ll: RH */
 225                                 l->avl_right = lrl;     /* lrl: RH or RH-1 */
 226                                 l->avl_height = rh + 1; /* l: RH+1 */
 227                                 lr->avl_left = l;       /* l: RH+1 */
 228                                 lr->avl_right = node;   /* node: RH+1 */
 229                                 lr->avl_height = rh + 2;
 230                                 *nodep = lr;
 231                         }
 232                 } else if (rh > lh + 1) { /* r: LH+2 */
 233                         struct inet_peer *rr, *rl, *rlr, *rll;
 234                         int rlh;
 235                         rr = r->avl_right;
 236                         rl = r->avl_left;
 237                         rlh = node_height(rl);
 238                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 239                                 node->avl_right = rl;   /* rl: LH or LH+1 */
 240                                 node->avl_left = l;     /* l: LH */
 241                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 242                                 r->avl_right = rr;      /* rr: LH+1 */
 243                                 r->avl_left = node;     /* node: LH+1 or LH+2 */
 244                                 r->avl_height = node->avl_height + 1;
 245                                 *nodep = r;
 246                         } else { /* rr: RH, rl: RH+1 */
 247                                 rlr = rl->avl_right;    /* rlr: LH or LH-1 */
 248                                 rll = rl->avl_left;     /* rll: LH or LH-1 */
 249                                 node->avl_right = rll;  /* rll: LH or LH-1 */
 250                                 node->avl_left = l;     /* l: LH */
 251                                 node->avl_height = lh + 1; /* node: LH+1 */
 252                                 r->avl_right = rr;      /* rr: LH */
 253                                 r->avl_left = rlr;      /* rlr: LH or LH-1 */
 254                                 r->avl_height = lh + 1; /* r: LH+1 */
 255                                 rl->avl_right = r;      /* r: LH+1 */
 256                                 rl->avl_left = node;    /* node: LH+1 */
 257                                 rl->avl_height = lh + 2;
 258                                 *nodep = rl;
 259                         }
 260                 } else {
 261                         node->avl_height = (lh > rh ? lh : rh) + 1;
 262                 }
 263         }
 264 }
 265
 266 /* Called with local BH disabled and the pool write lock held. */
 267 #define link_to_pool(n)                                         \
 268 do {                                                            \
 269         n->avl_height = 1;                                      \
 270         n->avl_left = peer_avl_empty;                           \
 271         n->avl_right = peer_avl_empty;                          \
 272         **--stackptr = n;                                       \
 273         peer_avl_rebalance(stack, stackptr);                    \
 274 } while(0)
 275
 276 /* May be called with local BH enabled. */
 277 static void unlink_from_pool(struct inet_peer *p)
 278 {
 279         int do_free;
 280
 281         do_free = 0;
 282
 283         write_lock_bh(&peer_pool_lock);
 284         /* Check the reference counter.  It was artificially incremented by 1
 285          * in cleanup() function to prevent sudden disappearing.  If the
 286          * reference count is still 1 then the node is referenced only as `p'
 287          * here and from the pool.  So under the exclusive pool lock it's safe
 288          * to remove the node and free it later. */
 289         if (atomic_read(&p->refcnt) == 1) {
 290                 struct inet_peer **stack[PEER_MAXDEPTH];
 291                 struct inet_peer ***stackptr, ***delp;
 292                 if (lookup(p->v4daddr) != p)
 293                         BUG();
 294                 delp = stackptr - 1; /* *delp[0] == p */
 295                 if (p->avl_left == peer_avl_empty) {
 296                         *delp[0] = p->avl_right;
 297                         --stackptr;
 298                 } else {
 299                         /* look for a node to insert instead of p */
 300                         struct inet_peer *t;
 301                         t = lookup_rightempty(p);
 302                         BUG_ON(*stackptr[-1] != t);
 303                         **--stackptr = t->avl_left;
 304                         /* t is removed, t->v4daddr > x->v4daddr for any
 305                          * x in p->avl_left subtree.
 306                          * Put t in the old place of p. */
 307                         *delp[0] = t;
 308                         t->avl_left = p->avl_left;
 309                         t->avl_right = p->avl_right;
 310                         t->avl_height = p->avl_height;
 311                         BUG_ON(delp[1] != &p->avl_left);
 312                         delp[1] = &t->avl_left; /* was &p->avl_left */
 313                 }
 314                 peer_avl_rebalance(stack, stackptr);
 315                 peer_total--;
 316                 do_free = 1;
 317         }
 318         write_unlock_bh(&peer_pool_lock);
 319
 320         if (do_free)
 321                 kmem_cache_free(peer_cachep, p);
 322         else
 323                 /* The node is used again.  Decrease the reference counter
 324                  * back.  The loop "cleanup -> unlink_from_unused
 325                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 326                  *   -> cleanup (for the same node)"
 327                  * doesn't really exist because the entry will have a
 328                  * recent deletion time and will not be cleaned again soon. */
 329                 inet_putpeer(p);
 330 }
 331
 332 /* May be called with local BH enabled. */
 333 static int cleanup_once(unsigned long ttl)
 334 {
 335         struct inet_peer *p;
 336
 337         /* Remove the first entry from the list of unused nodes. */
 338         spin_lock_bh(&inet_peer_unused_lock);
 339         p = inet_peer_unused_head;
 340         if (p != NULL) {
 341                 __u32 delta = (__u32)jiffies - p->dtime;
 342                 if (delta < ttl) {
 343                         /* Do not prune fresh entries. */
 344                         spin_unlock_bh(&inet_peer_unused_lock);
 345                         return -1;
 346                 }
 347                 inet_peer_unused_head = p->unused_next;
 348                 if (p->unused_next != NULL)
 349                         p->unused_next->unused_prevp = p->unused_prevp;
 350                 else
 351                         inet_peer_unused_tailp = p->unused_prevp;
 352                 p->unused_prevp = NULL; /* mark as not on the list */
 353                 /* Grab an extra reference to prevent node disappearing
 354                  * before unlink_from_pool() call. */
 355                 atomic_inc(&p->refcnt);
 356         }
 357         spin_unlock_bh(&inet_peer_unused_lock);
 358
 359         if (p == NULL)
 360                 /* It means that the total number of USED entries has
 361                  * grown over inet_peer_threshold.  It shouldn't really
 362                  * happen because of entry limits in route cache. */
 363                 return -1;
 364
 365         unlink_from_pool(p);
 366         return 0;
 367 }
 368
 369 /* Called with or without local BH being disabled. */
 370 struct inet_peer *inet_getpeer(__be32 daddr, int create)
 371 {
 372         struct inet_peer *p, *n;
 373         struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
 374
 375         /* Look up for the address quickly. */
 376         read_lock_bh(&peer_pool_lock);
 377         p = lookup(daddr);
 378         if (p != peer_avl_empty)
 379                 atomic_inc(&p->refcnt);
 380         read_unlock_bh(&peer_pool_lock);
 381
 382         if (p != peer_avl_empty) {
 383                 /* The existing node has been found. */
 384                 /* Remove the entry from unused list if it was there. */
 385                 unlink_from_unused(p);
 386                 return p;
 387         }
 388
 389         if (!create)
 390                 return NULL;
 391
 392         /* Allocate the space outside the locked region. */
 393         n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
 394         if (n == NULL)
 395                 return NULL;
 396         n->v4daddr = daddr;
 397         atomic_set(&n->refcnt, 1);
 398         atomic_set(&n->rid, 0);
 399         n->ip_id_count = secure_ip_id(daddr);
 400         n->tcp_ts_stamp = 0;
 401
 402         write_lock_bh(&peer_pool_lock);
 403         /* Check if an entry has suddenly appeared. */
 404         p = lookup(daddr);
 405         if (p != peer_avl_empty)
 406                 goto out_free;
 407
 408         /* Link the node. */
 409         link_to_pool(n);
 410         n->unused_prevp = NULL; /* not on the list */
 411         peer_total++;
 412         write_unlock_bh(&peer_pool_lock);
 413
 414         if (peer_total >= inet_peer_threshold)
 415                 /* Remove one less-recently-used entry. */
 416                 cleanup_once(0);
 417
 418         return n;
 419
 420 out_free:
 421         /* The appropriate node is already in the pool. */
 422         atomic_inc(&p->refcnt);
 423         write_unlock_bh(&peer_pool_lock);
 424         /* Remove the entry from unused list if it was there. */
 425         unlink_from_unused(p);
 426         /* Free preallocated the preallocated node. */
 427         kmem_cache_free(peer_cachep, n);
 428         return p;
 429 }
 430
 431 /* Called with local BH disabled. */
 432 static void peer_check_expire(unsigned long dummy)
 433 {
 434         unsigned long now = jiffies;
 435         int ttl;
 436
 437         if (peer_total >= inet_peer_threshold)
 438                 ttl = inet_peer_minttl;
 439         else
 440                 ttl = inet_peer_maxttl
 441                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 442                                         peer_total / inet_peer_threshold * HZ;
 443         while (!cleanup_once(ttl)) {
 444                 if (jiffies != now)
 445                         break;
 446         }
 447
 448         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 449          * interval depending on the total number of entries (more entries,
 450          * less interval). */
 451         if (peer_total >= inet_peer_threshold)
 452                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
 453         else
 454                 peer_periodic_timer.expires = jiffies
 455                         + inet_peer_gc_maxtime
 456                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
 457                                 peer_total / inet_peer_threshold * HZ;
 458         add_timer(&peer_periodic_timer);
 459 }
 460
 461 void inet_putpeer(struct inet_peer *p)
 462 {
 463         spin_lock_bh(&inet_peer_unused_lock);
 464         if (atomic_dec_and_test(&p->refcnt)) {
 465                 p->unused_prevp = inet_peer_unused_tailp;
 466                 p->unused_next = NULL;
 467                 *inet_peer_unused_tailp = p;
 468                 inet_peer_unused_tailp = &p->unused_next;
 469                 p->dtime = (__u32)jiffies;
 470         }
 471         spin_unlock_bh(&inet_peer_unused_lock);
 472 }