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/timer.h>
  18 #include <linux/time.h>
  19 #include <linux/kernel.h>
  20 #include <linux/mm.h>
  21 #include <linux/net.h>
  22 #include <net/ip.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: 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 struct kmem_cache *peer_cachep __read_mostly;
  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 int peer_total;
  89 /* Exported for sysctl_net_ipv4.  */
  90 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
  91                                          * aggressively at this stage */
  92 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
  93 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
  94 int inet_peer_gc_mintime __read_mostly = 10 * HZ;
  95 int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
  96
  97 static LIST_HEAD(unused_peers);
  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
 104 /* Called from ip_output.c:ip_init  */
 105 void __init inet_initpeers(void)
 106 {
 107         struct sysinfo si;
 108
 109         /* Use the straight interface to information about memory. */
 110         si_meminfo(&si);
 111         /* The values below were suggested by Alexey Kuznetsov
 112          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 113          * myself.  --SAW
 114          */
 115         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 116                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 117         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 118                 inet_peer_threshold >>= 1; /* about 512KB */
 119         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 120                 inet_peer_threshold >>= 2; /* about 128KB */
 121
 122         peer_cachep = kmem_cache_create("inet_peer_cache",
 123                         sizeof(struct inet_peer),
 124                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
 125                         NULL);
 126
 127         /* All the timers, started at system startup tend
 128            to synchronize. Perturb it a bit.
 129          */
 130         peer_periodic_timer.expires = jiffies
 131                 + net_random() % inet_peer_gc_maxtime
 132                 + inet_peer_gc_maxtime;
 133         add_timer(&peer_periodic_timer);
 134 }
 135
 136 /* Called with or without local BH being disabled. */
 137 static void unlink_from_unused(struct inet_peer *p)
 138 {
 139         spin_lock_bh(&inet_peer_unused_lock);
 140         list_del_init(&p->unused);
 141         spin_unlock_bh(&inet_peer_unused_lock);
 142 }
 143
 144 /*
 145  * Called with local BH disabled and the pool lock held.
 146  * _stack is known to be NULL or not at compile time,
 147  * so compiler will optimize the if (_stack) tests.
 148  */
 149 #define lookup(_daddr,_stack)                                   \
 150 ({                                                              \
 151         struct inet_peer *u, **v;                               \
 152         if (_stack != NULL) {                                   \
 153                 stackptr = _stack;                              \
 154                 *stackptr++ = &peer_root;                       \
 155         }                                                       \
 156         for (u = peer_root; u != peer_avl_empty; ) {            \
 157                 if (_daddr == u->v4daddr)                       \
 158                         break;                                  \
 159                 if ((__force __u32)_daddr < (__force __u32)u->v4daddr)  \
 160                         v = &u->avl_left;                       \
 161                 else                                            \
 162                         v = &u->avl_right;                      \
 163                 if (_stack != NULL)                             \
 164                         *stackptr++ = v;                        \
 165                 u = *v;                                         \
 166         }                                                       \
 167         u;                                                      \
 168 })
 169
 170 /* Called with local BH disabled and the pool write lock held. */
 171 #define lookup_rightempty(start)                                \
 172 ({                                                              \
 173         struct inet_peer *u, **v;                               \
 174         *stackptr++ = &start->avl_left;                         \
 175         v = &start->avl_left;                                   \
 176         for (u = *v; u->avl_right != peer_avl_empty; ) {        \
 177                 v = &u->avl_right;                              \
 178                 *stackptr++ = v;                                \
 179                 u = *v;                                         \
 180         }                                                       \
 181         u;                                                      \
 182 })
 183
 184 /* Called with local BH disabled and the pool write lock held.
 185  * Variable names are the proof of operation correctness.
 186  * Look into mm/map_avl.c for more detail description of the ideas.  */
 187 static void peer_avl_rebalance(struct inet_peer **stack[],
 188                 struct inet_peer ***stackend)
 189 {
 190         struct inet_peer **nodep, *node, *l, *r;
 191         int lh, rh;
 192
 193         while (stackend > stack) {
 194                 nodep = *--stackend;
 195                 node = *nodep;
 196                 l = node->avl_left;
 197                 r = node->avl_right;
 198                 lh = node_height(l);
 199                 rh = node_height(r);
 200                 if (lh > rh + 1) { /* l: RH+2 */
 201                         struct inet_peer *ll, *lr, *lrl, *lrr;
 202                         int lrh;
 203                         ll = l->avl_left;
 204                         lr = l->avl_right;
 205                         lrh = node_height(lr);
 206                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 207                                 node->avl_left = lr;    /* lr: RH or RH+1 */
 208                                 node->avl_right = r;    /* r: RH */
 209                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 210                                 l->avl_left = ll;       /* ll: RH+1 */
 211                                 l->avl_right = node;    /* node: RH+1 or RH+2 */
 212                                 l->avl_height = node->avl_height + 1;
 213                                 *nodep = l;
 214                         } else { /* ll: RH, lr: RH+1 */
 215                                 lrl = lr->avl_left;     /* lrl: RH or RH-1 */
 216                                 lrr = lr->avl_right;    /* lrr: RH or RH-1 */
 217                                 node->avl_left = lrr;   /* lrr: RH or RH-1 */
 218                                 node->avl_right = r;    /* r: RH */
 219                                 node->avl_height = rh + 1; /* node: RH+1 */
 220                                 l->avl_left = ll;       /* ll: RH */
 221                                 l->avl_right = lrl;     /* lrl: RH or RH-1 */
 222                                 l->avl_height = rh + 1; /* l: RH+1 */
 223                                 lr->avl_left = l;       /* l: RH+1 */
 224                                 lr->avl_right = node;   /* node: RH+1 */
 225                                 lr->avl_height = rh + 2;
 226                                 *nodep = lr;
 227                         }
 228                 } else if (rh > lh + 1) { /* r: LH+2 */
 229                         struct inet_peer *rr, *rl, *rlr, *rll;
 230                         int rlh;
 231                         rr = r->avl_right;
 232                         rl = r->avl_left;
 233                         rlh = node_height(rl);
 234                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 235                                 node->avl_right = rl;   /* rl: LH or LH+1 */
 236                                 node->avl_left = l;     /* l: LH */
 237                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 238                                 r->avl_right = rr;      /* rr: LH+1 */
 239                                 r->avl_left = node;     /* node: LH+1 or LH+2 */
 240                                 r->avl_height = node->avl_height + 1;
 241                                 *nodep = r;
 242                         } else { /* rr: RH, rl: RH+1 */
 243                                 rlr = rl->avl_right;    /* rlr: LH or LH-1 */
 244                                 rll = rl->avl_left;     /* rll: LH or LH-1 */
 245                                 node->avl_right = rll;  /* rll: LH or LH-1 */
 246                                 node->avl_left = l;     /* l: LH */
 247                                 node->avl_height = lh + 1; /* node: LH+1 */
 248                                 r->avl_right = rr;      /* rr: LH */
 249                                 r->avl_left = rlr;      /* rlr: LH or LH-1 */
 250                                 r->avl_height = lh + 1; /* r: LH+1 */
 251                                 rl->avl_right = r;      /* r: LH+1 */
 252                                 rl->avl_left = node;    /* node: LH+1 */
 253                                 rl->avl_height = lh + 2;
 254                                 *nodep = rl;
 255                         }
 256                 } else {
 257                         node->avl_height = (lh > rh ? lh : rh) + 1;
 258                 }
 259         }
 260 }
 261
 262 /* Called with local BH disabled and the pool write lock held. */
 263 #define link_to_pool(n)                                         \
 264 do {                                                            \
 265         n->avl_height = 1;                                      \
 266         n->avl_left = peer_avl_empty;                           \
 267         n->avl_right = peer_avl_empty;                          \
 268         **--stackptr = n;                                       \
 269         peer_avl_rebalance(stack, stackptr);                    \
 270 } while(0)
 271
 272 /* May be called with local BH enabled. */
 273 static void unlink_from_pool(struct inet_peer *p)
 274 {
 275         int do_free;
 276
 277         do_free = 0;
 278
 279         write_lock_bh(&peer_pool_lock);
 280         /* Check the reference counter.  It was artificially incremented by 1
 281          * in cleanup() function to prevent sudden disappearing.  If the
 282          * reference count is still 1 then the node is referenced only as `p'
 283          * here and from the pool.  So under the exclusive pool lock it's safe
 284          * to remove the node and free it later. */
 285         if (atomic_read(&p->refcnt) == 1) {
 286                 struct inet_peer **stack[PEER_MAXDEPTH];
 287                 struct inet_peer ***stackptr, ***delp;
 288                 if (lookup(p->v4daddr, stack) != p)
 289                         BUG();
 290                 delp = stackptr - 1; /* *delp[0] == p */
 291                 if (p->avl_left == peer_avl_empty) {
 292                         *delp[0] = p->avl_right;
 293                         --stackptr;
 294                 } else {
 295                         /* look for a node to insert instead of p */
 296                         struct inet_peer *t;
 297                         t = lookup_rightempty(p);
 298                         BUG_ON(*stackptr[-1] != t);
 299                         **--stackptr = t->avl_left;
 300                         /* t is removed, t->v4daddr > x->v4daddr for any
 301                          * x in p->avl_left subtree.
 302                          * Put t in the old place of p. */
 303                         *delp[0] = t;
 304                         t->avl_left = p->avl_left;
 305                         t->avl_right = p->avl_right;
 306                         t->avl_height = p->avl_height;
 307                         BUG_ON(delp[1] != &p->avl_left);
 308                         delp[1] = &t->avl_left; /* was &p->avl_left */
 309                 }
 310                 peer_avl_rebalance(stack, stackptr);
 311                 peer_total--;
 312                 do_free = 1;
 313         }
 314         write_unlock_bh(&peer_pool_lock);
 315
 316         if (do_free)
 317                 kmem_cache_free(peer_cachep, p);
 318         else
 319                 /* The node is used again.  Decrease the reference counter
 320                  * back.  The loop "cleanup -> unlink_from_unused
 321                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 322                  *   -> cleanup (for the same node)"
 323                  * doesn't really exist because the entry will have a
 324                  * recent deletion time and will not be cleaned again soon. */
 325                 inet_putpeer(p);
 326 }
 327
 328 /* May be called with local BH enabled. */
 329 static int cleanup_once(unsigned long ttl)
 330 {
 331         struct inet_peer *p = NULL;
 332
 333         /* Remove the first entry from the list of unused nodes. */
 334         spin_lock_bh(&inet_peer_unused_lock);
 335         if (!list_empty(&unused_peers)) {
 336                 __u32 delta;
 337
 338                 p = list_first_entry(&unused_peers, struct inet_peer, unused);
 339                 delta = (__u32)jiffies - p->dtime;
 340
 341                 if (delta < ttl) {
 342                         /* Do not prune fresh entries. */
 343                         spin_unlock_bh(&inet_peer_unused_lock);
 344                         return -1;
 345                 }
 346
 347                 list_del_init(&p->unused);
 348
 349                 /* Grab an extra reference to prevent node disappearing
 350                  * before unlink_from_pool() call. */
 351                 atomic_inc(&p->refcnt);
 352         }
 353         spin_unlock_bh(&inet_peer_unused_lock);
 354
 355         if (p == NULL)
 356                 /* It means that the total number of USED entries has
 357                  * grown over inet_peer_threshold.  It shouldn't really
 358                  * happen because of entry limits in route cache. */
 359                 return -1;
 360
 361         unlink_from_pool(p);
 362         return 0;
 363 }
 364
 365 /* Called with or without local BH being disabled. */
 366 struct inet_peer *inet_getpeer(__be32 daddr, int create)
 367 {
 368         struct inet_peer *p, *n;
 369         struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
 370
 371         /* Look up for the address quickly. */
 372         read_lock_bh(&peer_pool_lock);
 373         p = lookup(daddr, NULL);
 374         if (p != peer_avl_empty)
 375                 atomic_inc(&p->refcnt);
 376         read_unlock_bh(&peer_pool_lock);
 377
 378         if (p != peer_avl_empty) {
 379                 /* The existing node has been found. */
 380                 /* Remove the entry from unused list if it was there. */
 381                 unlink_from_unused(p);
 382                 return p;
 383         }
 384
 385         if (!create)
 386                 return NULL;
 387
 388         /* Allocate the space outside the locked region. */
 389         n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
 390         if (n == NULL)
 391                 return NULL;
 392         n->v4daddr = daddr;
 393         atomic_set(&n->refcnt, 1);
 394         atomic_set(&n->rid, 0);
 395         n->ip_id_count = secure_ip_id(daddr);
 396         n->tcp_ts_stamp = 0;
 397
 398         write_lock_bh(&peer_pool_lock);
 399         /* Check if an entry has suddenly appeared. */
 400         p = lookup(daddr, stack);
 401         if (p != peer_avl_empty)
 402                 goto out_free;
 403
 404         /* Link the node. */
 405         link_to_pool(n);
 406         INIT_LIST_HEAD(&n->unused);
 407         peer_total++;
 408         write_unlock_bh(&peer_pool_lock);
 409
 410         if (peer_total >= inet_peer_threshold)
 411                 /* Remove one less-recently-used entry. */
 412                 cleanup_once(0);
 413
 414         return n;
 415
 416 out_free:
 417         /* The appropriate node is already in the pool. */
 418         atomic_inc(&p->refcnt);
 419         write_unlock_bh(&peer_pool_lock);
 420         /* Remove the entry from unused list if it was there. */
 421         unlink_from_unused(p);
 422         /* Free preallocated the preallocated node. */
 423         kmem_cache_free(peer_cachep, n);
 424         return p;
 425 }
 426
 427 /* Called with local BH disabled. */
 428 static void peer_check_expire(unsigned long dummy)
 429 {
 430         unsigned long now = jiffies;
 431         int ttl;
 432
 433         if (peer_total >= inet_peer_threshold)
 434                 ttl = inet_peer_minttl;
 435         else
 436                 ttl = inet_peer_maxttl
 437                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 438                                         peer_total / inet_peer_threshold * HZ;
 439         while (!cleanup_once(ttl)) {
 440                 if (jiffies != now)
 441                         break;
 442         }
 443
 444         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 445          * interval depending on the total number of entries (more entries,
 446          * less interval). */
 447         if (peer_total >= inet_peer_threshold)
 448                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
 449         else
 450                 peer_periodic_timer.expires = jiffies
 451                         + inet_peer_gc_maxtime
 452                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
 453                                 peer_total / inet_peer_threshold * HZ;
 454         add_timer(&peer_periodic_timer);
 455 }
 456
 457 void inet_putpeer(struct inet_peer *p)
 458 {
 459         spin_lock_bh(&inet_peer_unused_lock);
 460         if (atomic_dec_and_test(&p->refcnt)) {
 461                 list_add_tail(&p->unused, &unused_peers);
 462                 p->dtime = (__u32)jiffies;
 463         }
 464         spin_unlock_bh(&inet_peer_unused_lock);
 465 }