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 /* Exported for inet_getid inline function.  */
  71 DEFINE_SPINLOCK(inet_peer_idlock);
  72
  73 static struct kmem_cache *peer_cachep __read_mostly;
  74
  75 #define node_height(x) x->avl_height
  76 static struct inet_peer peer_fake_node = {
  77         .avl_left       = &peer_fake_node,
  78         .avl_right      = &peer_fake_node,
  79         .avl_height     = 0
  80 };
  81 #define peer_avl_empty (&peer_fake_node)
  82 static struct inet_peer *peer_root = peer_avl_empty;
  83 static DEFINE_RWLOCK(peer_pool_lock);
  84 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
  85
  86 static int peer_total;
  87 /* Exported for sysctl_net_ipv4.  */
  88 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
  89                                          * aggressively at this stage */
  90 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
  91 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
  92 int inet_peer_gc_mintime __read_mostly = 10 * HZ;
  93 int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
  94
  95 static LIST_HEAD(unused_peers);
  96 static DEFINE_SPINLOCK(inet_peer_unused_lock);
  97
  98 static void peer_check_expire(unsigned long dummy);
  99 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
 100
 101
 102 /* Called from ip_output.c:ip_init  */
 103 void __init inet_initpeers(void)
 104 {
 105         struct sysinfo si;
 106
 107         /* Use the straight interface to information about memory. */
 108         si_meminfo(&si);
 109         /* The values below were suggested by Alexey Kuznetsov
 110          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 111          * myself.  --SAW
 112          */
 113         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 114                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 115         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 116                 inet_peer_threshold >>= 1; /* about 512KB */
 117         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 118                 inet_peer_threshold >>= 2; /* about 128KB */
 119
 120         peer_cachep = kmem_cache_create("inet_peer_cache",
 121                         sizeof(struct inet_peer),
 122                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
 123                         NULL);
 124
 125         /* All the timers, started at system startup tend
 126            to synchronize. Perturb it a bit.
 127          */
 128         peer_periodic_timer.expires = jiffies
 129                 + net_random() % inet_peer_gc_maxtime
 130                 + inet_peer_gc_maxtime;
 131         add_timer(&peer_periodic_timer);
 132 }
 133
 134 /* Called with or without local BH being disabled. */
 135 static void unlink_from_unused(struct inet_peer *p)
 136 {
 137         spin_lock_bh(&inet_peer_unused_lock);
 138         list_del_init(&p->unused);
 139         spin_unlock_bh(&inet_peer_unused_lock);
 140 }
 141
 142 /*
 143  * Called with local BH disabled and the pool lock held.
 144  * _stack is known to be NULL or not at compile time,
 145  * so compiler will optimize the if (_stack) tests.
 146  */
 147 #define lookup(_daddr, _stack)                                  \
 148 ({                                                              \
 149         struct inet_peer *u, **v;                               \
 150         if (_stack != NULL) {                                   \
 151                 stackptr = _stack;                              \
 152                 *stackptr++ = &peer_root;                       \
 153         }                                                       \
 154         for (u = peer_root; u != peer_avl_empty; ) {            \
 155                 if (_daddr == u->v4daddr)                       \
 156                         break;                                  \
 157                 if ((__force __u32)_daddr < (__force __u32)u->v4daddr)  \
 158                         v = &u->avl_left;                       \
 159                 else                                            \
 160                         v = &u->avl_right;                      \
 161                 if (_stack != NULL)                             \
 162                         *stackptr++ = v;                        \
 163                 u = *v;                                         \
 164         }                                                       \
 165         u;                                                      \
 166 })
 167
 168 /* Called with local BH disabled and the pool write lock held. */
 169 #define lookup_rightempty(start)                                \
 170 ({                                                              \
 171         struct inet_peer *u, **v;                               \
 172         *stackptr++ = &start->avl_left;                         \
 173         v = &start->avl_left;                                   \
 174         for (u = *v; u->avl_right != peer_avl_empty; ) {        \
 175                 v = &u->avl_right;                              \
 176                 *stackptr++ = v;                                \
 177                 u = *v;                                         \
 178         }                                                       \
 179         u;                                                      \
 180 })
 181
 182 /* Called with local BH disabled and the pool write lock held.
 183  * Variable names are the proof of operation correctness.
 184  * Look into mm/map_avl.c for more detail description of the ideas.  */
 185 static void peer_avl_rebalance(struct inet_peer **stack[],
 186                 struct inet_peer ***stackend)
 187 {
 188         struct inet_peer **nodep, *node, *l, *r;
 189         int lh, rh;
 190
 191         while (stackend > stack) {
 192                 nodep = *--stackend;
 193                 node = *nodep;
 194                 l = node->avl_left;
 195                 r = node->avl_right;
 196                 lh = node_height(l);
 197                 rh = node_height(r);
 198                 if (lh > rh + 1) { /* l: RH+2 */
 199                         struct inet_peer *ll, *lr, *lrl, *lrr;
 200                         int lrh;
 201                         ll = l->avl_left;
 202                         lr = l->avl_right;
 203                         lrh = node_height(lr);
 204                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 205                                 node->avl_left = lr;    /* lr: RH or RH+1 */
 206                                 node->avl_right = r;    /* r: RH */
 207                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 208                                 l->avl_left = ll;       /* ll: RH+1 */
 209                                 l->avl_right = node;    /* node: RH+1 or RH+2 */
 210                                 l->avl_height = node->avl_height + 1;
 211                                 *nodep = l;
 212                         } else { /* ll: RH, lr: RH+1 */
 213                                 lrl = lr->avl_left;     /* lrl: RH or RH-1 */
 214                                 lrr = lr->avl_right;    /* lrr: RH or RH-1 */
 215                                 node->avl_left = lrr;   /* lrr: RH or RH-1 */
 216                                 node->avl_right = r;    /* r: RH */
 217                                 node->avl_height = rh + 1; /* node: RH+1 */
 218                                 l->avl_left = ll;       /* ll: RH */
 219                                 l->avl_right = lrl;     /* lrl: RH or RH-1 */
 220                                 l->avl_height = rh + 1; /* l: RH+1 */
 221                                 lr->avl_left = l;       /* l: RH+1 */
 222                                 lr->avl_right = node;   /* node: RH+1 */
 223                                 lr->avl_height = rh + 2;
 224                                 *nodep = lr;
 225                         }
 226                 } else if (rh > lh + 1) { /* r: LH+2 */
 227                         struct inet_peer *rr, *rl, *rlr, *rll;
 228                         int rlh;
 229                         rr = r->avl_right;
 230                         rl = r->avl_left;
 231                         rlh = node_height(rl);
 232                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 233                                 node->avl_right = rl;   /* rl: LH or LH+1 */
 234                                 node->avl_left = l;     /* l: LH */
 235                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 236                                 r->avl_right = rr;      /* rr: LH+1 */
 237                                 r->avl_left = node;     /* node: LH+1 or LH+2 */
 238                                 r->avl_height = node->avl_height + 1;
 239                                 *nodep = r;
 240                         } else { /* rr: RH, rl: RH+1 */
 241                                 rlr = rl->avl_right;    /* rlr: LH or LH-1 */
 242                                 rll = rl->avl_left;     /* rll: LH or LH-1 */
 243                                 node->avl_right = rll;  /* rll: LH or LH-1 */
 244                                 node->avl_left = l;     /* l: LH */
 245                                 node->avl_height = lh + 1; /* node: LH+1 */
 246                                 r->avl_right = rr;      /* rr: LH */
 247                                 r->avl_left = rlr;      /* rlr: LH or LH-1 */
 248                                 r->avl_height = lh + 1; /* r: LH+1 */
 249                                 rl->avl_right = r;      /* r: LH+1 */
 250                                 rl->avl_left = node;    /* node: LH+1 */
 251                                 rl->avl_height = lh + 2;
 252                                 *nodep = rl;
 253                         }
 254                 } else {
 255                         node->avl_height = (lh > rh ? lh : rh) + 1;
 256                 }
 257         }
 258 }
 259
 260 /* Called with local BH disabled and the pool write lock held. */
 261 #define link_to_pool(n)                                         \
 262 do {                                                            \
 263         n->avl_height = 1;                                      \
 264         n->avl_left = peer_avl_empty;                           \
 265         n->avl_right = peer_avl_empty;                          \
 266         **--stackptr = n;                                       \
 267         peer_avl_rebalance(stack, stackptr);                    \
 268 } while(0)
 269
 270 /* May be called with local BH enabled. */
 271 static void unlink_from_pool(struct inet_peer *p)
 272 {
 273         int do_free;
 274
 275         do_free = 0;
 276
 277         write_lock_bh(&peer_pool_lock);
 278         /* Check the reference counter.  It was artificially incremented by 1
 279          * in cleanup() function to prevent sudden disappearing.  If the
 280          * reference count is still 1 then the node is referenced only as `p'
 281          * here and from the pool.  So under the exclusive pool lock it's safe
 282          * to remove the node and free it later. */
 283         if (atomic_read(&p->refcnt) == 1) {
 284                 struct inet_peer **stack[PEER_MAXDEPTH];
 285                 struct inet_peer ***stackptr, ***delp;
 286                 if (lookup(p->v4daddr, stack) != p)
 287                         BUG();
 288                 delp = stackptr - 1; /* *delp[0] == p */
 289                 if (p->avl_left == peer_avl_empty) {
 290                         *delp[0] = p->avl_right;
 291                         --stackptr;
 292                 } else {
 293                         /* look for a node to insert instead of p */
 294                         struct inet_peer *t;
 295                         t = lookup_rightempty(p);
 296                         BUG_ON(*stackptr[-1] != t);
 297                         **--stackptr = t->avl_left;
 298                         /* t is removed, t->v4daddr > x->v4daddr for any
 299                          * x in p->avl_left subtree.
 300                          * Put t in the old place of p. */
 301                         *delp[0] = t;
 302                         t->avl_left = p->avl_left;
 303                         t->avl_right = p->avl_right;
 304                         t->avl_height = p->avl_height;
 305                         BUG_ON(delp[1] != &p->avl_left);
 306                         delp[1] = &t->avl_left; /* was &p->avl_left */
 307                 }
 308                 peer_avl_rebalance(stack, stackptr);
 309                 peer_total--;
 310                 do_free = 1;
 311         }
 312         write_unlock_bh(&peer_pool_lock);
 313
 314         if (do_free)
 315                 kmem_cache_free(peer_cachep, p);
 316         else
 317                 /* The node is used again.  Decrease the reference counter
 318                  * back.  The loop "cleanup -> unlink_from_unused
 319                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 320                  *   -> cleanup (for the same node)"
 321                  * doesn't really exist because the entry will have a
 322                  * recent deletion time and will not be cleaned again soon. */
 323                 inet_putpeer(p);
 324 }
 325
 326 /* May be called with local BH enabled. */
 327 static int cleanup_once(unsigned long ttl)
 328 {
 329         struct inet_peer *p = NULL;
 330
 331         /* Remove the first entry from the list of unused nodes. */
 332         spin_lock_bh(&inet_peer_unused_lock);
 333         if (!list_empty(&unused_peers)) {
 334                 __u32 delta;
 335
 336                 p = list_first_entry(&unused_peers, struct inet_peer, unused);
 337                 delta = (__u32)jiffies - p->dtime;
 338
 339                 if (delta < ttl) {
 340                         /* Do not prune fresh entries. */
 341                         spin_unlock_bh(&inet_peer_unused_lock);
 342                         return -1;
 343                 }
 344
 345                 list_del_init(&p->unused);
 346
 347                 /* Grab an extra reference to prevent node disappearing
 348                  * before unlink_from_pool() call. */
 349                 atomic_inc(&p->refcnt);
 350         }
 351         spin_unlock_bh(&inet_peer_unused_lock);
 352
 353         if (p == NULL)
 354                 /* It means that the total number of USED entries has
 355                  * grown over inet_peer_threshold.  It shouldn't really
 356                  * happen because of entry limits in route cache. */
 357                 return -1;
 358
 359         unlink_from_pool(p);
 360         return 0;
 361 }
 362
 363 /* Called with or without local BH being disabled. */
 364 struct inet_peer *inet_getpeer(__be32 daddr, int create)
 365 {
 366         struct inet_peer *p, *n;
 367         struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
 368
 369         /* Look up for the address quickly. */
 370         read_lock_bh(&peer_pool_lock);
 371         p = lookup(daddr, NULL);
 372         if (p != peer_avl_empty)
 373                 atomic_inc(&p->refcnt);
 374         read_unlock_bh(&peer_pool_lock);
 375
 376         if (p != peer_avl_empty) {
 377                 /* The existing node has been found. */
 378                 /* Remove the entry from unused list if it was there. */
 379                 unlink_from_unused(p);
 380                 return p;
 381         }
 382
 383         if (!create)
 384                 return NULL;
 385
 386         /* Allocate the space outside the locked region. */
 387         n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
 388         if (n == NULL)
 389                 return NULL;
 390         n->v4daddr = daddr;
 391         atomic_set(&n->refcnt, 1);
 392         atomic_set(&n->rid, 0);
 393         n->ip_id_count = secure_ip_id(daddr);
 394         n->tcp_ts_stamp = 0;
 395
 396         write_lock_bh(&peer_pool_lock);
 397         /* Check if an entry has suddenly appeared. */
 398         p = lookup(daddr, stack);
 399         if (p != peer_avl_empty)
 400                 goto out_free;
 401
 402         /* Link the node. */
 403         link_to_pool(n);
 404         INIT_LIST_HEAD(&n->unused);
 405         peer_total++;
 406         write_unlock_bh(&peer_pool_lock);
 407
 408         if (peer_total >= inet_peer_threshold)
 409                 /* Remove one less-recently-used entry. */
 410                 cleanup_once(0);
 411
 412         return n;
 413
 414 out_free:
 415         /* The appropriate node is already in the pool. */
 416         atomic_inc(&p->refcnt);
 417         write_unlock_bh(&peer_pool_lock);
 418         /* Remove the entry from unused list if it was there. */
 419         unlink_from_unused(p);
 420         /* Free preallocated the preallocated node. */
 421         kmem_cache_free(peer_cachep, n);
 422         return p;
 423 }
 424
 425 /* Called with local BH disabled. */
 426 static void peer_check_expire(unsigned long dummy)
 427 {
 428         unsigned long now = jiffies;
 429         int ttl;
 430
 431         if (peer_total >= inet_peer_threshold)
 432                 ttl = inet_peer_minttl;
 433         else
 434                 ttl = inet_peer_maxttl
 435                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 436                                         peer_total / inet_peer_threshold * HZ;
 437         while (!cleanup_once(ttl)) {
 438                 if (jiffies != now)
 439                         break;
 440         }
 441
 442         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 443          * interval depending on the total number of entries (more entries,
 444          * less interval). */
 445         if (peer_total >= inet_peer_threshold)
 446                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
 447         else
 448                 peer_periodic_timer.expires = jiffies
 449                         + inet_peer_gc_maxtime
 450                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
 451                                 peer_total / inet_peer_threshold * HZ;
 452         add_timer(&peer_periodic_timer);
 453 }
 454
 455 void inet_putpeer(struct inet_peer *p)
 456 {
 457         spin_lock_bh(&inet_peer_unused_lock);
 458         if (atomic_dec_and_test(&p->refcnt)) {
 459                 list_add_tail(&p->unused, &unused_peers);
 460                 p->dtime = (__u32)jiffies;
 461         }
 462         spin_unlock_bh(&inet_peer_unused_lock);
 463 }