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