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