net/ipv4/ip_fragment.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              The IP fragmentation functionality.
   7  *
   8  * Version:     $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
   9  *
  10  * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
  11  *              Alan Cox <Alan.Cox@linux.org>
  12  *
  13  * Fixes:
  14  *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
  15  *              David S. Miller :       Begin massive cleanup...
  16  *              Andi Kleen      :       Add sysctls.
  17  *              xxxx            :       Overlapfrag bug.
  18  *              Ultima          :       ip_expire() kernel panic.
  19  *              Bill Hawes      :       Frag accounting and evictor fixes.
  20  *              John McDonald   :       0 length frag bug.
  21  *              Alexey Kuznetsov:       SMP races, threading, cleanup.
  22  *              Patrick McHardy :       LRU queue of frag heads for evictor.
  23  */
  24
  25 #include <linux/config.h>
  26 #include <linux/module.h>
  27 #include <linux/types.h>
  28 #include <linux/mm.h>
  29 #include <linux/jiffies.h>
  30 #include <linux/skbuff.h>
  31 #include <linux/list.h>
  32 #include <linux/ip.h>
  33 #include <linux/icmp.h>
  34 #include <linux/netdevice.h>
  35 #include <linux/jhash.h>
  36 #include <linux/random.h>
  37 #include <net/sock.h>
  38 #include <net/ip.h>
  39 #include <net/icmp.h>
  40 #include <net/checksum.h>
  41 #include <linux/tcp.h>
  42 #include <linux/udp.h>
  43 #include <linux/inet.h>
  44 #include <linux/netfilter_ipv4.h>
  45
  46 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
  47  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
  48  * as well. Or notify me, at least. --ANK
  49  */
  50
  51 /* Fragment cache limits. We will commit 256K at one time. Should we
  52  * cross that limit we will prune down to 192K. This should cope with
  53  * even the most extreme cases without allowing an attacker to measurably
  54  * harm machine performance.
  55  */
  56 int sysctl_ipfrag_high_thresh = 256*1024;
  57 int sysctl_ipfrag_low_thresh = 192*1024;
  58
  59 /* Important NOTE! Fragment queue must be destroyed before MSL expires.
  60  * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
  61  */
  62 int sysctl_ipfrag_time = IP_FRAG_TIME;
  63
  64 struct ipfrag_skb_cb
  65 {
  66         struct inet_skb_parm    h;
  67         int                     offset;
  68 };
  69
  70 #define FRAG_CB(skb)    ((struct ipfrag_skb_cb*)((skb)->cb))
  71
  72 /* Describe an entry in the "incomplete datagrams" queue. */
  73 struct ipq {
  74         struct ipq      *next;          /* linked list pointers                 */
  75         struct list_head lru_list;      /* lru list member                      */
  76         u32             saddr;
  77         u32             daddr;
  78         u16             id;
  79         u8              protocol;
  80         u8              last_in;
  81 #define COMPLETE                4
  82 #define FIRST_IN                2
  83 #define LAST_IN                 1
  84
  85         struct sk_buff  *fragments;     /* linked list of received fragments    */
  86         int             len;            /* total length of original datagram    */
  87         int             meat;
  88         spinlock_t      lock;
  89         atomic_t        refcnt;
  90         struct timer_list timer;        /* when will this queue expire?         */
  91         struct ipq      **pprev;
  92         int             iif;
  93         struct timeval  stamp;
  94 };
  95
  96 /* Hash table. */
  97
  98 #define IPQ_HASHSZ      64
  99
 100 /* Per-bucket lock is easy to add now. */
 101 static struct ipq *ipq_hash[IPQ_HASHSZ];
 102 static rwlock_t ipfrag_lock = RW_LOCK_UNLOCKED;
 103 static u32 ipfrag_hash_rnd;
 104 static LIST_HEAD(ipq_lru_list);
 105 int ip_frag_nqueues = 0;
 106
 107 static __inline__ void __ipq_unlink(struct ipq *qp)
 108 {
 109         if(qp->next)
 110                 qp->next->pprev = qp->pprev;
 111         *qp->pprev = qp->next;
 112         list_del(&qp->lru_list);
 113         ip_frag_nqueues--;
 114 }
 115
 116 static __inline__ void ipq_unlink(struct ipq *ipq)
 117 {
 118         write_lock(&ipfrag_lock);
 119         __ipq_unlink(ipq);
 120         write_unlock(&ipfrag_lock);
 121 }
 122
 123 static unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
 124 {
 125         return jhash_3words((u32)id << 16 | prot, saddr, daddr,
 126                             ipfrag_hash_rnd) & (IPQ_HASHSZ - 1);
 127 }
 128
 129 static struct timer_list ipfrag_secret_timer;
 130 int sysctl_ipfrag_secret_interval = 10 * 60 * HZ;
 131
 132 static void ipfrag_secret_rebuild(unsigned long dummy)
 133 {
 134         unsigned long now = jiffies;
 135         int i;
 136
 137         write_lock(&ipfrag_lock);
 138         get_random_bytes(&ipfrag_hash_rnd, sizeof(u32));
 139         for (i = 0; i < IPQ_HASHSZ; i++) {
 140                 struct ipq *q;
 141
 142                 q = ipq_hash[i];
 143                 while (q) {
 144                         struct ipq *next = q->next;
 145                         unsigned int hval = ipqhashfn(q->id, q->saddr,
 146                                                       q->daddr, q->protocol);
 147
 148                         if (hval != i) {
 149                                 /* Unlink. */
 150                                 if (q->next)
 151                                         q->next->pprev = q->pprev;
 152                                 *q->pprev = q->next;
 153
 154                                 /* Relink to new hash chain. */
 155                                 if ((q->next = ipq_hash[hval]) != NULL)
 156                                         q->next->pprev = &q->next;
 157                                 ipq_hash[hval] = q;
 158                                 q->pprev = &ipq_hash[hval];
 159                         }
 160
 161                         q = next;
 162                 }
 163         }
 164         write_unlock(&ipfrag_lock);
 165
 166         mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval);
 167 }
 168
 169 atomic_t ip_frag_mem = ATOMIC_INIT(0);  /* Memory used for fragments */
 170
 171 /* Memory Tracking Functions. */
 172 static __inline__ void frag_kfree_skb(struct sk_buff *skb)
 173 {
 174         atomic_sub(skb->truesize, &ip_frag_mem);
 175         kfree_skb(skb);
 176 }
 177
 178 static __inline__ void frag_free_queue(struct ipq *qp)
 179 {
 180         atomic_sub(sizeof(struct ipq), &ip_frag_mem);
 181         kfree(qp);
 182 }
 183
 184 static __inline__ struct ipq *frag_alloc_queue(void)
 185 {
 186         struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
 187
 188         if(!qp)
 189                 return NULL;
 190         atomic_add(sizeof(struct ipq), &ip_frag_mem);
 191         return qp;
 192 }
 193
 194
 195 /* Destruction primitives. */
 196
 197 /* Complete destruction of ipq. */
 198 static void ip_frag_destroy(struct ipq *qp)
 199 {
 200         struct sk_buff *fp;
 201
 202         BUG_TRAP(qp->last_in&COMPLETE);
 203         BUG_TRAP(del_timer(&qp->timer) == 0);
 204
 205         /* Release all fragment data. */
 206         fp = qp->fragments;
 207         while (fp) {
 208                 struct sk_buff *xp = fp->next;
 209
 210                 frag_kfree_skb(fp);
 211                 fp = xp;
 212         }
 213
 214         /* Finally, release the queue descriptor itself. */
 215         frag_free_queue(qp);
 216 }
 217
 218 static __inline__ void ipq_put(struct ipq *ipq)
 219 {
 220         if (atomic_dec_and_test(&ipq->refcnt))
 221                 ip_frag_destroy(ipq);
 222 }
 223
 224 /* Kill ipq entry. It is not destroyed immediately,
 225  * because caller (and someone more) holds reference count.
 226  */
 227 static void ipq_kill(struct ipq *ipq)
 228 {
 229         if (del_timer(&ipq->timer))
 230                 atomic_dec(&ipq->refcnt);
 231
 232         if (!(ipq->last_in & COMPLETE)) {
 233                 ipq_unlink(ipq);
 234                 atomic_dec(&ipq->refcnt);
 235                 ipq->last_in |= COMPLETE;
 236         }
 237 }
 238
 239 /* Memory limiting on fragments.  Evictor trashes the oldest
 240  * fragment queue until we are back under the low threshold.
 241  */
 242 static void ip_evictor(void)
 243 {
 244         struct ipq *qp;
 245         struct list_head *tmp;
 246
 247         for(;;) {
 248                 if (atomic_read(&ip_frag_mem) <= sysctl_ipfrag_low_thresh)
 249                         return;
 250                 read_lock(&ipfrag_lock);
 251                 if (list_empty(&ipq_lru_list)) {
 252                         read_unlock(&ipfrag_lock);
 253                         return;
 254                 }
 255                 tmp = ipq_lru_list.next;
 256                 qp = list_entry(tmp, struct ipq, lru_list);
 257                 atomic_inc(&qp->refcnt);
 258                 read_unlock(&ipfrag_lock);
 259
 260                 spin_lock(&qp->lock);
 261                 if (!(qp->last_in&COMPLETE))
 262                         ipq_kill(qp);
 263                 spin_unlock(&qp->lock);
 264
 265                 ipq_put(qp);
 266                 IP_INC_STATS_BH(ReasmFails);
 267         }
 268 }
 269
 270 /*
 271  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 272  */
 273 static void ip_expire(unsigned long arg)
 274 {
 275         struct ipq *qp = (struct ipq *) arg;
 276
 277         spin_lock(&qp->lock);
 278
 279         if (qp->last_in & COMPLETE)
 280                 goto out;
 281
 282         ipq_kill(qp);
 283
 284         IP_INC_STATS_BH(ReasmTimeout);
 285         IP_INC_STATS_BH(ReasmFails);
 286
 287         if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
 288                 struct sk_buff *head = qp->fragments;
 289                 /* Send an ICMP "Fragment Reassembly Timeout" message. */
 290                 if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
 291                         icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
 292                         dev_put(head->dev);
 293                 }
 294         }
 295 out:
 296         spin_unlock(&qp->lock);
 297         ipq_put(qp);
 298 }
 299
 300 /* Creation primitives. */
 301
 302 static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
 303 {
 304         struct ipq *qp;
 305
 306         write_lock(&ipfrag_lock);
 307 #ifdef CONFIG_SMP
 308         /* With SMP race we have to recheck hash table, because
 309          * such entry could be created on other cpu, while we
 310          * promoted read lock to write lock.
 311          */
 312         for(qp = ipq_hash[hash]; qp; qp = qp->next) {
 313                 if(qp->id == qp_in->id          &&
 314                    qp->saddr == qp_in->saddr    &&
 315                    qp->daddr == qp_in->daddr    &&
 316                    qp->protocol == qp_in->protocol) {
 317                         atomic_inc(&qp->refcnt);
 318                         write_unlock(&ipfrag_lock);
 319                         qp_in->last_in |= COMPLETE;
 320                         ipq_put(qp_in);
 321                         return qp;
 322                 }
 323         }
 324 #endif
 325         qp = qp_in;
 326
 327         if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
 328                 atomic_inc(&qp->refcnt);
 329
 330         atomic_inc(&qp->refcnt);
 331         if((qp->next = ipq_hash[hash]) != NULL)
 332                 qp->next->pprev = &qp->next;
 333         ipq_hash[hash] = qp;
 334         qp->pprev = &ipq_hash[hash];
 335         INIT_LIST_HEAD(&qp->lru_list);
 336         list_add_tail(&qp->lru_list, &ipq_lru_list);
 337         ip_frag_nqueues++;
 338         write_unlock(&ipfrag_lock);
 339         return qp;
 340 }
 341
 342 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
 343 static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph)
 344 {
 345         struct ipq *qp;
 346
 347         if ((qp = frag_alloc_queue()) == NULL)
 348                 goto out_nomem;
 349
 350         qp->protocol = iph->protocol;
 351         qp->last_in = 0;
 352         qp->id = iph->id;
 353         qp->saddr = iph->saddr;
 354         qp->daddr = iph->daddr;
 355         qp->len = 0;
 356         qp->meat = 0;
 357         qp->fragments = NULL;
 358         qp->iif = 0;
 359
 360         /* Initialize a timer for this entry. */
 361         init_timer(&qp->timer);
 362         qp->timer.data = (unsigned long) qp;    /* pointer to queue     */
 363         qp->timer.function = ip_expire;         /* expire function      */
 364         qp->lock = SPIN_LOCK_UNLOCKED;
 365         atomic_set(&qp->refcnt, 1);
 366
 367         return ip_frag_intern(hash, qp);
 368
 369 out_nomem:
 370         NETDEBUG(if (net_ratelimit()) printk(KERN_ERR "ip_frag_create: no memory left !\n"));
 371         return NULL;
 372 }
 373
 374 /* Find the correct entry in the "incomplete datagrams" queue for
 375  * this IP datagram, and create new one, if nothing is found.
 376  */
 377 static inline struct ipq *ip_find(struct iphdr *iph)
 378 {
 379         __u16 id = iph->id;
 380         __u32 saddr = iph->saddr;
 381         __u32 daddr = iph->daddr;
 382         __u8 protocol = iph->protocol;
 383         unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
 384         struct ipq *qp;
 385
 386         read_lock(&ipfrag_lock);
 387         for(qp = ipq_hash[hash]; qp; qp = qp->next) {
 388                 if(qp->id == id         &&
 389                    qp->saddr == saddr   &&
 390                    qp->daddr == daddr   &&
 391                    qp->protocol == protocol) {
 392                         atomic_inc(&qp->refcnt);
 393                         read_unlock(&ipfrag_lock);
 394                         return qp;
 395                 }
 396         }
 397         read_unlock(&ipfrag_lock);
 398
 399         return ip_frag_create(hash, iph);
 400 }
 401
 402 /* Add new segment to existing queue. */
 403 static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 404 {
 405         struct sk_buff *prev, *next;
 406         int flags, offset;
 407         int ihl, end;
 408
 409         if (qp->last_in & COMPLETE)
 410                 goto err;
 411
 412         offset = ntohs(skb->nh.iph->frag_off);
 413         flags = offset & ~IP_OFFSET;
 414         offset &= IP_OFFSET;
 415         offset <<= 3;           /* offset is in 8-byte chunks */
 416         ihl = skb->nh.iph->ihl * 4;
 417
 418         /* Determine the position of this fragment. */
 419         end = offset + skb->len - ihl;
 420
 421         /* Is this the final fragment? */
 422         if ((flags & IP_MF) == 0) {
 423                 /* If we already have some bits beyond end
 424                  * or have different end, the segment is corrrupted.
 425                  */
 426                 if (end < qp->len ||
 427                     ((qp->last_in & LAST_IN) && end != qp->len))
 428                         goto err;
 429                 qp->last_in |= LAST_IN;
 430                 qp->len = end;
 431         } else {
 432                 if (end&7) {
 433                         end &= ~7;
 434                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 435                                 skb->ip_summed = CHECKSUM_NONE;
 436                 }
 437                 if (end > qp->len) {
 438                         /* Some bits beyond end -> corruption. */
 439                         if (qp->last_in & LAST_IN)
 440                                 goto err;
 441                         qp->len = end;
 442                 }
 443         }
 444         if (end == offset)
 445                 goto err;
 446
 447         if (pskb_pull(skb, ihl) == NULL)
 448                 goto err;
 449         if (pskb_trim(skb, end-offset))
 450                 goto err;
 451
 452         /* Find out which fragments are in front and at the back of us
 453          * in the chain of fragments so far.  We must know where to put
 454          * this fragment, right?
 455          */
 456         prev = NULL;
 457         for(next = qp->fragments; next != NULL; next = next->next) {
 458                 if (FRAG_CB(next)->offset >= offset)
 459                         break;  /* bingo! */
 460                 prev = next;
 461         }
 462
 463         /* We found where to put this one.  Check for overlap with
 464          * preceding fragment, and, if needed, align things so that
 465          * any overlaps are eliminated.
 466          */
 467         if (prev) {
 468                 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
 469
 470                 if (i > 0) {
 471                         offset += i;
 472                         if (end <= offset)
 473                                 goto err;
 474                         if (!pskb_pull(skb, i))
 475                                 goto err;
 476                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 477                                 skb->ip_summed = CHECKSUM_NONE;
 478                 }
 479         }
 480
 481         while (next && FRAG_CB(next)->offset < end) {
 482                 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
 483
 484                 if (i < next->len) {
 485                         /* Eat head of the next overlapped fragment
 486                          * and leave the loop. The next ones cannot overlap.
 487                          */
 488                         if (!pskb_pull(next, i))
 489                                 goto err;
 490                         FRAG_CB(next)->offset += i;
 491                         qp->meat -= i;
 492                         if (next->ip_summed != CHECKSUM_UNNECESSARY)
 493                                 next->ip_summed = CHECKSUM_NONE;
 494                         break;
 495                 } else {
 496                         struct sk_buff *free_it = next;
 497
 498                         /* Old fragmnet is completely overridden with
 499                          * new one drop it.
 500                          */
 501                         next = next->next;
 502
 503                         if (prev)
 504                                 prev->next = next;
 505                         else
 506                                 qp->fragments = next;
 507
 508                         qp->meat -= free_it->len;
 509                         frag_kfree_skb(free_it);
 510                 }
 511         }
 512
 513         FRAG_CB(skb)->offset = offset;
 514
 515         /* Insert this fragment in the chain of fragments. */
 516         skb->next = next;
 517         if (prev)
 518                 prev->next = skb;
 519         else
 520                 qp->fragments = skb;
 521
 522         if (skb->dev)
 523                 qp->iif = skb->dev->ifindex;
 524         skb->dev = NULL;
 525         qp->stamp = skb->stamp;
 526         qp->meat += skb->len;
 527         atomic_add(skb->truesize, &ip_frag_mem);
 528         if (offset == 0)
 529                 qp->last_in |= FIRST_IN;
 530
 531         write_lock(&ipfrag_lock);
 532         list_move_tail(&qp->lru_list, &ipq_lru_list);
 533         write_unlock(&ipfrag_lock);
 534
 535         return;
 536
 537 err:
 538         kfree_skb(skb);
 539 }
 540
 541
 542 /* Build a new IP datagram from all its fragments. */
 543
 544 static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
 545 {
 546         struct iphdr *iph;
 547         struct sk_buff *fp, *head = qp->fragments;
 548         int len;
 549         int ihlen;
 550
 551         ipq_kill(qp);
 552
 553         BUG_TRAP(head != NULL);
 554         BUG_TRAP(FRAG_CB(head)->offset == 0);
 555
 556         /* Allocate a new buffer for the datagram. */
 557         ihlen = head->nh.iph->ihl*4;
 558         len = ihlen + qp->len;
 559
 560         if(len > 65535)
 561                 goto out_oversize;
 562
 563         /* Head of list must not be cloned. */
 564         if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
 565                 goto out_nomem;
 566
 567         /* If the first fragment is fragmented itself, we split
 568          * it to two chunks: the first with data and paged part
 569          * and the second, holding only fragments. */
 570         if (skb_shinfo(head)->frag_list) {
 571                 struct sk_buff *clone;
 572                 int i, plen = 0;
 573
 574                 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
 575                         goto out_nomem;
 576                 clone->next = head->next;
 577                 head->next = clone;
 578                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 579                 skb_shinfo(head)->frag_list = NULL;
 580                 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
 581                         plen += skb_shinfo(head)->frags[i].size;
 582                 clone->len = clone->data_len = head->data_len - plen;
 583                 head->data_len -= clone->len;
 584                 head->len -= clone->len;
 585                 clone->csum = 0;
 586                 clone->ip_summed = head->ip_summed;
 587                 atomic_add(clone->truesize, &ip_frag_mem);
 588         }
 589
 590         skb_shinfo(head)->frag_list = head->next;
 591         skb_push(head, head->data - head->nh.raw);
 592         atomic_sub(head->truesize, &ip_frag_mem);
 593
 594         for (fp=head->next; fp; fp = fp->next) {
 595                 head->data_len += fp->len;
 596                 head->len += fp->len;
 597                 if (head->ip_summed != fp->ip_summed)
 598                         head->ip_summed = CHECKSUM_NONE;
 599                 else if (head->ip_summed == CHECKSUM_HW)
 600                         head->csum = csum_add(head->csum, fp->csum);
 601                 head->truesize += fp->truesize;
 602                 atomic_sub(fp->truesize, &ip_frag_mem);
 603         }
 604
 605         head->next = NULL;
 606         head->dev = dev;
 607         head->stamp = qp->stamp;
 608
 609         iph = head->nh.iph;
 610         iph->frag_off = 0;
 611         iph->tot_len = htons(len);
 612         IP_INC_STATS_BH(ReasmOKs);
 613         qp->fragments = NULL;
 614         return head;
 615
 616 out_nomem:
 617         NETDEBUG(if (net_ratelimit())
 618                  printk(KERN_ERR
 619                         "IP: queue_glue: no memory for gluing queue %p\n",
 620                         qp));
 621         goto out_fail;
 622 out_oversize:
 623         if (net_ratelimit())
 624                 printk(KERN_INFO
 625                         "Oversized IP packet from %d.%d.%d.%d.\n",
 626                         NIPQUAD(qp->saddr));
 627 out_fail:
 628         IP_INC_STATS_BH(ReasmFails);
 629         return NULL;
 630 }
 631
 632 /* Process an incoming IP datagram fragment. */
 633 struct sk_buff *ip_defrag(struct sk_buff *skb)
 634 {
 635         struct iphdr *iph = skb->nh.iph;
 636         struct ipq *qp;
 637         struct net_device *dev;
 638
 639         IP_INC_STATS_BH(ReasmReqds);
 640
 641         /* Start by cleaning up the memory. */
 642         if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
 643                 ip_evictor();
 644
 645         dev = skb->dev;
 646
 647         /* Lookup (or create) queue header */
 648         if ((qp = ip_find(iph)) != NULL) {
 649                 struct sk_buff *ret = NULL;
 650
 651                 spin_lock(&qp->lock);
 652
 653                 ip_frag_queue(qp, skb);
 654
 655                 if (qp->last_in == (FIRST_IN|LAST_IN) &&
 656                     qp->meat == qp->len)
 657                         ret = ip_frag_reasm(qp, dev);
 658
 659                 spin_unlock(&qp->lock);
 660                 ipq_put(qp);
 661                 return ret;
 662         }
 663
 664         IP_INC_STATS_BH(ReasmFails);
 665         kfree_skb(skb);
 666         return NULL;
 667 }
 668
 669 void ipfrag_init(void)
 670 {
 671         ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
 672                                  (jiffies ^ (jiffies >> 6)));
 673
 674         init_timer(&ipfrag_secret_timer);
 675         ipfrag_secret_timer.function = ipfrag_secret_rebuild;
 676         ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval;
 677         add_timer(&ipfrag_secret_timer);
 678 }
 679
 680 EXPORT_SYMBOL(ip_defrag);