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/compiler.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 <net/inetpeer.h>
  42 #include <linux/tcp.h>
  43 #include <linux/udp.h>
  44 #include <linux/inet.h>
  45 #include <linux/netfilter_ipv4.h>
  46
  47 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
  48  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
  49  * as well. Or notify me, at least. --ANK
  50  */
  51
  52 /* Fragment cache limits. We will commit 256K at one time. Should we
  53  * cross that limit we will prune down to 192K. This should cope with
  54  * even the most extreme cases without allowing an attacker to measurably
  55  * harm machine performance.
  56  */
  57 int sysctl_ipfrag_high_thresh __read_mostly = 256*1024;
  58 int sysctl_ipfrag_low_thresh __read_mostly = 192*1024;
  59
  60 int sysctl_ipfrag_max_dist __read_mostly = 64;
  61
  62 /* Important NOTE! Fragment queue must be destroyed before MSL expires.
  63  * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
  64  */
  65 int sysctl_ipfrag_time __read_mostly = IP_FRAG_TIME;
  66
  67 struct ipfrag_skb_cb
  68 {
  69         struct inet_skb_parm    h;
  70         int                     offset;
  71 };
  72
  73 #define FRAG_CB(skb)    ((struct ipfrag_skb_cb*)((skb)->cb))
  74
  75 /* Describe an entry in the "incomplete datagrams" queue. */
  76 struct ipq {
  77         struct hlist_node list;
  78         struct list_head lru_list;      /* lru list member                      */
  79         u32             user;
  80         u32             saddr;
  81         u32             daddr;
  82         u16             id;
  83         u8              protocol;
  84         u8              last_in;
  85 #define COMPLETE                4
  86 #define FIRST_IN                2
  87 #define LAST_IN                 1
  88
  89         struct sk_buff  *fragments;     /* linked list of received fragments    */
  90         int             len;            /* total length of original datagram    */
  91         int             meat;
  92         spinlock_t      lock;
  93         atomic_t        refcnt;
  94         struct timer_list timer;        /* when will this queue expire?         */
  95         struct timeval  stamp;
  96         int             iif;
  97         unsigned int    rid;
  98         struct inet_peer *peer;
  99 };
 100
 101 /* Hash table. */
 102
 103 #define IPQ_HASHSZ      64
 104
 105 /* Per-bucket lock is easy to add now. */
 106 static struct hlist_head ipq_hash[IPQ_HASHSZ];
 107 static DEFINE_RWLOCK(ipfrag_lock);
 108 static u32 ipfrag_hash_rnd;
 109 static LIST_HEAD(ipq_lru_list);
 110 int ip_frag_nqueues = 0;
 111
 112 static __inline__ void __ipq_unlink(struct ipq *qp)
 113 {
 114         hlist_del(&qp->list);
 115         list_del(&qp->lru_list);
 116         ip_frag_nqueues--;
 117 }
 118
 119 static __inline__ void ipq_unlink(struct ipq *ipq)
 120 {
 121         write_lock(&ipfrag_lock);
 122         __ipq_unlink(ipq);
 123         write_unlock(&ipfrag_lock);
 124 }
 125
 126 static unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
 127 {
 128         return jhash_3words((u32)id << 16 | prot, saddr, daddr,
 129                             ipfrag_hash_rnd) & (IPQ_HASHSZ - 1);
 130 }
 131
 132 static struct timer_list ipfrag_secret_timer;
 133 int sysctl_ipfrag_secret_interval __read_mostly = 10 * 60 * HZ;
 134
 135 static void ipfrag_secret_rebuild(unsigned long dummy)
 136 {
 137         unsigned long now = jiffies;
 138         int i;
 139
 140         write_lock(&ipfrag_lock);
 141         get_random_bytes(&ipfrag_hash_rnd, sizeof(u32));
 142         for (i = 0; i < IPQ_HASHSZ; i++) {
 143                 struct ipq *q;
 144                 struct hlist_node *p, *n;
 145
 146                 hlist_for_each_entry_safe(q, p, n, &ipq_hash[i], list) {
 147                         unsigned int hval = ipqhashfn(q->id, q->saddr,
 148                                                       q->daddr, q->protocol);
 149
 150                         if (hval != i) {
 151                                 hlist_del(&q->list);
 152
 153                                 /* Relink to new hash chain. */
 154                                 hlist_add_head(&q->list, &ipq_hash[hval]);
 155                         }
 156                 }
 157         }
 158         write_unlock(&ipfrag_lock);
 159
 160         mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval);
 161 }
 162
 163 atomic_t ip_frag_mem = ATOMIC_INIT(0);  /* Memory used for fragments */
 164
 165 /* Memory Tracking Functions. */
 166 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work)
 167 {
 168         if (work)
 169                 *work -= skb->truesize;
 170         atomic_sub(skb->truesize, &ip_frag_mem);
 171         kfree_skb(skb);
 172 }
 173
 174 static __inline__ void frag_free_queue(struct ipq *qp, int *work)
 175 {
 176         if (work)
 177                 *work -= sizeof(struct ipq);
 178         atomic_sub(sizeof(struct ipq), &ip_frag_mem);
 179         kfree(qp);
 180 }
 181
 182 static __inline__ struct ipq *frag_alloc_queue(void)
 183 {
 184         struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
 185
 186         if(!qp)
 187                 return NULL;
 188         atomic_add(sizeof(struct ipq), &ip_frag_mem);
 189         return qp;
 190 }
 191
 192
 193 /* Destruction primitives. */
 194
 195 /* Complete destruction of ipq. */
 196 static void ip_frag_destroy(struct ipq *qp, int *work)
 197 {
 198         struct sk_buff *fp;
 199
 200         BUG_TRAP(qp->last_in&COMPLETE);
 201         BUG_TRAP(del_timer(&qp->timer) == 0);
 202
 203         if (qp->peer)
 204                 inet_putpeer(qp->peer);
 205
 206         /* Release all fragment data. */
 207         fp = qp->fragments;
 208         while (fp) {
 209                 struct sk_buff *xp = fp->next;
 210
 211                 frag_kfree_skb(fp, work);
 212                 fp = xp;
 213         }
 214
 215         /* Finally, release the queue descriptor itself. */
 216         frag_free_queue(qp, work);
 217 }
 218
 219 static __inline__ void ipq_put(struct ipq *ipq, int *work)
 220 {
 221         if (atomic_dec_and_test(&ipq->refcnt))
 222                 ip_frag_destroy(ipq, work);
 223 }
 224
 225 /* Kill ipq entry. It is not destroyed immediately,
 226  * because caller (and someone more) holds reference count.
 227  */
 228 static void ipq_kill(struct ipq *ipq)
 229 {
 230         if (del_timer(&ipq->timer))
 231                 atomic_dec(&ipq->refcnt);
 232
 233         if (!(ipq->last_in & COMPLETE)) {
 234                 ipq_unlink(ipq);
 235                 atomic_dec(&ipq->refcnt);
 236                 ipq->last_in |= COMPLETE;
 237         }
 238 }
 239
 240 /* Memory limiting on fragments.  Evictor trashes the oldest
 241  * fragment queue until we are back under the threshold.
 242  */
 243 static void ip_evictor(void)
 244 {
 245         struct ipq *qp;
 246         struct list_head *tmp;
 247         int work;
 248
 249         work = atomic_read(&ip_frag_mem) - sysctl_ipfrag_low_thresh;
 250         if (work <= 0)
 251                 return;
 252
 253         while (work > 0) {
 254                 read_lock(&ipfrag_lock);
 255                 if (list_empty(&ipq_lru_list)) {
 256                         read_unlock(&ipfrag_lock);
 257                         return;
 258                 }
 259                 tmp = ipq_lru_list.next;
 260                 qp = list_entry(tmp, struct ipq, lru_list);
 261                 atomic_inc(&qp->refcnt);
 262                 read_unlock(&ipfrag_lock);
 263
 264                 spin_lock(&qp->lock);
 265                 if (!(qp->last_in&COMPLETE))
 266                         ipq_kill(qp);
 267                 spin_unlock(&qp->lock);
 268
 269                 ipq_put(qp, &work);
 270                 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 271         }
 272 }
 273
 274 /*
 275  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 276  */
 277 static void ip_expire(unsigned long arg)
 278 {
 279         struct ipq *qp = (struct ipq *) arg;
 280
 281         spin_lock(&qp->lock);
 282
 283         if (qp->last_in & COMPLETE)
 284                 goto out;
 285
 286         ipq_kill(qp);
 287
 288         IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
 289         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 290
 291         if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
 292                 struct sk_buff *head = qp->fragments;
 293                 /* Send an ICMP "Fragment Reassembly Timeout" message. */
 294                 if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
 295                         icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
 296                         dev_put(head->dev);
 297                 }
 298         }
 299 out:
 300         spin_unlock(&qp->lock);
 301         ipq_put(qp, NULL);
 302 }
 303
 304 /* Creation primitives. */
 305
 306 static struct ipq *ip_frag_intern(struct ipq *qp_in)
 307 {
 308         struct ipq *qp;
 309 #ifdef CONFIG_SMP
 310         struct hlist_node *n;
 311 #endif
 312         unsigned int hash;
 313
 314         write_lock(&ipfrag_lock);
 315         hash = ipqhashfn(qp_in->id, qp_in->saddr, qp_in->daddr,
 316                          qp_in->protocol);
 317 #ifdef CONFIG_SMP
 318         /* With SMP race we have to recheck hash table, because
 319          * such entry could be created on other cpu, while we
 320          * promoted read lock to write lock.
 321          */
 322         hlist_for_each_entry(qp, n, &ipq_hash[hash], list) {
 323                 if(qp->id == qp_in->id          &&
 324                    qp->saddr == qp_in->saddr    &&
 325                    qp->daddr == qp_in->daddr    &&
 326                    qp->protocol == qp_in->protocol &&
 327                    qp->user == qp_in->user) {
 328                         atomic_inc(&qp->refcnt);
 329                         write_unlock(&ipfrag_lock);
 330                         qp_in->last_in |= COMPLETE;
 331                         ipq_put(qp_in, NULL);
 332                         return qp;
 333                 }
 334         }
 335 #endif
 336         qp = qp_in;
 337
 338         if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
 339                 atomic_inc(&qp->refcnt);
 340
 341         atomic_inc(&qp->refcnt);
 342         hlist_add_head(&qp->list, &ipq_hash[hash]);
 343         INIT_LIST_HEAD(&qp->lru_list);
 344         list_add_tail(&qp->lru_list, &ipq_lru_list);
 345         ip_frag_nqueues++;
 346         write_unlock(&ipfrag_lock);
 347         return qp;
 348 }
 349
 350 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
 351 static struct ipq *ip_frag_create(struct iphdr *iph, u32 user)
 352 {
 353         struct ipq *qp;
 354
 355         if ((qp = frag_alloc_queue()) == NULL)
 356                 goto out_nomem;
 357
 358         qp->protocol = iph->protocol;
 359         qp->last_in = 0;
 360         qp->id = iph->id;
 361         qp->saddr = iph->saddr;
 362         qp->daddr = iph->daddr;
 363         qp->user = user;
 364         qp->len = 0;
 365         qp->meat = 0;
 366         qp->fragments = NULL;
 367         qp->iif = 0;
 368         qp->peer = sysctl_ipfrag_max_dist ? inet_getpeer(iph->saddr, 1) : NULL;
 369
 370         /* Initialize a timer for this entry. */
 371         init_timer(&qp->timer);
 372         qp->timer.data = (unsigned long) qp;    /* pointer to queue     */
 373         qp->timer.function = ip_expire;         /* expire function      */
 374         spin_lock_init(&qp->lock);
 375         atomic_set(&qp->refcnt, 1);
 376
 377         return ip_frag_intern(qp);
 378
 379 out_nomem:
 380         LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
 381         return NULL;
 382 }
 383
 384 /* Find the correct entry in the "incomplete datagrams" queue for
 385  * this IP datagram, and create new one, if nothing is found.
 386  */
 387 static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
 388 {
 389         __be16 id = iph->id;
 390         __u32 saddr = iph->saddr;
 391         __u32 daddr = iph->daddr;
 392         __u8 protocol = iph->protocol;
 393         unsigned int hash;
 394         struct ipq *qp;
 395         struct hlist_node *n;
 396
 397         read_lock(&ipfrag_lock);
 398         hash = ipqhashfn(id, saddr, daddr, protocol);
 399         hlist_for_each_entry(qp, n, &ipq_hash[hash], list) {
 400                 if(qp->id == id         &&
 401                    qp->saddr == saddr   &&
 402                    qp->daddr == daddr   &&
 403                    qp->protocol == protocol &&
 404                    qp->user == user) {
 405                         atomic_inc(&qp->refcnt);
 406                         read_unlock(&ipfrag_lock);
 407                         return qp;
 408                 }
 409         }
 410         read_unlock(&ipfrag_lock);
 411
 412         return ip_frag_create(iph, user);
 413 }
 414
 415 /* Is the fragment too far ahead to be part of ipq? */
 416 static inline int ip_frag_too_far(struct ipq *qp)
 417 {
 418         struct inet_peer *peer = qp->peer;
 419         unsigned int max = sysctl_ipfrag_max_dist;
 420         unsigned int start, end;
 421
 422         int rc;
 423
 424         if (!peer || !max)
 425                 return 0;
 426
 427         start = qp->rid;
 428         end = atomic_inc_return(&peer->rid);
 429         qp->rid = end;
 430
 431         rc = qp->fragments && (end - start) > max;
 432
 433         if (rc) {
 434                 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 435         }
 436
 437         return rc;
 438 }
 439
 440 static int ip_frag_reinit(struct ipq *qp)
 441 {
 442         struct sk_buff *fp;
 443
 444         if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time)) {
 445                 atomic_inc(&qp->refcnt);
 446                 return -ETIMEDOUT;
 447         }
 448
 449         fp = qp->fragments;
 450         do {
 451                 struct sk_buff *xp = fp->next;
 452                 frag_kfree_skb(fp, NULL);
 453                 fp = xp;
 454         } while (fp);
 455
 456         qp->last_in = 0;
 457         qp->len = 0;
 458         qp->meat = 0;
 459         qp->fragments = NULL;
 460         qp->iif = 0;
 461
 462         return 0;
 463 }
 464
 465 /* Add new segment to existing queue. */
 466 static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 467 {
 468         struct sk_buff *prev, *next;
 469         int flags, offset;
 470         int ihl, end;
 471
 472         if (qp->last_in & COMPLETE)
 473                 goto err;
 474
 475         if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
 476             unlikely(ip_frag_too_far(qp)) && unlikely(ip_frag_reinit(qp))) {
 477                 ipq_kill(qp);
 478                 goto err;
 479         }
 480
 481         offset = ntohs(skb->nh.iph->frag_off);
 482         flags = offset & ~IP_OFFSET;
 483         offset &= IP_OFFSET;
 484         offset <<= 3;           /* offset is in 8-byte chunks */
 485         ihl = skb->nh.iph->ihl * 4;
 486
 487         /* Determine the position of this fragment. */
 488         end = offset + skb->len - ihl;
 489
 490         /* Is this the final fragment? */
 491         if ((flags & IP_MF) == 0) {
 492                 /* If we already have some bits beyond end
 493                  * or have different end, the segment is corrrupted.
 494                  */
 495                 if (end < qp->len ||
 496                     ((qp->last_in & LAST_IN) && end != qp->len))
 497                         goto err;
 498                 qp->last_in |= LAST_IN;
 499                 qp->len = end;
 500         } else {
 501                 if (end&7) {
 502                         end &= ~7;
 503                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 504                                 skb->ip_summed = CHECKSUM_NONE;
 505                 }
 506                 if (end > qp->len) {
 507                         /* Some bits beyond end -> corruption. */
 508                         if (qp->last_in & LAST_IN)
 509                                 goto err;
 510                         qp->len = end;
 511                 }
 512         }
 513         if (end == offset)
 514                 goto err;
 515
 516         if (pskb_pull(skb, ihl) == NULL)
 517                 goto err;
 518         if (pskb_trim_rcsum(skb, end-offset))
 519                 goto err;
 520
 521         /* Find out which fragments are in front and at the back of us
 522          * in the chain of fragments so far.  We must know where to put
 523          * this fragment, right?
 524          */
 525         prev = NULL;
 526         for(next = qp->fragments; next != NULL; next = next->next) {
 527                 if (FRAG_CB(next)->offset >= offset)
 528                         break;  /* bingo! */
 529                 prev = next;
 530         }
 531
 532         /* We found where to put this one.  Check for overlap with
 533          * preceding fragment, and, if needed, align things so that
 534          * any overlaps are eliminated.
 535          */
 536         if (prev) {
 537                 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
 538
 539                 if (i > 0) {
 540                         offset += i;
 541                         if (end <= offset)
 542                                 goto err;
 543                         if (!pskb_pull(skb, i))
 544                                 goto err;
 545                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 546                                 skb->ip_summed = CHECKSUM_NONE;
 547                 }
 548         }
 549
 550         while (next && FRAG_CB(next)->offset < end) {
 551                 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
 552
 553                 if (i < next->len) {
 554                         /* Eat head of the next overlapped fragment
 555                          * and leave the loop. The next ones cannot overlap.
 556                          */
 557                         if (!pskb_pull(next, i))
 558                                 goto err;
 559                         FRAG_CB(next)->offset += i;
 560                         qp->meat -= i;
 561                         if (next->ip_summed != CHECKSUM_UNNECESSARY)
 562                                 next->ip_summed = CHECKSUM_NONE;
 563                         break;
 564                 } else {
 565                         struct sk_buff *free_it = next;
 566
 567                         /* Old fragmnet is completely overridden with
 568                          * new one drop it.
 569                          */
 570                         next = next->next;
 571
 572                         if (prev)
 573                                 prev->next = next;
 574                         else
 575                                 qp->fragments = next;
 576
 577                         qp->meat -= free_it->len;
 578                         frag_kfree_skb(free_it, NULL);
 579                 }
 580         }
 581
 582         FRAG_CB(skb)->offset = offset;
 583
 584         /* Insert this fragment in the chain of fragments. */
 585         skb->next = next;
 586         if (prev)
 587                 prev->next = skb;
 588         else
 589                 qp->fragments = skb;
 590
 591         if (skb->dev)
 592                 qp->iif = skb->dev->ifindex;
 593         skb->dev = NULL;
 594         skb_get_timestamp(skb, &qp->stamp);
 595         qp->meat += skb->len;
 596         atomic_add(skb->truesize, &ip_frag_mem);
 597         if (offset == 0)
 598                 qp->last_in |= FIRST_IN;
 599
 600         write_lock(&ipfrag_lock);
 601         list_move_tail(&qp->lru_list, &ipq_lru_list);
 602         write_unlock(&ipfrag_lock);
 603
 604         return;
 605
 606 err:
 607         kfree_skb(skb);
 608 }
 609
 610
 611 /* Build a new IP datagram from all its fragments. */
 612
 613 static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
 614 {
 615         struct iphdr *iph;
 616         struct sk_buff *fp, *head = qp->fragments;
 617         int len;
 618         int ihlen;
 619
 620         ipq_kill(qp);
 621
 622         BUG_TRAP(head != NULL);
 623         BUG_TRAP(FRAG_CB(head)->offset == 0);
 624
 625         /* Allocate a new buffer for the datagram. */
 626         ihlen = head->nh.iph->ihl*4;
 627         len = ihlen + qp->len;
 628
 629         if(len > 65535)
 630                 goto out_oversize;
 631
 632         /* Head of list must not be cloned. */
 633         if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
 634                 goto out_nomem;
 635
 636         /* If the first fragment is fragmented itself, we split
 637          * it to two chunks: the first with data and paged part
 638          * and the second, holding only fragments. */
 639         if (skb_shinfo(head)->frag_list) {
 640                 struct sk_buff *clone;
 641                 int i, plen = 0;
 642
 643                 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
 644                         goto out_nomem;
 645                 clone->next = head->next;
 646                 head->next = clone;
 647                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 648                 skb_shinfo(head)->frag_list = NULL;
 649                 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
 650                         plen += skb_shinfo(head)->frags[i].size;
 651                 clone->len = clone->data_len = head->data_len - plen;
 652                 head->data_len -= clone->len;
 653                 head->len -= clone->len;
 654                 clone->csum = 0;
 655                 clone->ip_summed = head->ip_summed;
 656                 atomic_add(clone->truesize, &ip_frag_mem);
 657         }
 658
 659         skb_shinfo(head)->frag_list = head->next;
 660         skb_push(head, head->data - head->nh.raw);
 661         atomic_sub(head->truesize, &ip_frag_mem);
 662
 663         for (fp=head->next; fp; fp = fp->next) {
 664                 head->data_len += fp->len;
 665                 head->len += fp->len;
 666                 if (head->ip_summed != fp->ip_summed)
 667                         head->ip_summed = CHECKSUM_NONE;
 668                 else if (head->ip_summed == CHECKSUM_COMPLETE)
 669                         head->csum = csum_add(head->csum, fp->csum);
 670                 head->truesize += fp->truesize;
 671                 atomic_sub(fp->truesize, &ip_frag_mem);
 672         }
 673
 674         head->next = NULL;
 675         head->dev = dev;
 676         skb_set_timestamp(head, &qp->stamp);
 677
 678         iph = head->nh.iph;
 679         iph->frag_off = 0;
 680         iph->tot_len = htons(len);
 681         IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
 682         qp->fragments = NULL;
 683         return head;
 684
 685 out_nomem:
 686         LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
 687                               "queue %p\n", qp);
 688         goto out_fail;
 689 out_oversize:
 690         if (net_ratelimit())
 691                 printk(KERN_INFO
 692                         "Oversized IP packet from %d.%d.%d.%d.\n",
 693                         NIPQUAD(qp->saddr));
 694 out_fail:
 695         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 696         return NULL;
 697 }
 698
 699 /* Process an incoming IP datagram fragment. */
 700 struct sk_buff *ip_defrag(struct sk_buff *skb, u32 user)
 701 {
 702         struct iphdr *iph = skb->nh.iph;
 703         struct ipq *qp;
 704         struct net_device *dev;
 705
 706         IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
 707
 708         /* Start by cleaning up the memory. */
 709         if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
 710                 ip_evictor();
 711
 712         dev = skb->dev;
 713
 714         /* Lookup (or create) queue header */
 715         if ((qp = ip_find(iph, user)) != NULL) {
 716                 struct sk_buff *ret = NULL;
 717
 718                 spin_lock(&qp->lock);
 719
 720                 ip_frag_queue(qp, skb);
 721
 722                 if (qp->last_in == (FIRST_IN|LAST_IN) &&
 723                     qp->meat == qp->len)
 724                         ret = ip_frag_reasm(qp, dev);
 725
 726                 spin_unlock(&qp->lock);
 727                 ipq_put(qp, NULL);
 728                 return ret;
 729         }
 730
 731         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 732         kfree_skb(skb);
 733         return NULL;
 734 }
 735
 736 void ipfrag_init(void)
 737 {
 738         ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
 739                                  (jiffies ^ (jiffies >> 6)));
 740
 741         init_timer(&ipfrag_secret_timer);
 742         ipfrag_secret_timer.function = ipfrag_secret_rebuild;
 743         ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval;
 744         add_timer(&ipfrag_secret_timer);
 745 }
 746
 747 EXPORT_SYMBOL(ip_defrag);