linux/net/ipv4/ip_fragment.c
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   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 * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
   9 *              Alan Cox <alan@lxorguk.ukuu.org.uk>
  10 *
  11 * Fixes:
  12 *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
  13 *              David S. Miller :       Begin massive cleanup...
  14 *              Andi Kleen      :       Add sysctls.
  15 *              xxxx            :       Overlapfrag bug.
  16 *              Ultima          :       ip_expire() kernel panic.
  17 *              Bill Hawes      :       Frag accounting and evictor fixes.
  18 *              John McDonald   :       0 length frag bug.
  19 *              Alexey Kuznetsov:       SMP races, threading, cleanup.
  20 *              Patrick McHardy :       LRU queue of frag heads for evictor.
  21 */
  22
  23#define pr_fmt(fmt) "IPv4: " fmt
  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 <linux/slab.h>
  38#include <net/route.h>
  39#include <net/dst.h>
  40#include <net/sock.h>
  41#include <net/ip.h>
  42#include <net/icmp.h>
  43#include <net/checksum.h>
  44#include <net/inetpeer.h>
  45#include <net/inet_frag.h>
  46#include <linux/tcp.h>
  47#include <linux/udp.h>
  48#include <linux/inet.h>
  49#include <linux/netfilter_ipv4.h>
  50#include <net/inet_ecn.h>
  51
  52/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
  53 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
  54 * as well. Or notify me, at least. --ANK
  55 */
  56
  57static int sysctl_ipfrag_max_dist __read_mostly = 64;
  58
  59struct ipfrag_skb_cb
  60{
  61        struct inet_skb_parm    h;
  62        int                     offset;
  63};
  64
  65#define FRAG_CB(skb)    ((struct ipfrag_skb_cb *)((skb)->cb))
  66
  67/* Describe an entry in the "incomplete datagrams" queue. */
  68struct ipq {
  69        struct inet_frag_queue q;
  70
  71        u32             user;
  72        __be32          saddr;
  73        __be32          daddr;
  74        __be16          id;
  75        u8              protocol;
  76        u8              ecn; /* RFC3168 support */
  77        int             iif;
  78        unsigned int    rid;
  79        struct inet_peer *peer;
  80};
  81
  82/* RFC 3168 support :
  83 * We want to check ECN values of all fragments, do detect invalid combinations.
  84 * In ipq->ecn, we store the OR value of each ip4_frag_ecn() fragment value.
  85 */
  86#define IPFRAG_ECN_NOT_ECT      0x01 /* one frag had ECN_NOT_ECT */
  87#define IPFRAG_ECN_ECT_1        0x02 /* one frag had ECN_ECT_1 */
  88#define IPFRAG_ECN_ECT_0        0x04 /* one frag had ECN_ECT_0 */
  89#define IPFRAG_ECN_CE           0x08 /* one frag had ECN_CE */
  90
  91static inline u8 ip4_frag_ecn(u8 tos)
  92{
  93        return 1 << (tos & INET_ECN_MASK);
  94}
  95
  96/* Given the OR values of all fragments, apply RFC 3168 5.3 requirements
  97 * Value : 0xff if frame should be dropped.
  98 *         0 or INET_ECN_CE value, to be ORed in to final iph->tos field
  99 */
 100static const u8 ip4_frag_ecn_table[16] = {
 101        /* at least one fragment had CE, and others ECT_0 or ECT_1 */
 102        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0]                      = INET_ECN_CE,
 103        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1]                      = INET_ECN_CE,
 104        [IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1]   = INET_ECN_CE,
 105
 106        /* invalid combinations : drop frame */
 107        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE] = 0xff,
 108        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0] = 0xff,
 109        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_1] = 0xff,
 110        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
 111        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0] = 0xff,
 112        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_1] = 0xff,
 113        [IPFRAG_ECN_NOT_ECT | IPFRAG_ECN_CE | IPFRAG_ECN_ECT_0 | IPFRAG_ECN_ECT_1] = 0xff,
 114};
 115
 116static struct inet_frags ip4_frags;
 117
 118int ip_frag_nqueues(struct net *net)
 119{
 120        return net->ipv4.frags.nqueues;
 121}
 122
 123int ip_frag_mem(struct net *net)
 124{
 125        return atomic_read(&net->ipv4.frags.mem);
 126}
 127
 128static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
 129                         struct net_device *dev);
 130
 131struct ip4_create_arg {
 132        struct iphdr *iph;
 133        u32 user;
 134};
 135
 136static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
 137{
 138        return jhash_3words((__force u32)id << 16 | prot,
 139                            (__force u32)saddr, (__force u32)daddr,
 140                            ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
 141}
 142
 143static unsigned int ip4_hashfn(struct inet_frag_queue *q)
 144{
 145        struct ipq *ipq;
 146
 147        ipq = container_of(q, struct ipq, q);
 148        return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
 149}
 150
 151static bool ip4_frag_match(struct inet_frag_queue *q, void *a)
 152{
 153        struct ipq *qp;
 154        struct ip4_create_arg *arg = a;
 155
 156        qp = container_of(q, struct ipq, q);
 157        return  qp->id == arg->iph->id &&
 158                qp->saddr == arg->iph->saddr &&
 159                qp->daddr == arg->iph->daddr &&
 160                qp->protocol == arg->iph->protocol &&
 161                qp->user == arg->user;
 162}
 163
 164/* Memory Tracking Functions. */
 165static void frag_kfree_skb(struct netns_frags *nf, struct sk_buff *skb)
 166{
 167        atomic_sub(skb->truesize, &nf->mem);
 168        kfree_skb(skb);
 169}
 170
 171static void ip4_frag_init(struct inet_frag_queue *q, void *a)
 172{
 173        struct ipq *qp = container_of(q, struct ipq, q);
 174        struct netns_ipv4 *ipv4 = container_of(q->net, struct netns_ipv4,
 175                                               frags);
 176        struct net *net = container_of(ipv4, struct net, ipv4);
 177
 178        struct ip4_create_arg *arg = a;
 179
 180        qp->protocol = arg->iph->protocol;
 181        qp->id = arg->iph->id;
 182        qp->ecn = ip4_frag_ecn(arg->iph->tos);
 183        qp->saddr = arg->iph->saddr;
 184        qp->daddr = arg->iph->daddr;
 185        qp->user = arg->user;
 186        qp->peer = sysctl_ipfrag_max_dist ?
 187                inet_getpeer_v4(net->ipv4.peers, arg->iph->saddr, 1) : NULL;
 188}
 189
 190static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
 191{
 192        struct ipq *qp;
 193
 194        qp = container_of(q, struct ipq, q);
 195        if (qp->peer)
 196                inet_putpeer(qp->peer);
 197}
 198
 199
 200/* Destruction primitives. */
 201
 202static __inline__ void ipq_put(struct ipq *ipq)
 203{
 204        inet_frag_put(&ipq->q, &ip4_frags);
 205}
 206
 207/* Kill ipq entry. It is not destroyed immediately,
 208 * because caller (and someone more) holds reference count.
 209 */
 210static void ipq_kill(struct ipq *ipq)
 211{
 212        inet_frag_kill(&ipq->q, &ip4_frags);
 213}
 214
 215/* Memory limiting on fragments.  Evictor trashes the oldest
 216 * fragment queue until we are back under the threshold.
 217 */
 218static void ip_evictor(struct net *net)
 219{
 220        int evicted;
 221
 222        evicted = inet_frag_evictor(&net->ipv4.frags, &ip4_frags, false);
 223        if (evicted)
 224                IP_ADD_STATS_BH(net, IPSTATS_MIB_REASMFAILS, evicted);
 225}
 226
 227/*
 228 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 229 */
 230static void ip_expire(unsigned long arg)
 231{
 232        struct ipq *qp;
 233        struct net *net;
 234
 235        qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
 236        net = container_of(qp->q.net, struct net, ipv4.frags);
 237
 238        spin_lock(&qp->q.lock);
 239
 240        if (qp->q.last_in & INET_FRAG_COMPLETE)
 241                goto out;
 242
 243        ipq_kill(qp);
 244
 245        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMTIMEOUT);
 246        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
 247
 248        if ((qp->q.last_in & INET_FRAG_FIRST_IN) && qp->q.fragments != NULL) {
 249                struct sk_buff *head = qp->q.fragments;
 250                const struct iphdr *iph;
 251                int err;
 252
 253                rcu_read_lock();
 254                head->dev = dev_get_by_index_rcu(net, qp->iif);
 255                if (!head->dev)
 256                        goto out_rcu_unlock;
 257
 258                /* skb dst is stale, drop it, and perform route lookup again */
 259                skb_dst_drop(head);
 260                iph = ip_hdr(head);
 261                err = ip_route_input_noref(head, iph->daddr, iph->saddr,
 262                                           iph->tos, head->dev);
 263                if (err)
 264                        goto out_rcu_unlock;
 265
 266                /*
 267                 * Only an end host needs to send an ICMP
 268                 * "Fragment Reassembly Timeout" message, per RFC792.
 269                 */
 270                if (qp->user == IP_DEFRAG_AF_PACKET ||
 271                    (qp->user == IP_DEFRAG_CONNTRACK_IN &&
 272                     skb_rtable(head)->rt_type != RTN_LOCAL))
 273                        goto out_rcu_unlock;
 274
 275
 276                /* Send an ICMP "Fragment Reassembly Timeout" message. */
 277                icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
 278out_rcu_unlock:
 279                rcu_read_unlock();
 280        }
 281out:
 282        spin_unlock(&qp->q.lock);
 283        ipq_put(qp);
 284}
 285
 286/* Find the correct entry in the "incomplete datagrams" queue for
 287 * this IP datagram, and create new one, if nothing is found.
 288 */
 289static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
 290{
 291        struct inet_frag_queue *q;
 292        struct ip4_create_arg arg;
 293        unsigned int hash;
 294
 295        arg.iph = iph;
 296        arg.user = user;
 297
 298        read_lock(&ip4_frags.lock);
 299        hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
 300
 301        q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
 302        if (q == NULL)
 303                goto out_nomem;
 304
 305        return container_of(q, struct ipq, q);
 306
 307out_nomem:
 308        LIMIT_NETDEBUG(KERN_ERR pr_fmt("ip_frag_create: no memory left !\n"));
 309        return NULL;
 310}
 311
 312/* Is the fragment too far ahead to be part of ipq? */
 313static inline int ip_frag_too_far(struct ipq *qp)
 314{
 315        struct inet_peer *peer = qp->peer;
 316        unsigned int max = sysctl_ipfrag_max_dist;
 317        unsigned int start, end;
 318
 319        int rc;
 320
 321        if (!peer || !max)
 322                return 0;
 323
 324        start = qp->rid;
 325        end = atomic_inc_return(&peer->rid);
 326        qp->rid = end;
 327
 328        rc = qp->q.fragments && (end - start) > max;
 329
 330        if (rc) {
 331                struct net *net;
 332
 333                net = container_of(qp->q.net, struct net, ipv4.frags);
 334                IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
 335        }
 336
 337        return rc;
 338}
 339
 340static int ip_frag_reinit(struct ipq *qp)
 341{
 342        struct sk_buff *fp;
 343
 344        if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
 345                atomic_inc(&qp->q.refcnt);
 346                return -ETIMEDOUT;
 347        }
 348
 349        fp = qp->q.fragments;
 350        do {
 351                struct sk_buff *xp = fp->next;
 352                frag_kfree_skb(qp->q.net, fp);
 353                fp = xp;
 354        } while (fp);
 355
 356        qp->q.last_in = 0;
 357        qp->q.len = 0;
 358        qp->q.meat = 0;
 359        qp->q.fragments = NULL;
 360        qp->q.fragments_tail = NULL;
 361        qp->iif = 0;
 362        qp->ecn = 0;
 363
 364        return 0;
 365}
 366
 367/* Add new segment to existing queue. */
 368static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 369{
 370        struct sk_buff *prev, *next;
 371        struct net_device *dev;
 372        int flags, offset;
 373        int ihl, end;
 374        int err = -ENOENT;
 375        u8 ecn;
 376
 377        if (qp->q.last_in & INET_FRAG_COMPLETE)
 378                goto err;
 379
 380        if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
 381            unlikely(ip_frag_too_far(qp)) &&
 382            unlikely(err = ip_frag_reinit(qp))) {
 383                ipq_kill(qp);
 384                goto err;
 385        }
 386
 387        ecn = ip4_frag_ecn(ip_hdr(skb)->tos);
 388        offset = ntohs(ip_hdr(skb)->frag_off);
 389        flags = offset & ~IP_OFFSET;
 390        offset &= IP_OFFSET;
 391        offset <<= 3;           /* offset is in 8-byte chunks */
 392        ihl = ip_hdrlen(skb);
 393
 394        /* Determine the position of this fragment. */
 395        end = offset + skb->len - ihl;
 396        err = -EINVAL;
 397
 398        /* Is this the final fragment? */
 399        if ((flags & IP_MF) == 0) {
 400                /* If we already have some bits beyond end
 401                 * or have different end, the segment is corrupted.
 402                 */
 403                if (end < qp->q.len ||
 404                    ((qp->q.last_in & INET_FRAG_LAST_IN) && end != qp->q.len))
 405                        goto err;
 406                qp->q.last_in |= INET_FRAG_LAST_IN;
 407                qp->q.len = end;
 408        } else {
 409                if (end&7) {
 410                        end &= ~7;
 411                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 412                                skb->ip_summed = CHECKSUM_NONE;
 413                }
 414                if (end > qp->q.len) {
 415                        /* Some bits beyond end -> corruption. */
 416                        if (qp->q.last_in & INET_FRAG_LAST_IN)
 417                                goto err;
 418                        qp->q.len = end;
 419                }
 420        }
 421        if (end == offset)
 422                goto err;
 423
 424        err = -ENOMEM;
 425        if (pskb_pull(skb, ihl) == NULL)
 426                goto err;
 427
 428        err = pskb_trim_rcsum(skb, end - offset);
 429        if (err)
 430                goto err;
 431
 432        /* Find out which fragments are in front and at the back of us
 433         * in the chain of fragments so far.  We must know where to put
 434         * this fragment, right?
 435         */
 436        prev = qp->q.fragments_tail;
 437        if (!prev || FRAG_CB(prev)->offset < offset) {
 438                next = NULL;
 439                goto found;
 440        }
 441        prev = NULL;
 442        for (next = qp->q.fragments; next != NULL; next = next->next) {
 443                if (FRAG_CB(next)->offset >= offset)
 444                        break;  /* bingo! */
 445                prev = next;
 446        }
 447
 448found:
 449        /* We found where to put this one.  Check for overlap with
 450         * preceding fragment, and, if needed, align things so that
 451         * any overlaps are eliminated.
 452         */
 453        if (prev) {
 454                int i = (FRAG_CB(prev)->offset + prev->len) - offset;
 455
 456                if (i > 0) {
 457                        offset += i;
 458                        err = -EINVAL;
 459                        if (end <= offset)
 460                                goto err;
 461                        err = -ENOMEM;
 462                        if (!pskb_pull(skb, i))
 463                                goto err;
 464                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 465                                skb->ip_summed = CHECKSUM_NONE;
 466                }
 467        }
 468
 469        err = -ENOMEM;
 470
 471        while (next && FRAG_CB(next)->offset < end) {
 472                int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
 473
 474                if (i < next->len) {
 475                        /* Eat head of the next overlapped fragment
 476                         * and leave the loop. The next ones cannot overlap.
 477                         */
 478                        if (!pskb_pull(next, i))
 479                                goto err;
 480                        FRAG_CB(next)->offset += i;
 481                        qp->q.meat -= i;
 482                        if (next->ip_summed != CHECKSUM_UNNECESSARY)
 483                                next->ip_summed = CHECKSUM_NONE;
 484                        break;
 485                } else {
 486                        struct sk_buff *free_it = next;
 487
 488                        /* Old fragment is completely overridden with
 489                         * new one drop it.
 490                         */
 491                        next = next->next;
 492
 493                        if (prev)
 494                                prev->next = next;
 495                        else
 496                                qp->q.fragments = next;
 497
 498                        qp->q.meat -= free_it->len;
 499                        frag_kfree_skb(qp->q.net, free_it);
 500                }
 501        }
 502
 503        FRAG_CB(skb)->offset = offset;
 504
 505        /* Insert this fragment in the chain of fragments. */
 506        skb->next = next;
 507        if (!next)
 508                qp->q.fragments_tail = skb;
 509        if (prev)
 510                prev->next = skb;
 511        else
 512                qp->q.fragments = skb;
 513
 514        dev = skb->dev;
 515        if (dev) {
 516                qp->iif = dev->ifindex;
 517                skb->dev = NULL;
 518        }
 519        qp->q.stamp = skb->tstamp;
 520        qp->q.meat += skb->len;
 521        qp->ecn |= ecn;
 522        atomic_add(skb->truesize, &qp->q.net->mem);
 523        if (offset == 0)
 524                qp->q.last_in |= INET_FRAG_FIRST_IN;
 525
 526        if (ip_hdr(skb)->frag_off & htons(IP_DF) &&
 527            skb->len + ihl > qp->q.max_size)
 528                qp->q.max_size = skb->len + ihl;
 529
 530        if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
 531            qp->q.meat == qp->q.len)
 532                return ip_frag_reasm(qp, prev, dev);
 533
 534        write_lock(&ip4_frags.lock);
 535        list_move_tail(&qp->q.lru_list, &qp->q.net->lru_list);
 536        write_unlock(&ip4_frags.lock);
 537        return -EINPROGRESS;
 538
 539err:
 540        kfree_skb(skb);
 541        return err;
 542}
 543
 544
 545/* Build a new IP datagram from all its fragments. */
 546
 547static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
 548                         struct net_device *dev)
 549{
 550        struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
 551        struct iphdr *iph;
 552        struct sk_buff *fp, *head = qp->q.fragments;
 553        int len;
 554        int ihlen;
 555        int err;
 556        int sum_truesize;
 557        u8 ecn;
 558
 559        ipq_kill(qp);
 560
 561        ecn = ip4_frag_ecn_table[qp->ecn];
 562        if (unlikely(ecn == 0xff)) {
 563                err = -EINVAL;
 564                goto out_fail;
 565        }
 566        /* Make the one we just received the head. */
 567        if (prev) {
 568                head = prev->next;
 569                fp = skb_clone(head, GFP_ATOMIC);
 570                if (!fp)
 571                        goto out_nomem;
 572
 573                fp->next = head->next;
 574                if (!fp->next)
 575                        qp->q.fragments_tail = fp;
 576                prev->next = fp;
 577
 578                skb_morph(head, qp->q.fragments);
 579                head->next = qp->q.fragments->next;
 580
 581                consume_skb(qp->q.fragments);
 582                qp->q.fragments = head;
 583        }
 584
 585        WARN_ON(head == NULL);
 586        WARN_ON(FRAG_CB(head)->offset != 0);
 587
 588        /* Allocate a new buffer for the datagram. */
 589        ihlen = ip_hdrlen(head);
 590        len = ihlen + qp->q.len;
 591
 592        err = -E2BIG;
 593        if (len > 65535)
 594                goto out_oversize;
 595
 596        /* Head of list must not be cloned. */
 597        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
 598                goto out_nomem;
 599
 600        /* If the first fragment is fragmented itself, we split
 601         * it to two chunks: the first with data and paged part
 602         * and the second, holding only fragments. */
 603        if (skb_has_frag_list(head)) {
 604                struct sk_buff *clone;
 605                int i, plen = 0;
 606
 607                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
 608                        goto out_nomem;
 609                clone->next = head->next;
 610                head->next = clone;
 611                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 612                skb_frag_list_init(head);
 613                for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
 614                        plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
 615                clone->len = clone->data_len = head->data_len - plen;
 616                head->data_len -= clone->len;
 617                head->len -= clone->len;
 618                clone->csum = 0;
 619                clone->ip_summed = head->ip_summed;
 620                atomic_add(clone->truesize, &qp->q.net->mem);
 621        }
 622
 623        skb_push(head, head->data - skb_network_header(head));
 624
 625        sum_truesize = head->truesize;
 626        for (fp = head->next; fp;) {
 627                bool headstolen;
 628                int delta;
 629                struct sk_buff *next = fp->next;
 630
 631                sum_truesize += fp->truesize;
 632                if (head->ip_summed != fp->ip_summed)
 633                        head->ip_summed = CHECKSUM_NONE;
 634                else if (head->ip_summed == CHECKSUM_COMPLETE)
 635                        head->csum = csum_add(head->csum, fp->csum);
 636
 637                if (skb_try_coalesce(head, fp, &headstolen, &delta)) {
 638                        kfree_skb_partial(fp, headstolen);
 639                } else {
 640                        if (!skb_shinfo(head)->frag_list)
 641                                skb_shinfo(head)->frag_list = fp;
 642                        head->data_len += fp->len;
 643                        head->len += fp->len;
 644                        head->truesize += fp->truesize;
 645                }
 646                fp = next;
 647        }
 648        atomic_sub(sum_truesize, &qp->q.net->mem);
 649
 650        head->next = NULL;
 651        head->dev = dev;
 652        head->tstamp = qp->q.stamp;
 653        IPCB(head)->frag_max_size = qp->q.max_size;
 654
 655        iph = ip_hdr(head);
 656        /* max_size != 0 implies at least one fragment had IP_DF set */
 657        iph->frag_off = qp->q.max_size ? htons(IP_DF) : 0;
 658        iph->tot_len = htons(len);
 659        iph->tos |= ecn;
 660        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
 661        qp->q.fragments = NULL;
 662        qp->q.fragments_tail = NULL;
 663        return 0;
 664
 665out_nomem:
 666        LIMIT_NETDEBUG(KERN_ERR pr_fmt("queue_glue: no memory for gluing queue %p\n"),
 667                       qp);
 668        err = -ENOMEM;
 669        goto out_fail;
 670out_oversize:
 671        net_info_ratelimited("Oversized IP packet from %pI4\n", &qp->saddr);
 672out_fail:
 673        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
 674        return err;
 675}
 676
 677/* Process an incoming IP datagram fragment. */
 678int ip_defrag(struct sk_buff *skb, u32 user)
 679{
 680        struct ipq *qp;
 681        struct net *net;
 682
 683        net = skb->dev ? dev_net(skb->dev) : dev_net(skb_dst(skb)->dev);
 684        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);
 685
 686        /* Start by cleaning up the memory. */
 687        ip_evictor(net);
 688
 689        /* Lookup (or create) queue header */
 690        if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
 691                int ret;
 692
 693                spin_lock(&qp->q.lock);
 694
 695                ret = ip_frag_queue(qp, skb);
 696
 697                spin_unlock(&qp->q.lock);
 698                ipq_put(qp);
 699                return ret;
 700        }
 701
 702        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
 703        kfree_skb(skb);
 704        return -ENOMEM;
 705}
 706EXPORT_SYMBOL(ip_defrag);
 707
 708struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user)
 709{
 710        struct iphdr iph;
 711        u32 len;
 712
 713        if (skb->protocol != htons(ETH_P_IP))
 714                return skb;
 715
 716        if (!skb_copy_bits(skb, 0, &iph, sizeof(iph)))
 717                return skb;
 718
 719        if (iph.ihl < 5 || iph.version != 4)
 720                return skb;
 721
 722        len = ntohs(iph.tot_len);
 723        if (skb->len < len || len < (iph.ihl * 4))
 724                return skb;
 725
 726        if (ip_is_fragment(&iph)) {
 727                skb = skb_share_check(skb, GFP_ATOMIC);
 728                if (skb) {
 729                        if (!pskb_may_pull(skb, iph.ihl*4))
 730                                return skb;
 731                        if (pskb_trim_rcsum(skb, len))
 732                                return skb;
 733                        memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
 734                        if (ip_defrag(skb, user))
 735                                return NULL;
 736                        skb->rxhash = 0;
 737                }
 738        }
 739        return skb;
 740}
 741EXPORT_SYMBOL(ip_check_defrag);
 742
 743#ifdef CONFIG_SYSCTL
 744static int zero;
 745
 746static struct ctl_table ip4_frags_ns_ctl_table[] = {
 747        {
 748                .procname       = "ipfrag_high_thresh",
 749                .data           = &init_net.ipv4.frags.high_thresh,
 750                .maxlen         = sizeof(int),
 751                .mode           = 0644,
 752                .proc_handler   = proc_dointvec
 753        },
 754        {
 755                .procname       = "ipfrag_low_thresh",
 756                .data           = &init_net.ipv4.frags.low_thresh,
 757                .maxlen         = sizeof(int),
 758                .mode           = 0644,
 759                .proc_handler   = proc_dointvec
 760        },
 761        {
 762                .procname       = "ipfrag_time",
 763                .data           = &init_net.ipv4.frags.timeout,
 764                .maxlen         = sizeof(int),
 765                .mode           = 0644,
 766                .proc_handler   = proc_dointvec_jiffies,
 767        },
 768        { }
 769};
 770
 771static struct ctl_table ip4_frags_ctl_table[] = {
 772        {
 773                .procname       = "ipfrag_secret_interval",
 774                .data           = &ip4_frags.secret_interval,
 775                .maxlen         = sizeof(int),
 776                .mode           = 0644,
 777                .proc_handler   = proc_dointvec_jiffies,
 778        },
 779        {
 780                .procname       = "ipfrag_max_dist",
 781                .data           = &sysctl_ipfrag_max_dist,
 782                .maxlen         = sizeof(int),
 783                .mode           = 0644,
 784                .proc_handler   = proc_dointvec_minmax,
 785                .extra1         = &zero
 786        },
 787        { }
 788};
 789
 790static int __net_init ip4_frags_ns_ctl_register(struct net *net)
 791{
 792        struct ctl_table *table;
 793        struct ctl_table_header *hdr;
 794
 795        table = ip4_frags_ns_ctl_table;
 796        if (!net_eq(net, &init_net)) {
 797                table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
 798                if (table == NULL)
 799                        goto err_alloc;
 800
 801                table[0].data = &net->ipv4.frags.high_thresh;
 802                table[1].data = &net->ipv4.frags.low_thresh;
 803                table[2].data = &net->ipv4.frags.timeout;
 804        }
 805
 806        hdr = register_net_sysctl(net, "net/ipv4", table);
 807        if (hdr == NULL)
 808                goto err_reg;
 809
 810        net->ipv4.frags_hdr = hdr;
 811        return 0;
 812
 813err_reg:
 814        if (!net_eq(net, &init_net))
 815                kfree(table);
 816err_alloc:
 817        return -ENOMEM;
 818}
 819
 820static void __net_exit ip4_frags_ns_ctl_unregister(struct net *net)
 821{
 822        struct ctl_table *table;
 823
 824        table = net->ipv4.frags_hdr->ctl_table_arg;
 825        unregister_net_sysctl_table(net->ipv4.frags_hdr);
 826        kfree(table);
 827}
 828
 829static void ip4_frags_ctl_register(void)
 830{
 831        register_net_sysctl(&init_net, "net/ipv4", ip4_frags_ctl_table);
 832}
 833#else
 834static inline int ip4_frags_ns_ctl_register(struct net *net)
 835{
 836        return 0;
 837}
 838
 839static inline void ip4_frags_ns_ctl_unregister(struct net *net)
 840{
 841}
 842
 843static inline void ip4_frags_ctl_register(void)
 844{
 845}
 846#endif
 847
 848static int __net_init ipv4_frags_init_net(struct net *net)
 849{
 850        /*
 851         * Fragment cache limits. We will commit 256K at one time. Should we
 852         * cross that limit we will prune down to 192K. This should cope with
 853         * even the most extreme cases without allowing an attacker to
 854         * measurably harm machine performance.
 855         */
 856        net->ipv4.frags.high_thresh = 256 * 1024;
 857        net->ipv4.frags.low_thresh = 192 * 1024;
 858        /*
 859         * Important NOTE! Fragment queue must be destroyed before MSL expires.
 860         * RFC791 is wrong proposing to prolongate timer each fragment arrival
 861         * by TTL.
 862         */
 863        net->ipv4.frags.timeout = IP_FRAG_TIME;
 864
 865        inet_frags_init_net(&net->ipv4.frags);
 866
 867        return ip4_frags_ns_ctl_register(net);
 868}
 869
 870static void __net_exit ipv4_frags_exit_net(struct net *net)
 871{
 872        ip4_frags_ns_ctl_unregister(net);
 873        inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
 874}
 875
 876static struct pernet_operations ip4_frags_ops = {
 877        .init = ipv4_frags_init_net,
 878        .exit = ipv4_frags_exit_net,
 879};
 880
 881void __init ipfrag_init(void)
 882{
 883        ip4_frags_ctl_register();
 884        register_pernet_subsys(&ip4_frags_ops);
 885        ip4_frags.hashfn = ip4_hashfn;
 886        ip4_frags.constructor = ip4_frag_init;
 887        ip4_frags.destructor = ip4_frag_free;
 888        ip4_frags.skb_free = NULL;
 889        ip4_frags.qsize = sizeof(struct ipq);
 890        ip4_frags.match = ip4_frag_match;
 891        ip4_frags.frag_expire = ip_expire;
 892        ip4_frags.secret_interval = 10 * 60 * HZ;
 893        inet_frags_init(&ip4_frags);
 894}
 895
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