net/ipv6/netfilter/nf_conntrack_reasm.c

   1 /*
   2  * IPv6 fragment reassembly for connection tracking
   3  *
   4  * Copyright (C)2004 USAGI/WIDE Project
   5  *
   6  * Author:
   7  *      Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
   8  *
   9  * Based on: net/ipv6/reassembly.c
  10  *
  11  * This program is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU General Public License
  13  * as published by the Free Software Foundation; either version
  14  * 2 of the License, or (at your option) any later version.
  15  */
  16
  17 #include <linux/errno.h>
  18 #include <linux/types.h>
  19 #include <linux/string.h>
  20 #include <linux/socket.h>
  21 #include <linux/sockios.h>
  22 #include <linux/jiffies.h>
  23 #include <linux/net.h>
  24 #include <linux/list.h>
  25 #include <linux/netdevice.h>
  26 #include <linux/in6.h>
  27 #include <linux/ipv6.h>
  28 #include <linux/icmpv6.h>
  29 #include <linux/random.h>
  30 #include <linux/slab.h>
  31
  32 #include <net/sock.h>
  33 #include <net/snmp.h>
  34 #include <net/inet_frag.h>
  35
  36 #include <net/ipv6.h>
  37 #include <net/protocol.h>
  38 #include <net/transp_v6.h>
  39 #include <net/rawv6.h>
  40 #include <net/ndisc.h>
  41 #include <net/addrconf.h>
  42 #include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
  43 #include <linux/sysctl.h>
  44 #include <linux/netfilter.h>
  45 #include <linux/netfilter_ipv6.h>
  46 #include <linux/kernel.h>
  47 #include <linux/module.h>
  48
  49
  50 struct nf_ct_frag6_skb_cb
  51 {
  52         struct inet6_skb_parm   h;
  53         int                     offset;
  54         struct sk_buff          *orig;
  55 };
  56
  57 #define NFCT_FRAG6_CB(skb)      ((struct nf_ct_frag6_skb_cb*)((skb)->cb))
  58
  59 struct nf_ct_frag6_queue
  60 {
  61         struct inet_frag_queue  q;
  62
  63         __be32                  id;             /* fragment id          */
  64         u32                     user;
  65         struct in6_addr         saddr;
  66         struct in6_addr         daddr;
  67
  68         unsigned int            csum;
  69         __u16                   nhoffset;
  70 };
  71
  72 static struct inet_frags nf_frags;
  73 static struct netns_frags nf_init_frags;
  74
  75 #ifdef CONFIG_SYSCTL
  76 struct ctl_table nf_ct_ipv6_sysctl_table[] = {
  77         {
  78                 .procname       = "nf_conntrack_frag6_timeout",
  79                 .data           = &nf_init_frags.timeout,
  80                 .maxlen         = sizeof(unsigned int),
  81                 .mode           = 0644,
  82                 .proc_handler   = proc_dointvec_jiffies,
  83         },
  84         {
  85                 .procname       = "nf_conntrack_frag6_low_thresh",
  86                 .data           = &nf_init_frags.low_thresh,
  87                 .maxlen         = sizeof(unsigned int),
  88                 .mode           = 0644,
  89                 .proc_handler   = proc_dointvec,
  90         },
  91         {
  92                 .procname       = "nf_conntrack_frag6_high_thresh",
  93                 .data           = &nf_init_frags.high_thresh,
  94                 .maxlen         = sizeof(unsigned int),
  95                 .mode           = 0644,
  96                 .proc_handler   = proc_dointvec,
  97         },
  98         { }
  99 };
 100 #endif
 101
 102 static unsigned int nf_hashfn(struct inet_frag_queue *q)
 103 {
 104         const struct nf_ct_frag6_queue *nq;
 105
 106         nq = container_of(q, struct nf_ct_frag6_queue, q);
 107         return inet6_hash_frag(nq->id, &nq->saddr, &nq->daddr, nf_frags.rnd);
 108 }
 109
 110 static void nf_skb_free(struct sk_buff *skb)
 111 {
 112         if (NFCT_FRAG6_CB(skb)->orig)
 113                 kfree_skb(NFCT_FRAG6_CB(skb)->orig);
 114 }
 115
 116 /* Destruction primitives. */
 117
 118 static __inline__ void fq_put(struct nf_ct_frag6_queue *fq)
 119 {
 120         inet_frag_put(&fq->q, &nf_frags);
 121 }
 122
 123 /* Kill fq entry. It is not destroyed immediately,
 124  * because caller (and someone more) holds reference count.
 125  */
 126 static __inline__ void fq_kill(struct nf_ct_frag6_queue *fq)
 127 {
 128         inet_frag_kill(&fq->q, &nf_frags);
 129 }
 130
 131 static void nf_ct_frag6_evictor(void)
 132 {
 133         local_bh_disable();
 134         inet_frag_evictor(&nf_init_frags, &nf_frags);
 135         local_bh_enable();
 136 }
 137
 138 static void nf_ct_frag6_expire(unsigned long data)
 139 {
 140         struct nf_ct_frag6_queue *fq;
 141
 142         fq = container_of((struct inet_frag_queue *)data,
 143                         struct nf_ct_frag6_queue, q);
 144
 145         spin_lock(&fq->q.lock);
 146
 147         if (fq->q.last_in & INET_FRAG_COMPLETE)
 148                 goto out;
 149
 150         fq_kill(fq);
 151
 152 out:
 153         spin_unlock(&fq->q.lock);
 154         fq_put(fq);
 155 }
 156
 157 /* Creation primitives. */
 158
 159 static __inline__ struct nf_ct_frag6_queue *
 160 fq_find(__be32 id, u32 user, struct in6_addr *src, struct in6_addr *dst)
 161 {
 162         struct inet_frag_queue *q;
 163         struct ip6_create_arg arg;
 164         unsigned int hash;
 165
 166         arg.id = id;
 167         arg.user = user;
 168         arg.src = src;
 169         arg.dst = dst;
 170
 171         read_lock_bh(&nf_frags.lock);
 172         hash = inet6_hash_frag(id, src, dst, nf_frags.rnd);
 173
 174         q = inet_frag_find(&nf_init_frags, &nf_frags, &arg, hash);
 175         local_bh_enable();
 176         if (q == NULL)
 177                 goto oom;
 178
 179         return container_of(q, struct nf_ct_frag6_queue, q);
 180
 181 oom:
 182         pr_debug("Can't alloc new queue\n");
 183         return NULL;
 184 }
 185
 186
 187 static int nf_ct_frag6_queue(struct nf_ct_frag6_queue *fq, struct sk_buff *skb,
 188                              const struct frag_hdr *fhdr, int nhoff)
 189 {
 190         struct sk_buff *prev, *next;
 191         int offset, end;
 192
 193         if (fq->q.last_in & INET_FRAG_COMPLETE) {
 194                 pr_debug("Already completed\n");
 195                 goto err;
 196         }
 197
 198         offset = ntohs(fhdr->frag_off) & ~0x7;
 199         end = offset + (ntohs(ipv6_hdr(skb)->payload_len) -
 200                         ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));
 201
 202         if ((unsigned int)end > IPV6_MAXPLEN) {
 203                 pr_debug("offset is too large.\n");
 204                 return -1;
 205         }
 206
 207         if (skb->ip_summed == CHECKSUM_COMPLETE) {
 208                 const unsigned char *nh = skb_network_header(skb);
 209                 skb->csum = csum_sub(skb->csum,
 210                                      csum_partial(nh, (u8 *)(fhdr + 1) - nh,
 211                                                   0));
 212         }
 213
 214         /* Is this the final fragment? */
 215         if (!(fhdr->frag_off & htons(IP6_MF))) {
 216                 /* If we already have some bits beyond end
 217                  * or have different end, the segment is corrupted.
 218                  */
 219                 if (end < fq->q.len ||
 220                     ((fq->q.last_in & INET_FRAG_LAST_IN) && end != fq->q.len)) {
 221                         pr_debug("already received last fragment\n");
 222                         goto err;
 223                 }
 224                 fq->q.last_in |= INET_FRAG_LAST_IN;
 225                 fq->q.len = end;
 226         } else {
 227                 /* Check if the fragment is rounded to 8 bytes.
 228                  * Required by the RFC.
 229                  */
 230                 if (end & 0x7) {
 231                         /* RFC2460 says always send parameter problem in
 232                          * this case. -DaveM
 233                          */
 234                         pr_debug("end of fragment not rounded to 8 bytes.\n");
 235                         return -1;
 236                 }
 237                 if (end > fq->q.len) {
 238                         /* Some bits beyond end -> corruption. */
 239                         if (fq->q.last_in & INET_FRAG_LAST_IN) {
 240                                 pr_debug("last packet already reached.\n");
 241                                 goto err;
 242                         }
 243                         fq->q.len = end;
 244                 }
 245         }
 246
 247         if (end == offset)
 248                 goto err;
 249
 250         /* Point into the IP datagram 'data' part. */
 251         if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
 252                 pr_debug("queue: message is too short.\n");
 253                 goto err;
 254         }
 255         if (pskb_trim_rcsum(skb, end - offset)) {
 256                 pr_debug("Can't trim\n");
 257                 goto err;
 258         }
 259
 260         /* Find out which fragments are in front and at the back of us
 261          * in the chain of fragments so far.  We must know where to put
 262          * this fragment, right?
 263          */
 264         prev = fq->q.fragments_tail;
 265         if (!prev || NFCT_FRAG6_CB(prev)->offset < offset) {
 266                 next = NULL;
 267                 goto found;
 268         }
 269         prev = NULL;
 270         for (next = fq->q.fragments; next != NULL; next = next->next) {
 271                 if (NFCT_FRAG6_CB(next)->offset >= offset)
 272                         break;  /* bingo! */
 273                 prev = next;
 274         }
 275
 276 found:
 277         /* RFC5722, Section 4:
 278          *                                  When reassembling an IPv6 datagram, if
 279          *   one or more its constituent fragments is determined to be an
 280          *   overlapping fragment, the entire datagram (and any constituent
 281          *   fragments, including those not yet received) MUST be silently
 282          *   discarded.
 283          */
 284
 285         /* Check for overlap with preceding fragment. */
 286         if (prev &&
 287             (NFCT_FRAG6_CB(prev)->offset + prev->len) - offset > 0)
 288                 goto discard_fq;
 289
 290         /* Look for overlap with succeeding segment. */
 291         if (next && NFCT_FRAG6_CB(next)->offset < end)
 292                 goto discard_fq;
 293
 294         NFCT_FRAG6_CB(skb)->offset = offset;
 295
 296         /* Insert this fragment in the chain of fragments. */
 297         skb->next = next;
 298         if (!next)
 299                 fq->q.fragments_tail = skb;
 300         if (prev)
 301                 prev->next = skb;
 302         else
 303                 fq->q.fragments = skb;
 304
 305         skb->dev = NULL;
 306         fq->q.stamp = skb->tstamp;
 307         fq->q.meat += skb->len;
 308         atomic_add(skb->truesize, &nf_init_frags.mem);
 309
 310         /* The first fragment.
 311          * nhoffset is obtained from the first fragment, of course.
 312          */
 313         if (offset == 0) {
 314                 fq->nhoffset = nhoff;
 315                 fq->q.last_in |= INET_FRAG_FIRST_IN;
 316         }
 317         write_lock(&nf_frags.lock);
 318         list_move_tail(&fq->q.lru_list, &nf_init_frags.lru_list);
 319         write_unlock(&nf_frags.lock);
 320         return 0;
 321
 322 discard_fq:
 323         fq_kill(fq);
 324 err:
 325         return -1;
 326 }
 327
 328 /*
 329  *      Check if this packet is complete.
 330  *      Returns NULL on failure by any reason, and pointer
 331  *      to current nexthdr field in reassembled frame.
 332  *
 333  *      It is called with locked fq, and caller must check that
 334  *      queue is eligible for reassembly i.e. it is not COMPLETE,
 335  *      the last and the first frames arrived and all the bits are here.
 336  */
 337 static struct sk_buff *
 338 nf_ct_frag6_reasm(struct nf_ct_frag6_queue *fq, struct net_device *dev)
 339 {
 340         struct sk_buff *fp, *op, *head = fq->q.fragments;
 341         int    payload_len;
 342
 343         fq_kill(fq);
 344
 345         WARN_ON(head == NULL);
 346         WARN_ON(NFCT_FRAG6_CB(head)->offset != 0);
 347
 348         /* Unfragmented part is taken from the first segment. */
 349         payload_len = ((head->data - skb_network_header(head)) -
 350                        sizeof(struct ipv6hdr) + fq->q.len -
 351                        sizeof(struct frag_hdr));
 352         if (payload_len > IPV6_MAXPLEN) {
 353                 pr_debug("payload len is too large.\n");
 354                 goto out_oversize;
 355         }
 356
 357         /* Head of list must not be cloned. */
 358         if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
 359                 pr_debug("skb is cloned but can't expand head");
 360                 goto out_oom;
 361         }
 362
 363         /* If the first fragment is fragmented itself, we split
 364          * it to two chunks: the first with data and paged part
 365          * and the second, holding only fragments. */
 366         if (skb_has_frags(head)) {
 367                 struct sk_buff *clone;
 368                 int i, plen = 0;
 369
 370                 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL) {
 371                         pr_debug("Can't alloc skb\n");
 372                         goto out_oom;
 373                 }
 374                 clone->next = head->next;
 375                 head->next = clone;
 376                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 377                 skb_frag_list_init(head);
 378                 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
 379                         plen += skb_shinfo(head)->frags[i].size;
 380                 clone->len = clone->data_len = head->data_len - plen;
 381                 head->data_len -= clone->len;
 382                 head->len -= clone->len;
 383                 clone->csum = 0;
 384                 clone->ip_summed = head->ip_summed;
 385
 386                 NFCT_FRAG6_CB(clone)->orig = NULL;
 387                 atomic_add(clone->truesize, &nf_init_frags.mem);
 388         }
 389
 390         /* We have to remove fragment header from datagram and to relocate
 391          * header in order to calculate ICV correctly. */
 392         skb_network_header(head)[fq->nhoffset] = skb_transport_header(head)[0];
 393         memmove(head->head + sizeof(struct frag_hdr), head->head,
 394                 (head->data - head->head) - sizeof(struct frag_hdr));
 395         head->mac_header += sizeof(struct frag_hdr);
 396         head->network_header += sizeof(struct frag_hdr);
 397
 398         skb_shinfo(head)->frag_list = head->next;
 399         skb_reset_transport_header(head);
 400         skb_push(head, head->data - skb_network_header(head));
 401
 402         for (fp=head->next; fp; fp = fp->next) {
 403                 head->data_len += fp->len;
 404                 head->len += fp->len;
 405                 if (head->ip_summed != fp->ip_summed)
 406                         head->ip_summed = CHECKSUM_NONE;
 407                 else if (head->ip_summed == CHECKSUM_COMPLETE)
 408                         head->csum = csum_add(head->csum, fp->csum);
 409                 head->truesize += fp->truesize;
 410         }
 411         atomic_sub(head->truesize, &nf_init_frags.mem);
 412
 413         head->next = NULL;
 414         head->dev = dev;
 415         head->tstamp = fq->q.stamp;
 416         ipv6_hdr(head)->payload_len = htons(payload_len);
 417
 418         /* Yes, and fold redundant checksum back. 8) */
 419         if (head->ip_summed == CHECKSUM_COMPLETE)
 420                 head->csum = csum_partial(skb_network_header(head),
 421                                           skb_network_header_len(head),
 422                                           head->csum);
 423
 424         fq->q.fragments = NULL;
 425         fq->q.fragments_tail = NULL;
 426
 427         /* all original skbs are linked into the NFCT_FRAG6_CB(head).orig */
 428         fp = skb_shinfo(head)->frag_list;
 429         if (fp && NFCT_FRAG6_CB(fp)->orig == NULL)
 430                 /* at above code, head skb is divided into two skbs. */
 431                 fp = fp->next;
 432
 433         op = NFCT_FRAG6_CB(head)->orig;
 434         for (; fp; fp = fp->next) {
 435                 struct sk_buff *orig = NFCT_FRAG6_CB(fp)->orig;
 436
 437                 op->next = orig;
 438                 op = orig;
 439                 NFCT_FRAG6_CB(fp)->orig = NULL;
 440         }
 441
 442         return head;
 443
 444 out_oversize:
 445         if (net_ratelimit())
 446                 printk(KERN_DEBUG "nf_ct_frag6_reasm: payload len = %d\n", payload_len);
 447         goto out_fail;
 448 out_oom:
 449         if (net_ratelimit())
 450                 printk(KERN_DEBUG "nf_ct_frag6_reasm: no memory for reassembly\n");
 451 out_fail:
 452         return NULL;
 453 }
 454
 455 /*
 456  * find the header just before Fragment Header.
 457  *
 458  * if success return 0 and set ...
 459  * (*prevhdrp): the value of "Next Header Field" in the header
 460  *              just before Fragment Header.
 461  * (*prevhoff): the offset of "Next Header Field" in the header
 462  *              just before Fragment Header.
 463  * (*fhoff)   : the offset of Fragment Header.
 464  *
 465  * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
 466  *
 467  */
 468 static int
 469 find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
 470 {
 471         u8 nexthdr = ipv6_hdr(skb)->nexthdr;
 472         const int netoff = skb_network_offset(skb);
 473         u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
 474         int start = netoff + sizeof(struct ipv6hdr);
 475         int len = skb->len - start;
 476         u8 prevhdr = NEXTHDR_IPV6;
 477
 478         while (nexthdr != NEXTHDR_FRAGMENT) {
 479                 struct ipv6_opt_hdr hdr;
 480                 int hdrlen;
 481
 482                 if (!ipv6_ext_hdr(nexthdr)) {
 483                         return -1;
 484                 }
 485                 if (nexthdr == NEXTHDR_NONE) {
 486                         pr_debug("next header is none\n");
 487                         return -1;
 488                 }
 489                 if (len < (int)sizeof(struct ipv6_opt_hdr)) {
 490                         pr_debug("too short\n");
 491                         return -1;
 492                 }
 493                 if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
 494                         BUG();
 495                 if (nexthdr == NEXTHDR_AUTH)
 496                         hdrlen = (hdr.hdrlen+2)<<2;
 497                 else
 498                         hdrlen = ipv6_optlen(&hdr);
 499
 500                 prevhdr = nexthdr;
 501                 prev_nhoff = start;
 502
 503                 nexthdr = hdr.nexthdr;
 504                 len -= hdrlen;
 505                 start += hdrlen;
 506         }
 507
 508         if (len < 0)
 509                 return -1;
 510
 511         *prevhdrp = prevhdr;
 512         *prevhoff = prev_nhoff;
 513         *fhoff = start;
 514
 515         return 0;
 516 }
 517
 518 struct sk_buff *nf_ct_frag6_gather(struct sk_buff *skb, u32 user)
 519 {
 520         struct sk_buff *clone;
 521         struct net_device *dev = skb->dev;
 522         struct frag_hdr *fhdr;
 523         struct nf_ct_frag6_queue *fq;
 524         struct ipv6hdr *hdr;
 525         int fhoff, nhoff;
 526         u8 prevhdr;
 527         struct sk_buff *ret_skb = NULL;
 528
 529         /* Jumbo payload inhibits frag. header */
 530         if (ipv6_hdr(skb)->payload_len == 0) {
 531                 pr_debug("payload len = 0\n");
 532                 return skb;
 533         }
 534
 535         if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
 536                 return skb;
 537
 538         clone = skb_clone(skb, GFP_ATOMIC);
 539         if (clone == NULL) {
 540                 pr_debug("Can't clone skb\n");
 541                 return skb;
 542         }
 543
 544         NFCT_FRAG6_CB(clone)->orig = skb;
 545
 546         if (!pskb_may_pull(clone, fhoff + sizeof(*fhdr))) {
 547                 pr_debug("message is too short.\n");
 548                 goto ret_orig;
 549         }
 550
 551         skb_set_transport_header(clone, fhoff);
 552         hdr = ipv6_hdr(clone);
 553         fhdr = (struct frag_hdr *)skb_transport_header(clone);
 554
 555         if (atomic_read(&nf_init_frags.mem) > nf_init_frags.high_thresh)
 556                 nf_ct_frag6_evictor();
 557
 558         fq = fq_find(fhdr->identification, user, &hdr->saddr, &hdr->daddr);
 559         if (fq == NULL) {
 560                 pr_debug("Can't find and can't create new queue\n");
 561                 goto ret_orig;
 562         }
 563
 564         spin_lock_bh(&fq->q.lock);
 565
 566         if (nf_ct_frag6_queue(fq, clone, fhdr, nhoff) < 0) {
 567                 spin_unlock_bh(&fq->q.lock);
 568                 pr_debug("Can't insert skb to queue\n");
 569                 fq_put(fq);
 570                 goto ret_orig;
 571         }
 572
 573         if (fq->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
 574             fq->q.meat == fq->q.len) {
 575                 ret_skb = nf_ct_frag6_reasm(fq, dev);
 576                 if (ret_skb == NULL)
 577                         pr_debug("Can't reassemble fragmented packets\n");
 578         }
 579         spin_unlock_bh(&fq->q.lock);
 580
 581         fq_put(fq);
 582         return ret_skb;
 583
 584 ret_orig:
 585         kfree_skb(clone);
 586         return skb;
 587 }
 588
 589 void nf_ct_frag6_output(unsigned int hooknum, struct sk_buff *skb,
 590                         struct net_device *in, struct net_device *out,
 591                         int (*okfn)(struct sk_buff *))
 592 {
 593         struct sk_buff *s, *s2;
 594
 595         for (s = NFCT_FRAG6_CB(skb)->orig; s;) {
 596                 nf_conntrack_put_reasm(s->nfct_reasm);
 597                 nf_conntrack_get_reasm(skb);
 598                 s->nfct_reasm = skb;
 599
 600                 s2 = s->next;
 601                 s->next = NULL;
 602
 603                 NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, s, in, out, okfn,
 604                                NF_IP6_PRI_CONNTRACK_DEFRAG + 1);
 605                 s = s2;
 606         }
 607         nf_conntrack_put_reasm(skb);
 608 }
 609
 610 int nf_ct_frag6_init(void)
 611 {
 612         nf_frags.hashfn = nf_hashfn;
 613         nf_frags.constructor = ip6_frag_init;
 614         nf_frags.destructor = NULL;
 615         nf_frags.skb_free = nf_skb_free;
 616         nf_frags.qsize = sizeof(struct nf_ct_frag6_queue);
 617         nf_frags.match = ip6_frag_match;
 618         nf_frags.frag_expire = nf_ct_frag6_expire;
 619         nf_frags.secret_interval = 10 * 60 * HZ;
 620         nf_init_frags.timeout = IPV6_FRAG_TIMEOUT;
 621         nf_init_frags.high_thresh = IPV6_FRAG_HIGH_THRESH;
 622         nf_init_frags.low_thresh = IPV6_FRAG_LOW_THRESH;
 623         inet_frags_init_net(&nf_init_frags);
 624         inet_frags_init(&nf_frags);
 625
 626         return 0;
 627 }
 628
 629 void nf_ct_frag6_cleanup(void)
 630 {
 631         inet_frags_fini(&nf_frags);
 632
 633         nf_init_frags.low_thresh = 0;
 634         nf_ct_frag6_evictor();
 635 }