net/ipv4/netfilter/nf_nat_helper.c

   1 /* ip_nat_helper.c - generic support functions for NAT helpers
   2  *
   3  * (C) 2000-2002 Harald Welte <laforge@netfilter.org>
   4  * (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10 #include <linux/module.h>
  11 #include <linux/kmod.h>
  12 #include <linux/types.h>
  13 #include <linux/timer.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/tcp.h>
  16 #include <linux/udp.h>
  17 #include <net/checksum.h>
  18 #include <net/tcp.h>
  19 #include <net/route.h>
  20
  21 #include <linux/netfilter_ipv4.h>
  22 #include <net/netfilter/nf_conntrack.h>
  23 #include <net/netfilter/nf_conntrack_helper.h>
  24 #include <net/netfilter/nf_conntrack_ecache.h>
  25 #include <net/netfilter/nf_conntrack_expect.h>
  26 #include <net/netfilter/nf_nat.h>
  27 #include <net/netfilter/nf_nat_protocol.h>
  28 #include <net/netfilter/nf_nat_core.h>
  29 #include <net/netfilter/nf_nat_helper.h>
  30
  31 #define DUMP_OFFSET(x) \
  32         pr_debug("offset_before=%d, offset_after=%d, correction_pos=%u\n", \
  33                  x->offset_before, x->offset_after, x->correction_pos);
  34
  35 static DEFINE_SPINLOCK(nf_nat_seqofs_lock);
  36
  37 /* Setup TCP sequence correction given this change at this sequence */
  38 static inline void
  39 adjust_tcp_sequence(u32 seq,
  40                     int sizediff,
  41                     struct nf_conn *ct,
  42                     enum ip_conntrack_info ctinfo)
  43 {
  44         int dir;
  45         struct nf_nat_seq *this_way, *other_way;
  46         struct nf_conn_nat *nat = nfct_nat(ct);
  47
  48         pr_debug("adjust_tcp_sequence: seq = %u, sizediff = %d\n", seq, seq);
  49
  50         dir = CTINFO2DIR(ctinfo);
  51
  52         this_way = &nat->seq[dir];
  53         other_way = &nat->seq[!dir];
  54
  55         pr_debug("nf_nat_resize_packet: Seq_offset before: ");
  56         DUMP_OFFSET(this_way);
  57
  58         spin_lock_bh(&nf_nat_seqofs_lock);
  59
  60         /* SYN adjust. If it's uninitialized, or this is after last
  61          * correction, record it: we don't handle more than one
  62          * adjustment in the window, but do deal with common case of a
  63          * retransmit */
  64         if (this_way->offset_before == this_way->offset_after ||
  65             before(this_way->correction_pos, seq)) {
  66                    this_way->correction_pos = seq;
  67                    this_way->offset_before = this_way->offset_after;
  68                    this_way->offset_after += sizediff;
  69         }
  70         spin_unlock_bh(&nf_nat_seqofs_lock);
  71
  72         pr_debug("nf_nat_resize_packet: Seq_offset after: ");
  73         DUMP_OFFSET(this_way);
  74 }
  75
  76 /* Frobs data inside this packet, which is linear. */
  77 static void mangle_contents(struct sk_buff *skb,
  78                             unsigned int dataoff,
  79                             unsigned int match_offset,
  80                             unsigned int match_len,
  81                             const char *rep_buffer,
  82                             unsigned int rep_len)
  83 {
  84         unsigned char *data;
  85
  86         BUG_ON(skb_is_nonlinear(skb));
  87         data = skb_network_header(skb) + dataoff;
  88
  89         /* move post-replacement */
  90         memmove(data + match_offset + rep_len,
  91                 data + match_offset + match_len,
  92                 skb->tail - (skb->network_header + dataoff +
  93                              match_offset + match_len));
  94
  95         /* insert data from buffer */
  96         memcpy(data + match_offset, rep_buffer, rep_len);
  97
  98         /* update skb info */
  99         if (rep_len > match_len) {
 100                 pr_debug("nf_nat_mangle_packet: Extending packet by "
 101                          "%u from %u bytes\n", rep_len - match_len, skb->len);
 102                 skb_put(skb, rep_len - match_len);
 103         } else {
 104                 pr_debug("nf_nat_mangle_packet: Shrinking packet from "
 105                          "%u from %u bytes\n", match_len - rep_len, skb->len);
 106                 __skb_trim(skb, skb->len + rep_len - match_len);
 107         }
 108
 109         /* fix IP hdr checksum information */
 110         ip_hdr(skb)->tot_len = htons(skb->len);
 111         ip_send_check(ip_hdr(skb));
 112 }
 113
 114 /* Unusual, but possible case. */
 115 static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
 116 {
 117         if (skb->len + extra > 65535)
 118                 return 0;
 119
 120         if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
 121                 return 0;
 122
 123         return 1;
 124 }
 125
 126 /* Generic function for mangling variable-length address changes inside
 127  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
 128  * command in FTP).
 129  *
 130  * Takes care about all the nasty sequence number changes, checksumming,
 131  * skb enlargement, ...
 132  *
 133  * */
 134 int
 135 nf_nat_mangle_tcp_packet(struct sk_buff *skb,
 136                          struct nf_conn *ct,
 137                          enum ip_conntrack_info ctinfo,
 138                          unsigned int match_offset,
 139                          unsigned int match_len,
 140                          const char *rep_buffer,
 141                          unsigned int rep_len)
 142 {
 143         struct rtable *rt = skb_rtable(skb);
 144         struct iphdr *iph;
 145         struct tcphdr *tcph;
 146         int oldlen, datalen;
 147
 148         if (!skb_make_writable(skb, skb->len))
 149                 return 0;
 150
 151         if (rep_len > match_len &&
 152             rep_len - match_len > skb_tailroom(skb) &&
 153             !enlarge_skb(skb, rep_len - match_len))
 154                 return 0;
 155
 156         SKB_LINEAR_ASSERT(skb);
 157
 158         iph = ip_hdr(skb);
 159         tcph = (void *)iph + iph->ihl*4;
 160
 161         oldlen = skb->len - iph->ihl*4;
 162         mangle_contents(skb, iph->ihl*4 + tcph->doff*4,
 163                         match_offset, match_len, rep_buffer, rep_len);
 164
 165         datalen = skb->len - iph->ihl*4;
 166         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 167                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 168                     skb->dev->features & NETIF_F_V4_CSUM) {
 169                         skb->ip_summed = CHECKSUM_PARTIAL;
 170                         skb->csum_start = skb_headroom(skb) +
 171                                           skb_network_offset(skb) +
 172                                           iph->ihl * 4;
 173                         skb->csum_offset = offsetof(struct tcphdr, check);
 174                         tcph->check = ~tcp_v4_check(datalen,
 175                                                     iph->saddr, iph->daddr, 0);
 176                 } else {
 177                         tcph->check = 0;
 178                         tcph->check = tcp_v4_check(datalen,
 179                                                    iph->saddr, iph->daddr,
 180                                                    csum_partial(tcph,
 181                                                                 datalen, 0));
 182                 }
 183         } else
 184                 inet_proto_csum_replace2(&tcph->check, skb,
 185                                          htons(oldlen), htons(datalen), 1);
 186
 187         if (rep_len != match_len) {
 188                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
 189                 adjust_tcp_sequence(ntohl(tcph->seq),
 190                                     (int)rep_len - (int)match_len,
 191                                     ct, ctinfo);
 192                 /* Tell TCP window tracking about seq change */
 193                 nf_conntrack_tcp_update(skb, ip_hdrlen(skb),
 194                                         ct, CTINFO2DIR(ctinfo),
 195                                         (int)rep_len - (int)match_len);
 196
 197                 nf_conntrack_event_cache(IPCT_NATSEQADJ, ct);
 198         }
 199         return 1;
 200 }
 201 EXPORT_SYMBOL(nf_nat_mangle_tcp_packet);
 202
 203 /* Generic function for mangling variable-length address changes inside
 204  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
 205  * command in the Amanda protocol)
 206  *
 207  * Takes care about all the nasty sequence number changes, checksumming,
 208  * skb enlargement, ...
 209  *
 210  * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
 211  *       should be fairly easy to do.
 212  */
 213 int
 214 nf_nat_mangle_udp_packet(struct sk_buff *skb,
 215                          struct nf_conn *ct,
 216                          enum ip_conntrack_info ctinfo,
 217                          unsigned int match_offset,
 218                          unsigned int match_len,
 219                          const char *rep_buffer,
 220                          unsigned int rep_len)
 221 {
 222         struct rtable *rt = skb_rtable(skb);
 223         struct iphdr *iph;
 224         struct udphdr *udph;
 225         int datalen, oldlen;
 226
 227         /* UDP helpers might accidentally mangle the wrong packet */
 228         iph = ip_hdr(skb);
 229         if (skb->len < iph->ihl*4 + sizeof(*udph) +
 230                                match_offset + match_len)
 231                 return 0;
 232
 233         if (!skb_make_writable(skb, skb->len))
 234                 return 0;
 235
 236         if (rep_len > match_len &&
 237             rep_len - match_len > skb_tailroom(skb) &&
 238             !enlarge_skb(skb, rep_len - match_len))
 239                 return 0;
 240
 241         iph = ip_hdr(skb);
 242         udph = (void *)iph + iph->ihl*4;
 243
 244         oldlen = skb->len - iph->ihl*4;
 245         mangle_contents(skb, iph->ihl*4 + sizeof(*udph),
 246                         match_offset, match_len, rep_buffer, rep_len);
 247
 248         /* update the length of the UDP packet */
 249         datalen = skb->len - iph->ihl*4;
 250         udph->len = htons(datalen);
 251
 252         /* fix udp checksum if udp checksum was previously calculated */
 253         if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
 254                 return 1;
 255
 256         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 257                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 258                     skb->dev->features & NETIF_F_V4_CSUM) {
 259                         skb->ip_summed = CHECKSUM_PARTIAL;
 260                         skb->csum_start = skb_headroom(skb) +
 261                                           skb_network_offset(skb) +
 262                                           iph->ihl * 4;
 263                         skb->csum_offset = offsetof(struct udphdr, check);
 264                         udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
 265                                                          datalen, IPPROTO_UDP,
 266                                                          0);
 267                 } else {
 268                         udph->check = 0;
 269                         udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 270                                                         datalen, IPPROTO_UDP,
 271                                                         csum_partial(udph,
 272                                                                      datalen, 0));
 273                         if (!udph->check)
 274                                 udph->check = CSUM_MANGLED_0;
 275                 }
 276         } else
 277                 inet_proto_csum_replace2(&udph->check, skb,
 278                                          htons(oldlen), htons(datalen), 1);
 279
 280         return 1;
 281 }
 282 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
 283
 284 /* Adjust one found SACK option including checksum correction */
 285 static void
 286 sack_adjust(struct sk_buff *skb,
 287             struct tcphdr *tcph,
 288             unsigned int sackoff,
 289             unsigned int sackend,
 290             struct nf_nat_seq *natseq)
 291 {
 292         while (sackoff < sackend) {
 293                 struct tcp_sack_block_wire *sack;
 294                 __be32 new_start_seq, new_end_seq;
 295
 296                 sack = (void *)skb->data + sackoff;
 297                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
 298                           natseq->correction_pos))
 299                         new_start_seq = htonl(ntohl(sack->start_seq)
 300                                         - natseq->offset_after);
 301                 else
 302                         new_start_seq = htonl(ntohl(sack->start_seq)
 303                                         - natseq->offset_before);
 304
 305                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
 306                           natseq->correction_pos))
 307                         new_end_seq = htonl(ntohl(sack->end_seq)
 308                                       - natseq->offset_after);
 309                 else
 310                         new_end_seq = htonl(ntohl(sack->end_seq)
 311                                       - natseq->offset_before);
 312
 313                 pr_debug("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
 314                          ntohl(sack->start_seq), new_start_seq,
 315                          ntohl(sack->end_seq), new_end_seq);
 316
 317                 inet_proto_csum_replace4(&tcph->check, skb,
 318                                          sack->start_seq, new_start_seq, 0);
 319                 inet_proto_csum_replace4(&tcph->check, skb,
 320                                          sack->end_seq, new_end_seq, 0);
 321                 sack->start_seq = new_start_seq;
 322                 sack->end_seq = new_end_seq;
 323                 sackoff += sizeof(*sack);
 324         }
 325 }
 326
 327 /* TCP SACK sequence number adjustment */
 328 static inline unsigned int
 329 nf_nat_sack_adjust(struct sk_buff *skb,
 330                    struct tcphdr *tcph,
 331                    struct nf_conn *ct,
 332                    enum ip_conntrack_info ctinfo)
 333 {
 334         unsigned int dir, optoff, optend;
 335         struct nf_conn_nat *nat = nfct_nat(ct);
 336
 337         optoff = ip_hdrlen(skb) + sizeof(struct tcphdr);
 338         optend = ip_hdrlen(skb) + tcph->doff * 4;
 339
 340         if (!skb_make_writable(skb, optend))
 341                 return 0;
 342
 343         dir = CTINFO2DIR(ctinfo);
 344
 345         while (optoff < optend) {
 346                 /* Usually: option, length. */
 347                 unsigned char *op = skb->data + optoff;
 348
 349                 switch (op[0]) {
 350                 case TCPOPT_EOL:
 351                         return 1;
 352                 case TCPOPT_NOP:
 353                         optoff++;
 354                         continue;
 355                 default:
 356                         /* no partial options */
 357                         if (optoff + 1 == optend ||
 358                             optoff + op[1] > optend ||
 359                             op[1] < 2)
 360                                 return 0;
 361                         if (op[0] == TCPOPT_SACK &&
 362                             op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
 363                             ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
 364                                 sack_adjust(skb, tcph, optoff+2,
 365                                             optoff+op[1], &nat->seq[!dir]);
 366                         optoff += op[1];
 367                 }
 368         }
 369         return 1;
 370 }
 371
 372 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
 373 int
 374 nf_nat_seq_adjust(struct sk_buff *skb,
 375                   struct nf_conn *ct,
 376                   enum ip_conntrack_info ctinfo)
 377 {
 378         struct tcphdr *tcph;
 379         int dir;
 380         __be32 newseq, newack;
 381         s16 seqoff, ackoff;
 382         struct nf_conn_nat *nat = nfct_nat(ct);
 383         struct nf_nat_seq *this_way, *other_way;
 384
 385         dir = CTINFO2DIR(ctinfo);
 386
 387         this_way = &nat->seq[dir];
 388         other_way = &nat->seq[!dir];
 389
 390         if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
 391                 return 0;
 392
 393         tcph = (void *)skb->data + ip_hdrlen(skb);
 394         if (after(ntohl(tcph->seq), this_way->correction_pos))
 395                 seqoff = this_way->offset_after;
 396         else
 397                 seqoff = this_way->offset_before;
 398
 399         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
 400                   other_way->correction_pos))
 401                 ackoff = other_way->offset_after;
 402         else
 403                 ackoff = other_way->offset_before;
 404
 405         newseq = htonl(ntohl(tcph->seq) + seqoff);
 406         newack = htonl(ntohl(tcph->ack_seq) - ackoff);
 407
 408         inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, 0);
 409         inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack, 0);
 410
 411         pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
 412                  ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
 413                  ntohl(newack));
 414
 415         tcph->seq = newseq;
 416         tcph->ack_seq = newack;
 417
 418         if (!nf_nat_sack_adjust(skb, tcph, ct, ctinfo))
 419                 return 0;
 420
 421         nf_conntrack_tcp_update(skb, ip_hdrlen(skb), ct, dir, seqoff);
 422
 423         return 1;
 424 }
 425
 426 /* Setup NAT on this expected conntrack so it follows master. */
 427 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
 428 void nf_nat_follow_master(struct nf_conn *ct,
 429                           struct nf_conntrack_expect *exp)
 430 {
 431         struct nf_nat_range range;
 432
 433         /* This must be a fresh one. */
 434         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 435
 436         /* Change src to where master sends to */
 437         range.flags = IP_NAT_RANGE_MAP_IPS;
 438         range.min_ip = range.max_ip
 439                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 440         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
 441
 442         /* For DST manip, map port here to where it's expected. */
 443         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 444         range.min = range.max = exp->saved_proto;
 445         range.min_ip = range.max_ip
 446                 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 447         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 448 }
 449 EXPORT_SYMBOL(nf_nat_follow_master);