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   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         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  45         struct nf_conn_nat *nat = nfct_nat(ct);
  46         struct nf_nat_seq *this_way = &nat->seq[dir];
  47
  48         pr_debug("adjust_tcp_sequence: seq = %u, sizediff = %d\n",
  49                  seq, sizediff);
  50
  51         pr_debug("adjust_tcp_sequence: Seq_offset before: ");
  52         DUMP_OFFSET(this_way);
  53
  54         spin_lock_bh(&nf_nat_seqofs_lock);
  55
  56         /* SYN adjust. If it's uninitialized, or this is after last
  57          * correction, record it: we don't handle more than one
  58          * adjustment in the window, but do deal with common case of a
  59          * retransmit */
  60         if (this_way->offset_before == this_way->offset_after ||
  61             before(this_way->correction_pos, seq)) {
  62                 this_way->correction_pos = seq;
  63                 this_way->offset_before = this_way->offset_after;
  64                 this_way->offset_after += sizediff;
  65         }
  66         spin_unlock_bh(&nf_nat_seqofs_lock);
  67
  68         pr_debug("adjust_tcp_sequence: Seq_offset after: ");
  69         DUMP_OFFSET(this_way);
  70 }
  71
  72 /* Get the offset value, for conntrack */
  73 s16 nf_nat_get_offset(const struct nf_conn *ct,
  74                       enum ip_conntrack_dir dir,
  75                       u32 seq)
  76 {
  77         struct nf_conn_nat *nat = nfct_nat(ct);
  78         struct nf_nat_seq *this_way;
  79         s16 offset;
  80
  81         if (!nat)
  82                 return 0;
  83
  84         this_way = &nat->seq[dir];
  85         spin_lock_bh(&nf_nat_seqofs_lock);
  86         offset = after(seq, this_way->correction_pos)
  87                  ? this_way->offset_after : this_way->offset_before;
  88         spin_unlock_bh(&nf_nat_seqofs_lock);
  89
  90         return offset;
  91 }
  92 EXPORT_SYMBOL_GPL(nf_nat_get_offset);
  93
  94 /* Frobs data inside this packet, which is linear. */
  95 static void mangle_contents(struct sk_buff *skb,
  96                             unsigned int dataoff,
  97                             unsigned int match_offset,
  98                             unsigned int match_len,
  99                             const char *rep_buffer,
 100                             unsigned int rep_len)
 101 {
 102         unsigned char *data;
 103
 104         BUG_ON(skb_is_nonlinear(skb));
 105         data = skb_network_header(skb) + dataoff;
 106
 107         /* move post-replacement */
 108         memmove(data + match_offset + rep_len,
 109                 data + match_offset + match_len,
 110                 skb->tail - (skb->network_header + dataoff +
 111                              match_offset + match_len));
 112
 113         /* insert data from buffer */
 114         memcpy(data + match_offset, rep_buffer, rep_len);
 115
 116         /* update skb info */
 117         if (rep_len > match_len) {
 118                 pr_debug("nf_nat_mangle_packet: Extending packet by "
 119                          "%u from %u bytes\n", rep_len - match_len, skb->len);
 120                 skb_put(skb, rep_len - match_len);
 121         } else {
 122                 pr_debug("nf_nat_mangle_packet: Shrinking packet from "
 123                          "%u from %u bytes\n", match_len - rep_len, skb->len);
 124                 __skb_trim(skb, skb->len + rep_len - match_len);
 125         }
 126
 127         /* fix IP hdr checksum information */
 128         ip_hdr(skb)->tot_len = htons(skb->len);
 129         ip_send_check(ip_hdr(skb));
 130 }
 131
 132 /* Unusual, but possible case. */
 133 static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
 134 {
 135         if (skb->len + extra > 65535)
 136                 return 0;
 137
 138         if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
 139                 return 0;
 140
 141         return 1;
 142 }
 143
 144 /* Generic function for mangling variable-length address changes inside
 145  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
 146  * command in FTP).
 147  *
 148  * Takes care about all the nasty sequence number changes, checksumming,
 149  * skb enlargement, ...
 150  *
 151  * */
 152 int
 153 nf_nat_mangle_tcp_packet(struct sk_buff *skb,
 154                          struct nf_conn *ct,
 155                          enum ip_conntrack_info ctinfo,
 156                          unsigned int match_offset,
 157                          unsigned int match_len,
 158                          const char *rep_buffer,
 159                          unsigned int rep_len)
 160 {
 161         struct rtable *rt = skb_rtable(skb);
 162         struct iphdr *iph;
 163         struct tcphdr *tcph;
 164         int oldlen, datalen;
 165
 166         if (!skb_make_writable(skb, skb->len))
 167                 return 0;
 168
 169         if (rep_len > match_len &&
 170             rep_len - match_len > skb_tailroom(skb) &&
 171             !enlarge_skb(skb, rep_len - match_len))
 172                 return 0;
 173
 174         SKB_LINEAR_ASSERT(skb);
 175
 176         iph = ip_hdr(skb);
 177         tcph = (void *)iph + iph->ihl*4;
 178
 179         oldlen = skb->len - iph->ihl*4;
 180         mangle_contents(skb, iph->ihl*4 + tcph->doff*4,
 181                         match_offset, match_len, rep_buffer, rep_len);
 182
 183         datalen = skb->len - iph->ihl*4;
 184         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 185                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 186                     skb->dev->features & NETIF_F_V4_CSUM) {
 187                         skb->ip_summed = CHECKSUM_PARTIAL;
 188                         skb->csum_start = skb_headroom(skb) +
 189                                           skb_network_offset(skb) +
 190                                           iph->ihl * 4;
 191                         skb->csum_offset = offsetof(struct tcphdr, check);
 192                         tcph->check = ~tcp_v4_check(datalen,
 193                                                     iph->saddr, iph->daddr, 0);
 194                 } else {
 195                         tcph->check = 0;
 196                         tcph->check = tcp_v4_check(datalen,
 197                                                    iph->saddr, iph->daddr,
 198                                                    csum_partial(tcph,
 199                                                                 datalen, 0));
 200                 }
 201         } else
 202                 inet_proto_csum_replace2(&tcph->check, skb,
 203                                          htons(oldlen), htons(datalen), 1);
 204
 205         if (rep_len != match_len) {
 206                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
 207                 adjust_tcp_sequence(ntohl(tcph->seq),
 208                                     (int)rep_len - (int)match_len,
 209                                     ct, ctinfo);
 210                 nf_conntrack_event_cache(IPCT_NATSEQADJ, ct);
 211         }
 212         return 1;
 213 }
 214 EXPORT_SYMBOL(nf_nat_mangle_tcp_packet);
 215
 216 /* Generic function for mangling variable-length address changes inside
 217  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
 218  * command in the Amanda protocol)
 219  *
 220  * Takes care about all the nasty sequence number changes, checksumming,
 221  * skb enlargement, ...
 222  *
 223  * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
 224  *       should be fairly easy to do.
 225  */
 226 int
 227 nf_nat_mangle_udp_packet(struct sk_buff *skb,
 228                          struct nf_conn *ct,
 229                          enum ip_conntrack_info ctinfo,
 230                          unsigned int match_offset,
 231                          unsigned int match_len,
 232                          const char *rep_buffer,
 233                          unsigned int rep_len)
 234 {
 235         struct rtable *rt = skb_rtable(skb);
 236         struct iphdr *iph;
 237         struct udphdr *udph;
 238         int datalen, oldlen;
 239
 240         /* UDP helpers might accidentally mangle the wrong packet */
 241         iph = ip_hdr(skb);
 242         if (skb->len < iph->ihl*4 + sizeof(*udph) +
 243                                match_offset + match_len)
 244                 return 0;
 245
 246         if (!skb_make_writable(skb, skb->len))
 247                 return 0;
 248
 249         if (rep_len > match_len &&
 250             rep_len - match_len > skb_tailroom(skb) &&
 251             !enlarge_skb(skb, rep_len - match_len))
 252                 return 0;
 253
 254         iph = ip_hdr(skb);
 255         udph = (void *)iph + iph->ihl*4;
 256
 257         oldlen = skb->len - iph->ihl*4;
 258         mangle_contents(skb, iph->ihl*4 + sizeof(*udph),
 259                         match_offset, match_len, rep_buffer, rep_len);
 260
 261         /* update the length of the UDP packet */
 262         datalen = skb->len - iph->ihl*4;
 263         udph->len = htons(datalen);
 264
 265         /* fix udp checksum if udp checksum was previously calculated */
 266         if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
 267                 return 1;
 268
 269         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 270                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 271                     skb->dev->features & NETIF_F_V4_CSUM) {
 272                         skb->ip_summed = CHECKSUM_PARTIAL;
 273                         skb->csum_start = skb_headroom(skb) +
 274                                           skb_network_offset(skb) +
 275                                           iph->ihl * 4;
 276                         skb->csum_offset = offsetof(struct udphdr, check);
 277                         udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
 278                                                          datalen, IPPROTO_UDP,
 279                                                          0);
 280                 } else {
 281                         udph->check = 0;
 282                         udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 283                                                         datalen, IPPROTO_UDP,
 284                                                         csum_partial(udph,
 285                                                                      datalen, 0));
 286                         if (!udph->check)
 287                                 udph->check = CSUM_MANGLED_0;
 288                 }
 289         } else
 290                 inet_proto_csum_replace2(&udph->check, skb,
 291                                          htons(oldlen), htons(datalen), 1);
 292
 293         return 1;
 294 }
 295 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
 296
 297 /* Adjust one found SACK option including checksum correction */
 298 static void
 299 sack_adjust(struct sk_buff *skb,
 300             struct tcphdr *tcph,
 301             unsigned int sackoff,
 302             unsigned int sackend,
 303             struct nf_nat_seq *natseq)
 304 {
 305         while (sackoff < sackend) {
 306                 struct tcp_sack_block_wire *sack;
 307                 __be32 new_start_seq, new_end_seq;
 308
 309                 sack = (void *)skb->data + sackoff;
 310                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
 311                           natseq->correction_pos))
 312                         new_start_seq = htonl(ntohl(sack->start_seq)
 313                                         - natseq->offset_after);
 314                 else
 315                         new_start_seq = htonl(ntohl(sack->start_seq)
 316                                         - natseq->offset_before);
 317
 318                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
 319                           natseq->correction_pos))
 320                         new_end_seq = htonl(ntohl(sack->end_seq)
 321                                       - natseq->offset_after);
 322                 else
 323                         new_end_seq = htonl(ntohl(sack->end_seq)
 324                                       - natseq->offset_before);
 325
 326                 pr_debug("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
 327                          ntohl(sack->start_seq), new_start_seq,
 328                          ntohl(sack->end_seq), new_end_seq);
 329
 330                 inet_proto_csum_replace4(&tcph->check, skb,
 331                                          sack->start_seq, new_start_seq, 0);
 332                 inet_proto_csum_replace4(&tcph->check, skb,
 333                                          sack->end_seq, new_end_seq, 0);
 334                 sack->start_seq = new_start_seq;
 335                 sack->end_seq = new_end_seq;
 336                 sackoff += sizeof(*sack);
 337         }
 338 }
 339
 340 /* TCP SACK sequence number adjustment */
 341 static inline unsigned int
 342 nf_nat_sack_adjust(struct sk_buff *skb,
 343                    struct tcphdr *tcph,
 344                    struct nf_conn *ct,
 345                    enum ip_conntrack_info ctinfo)
 346 {
 347         unsigned int dir, optoff, optend;
 348         struct nf_conn_nat *nat = nfct_nat(ct);
 349
 350         optoff = ip_hdrlen(skb) + sizeof(struct tcphdr);
 351         optend = ip_hdrlen(skb) + tcph->doff * 4;
 352
 353         if (!skb_make_writable(skb, optend))
 354                 return 0;
 355
 356         dir = CTINFO2DIR(ctinfo);
 357
 358         while (optoff < optend) {
 359                 /* Usually: option, length. */
 360                 unsigned char *op = skb->data + optoff;
 361
 362                 switch (op[0]) {
 363                 case TCPOPT_EOL:
 364                         return 1;
 365                 case TCPOPT_NOP:
 366                         optoff++;
 367                         continue;
 368                 default:
 369                         /* no partial options */
 370                         if (optoff + 1 == optend ||
 371                             optoff + op[1] > optend ||
 372                             op[1] < 2)
 373                                 return 0;
 374                         if (op[0] == TCPOPT_SACK &&
 375                             op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
 376                             ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
 377                                 sack_adjust(skb, tcph, optoff+2,
 378                                             optoff+op[1], &nat->seq[!dir]);
 379                         optoff += op[1];
 380                 }
 381         }
 382         return 1;
 383 }
 384
 385 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
 386 int
 387 nf_nat_seq_adjust(struct sk_buff *skb,
 388                   struct nf_conn *ct,
 389                   enum ip_conntrack_info ctinfo)
 390 {
 391         struct tcphdr *tcph;
 392         int dir;
 393         __be32 newseq, newack;
 394         s16 seqoff, ackoff;
 395         struct nf_conn_nat *nat = nfct_nat(ct);
 396         struct nf_nat_seq *this_way, *other_way;
 397
 398         dir = CTINFO2DIR(ctinfo);
 399
 400         this_way = &nat->seq[dir];
 401         other_way = &nat->seq[!dir];
 402
 403         if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
 404                 return 0;
 405
 406         tcph = (void *)skb->data + ip_hdrlen(skb);
 407         if (after(ntohl(tcph->seq), this_way->correction_pos))
 408                 seqoff = this_way->offset_after;
 409         else
 410                 seqoff = this_way->offset_before;
 411
 412         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
 413                   other_way->correction_pos))
 414                 ackoff = other_way->offset_after;
 415         else
 416                 ackoff = other_way->offset_before;
 417
 418         newseq = htonl(ntohl(tcph->seq) + seqoff);
 419         newack = htonl(ntohl(tcph->ack_seq) - ackoff);
 420
 421         inet_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, 0);
 422         inet_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack, 0);
 423
 424         pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
 425                  ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
 426                  ntohl(newack));
 427
 428         tcph->seq = newseq;
 429         tcph->ack_seq = newack;
 430
 431         return nf_nat_sack_adjust(skb, tcph, ct, ctinfo);
 432 }
 433
 434 /* Setup NAT on this expected conntrack so it follows master. */
 435 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
 436 void nf_nat_follow_master(struct nf_conn *ct,
 437                           struct nf_conntrack_expect *exp)
 438 {
 439         struct nf_nat_range range;
 440
 441         /* This must be a fresh one. */
 442         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 443
 444         /* Change src to where master sends to */
 445         range.flags = IP_NAT_RANGE_MAP_IPS;
 446         range.min_ip = range.max_ip
 447                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 448         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
 449
 450         /* For DST manip, map port here to where it's expected. */
 451         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 452         range.min = range.max = exp->saved_proto;
 453         range.min_ip = range.max_ip
 454                 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 455         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 456 }
 457 EXPORT_SYMBOL(nf_nat_follow_master);