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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
  20 #include <linux/netfilter_ipv4.h>
  21 #include <net/netfilter/nf_conntrack.h>
  22 #include <net/netfilter/nf_conntrack_helper.h>
  23 #include <net/netfilter/nf_conntrack_expect.h>
  24 #include <net/netfilter/nf_nat.h>
  25 #include <net/netfilter/nf_nat_protocol.h>
  26 #include <net/netfilter/nf_nat_core.h>
  27 #include <net/netfilter/nf_nat_helper.h>
  28
  29 #define DUMP_OFFSET(x) \
  30         pr_debug("offset_before=%d, offset_after=%d, correction_pos=%u\n", \
  31                  x->offset_before, x->offset_after, x->correction_pos);
  32
  33 static DEFINE_SPINLOCK(nf_nat_seqofs_lock);
  34
  35 /* Setup TCP sequence correction given this change at this sequence */
  36 static inline void
  37 adjust_tcp_sequence(u32 seq,
  38                     int sizediff,
  39                     struct nf_conn *ct,
  40                     enum ip_conntrack_info ctinfo)
  41 {
  42         int dir;
  43         struct nf_nat_seq *this_way, *other_way;
  44         struct nf_conn_nat *nat = nfct_nat(ct);
  45
  46         pr_debug("adjust_tcp_sequence: seq = %u, sizediff = %d\n",
  47                  ntohl(seq), seq);
  48
  49         dir = CTINFO2DIR(ctinfo);
  50
  51         this_way = &nat->seq[dir];
  52         other_way = &nat->seq[!dir];
  53
  54         pr_debug("nf_nat_resize_packet: Seq_offset before: ");
  55         DUMP_OFFSET(this_way);
  56
  57         spin_lock_bh(&nf_nat_seqofs_lock);
  58
  59         /* SYN adjust. If it's uninitialized, or this is after last
  60          * correction, record it: we don't handle more than one
  61          * adjustment in the window, but do deal with common case of a
  62          * retransmit */
  63         if (this_way->offset_before == this_way->offset_after ||
  64             before(this_way->correction_pos, seq)) {
  65                    this_way->correction_pos = seq;
  66                    this_way->offset_before = this_way->offset_after;
  67                    this_way->offset_after += sizediff;
  68         }
  69         spin_unlock_bh(&nf_nat_seqofs_lock);
  70
  71         pr_debug("nf_nat_resize_packet: Seq_offset after: ");
  72         DUMP_OFFSET(this_way);
  73 }
  74
  75 /* Frobs data inside this packet, which is linear. */
  76 static void mangle_contents(struct sk_buff *skb,
  77                             unsigned int dataoff,
  78                             unsigned int match_offset,
  79                             unsigned int match_len,
  80                             const char *rep_buffer,
  81                             unsigned int rep_len)
  82 {
  83         unsigned char *data;
  84
  85         BUG_ON(skb_is_nonlinear(skb));
  86         data = skb_network_header(skb) + dataoff;
  87
  88         /* move post-replacement */
  89         memmove(data + match_offset + rep_len,
  90                 data + match_offset + match_len,
  91                 skb->tail - (skb->network_header + dataoff +
  92                              match_offset + match_len));
  93
  94         /* insert data from buffer */
  95         memcpy(data + match_offset, rep_buffer, rep_len);
  96
  97         /* update skb info */
  98         if (rep_len > match_len) {
  99                 pr_debug("nf_nat_mangle_packet: Extending packet by "
 100                          "%u from %u bytes\n", rep_len - match_len, skb->len);
 101                 skb_put(skb, rep_len - match_len);
 102         } else {
 103                 pr_debug("nf_nat_mangle_packet: Shrinking packet from "
 104                          "%u from %u bytes\n", match_len - rep_len, skb->len);
 105                 __skb_trim(skb, skb->len + rep_len - match_len);
 106         }
 107
 108         /* fix IP hdr checksum information */
 109         ip_hdr(skb)->tot_len = htons(skb->len);
 110         ip_send_check(ip_hdr(skb));
 111 }
 112
 113 /* Unusual, but possible case. */
 114 static int enlarge_skb(struct sk_buff *skb, unsigned int extra)
 115 {
 116         if (skb->len + extra > 65535)
 117                 return 0;
 118
 119         if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
 120                 return 0;
 121
 122         return 1;
 123 }
 124
 125 /* Generic function for mangling variable-length address changes inside
 126  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
 127  * command in FTP).
 128  *
 129  * Takes care about all the nasty sequence number changes, checksumming,
 130  * skb enlargement, ...
 131  *
 132  * */
 133 int
 134 nf_nat_mangle_tcp_packet(struct sk_buff *skb,
 135                          struct nf_conn *ct,
 136                          enum ip_conntrack_info ctinfo,
 137                          unsigned int match_offset,
 138                          unsigned int match_len,
 139                          const char *rep_buffer,
 140                          unsigned int rep_len)
 141 {
 142         struct rtable *rt = (struct rtable *)skb->dst;
 143         struct iphdr *iph;
 144         struct tcphdr *tcph;
 145         int oldlen, datalen;
 146
 147         if (!skb_make_writable(skb, skb->len))
 148                 return 0;
 149
 150         if (rep_len > match_len &&
 151             rep_len - match_len > skb_tailroom(skb) &&
 152             !enlarge_skb(skb, rep_len - match_len))
 153                 return 0;
 154
 155         SKB_LINEAR_ASSERT(skb);
 156
 157         iph = ip_hdr(skb);
 158         tcph = (void *)iph + iph->ihl*4;
 159
 160         oldlen = skb->len - iph->ihl*4;
 161         mangle_contents(skb, iph->ihl*4 + tcph->doff*4,
 162                         match_offset, match_len, rep_buffer, rep_len);
 163
 164         datalen = skb->len - iph->ihl*4;
 165         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 166                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 167                     skb->dev->features & NETIF_F_V4_CSUM) {
 168                         skb->ip_summed = CHECKSUM_PARTIAL;
 169                         skb->csum_start = skb_headroom(skb) +
 170                                           skb_network_offset(skb) +
 171                                           iph->ihl * 4;
 172                         skb->csum_offset = offsetof(struct tcphdr, check);
 173                         tcph->check = ~tcp_v4_check(datalen,
 174                                                     iph->saddr, iph->daddr, 0);
 175                 } else {
 176                         tcph->check = 0;
 177                         tcph->check = tcp_v4_check(datalen,
 178                                                    iph->saddr, iph->daddr,
 179                                                    csum_partial(tcph,
 180                                                                 datalen, 0));
 181                 }
 182         } else
 183                 nf_proto_csum_replace2(&tcph->check, skb,
 184                                        htons(oldlen), htons(datalen), 1);
 185
 186         if (rep_len != match_len) {
 187                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
 188                 adjust_tcp_sequence(ntohl(tcph->seq),
 189                                     (int)rep_len - (int)match_len,
 190                                     ct, ctinfo);
 191                 /* Tell TCP window tracking about seq change */
 192                 nf_conntrack_tcp_update(skb, ip_hdrlen(skb),
 193                                         ct, CTINFO2DIR(ctinfo));
 194         }
 195         return 1;
 196 }
 197 EXPORT_SYMBOL(nf_nat_mangle_tcp_packet);
 198
 199 /* Generic function for mangling variable-length address changes inside
 200  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
 201  * command in the Amanda protocol)
 202  *
 203  * Takes care about all the nasty sequence number changes, checksumming,
 204  * skb enlargement, ...
 205  *
 206  * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
 207  *       should be fairly easy to do.
 208  */
 209 int
 210 nf_nat_mangle_udp_packet(struct sk_buff *skb,
 211                          struct nf_conn *ct,
 212                          enum ip_conntrack_info ctinfo,
 213                          unsigned int match_offset,
 214                          unsigned int match_len,
 215                          const char *rep_buffer,
 216                          unsigned int rep_len)
 217 {
 218         struct rtable *rt = (struct rtable *)skb->dst;
 219         struct iphdr *iph;
 220         struct udphdr *udph;
 221         int datalen, oldlen;
 222
 223         /* UDP helpers might accidentally mangle the wrong packet */
 224         iph = ip_hdr(skb);
 225         if (skb->len < iph->ihl*4 + sizeof(*udph) +
 226                                match_offset + match_len)
 227                 return 0;
 228
 229         if (!skb_make_writable(skb, skb->len))
 230                 return 0;
 231
 232         if (rep_len > match_len &&
 233             rep_len - match_len > skb_tailroom(skb) &&
 234             !enlarge_skb(skb, rep_len - match_len))
 235                 return 0;
 236
 237         iph = ip_hdr(skb);
 238         udph = (void *)iph + iph->ihl*4;
 239
 240         oldlen = skb->len - iph->ihl*4;
 241         mangle_contents(skb, iph->ihl*4 + sizeof(*udph),
 242                         match_offset, match_len, rep_buffer, rep_len);
 243
 244         /* update the length of the UDP packet */
 245         datalen = skb->len - iph->ihl*4;
 246         udph->len = htons(datalen);
 247
 248         /* fix udp checksum if udp checksum was previously calculated */
 249         if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
 250                 return 1;
 251
 252         if (skb->ip_summed != CHECKSUM_PARTIAL) {
 253                 if (!(rt->rt_flags & RTCF_LOCAL) &&
 254                     skb->dev->features & NETIF_F_V4_CSUM) {
 255                         skb->ip_summed = CHECKSUM_PARTIAL;
 256                         skb->csum_start = skb_headroom(skb) +
 257                                           skb_network_offset(skb) +
 258                                           iph->ihl * 4;
 259                         skb->csum_offset = offsetof(struct udphdr, check);
 260                         udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
 261                                                          datalen, IPPROTO_UDP,
 262                                                          0);
 263                 } else {
 264                         udph->check = 0;
 265                         udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 266                                                         datalen, IPPROTO_UDP,
 267                                                         csum_partial(udph,
 268                                                                      datalen, 0));
 269                         if (!udph->check)
 270                                 udph->check = CSUM_MANGLED_0;
 271                 }
 272         } else
 273                 nf_proto_csum_replace2(&udph->check, skb,
 274                                        htons(oldlen), htons(datalen), 1);
 275
 276         return 1;
 277 }
 278 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
 279
 280 /* Adjust one found SACK option including checksum correction */
 281 static void
 282 sack_adjust(struct sk_buff *skb,
 283             struct tcphdr *tcph,
 284             unsigned int sackoff,
 285             unsigned int sackend,
 286             struct nf_nat_seq *natseq)
 287 {
 288         while (sackoff < sackend) {
 289                 struct tcp_sack_block_wire *sack;
 290                 __be32 new_start_seq, new_end_seq;
 291
 292                 sack = (void *)skb->data + sackoff;
 293                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
 294                           natseq->correction_pos))
 295                         new_start_seq = htonl(ntohl(sack->start_seq)
 296                                         - natseq->offset_after);
 297                 else
 298                         new_start_seq = htonl(ntohl(sack->start_seq)
 299                                         - natseq->offset_before);
 300
 301                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
 302                           natseq->correction_pos))
 303                         new_end_seq = htonl(ntohl(sack->end_seq)
 304                                       - natseq->offset_after);
 305                 else
 306                         new_end_seq = htonl(ntohl(sack->end_seq)
 307                                       - natseq->offset_before);
 308
 309                 pr_debug("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
 310                          ntohl(sack->start_seq), new_start_seq,
 311                          ntohl(sack->end_seq), new_end_seq);
 312
 313                 nf_proto_csum_replace4(&tcph->check, skb,
 314                                        sack->start_seq, new_start_seq, 0);
 315                 nf_proto_csum_replace4(&tcph->check, skb,
 316                                        sack->end_seq, new_end_seq, 0);
 317                 sack->start_seq = new_start_seq;
 318                 sack->end_seq = new_end_seq;
 319                 sackoff += sizeof(*sack);
 320         }
 321 }
 322
 323 /* TCP SACK sequence number adjustment */
 324 static inline unsigned int
 325 nf_nat_sack_adjust(struct sk_buff *skb,
 326                    struct tcphdr *tcph,
 327                    struct nf_conn *ct,
 328                    enum ip_conntrack_info ctinfo)
 329 {
 330         unsigned int dir, optoff, optend;
 331         struct nf_conn_nat *nat = nfct_nat(ct);
 332
 333         optoff = ip_hdrlen(skb) + sizeof(struct tcphdr);
 334         optend = ip_hdrlen(skb) + tcph->doff * 4;
 335
 336         if (!skb_make_writable(skb, optend))
 337                 return 0;
 338
 339         dir = CTINFO2DIR(ctinfo);
 340
 341         while (optoff < optend) {
 342                 /* Usually: option, length. */
 343                 unsigned char *op = skb->data + optoff;
 344
 345                 switch (op[0]) {
 346                 case TCPOPT_EOL:
 347                         return 1;
 348                 case TCPOPT_NOP:
 349                         optoff++;
 350                         continue;
 351                 default:
 352                         /* no partial options */
 353                         if (optoff + 1 == optend ||
 354                             optoff + op[1] > optend ||
 355                             op[1] < 2)
 356                                 return 0;
 357                         if (op[0] == TCPOPT_SACK &&
 358                             op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
 359                             ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
 360                                 sack_adjust(skb, tcph, optoff+2,
 361                                             optoff+op[1], &nat->seq[!dir]);
 362                         optoff += op[1];
 363                 }
 364         }
 365         return 1;
 366 }
 367
 368 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
 369 int
 370 nf_nat_seq_adjust(struct sk_buff *skb,
 371                   struct nf_conn *ct,
 372                   enum ip_conntrack_info ctinfo)
 373 {
 374         struct tcphdr *tcph;
 375         int dir;
 376         __be32 newseq, newack;
 377         struct nf_conn_nat *nat = nfct_nat(ct);
 378         struct nf_nat_seq *this_way, *other_way;
 379
 380         dir = CTINFO2DIR(ctinfo);
 381
 382         this_way = &nat->seq[dir];
 383         other_way = &nat->seq[!dir];
 384
 385         if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
 386                 return 0;
 387
 388         tcph = (void *)skb->data + ip_hdrlen(skb);
 389         if (after(ntohl(tcph->seq), this_way->correction_pos))
 390                 newseq = htonl(ntohl(tcph->seq) + this_way->offset_after);
 391         else
 392                 newseq = htonl(ntohl(tcph->seq) + this_way->offset_before);
 393
 394         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
 395                   other_way->correction_pos))
 396                 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_after);
 397         else
 398                 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_before);
 399
 400         nf_proto_csum_replace4(&tcph->check, skb, tcph->seq, newseq, 0);
 401         nf_proto_csum_replace4(&tcph->check, skb, tcph->ack_seq, newack, 0);
 402
 403         pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
 404                  ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
 405                  ntohl(newack));
 406
 407         tcph->seq = newseq;
 408         tcph->ack_seq = newack;
 409
 410         if (!nf_nat_sack_adjust(skb, tcph, ct, ctinfo))
 411                 return 0;
 412
 413         nf_conntrack_tcp_update(skb, ip_hdrlen(skb), ct, dir);
 414
 415         return 1;
 416 }
 417 EXPORT_SYMBOL(nf_nat_seq_adjust);
 418
 419 /* Setup NAT on this expected conntrack so it follows master. */
 420 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
 421 void nf_nat_follow_master(struct nf_conn *ct,
 422                           struct nf_conntrack_expect *exp)
 423 {
 424         struct nf_nat_range range;
 425
 426         /* This must be a fresh one. */
 427         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 428
 429         /* Change src to where master sends to */
 430         range.flags = IP_NAT_RANGE_MAP_IPS;
 431         range.min_ip = range.max_ip
 432                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 433         /* hook doesn't matter, but it has to do source manip */
 434         nf_nat_setup_info(ct, &range, NF_INET_POST_ROUTING);
 435
 436         /* For DST manip, map port here to where it's expected. */
 437         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 438         range.min = range.max = exp->saved_proto;
 439         range.min_ip = range.max_ip
 440                 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 441         /* hook doesn't matter, but it has to do destination manip */
 442         nf_nat_setup_info(ct, &range, NF_INET_PRE_ROUTING);
 443 }
 444 EXPORT_SYMBOL(nf_nat_follow_master);