net/ipv4/netfilter/ip_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) 2003-2004 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  *      14 Jan 2002 Harald Welte <laforge@gnumonks.org>:
  11  *              - add support for SACK adjustment
  12  *      14 Mar 2002 Harald Welte <laforge@gnumonks.org>:
  13  *              - merge SACK support into newnat API
  14  *      16 Aug 2002 Brian J. Murrell <netfilter@interlinx.bc.ca>:
  15  *              - make ip_nat_resize_packet more generic (TCP and UDP)
  16  *              - add ip_nat_mangle_udp_packet
  17  */
  18 #include <linux/module.h>
  19 #include <linux/kmod.h>
  20 #include <linux/types.h>
  21 #include <linux/timer.h>
  22 #include <linux/skbuff.h>
  23 #include <linux/netfilter_ipv4.h>
  24 #include <net/checksum.h>
  25 #include <net/icmp.h>
  26 #include <net/ip.h>
  27 #include <net/tcp.h>
  28 #include <net/udp.h>
  29
  30 #include <linux/netfilter_ipv4/ip_conntrack.h>
  31 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  32 #include <linux/netfilter_ipv4/ip_nat.h>
  33 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  34 #include <linux/netfilter_ipv4/ip_nat_core.h>
  35 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  36
  37 #if 0
  38 #define DEBUGP printk
  39 #define DUMP_OFFSET(x)  printk("offset_before=%d, offset_after=%d, correction_pos=%u\n", x->offset_before, x->offset_after, x->correction_pos);
  40 #else
  41 #define DEBUGP(format, args...)
  42 #define DUMP_OFFSET(x)
  43 #endif
  44
  45 static DEFINE_SPINLOCK(ip_nat_seqofs_lock);
  46
  47 /* Setup TCP sequence correction given this change at this sequence */
  48 static inline void
  49 adjust_tcp_sequence(u32 seq,
  50                     int sizediff,
  51                     struct ip_conntrack *ct,
  52                     enum ip_conntrack_info ctinfo)
  53 {
  54         int dir;
  55         struct ip_nat_seq *this_way, *other_way;
  56
  57         DEBUGP("ip_nat_resize_packet: old_size = %u, new_size = %u\n",
  58                 (*skb)->len, new_size);
  59
  60         dir = CTINFO2DIR(ctinfo);
  61
  62         this_way = &ct->nat.info.seq[dir];
  63         other_way = &ct->nat.info.seq[!dir];
  64
  65         DEBUGP("ip_nat_resize_packet: Seq_offset before: ");
  66         DUMP_OFFSET(this_way);
  67
  68         spin_lock_bh(&ip_nat_seqofs_lock);
  69
  70         /* SYN adjust. If it's uninitialized, or this is after last
  71          * correction, record it: we don't handle more than one
  72          * adjustment in the window, but do deal with common case of a
  73          * retransmit */
  74         if (this_way->offset_before == this_way->offset_after
  75             || before(this_way->correction_pos, seq)) {
  76                     this_way->correction_pos = seq;
  77                     this_way->offset_before = this_way->offset_after;
  78                     this_way->offset_after += sizediff;
  79         }
  80         spin_unlock_bh(&ip_nat_seqofs_lock);
  81
  82         DEBUGP("ip_nat_resize_packet: Seq_offset after: ");
  83         DUMP_OFFSET(this_way);
  84 }
  85
  86 /* Frobs data inside this packet, which is linear. */
  87 static void mangle_contents(struct sk_buff *skb,
  88                             unsigned int dataoff,
  89                             unsigned int match_offset,
  90                             unsigned int match_len,
  91                             const char *rep_buffer,
  92                             unsigned int rep_len)
  93 {
  94         unsigned char *data;
  95
  96         BUG_ON(skb_is_nonlinear(skb));
  97         data = (unsigned char *)skb->nh.iph + dataoff;
  98
  99         /* move post-replacement */
 100         memmove(data + match_offset + rep_len,
 101                 data + match_offset + match_len,
 102                 skb->tail - (data + match_offset + match_len));
 103
 104         /* insert data from buffer */
 105         memcpy(data + match_offset, rep_buffer, rep_len);
 106
 107         /* update skb info */
 108         if (rep_len > match_len) {
 109                 DEBUGP("ip_nat_mangle_packet: Extending packet by "
 110                         "%u from %u bytes\n", rep_len - match_len,
 111                        skb->len);
 112                 skb_put(skb, rep_len - match_len);
 113         } else {
 114                 DEBUGP("ip_nat_mangle_packet: Shrinking packet from "
 115                         "%u from %u bytes\n", match_len - rep_len,
 116                        skb->len);
 117                 __skb_trim(skb, skb->len + rep_len - match_len);
 118         }
 119
 120         /* fix IP hdr checksum information */
 121         skb->nh.iph->tot_len = htons(skb->len);
 122         ip_send_check(skb->nh.iph);
 123 }
 124
 125 /* Unusual, but possible case. */
 126 static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
 127 {
 128         struct sk_buff *nskb;
 129
 130         if ((*pskb)->len + extra > 65535)
 131                 return 0;
 132
 133         nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
 134         if (!nskb)
 135                 return 0;
 136
 137         /* Transfer socket to new skb. */
 138         if ((*pskb)->sk)
 139                 skb_set_owner_w(nskb, (*pskb)->sk);
 140         kfree_skb(*pskb);
 141         *pskb = nskb;
 142         return 1;
 143 }
 144
 145 /* Generic function for mangling variable-length address changes inside
 146  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
 147  * command in FTP).
 148  *
 149  * Takes care about all the nasty sequence number changes, checksumming,
 150  * skb enlargement, ...
 151  *
 152  * */
 153 int
 154 ip_nat_mangle_tcp_packet(struct sk_buff **pskb,
 155                          struct ip_conntrack *ct,
 156                          enum ip_conntrack_info ctinfo,
 157                          unsigned int match_offset,
 158                          unsigned int match_len,
 159                          const char *rep_buffer,
 160                          unsigned int rep_len)
 161 {
 162         struct iphdr *iph;
 163         struct tcphdr *tcph;
 164         int oldlen, datalen;
 165
 166         if (!skb_make_writable(pskb, (*pskb)->len))
 167                 return 0;
 168
 169         if (rep_len > match_len
 170             && rep_len - match_len > skb_tailroom(*pskb)
 171             && !enlarge_skb(pskb, rep_len - match_len))
 172                 return 0;
 173
 174         SKB_LINEAR_ASSERT(*pskb);
 175
 176         iph = (*pskb)->nh.iph;
 177         tcph = (void *)iph + iph->ihl*4;
 178
 179         oldlen = (*pskb)->len - iph->ihl*4;
 180         mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4,
 181                         match_offset, match_len, rep_buffer, rep_len);
 182
 183         datalen = (*pskb)->len - iph->ihl*4;
 184         if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
 185                 tcph->check = 0;
 186                 tcph->check = tcp_v4_check(tcph, datalen,
 187                                            iph->saddr, iph->daddr,
 188                                            csum_partial((char *)tcph,
 189                                                         datalen, 0));
 190         } else
 191                 nf_proto_csum_replace2(&tcph->check, *pskb,
 192                                         htons(oldlen), htons(datalen), 1);
 193
 194         if (rep_len != match_len) {
 195                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
 196                 adjust_tcp_sequence(ntohl(tcph->seq),
 197                                     (int)rep_len - (int)match_len,
 198                                     ct, ctinfo);
 199                 /* Tell TCP window tracking about seq change */
 200                 ip_conntrack_tcp_update(*pskb, ct, CTINFO2DIR(ctinfo));
 201         }
 202         return 1;
 203 }
 204 EXPORT_SYMBOL(ip_nat_mangle_tcp_packet);
 205
 206 /* Generic function for mangling variable-length address changes inside
 207  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
 208  * command in the Amanda protocol)
 209  *
 210  * Takes care about all the nasty sequence number changes, checksumming,
 211  * skb enlargement, ...
 212  *
 213  * XXX - This function could be merged with ip_nat_mangle_tcp_packet which
 214  *       should be fairly easy to do.
 215  */
 216 int
 217 ip_nat_mangle_udp_packet(struct sk_buff **pskb,
 218                          struct ip_conntrack *ct,
 219                          enum ip_conntrack_info ctinfo,
 220                          unsigned int match_offset,
 221                          unsigned int match_len,
 222                          const char *rep_buffer,
 223                          unsigned int rep_len)
 224 {
 225         struct iphdr *iph;
 226         struct udphdr *udph;
 227         int datalen, oldlen;
 228
 229         /* UDP helpers might accidentally mangle the wrong packet */
 230         iph = (*pskb)->nh.iph;
 231         if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) +
 232                                match_offset + match_len)
 233                 return 0;
 234
 235         if (!skb_make_writable(pskb, (*pskb)->len))
 236                 return 0;
 237
 238         if (rep_len > match_len
 239             && rep_len - match_len > skb_tailroom(*pskb)
 240             && !enlarge_skb(pskb, rep_len - match_len))
 241                 return 0;
 242
 243         iph = (*pskb)->nh.iph;
 244         udph = (void *)iph + iph->ihl*4;
 245
 246         oldlen = (*pskb)->len - iph->ihl*4;
 247         mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph),
 248                         match_offset, match_len, rep_buffer, rep_len);
 249
 250         /* update the length of the UDP packet */
 251         datalen = (*pskb)->len - iph->ihl*4;
 252         udph->len = htons(datalen);
 253
 254         /* fix udp checksum if udp checksum was previously calculated */
 255         if (!udph->check && (*pskb)->ip_summed != CHECKSUM_PARTIAL)
 256                 return 1;
 257
 258         if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
 259                 udph->check = 0;
 260                 udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 261                                                 datalen, IPPROTO_UDP,
 262                                                 csum_partial((char *)udph,
 263                                                              datalen, 0));
 264                 if (!udph->check)
 265                         udph->check = CSUM_MANGLED_0;
 266         } else
 267                 nf_proto_csum_replace2(&udph->check, *pskb,
 268                                         htons(oldlen), htons(datalen), 1);
 269         return 1;
 270 }
 271 EXPORT_SYMBOL(ip_nat_mangle_udp_packet);
 272
 273 /* Adjust one found SACK option including checksum correction */
 274 static void
 275 sack_adjust(struct sk_buff *skb,
 276             struct tcphdr *tcph,
 277             unsigned int sackoff,
 278             unsigned int sackend,
 279             struct ip_nat_seq *natseq)
 280 {
 281         while (sackoff < sackend) {
 282                 struct tcp_sack_block_wire *sack;
 283                 __be32 new_start_seq, new_end_seq;
 284
 285                 sack = (void *)skb->data + sackoff;
 286                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
 287                           natseq->correction_pos))
 288                         new_start_seq = htonl(ntohl(sack->start_seq)
 289                                         - natseq->offset_after);
 290                 else
 291                         new_start_seq = htonl(ntohl(sack->start_seq)
 292                                         - natseq->offset_before);
 293
 294                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
 295                           natseq->correction_pos))
 296                         new_end_seq = htonl(ntohl(sack->end_seq)
 297                                       - natseq->offset_after);
 298                 else
 299                         new_end_seq = htonl(ntohl(sack->end_seq)
 300                                       - natseq->offset_before);
 301
 302                 DEBUGP("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
 303                         ntohl(sack->start_seq), new_start_seq,
 304                         ntohl(sack->end_seq), new_end_seq);
 305
 306                 nf_proto_csum_replace4(&tcph->check, skb,
 307                                         sack->start_seq, new_start_seq, 0);
 308                 nf_proto_csum_replace4(&tcph->check, skb,
 309                                         sack->end_seq, new_end_seq, 0);
 310                 sack->start_seq = new_start_seq;
 311                 sack->end_seq = new_end_seq;
 312                 sackoff += sizeof(*sack);
 313         }
 314 }
 315
 316 /* TCP SACK sequence number adjustment */
 317 static inline unsigned int
 318 ip_nat_sack_adjust(struct sk_buff **pskb,
 319                    struct tcphdr *tcph,
 320                    struct ip_conntrack *ct,
 321                    enum ip_conntrack_info ctinfo)
 322 {
 323         unsigned int dir, optoff, optend;
 324
 325         optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr);
 326         optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4;
 327
 328         if (!skb_make_writable(pskb, optend))
 329                 return 0;
 330
 331         dir = CTINFO2DIR(ctinfo);
 332
 333         while (optoff < optend) {
 334                 /* Usually: option, length. */
 335                 unsigned char *op = (*pskb)->data + optoff;
 336
 337                 switch (op[0]) {
 338                 case TCPOPT_EOL:
 339                         return 1;
 340                 case TCPOPT_NOP:
 341                         optoff++;
 342                         continue;
 343                 default:
 344                         /* no partial options */
 345                         if (optoff + 1 == optend
 346                             || optoff + op[1] > optend
 347                             || op[1] < 2)
 348                                 return 0;
 349                         if (op[0] == TCPOPT_SACK
 350                             && op[1] >= 2+TCPOLEN_SACK_PERBLOCK
 351                             && ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
 352                                 sack_adjust(*pskb, tcph, optoff+2,
 353                                             optoff+op[1],
 354                                             &ct->nat.info.seq[!dir]);
 355                         optoff += op[1];
 356                 }
 357         }
 358         return 1;
 359 }
 360
 361 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
 362 int
 363 ip_nat_seq_adjust(struct sk_buff **pskb,
 364                   struct ip_conntrack *ct,
 365                   enum ip_conntrack_info ctinfo)
 366 {
 367         struct tcphdr *tcph;
 368         int dir;
 369         __be32 newseq, newack;
 370         struct ip_nat_seq *this_way, *other_way;
 371
 372         dir = CTINFO2DIR(ctinfo);
 373
 374         this_way = &ct->nat.info.seq[dir];
 375         other_way = &ct->nat.info.seq[!dir];
 376
 377         if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
 378                 return 0;
 379
 380         tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
 381         if (after(ntohl(tcph->seq), this_way->correction_pos))
 382                 newseq = htonl(ntohl(tcph->seq) + this_way->offset_after);
 383         else
 384                 newseq = htonl(ntohl(tcph->seq) + this_way->offset_before);
 385
 386         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
 387                   other_way->correction_pos))
 388                 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_after);
 389         else
 390                 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_before);
 391
 392         nf_proto_csum_replace4(&tcph->check, *pskb, tcph->seq, newseq, 0);
 393         nf_proto_csum_replace4(&tcph->check, *pskb, tcph->ack_seq, newack, 0);
 394
 395         DEBUGP("Adjusting sequence number from %u->%u, ack from %u->%u\n",
 396                 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
 397                 ntohl(newack));
 398
 399         tcph->seq = newseq;
 400         tcph->ack_seq = newack;
 401
 402         if (!ip_nat_sack_adjust(pskb, tcph, ct, ctinfo))
 403                 return 0;
 404
 405         ip_conntrack_tcp_update(*pskb, ct, dir);
 406
 407         return 1;
 408 }
 409 EXPORT_SYMBOL(ip_nat_seq_adjust);
 410
 411 /* Setup NAT on this expected conntrack so it follows master. */
 412 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
 413 void ip_nat_follow_master(struct ip_conntrack *ct,
 414                           struct ip_conntrack_expect *exp)
 415 {
 416         struct ip_nat_range range;
 417
 418         /* This must be a fresh one. */
 419         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 420
 421         /* Change src to where master sends to */
 422         range.flags = IP_NAT_RANGE_MAP_IPS;
 423         range.min_ip = range.max_ip
 424                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
 425         /* hook doesn't matter, but it has to do source manip */
 426         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 427
 428         /* For DST manip, map port here to where it's expected. */
 429         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 430         range.min = range.max = exp->saved_proto;
 431         range.min_ip = range.max_ip
 432                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
 433         /* hook doesn't matter, but it has to do destination manip */
 434         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 435 }
 436 EXPORT_SYMBOL(ip_nat_follow_master);