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/config.h>
  19 #include <linux/module.h>
  20 #include <linux/kmod.h>
  21 #include <linux/types.h>
  22 #include <linux/timer.h>
  23 #include <linux/skbuff.h>
  24 #include <linux/netfilter_ipv4.h>
  25 #include <net/checksum.h>
  26 #include <net/icmp.h>
  27 #include <net/ip.h>
  28 #include <net/tcp.h>
  29 #include <net/udp.h>
  30
  31 #define ASSERT_READ_LOCK(x) MUST_BE_READ_LOCKED(&ip_nat_lock)
  32 #define ASSERT_WRITE_LOCK(x) MUST_BE_WRITE_LOCKED(&ip_nat_lock)
  33
  34 #include <linux/netfilter_ipv4/ip_conntrack.h>
  35 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  36 #include <linux/netfilter_ipv4/ip_nat.h>
  37 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  38 #include <linux/netfilter_ipv4/ip_nat_core.h>
  39 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  40 #include <linux/netfilter_ipv4/listhelp.h>
  41
  42 #if 0
  43 #define DEBUGP printk
  44 #define DUMP_OFFSET(x)  printk("offset_before=%d, offset_after=%d, correction_pos=%u\n", x->offset_before, x->offset_after, x->correction_pos);
  45 #else
  46 #define DEBUGP(format, args...)
  47 #define DUMP_OFFSET(x)
  48 #endif
  49
  50 static DECLARE_LOCK(ip_nat_seqofs_lock);
  51
  52 /* Setup TCP sequence correction given this change at this sequence */
  53 static inline void
  54 adjust_tcp_sequence(u32 seq,
  55                     int sizediff,
  56                     struct ip_conntrack *ct,
  57                     enum ip_conntrack_info ctinfo)
  58 {
  59         int dir;
  60         struct ip_nat_seq *this_way, *other_way;
  61
  62         DEBUGP("ip_nat_resize_packet: old_size = %u, new_size = %u\n",
  63                 (*skb)->len, new_size);
  64
  65         dir = CTINFO2DIR(ctinfo);
  66
  67         this_way = &ct->nat.info.seq[dir];
  68         other_way = &ct->nat.info.seq[!dir];
  69
  70         DEBUGP("ip_nat_resize_packet: Seq_offset before: ");
  71         DUMP_OFFSET(this_way);
  72
  73         LOCK_BH(&ip_nat_seqofs_lock);
  74
  75         /* SYN adjust. If it's uninitialized, or this is after last
  76          * correction, record it: we don't handle more than one
  77          * adjustment in the window, but do deal with common case of a
  78          * retransmit */
  79         if (this_way->offset_before == this_way->offset_after
  80             || before(this_way->correction_pos, seq)) {
  81                     this_way->correction_pos = seq;
  82                     this_way->offset_before = this_way->offset_after;
  83                     this_way->offset_after += sizediff;
  84         }
  85         UNLOCK_BH(&ip_nat_seqofs_lock);
  86
  87         DEBUGP("ip_nat_resize_packet: Seq_offset after: ");
  88         DUMP_OFFSET(this_way);
  89 }
  90
  91 /* Frobs data inside this packet, which is linear. */
  92 static void mangle_contents(struct sk_buff *skb,
  93                             unsigned int dataoff,
  94                             unsigned int match_offset,
  95                             unsigned int match_len,
  96                             const char *rep_buffer,
  97                             unsigned int rep_len)
  98 {
  99         unsigned char *data;
 100
 101         BUG_ON(skb_is_nonlinear(skb));
 102         data = (unsigned char *)skb->nh.iph + dataoff;
 103
 104         /* move post-replacement */
 105         memmove(data + match_offset + rep_len,
 106                 data + match_offset + match_len,
 107                 skb->tail - (data + match_offset + match_len));
 108
 109         /* insert data from buffer */
 110         memcpy(data + match_offset, rep_buffer, rep_len);
 111
 112         /* update skb info */
 113         if (rep_len > match_len) {
 114                 DEBUGP("ip_nat_mangle_packet: Extending packet by "
 115                         "%u from %u bytes\n", rep_len - match_len,
 116                        skb->len);
 117                 skb_put(skb, rep_len - match_len);
 118         } else {
 119                 DEBUGP("ip_nat_mangle_packet: Shrinking packet from "
 120                         "%u from %u bytes\n", match_len - rep_len,
 121                        skb->len);
 122                 __skb_trim(skb, skb->len + rep_len - match_len);
 123         }
 124
 125         /* fix IP hdr checksum information */
 126         skb->nh.iph->tot_len = htons(skb->len);
 127         ip_send_check(skb->nh.iph);
 128 }
 129
 130 /* Unusual, but possible case. */
 131 static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
 132 {
 133         struct sk_buff *nskb;
 134
 135         if ((*pskb)->len + extra > 65535)
 136                 return 0;
 137
 138         nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
 139         if (!nskb)
 140                 return 0;
 141
 142         /* Transfer socket to new skb. */
 143         if ((*pskb)->sk)
 144                 skb_set_owner_w(nskb, (*pskb)->sk);
 145 #ifdef CONFIG_NETFILTER_DEBUG
 146         nskb->nf_debug = (*pskb)->nf_debug;
 147 #endif
 148         kfree_skb(*pskb);
 149         *pskb = nskb;
 150         return 1;
 151 }
 152
 153 /* Generic function for mangling variable-length address changes inside
 154  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
 155  * command in FTP).
 156  *
 157  * Takes care about all the nasty sequence number changes, checksumming,
 158  * skb enlargement, ...
 159  *
 160  * */
 161 int
 162 ip_nat_mangle_tcp_packet(struct sk_buff **pskb,
 163                          struct ip_conntrack *ct,
 164                          enum ip_conntrack_info ctinfo,
 165                          unsigned int match_offset,
 166                          unsigned int match_len,
 167                          const char *rep_buffer,
 168                          unsigned int rep_len)
 169 {
 170         struct iphdr *iph;
 171         struct tcphdr *tcph;
 172         int datalen;
 173
 174         if (!skb_ip_make_writable(pskb, (*pskb)->len))
 175                 return 0;
 176
 177         if (rep_len > match_len
 178             && rep_len - match_len > skb_tailroom(*pskb)
 179             && !enlarge_skb(pskb, rep_len - match_len))
 180                 return 0;
 181
 182         SKB_LINEAR_ASSERT(*pskb);
 183
 184         iph = (*pskb)->nh.iph;
 185         tcph = (void *)iph + iph->ihl*4;
 186
 187         mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4,
 188                         match_offset, match_len, rep_buffer, rep_len);
 189
 190         datalen = (*pskb)->len - iph->ihl*4;
 191         tcph->check = 0;
 192         tcph->check = tcp_v4_check(tcph, datalen, iph->saddr, iph->daddr,
 193                                    csum_partial((char *)tcph, datalen, 0));
 194
 195         if (rep_len != match_len) {
 196                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
 197                 adjust_tcp_sequence(ntohl(tcph->seq),
 198                                     (int)rep_len - (int)match_len,
 199                                     ct, ctinfo);
 200                 /* Tell TCP window tracking about seq change */
 201                 ip_conntrack_tcp_update(*pskb, ct, CTINFO2DIR(ctinfo));
 202         }
 203         return 1;
 204 }
 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
 228         /* UDP helpers might accidentally mangle the wrong packet */
 229         iph = (*pskb)->nh.iph;
 230         if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) +
 231                                match_offset + match_len)
 232                 return 0;
 233
 234         if (!skb_ip_make_writable(pskb, (*pskb)->len))
 235                 return 0;
 236
 237         if (rep_len > match_len
 238             && rep_len - match_len > skb_tailroom(*pskb)
 239             && !enlarge_skb(pskb, rep_len - match_len))
 240                 return 0;
 241
 242         iph = (*pskb)->nh.iph;
 243         udph = (void *)iph + iph->ihl*4;
 244         mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph),
 245                         match_offset, match_len, rep_buffer, rep_len);
 246
 247         /* update the length of the UDP packet */
 248         udph->len = htons((*pskb)->len - iph->ihl*4);
 249
 250         /* fix udp checksum if udp checksum was previously calculated */
 251         if (udph->check) {
 252                 int datalen = (*pskb)->len - iph->ihl * 4;
 253                 udph->check = 0;
 254                 udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
 255                                                 datalen, IPPROTO_UDP,
 256                                                 csum_partial((char *)udph,
 257                                                              datalen, 0));
 258         }
 259
 260         return 1;
 261 }
 262
 263 /* Adjust one found SACK option including checksum correction */
 264 static void
 265 sack_adjust(struct sk_buff *skb,
 266             struct tcphdr *tcph,
 267             unsigned int sackoff,
 268             unsigned int sackend,
 269             struct ip_nat_seq *natseq)
 270 {
 271         while (sackoff < sackend) {
 272                 struct tcp_sack_block *sack;
 273                 u_int32_t new_start_seq, new_end_seq;
 274
 275                 sack = (void *)skb->data + sackoff;
 276                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
 277                           natseq->correction_pos))
 278                         new_start_seq = ntohl(sack->start_seq)
 279                                         - natseq->offset_after;
 280                 else
 281                         new_start_seq = ntohl(sack->start_seq)
 282                                         - natseq->offset_before;
 283                 new_start_seq = htonl(new_start_seq);
 284
 285                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
 286                           natseq->correction_pos))
 287                         new_end_seq = ntohl(sack->end_seq)
 288                                       - natseq->offset_after;
 289                 else
 290                         new_end_seq = ntohl(sack->end_seq)
 291                                       - natseq->offset_before;
 292                 new_end_seq = htonl(new_end_seq);
 293
 294                 DEBUGP("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
 295                         ntohl(sack->start_seq), new_start_seq,
 296                         ntohl(sack->end_seq), new_end_seq);
 297
 298                 tcph->check =
 299                         ip_nat_cheat_check(~sack->start_seq, new_start_seq,
 300                                            ip_nat_cheat_check(~sack->end_seq,
 301                                                               new_end_seq,
 302                                                               tcph->check));
 303                 sack->start_seq = new_start_seq;
 304                 sack->end_seq = new_end_seq;
 305                 sackoff += sizeof(*sack);
 306         }
 307 }
 308
 309 /* TCP SACK sequence number adjustment */
 310 static inline unsigned int
 311 ip_nat_sack_adjust(struct sk_buff **pskb,
 312                    struct tcphdr *tcph,
 313                    struct ip_conntrack *ct,
 314                    enum ip_conntrack_info ctinfo)
 315 {
 316         unsigned int dir, optoff, optend;
 317
 318         optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr);
 319         optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4;
 320
 321         if (!skb_ip_make_writable(pskb, optend))
 322                 return 0;
 323
 324         dir = CTINFO2DIR(ctinfo);
 325
 326         while (optoff < optend) {
 327                 /* Usually: option, length. */
 328                 unsigned char *op = (*pskb)->data + optoff;
 329
 330                 switch (op[0]) {
 331                 case TCPOPT_EOL:
 332                         return 1;
 333                 case TCPOPT_NOP:
 334                         optoff++;
 335                         continue;
 336                 default:
 337                         /* no partial options */
 338                         if (optoff + 1 == optend
 339                             || optoff + op[1] > optend
 340                             || op[1] < 2)
 341                                 return 0;
 342                         if (op[0] == TCPOPT_SACK
 343                             && op[1] >= 2+TCPOLEN_SACK_PERBLOCK
 344                             && ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
 345                                 sack_adjust(*pskb, tcph, optoff+2,
 346                                             optoff+op[1],
 347                                             &ct->nat.info.seq[!dir]);
 348                         optoff += op[1];
 349                 }
 350         }
 351         return 1;
 352 }
 353
 354 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
 355 int
 356 ip_nat_seq_adjust(struct sk_buff **pskb,
 357                   struct ip_conntrack *ct,
 358                   enum ip_conntrack_info ctinfo)
 359 {
 360         struct tcphdr *tcph;
 361         int dir, newseq, newack;
 362         struct ip_nat_seq *this_way, *other_way;
 363
 364         dir = CTINFO2DIR(ctinfo);
 365
 366         this_way = &ct->nat.info.seq[dir];
 367         other_way = &ct->nat.info.seq[!dir];
 368
 369         if (!skb_ip_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
 370                 return 0;
 371
 372         tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
 373         if (after(ntohl(tcph->seq), this_way->correction_pos))
 374                 newseq = ntohl(tcph->seq) + this_way->offset_after;
 375         else
 376                 newseq = ntohl(tcph->seq) + this_way->offset_before;
 377         newseq = htonl(newseq);
 378
 379         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
 380                   other_way->correction_pos))
 381                 newack = ntohl(tcph->ack_seq) - other_way->offset_after;
 382         else
 383                 newack = ntohl(tcph->ack_seq) - other_way->offset_before;
 384         newack = htonl(newack);
 385
 386         tcph->check = ip_nat_cheat_check(~tcph->seq, newseq,
 387                                          ip_nat_cheat_check(~tcph->ack_seq,
 388                                                             newack,
 389                                                             tcph->check));
 390
 391         DEBUGP("Adjusting sequence number from %u->%u, ack from %u->%u\n",
 392                 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
 393                 ntohl(newack));
 394
 395         tcph->seq = newseq;
 396         tcph->ack_seq = newack;
 397
 398         if (!ip_nat_sack_adjust(pskb, tcph, ct, ctinfo))
 399                 return 0;
 400
 401         ip_conntrack_tcp_update(*pskb, ct, dir);
 402
 403         return 1;
 404 }
 405
 406 /* Setup NAT on this expected conntrack so it follows master. */
 407 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
 408 void ip_nat_follow_master(struct ip_conntrack *ct,
 409                           struct ip_conntrack_expect *exp)
 410 {
 411         struct ip_nat_range range;
 412
 413         /* This must be a fresh one. */
 414         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 415
 416         /* Change src to where master sends to */
 417         range.flags = IP_NAT_RANGE_MAP_IPS;
 418         range.min_ip = range.max_ip
 419                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
 420         /* hook doesn't matter, but it has to do source manip */
 421         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 422
 423         /* For DST manip, map port here to where it's expected. */
 424         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 425         range.min = range.max = exp->saved_proto;
 426         range.min_ip = range.max_ip
 427                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
 428         /* hook doesn't matter, but it has to do destination manip */
 429         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 430 }