1 /* ip_nat_helper.c - generic support functions for NAT helpers
3 * (C) 2000-2002 Harald Welte <laforge@netfilter.org>
4 * (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
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.
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>
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>
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);
33 static DEFINE_SPINLOCK(nf_nat_seqofs_lock);
35 /* Setup TCP sequence correction given this change at this sequence */
37 adjust_tcp_sequence(u32 seq,
40 enum ip_conntrack_info ctinfo)
43 struct nf_nat_seq *this_way, *other_way;
44 struct nf_conn_nat *nat = nfct_nat(ct);
46 pr_debug("adjust_tcp_sequence: seq = %u, sizediff = %d\n",
49 dir = CTINFO2DIR(ctinfo);
51 this_way = &nat->seq[dir];
52 other_way = &nat->seq[!dir];
54 pr_debug("nf_nat_resize_packet: Seq_offset before: ");
55 DUMP_OFFSET(this_way);
57 spin_lock_bh(&nf_nat_seqofs_lock);
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
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;
69 spin_unlock_bh(&nf_nat_seqofs_lock);
71 pr_debug("nf_nat_resize_packet: Seq_offset after: ");
72 DUMP_OFFSET(this_way);
75 /* Frobs data inside this packet, which is linear. */
76 static void mangle_contents(struct sk_buff *skb,
78 unsigned int match_offset,
79 unsigned int match_len,
80 const char *rep_buffer,
85 BUG_ON(skb_is_nonlinear(skb));
86 data = skb_network_header(skb) + dataoff;
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));
94 /* insert data from buffer */
95 memcpy(data + match_offset, rep_buffer, rep_len);
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);
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);
108 /* fix IP hdr checksum information */
109 ip_hdr(skb)->tot_len = htons(skb->len);
110 ip_send_check(ip_hdr(skb));
113 /* Unusual, but possible case. */
114 static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
116 struct sk_buff *nskb;
118 if ((*pskb)->len + extra > 65535)
121 nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
125 /* Transfer socket to new skb. */
127 skb_set_owner_w(nskb, (*pskb)->sk);
133 /* Generic function for mangling variable-length address changes inside
134 * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
137 * Takes care about all the nasty sequence number changes, checksumming,
138 * skb enlargement, ...
142 nf_nat_mangle_tcp_packet(struct sk_buff **pskb,
144 enum ip_conntrack_info ctinfo,
145 unsigned int match_offset,
146 unsigned int match_len,
147 const char *rep_buffer,
148 unsigned int rep_len)
150 struct rtable *rt = (struct rtable *)(*pskb)->dst;
155 if (!skb_make_writable(pskb, (*pskb)->len))
158 if (rep_len > match_len &&
159 rep_len - match_len > skb_tailroom(*pskb) &&
160 !enlarge_skb(pskb, rep_len - match_len))
163 SKB_LINEAR_ASSERT(*pskb);
166 tcph = (void *)iph + iph->ihl*4;
168 oldlen = (*pskb)->len - iph->ihl*4;
169 mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4,
170 match_offset, match_len, rep_buffer, rep_len);
172 datalen = (*pskb)->len - iph->ihl*4;
173 if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
174 if (!(rt->rt_flags & RTCF_LOCAL) &&
175 (*pskb)->dev->features & NETIF_F_V4_CSUM) {
176 (*pskb)->ip_summed = CHECKSUM_PARTIAL;
177 (*pskb)->csum_start = skb_headroom(*pskb) +
178 skb_network_offset(*pskb) +
180 (*pskb)->csum_offset = offsetof(struct tcphdr, check);
181 tcph->check = ~tcp_v4_check(datalen,
182 iph->saddr, iph->daddr, 0);
185 tcph->check = tcp_v4_check(datalen,
186 iph->saddr, iph->daddr,
191 nf_proto_csum_replace2(&tcph->check, *pskb,
192 htons(oldlen), htons(datalen), 1);
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,
199 /* Tell TCP window tracking about seq change */
200 nf_conntrack_tcp_update(*pskb, ip_hdrlen(*pskb),
201 ct, CTINFO2DIR(ctinfo));
205 EXPORT_SYMBOL(nf_nat_mangle_tcp_packet);
207 /* Generic function for mangling variable-length address changes inside
208 * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
209 * command in the Amanda protocol)
211 * Takes care about all the nasty sequence number changes, checksumming,
212 * skb enlargement, ...
214 * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
215 * should be fairly easy to do.
218 nf_nat_mangle_udp_packet(struct sk_buff **pskb,
220 enum ip_conntrack_info ctinfo,
221 unsigned int match_offset,
222 unsigned int match_len,
223 const char *rep_buffer,
224 unsigned int rep_len)
226 struct rtable *rt = (struct rtable *)(*pskb)->dst;
231 /* UDP helpers might accidentally mangle the wrong packet */
233 if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) +
234 match_offset + match_len)
237 if (!skb_make_writable(pskb, (*pskb)->len))
240 if (rep_len > match_len &&
241 rep_len - match_len > skb_tailroom(*pskb) &&
242 !enlarge_skb(pskb, rep_len - match_len))
246 udph = (void *)iph + iph->ihl*4;
248 oldlen = (*pskb)->len - iph->ihl*4;
249 mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph),
250 match_offset, match_len, rep_buffer, rep_len);
252 /* update the length of the UDP packet */
253 datalen = (*pskb)->len - iph->ihl*4;
254 udph->len = htons(datalen);
256 /* fix udp checksum if udp checksum was previously calculated */
257 if (!udph->check && (*pskb)->ip_summed != CHECKSUM_PARTIAL)
260 if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
261 if (!(rt->rt_flags & RTCF_LOCAL) &&
262 (*pskb)->dev->features & NETIF_F_V4_CSUM) {
263 (*pskb)->ip_summed = CHECKSUM_PARTIAL;
264 (*pskb)->csum_start = skb_headroom(*pskb) +
265 skb_network_offset(*pskb) +
267 (*pskb)->csum_offset = offsetof(struct udphdr, check);
268 udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
269 datalen, IPPROTO_UDP,
273 udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
274 datalen, IPPROTO_UDP,
278 udph->check = CSUM_MANGLED_0;
281 nf_proto_csum_replace2(&udph->check, *pskb,
282 htons(oldlen), htons(datalen), 1);
286 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
288 /* Adjust one found SACK option including checksum correction */
290 sack_adjust(struct sk_buff *skb,
292 unsigned int sackoff,
293 unsigned int sackend,
294 struct nf_nat_seq *natseq)
296 while (sackoff < sackend) {
297 struct tcp_sack_block_wire *sack;
298 __be32 new_start_seq, new_end_seq;
300 sack = (void *)skb->data + sackoff;
301 if (after(ntohl(sack->start_seq) - natseq->offset_before,
302 natseq->correction_pos))
303 new_start_seq = htonl(ntohl(sack->start_seq)
304 - natseq->offset_after);
306 new_start_seq = htonl(ntohl(sack->start_seq)
307 - natseq->offset_before);
309 if (after(ntohl(sack->end_seq) - natseq->offset_before,
310 natseq->correction_pos))
311 new_end_seq = htonl(ntohl(sack->end_seq)
312 - natseq->offset_after);
314 new_end_seq = htonl(ntohl(sack->end_seq)
315 - natseq->offset_before);
317 pr_debug("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
318 ntohl(sack->start_seq), new_start_seq,
319 ntohl(sack->end_seq), new_end_seq);
321 nf_proto_csum_replace4(&tcph->check, skb,
322 sack->start_seq, new_start_seq, 0);
323 nf_proto_csum_replace4(&tcph->check, skb,
324 sack->end_seq, new_end_seq, 0);
325 sack->start_seq = new_start_seq;
326 sack->end_seq = new_end_seq;
327 sackoff += sizeof(*sack);
331 /* TCP SACK sequence number adjustment */
332 static inline unsigned int
333 nf_nat_sack_adjust(struct sk_buff **pskb,
336 enum ip_conntrack_info ctinfo)
338 unsigned int dir, optoff, optend;
339 struct nf_conn_nat *nat = nfct_nat(ct);
341 optoff = ip_hdrlen(*pskb) + sizeof(struct tcphdr);
342 optend = ip_hdrlen(*pskb) + tcph->doff * 4;
344 if (!skb_make_writable(pskb, optend))
347 dir = CTINFO2DIR(ctinfo);
349 while (optoff < optend) {
350 /* Usually: option, length. */
351 unsigned char *op = (*pskb)->data + optoff;
360 /* no partial options */
361 if (optoff + 1 == optend ||
362 optoff + op[1] > optend ||
365 if (op[0] == TCPOPT_SACK &&
366 op[1] >= 2+TCPOLEN_SACK_PERBLOCK &&
367 ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
368 sack_adjust(*pskb, tcph, optoff+2,
369 optoff+op[1], &nat->seq[!dir]);
376 /* TCP sequence number adjustment. Returns 1 on success, 0 on failure */
378 nf_nat_seq_adjust(struct sk_buff **pskb,
380 enum ip_conntrack_info ctinfo)
384 __be32 newseq, newack;
385 struct nf_conn_nat *nat = nfct_nat(ct);
386 struct nf_nat_seq *this_way, *other_way;
388 dir = CTINFO2DIR(ctinfo);
390 this_way = &nat->seq[dir];
391 other_way = &nat->seq[!dir];
393 if (!skb_make_writable(pskb, ip_hdrlen(*pskb) + sizeof(*tcph)))
396 tcph = (void *)(*pskb)->data + ip_hdrlen(*pskb);
397 if (after(ntohl(tcph->seq), this_way->correction_pos))
398 newseq = htonl(ntohl(tcph->seq) + this_way->offset_after);
400 newseq = htonl(ntohl(tcph->seq) + this_way->offset_before);
402 if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
403 other_way->correction_pos))
404 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_after);
406 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_before);
408 nf_proto_csum_replace4(&tcph->check, *pskb, tcph->seq, newseq, 0);
409 nf_proto_csum_replace4(&tcph->check, *pskb, tcph->ack_seq, newack, 0);
411 pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
412 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
416 tcph->ack_seq = newack;
418 if (!nf_nat_sack_adjust(pskb, tcph, ct, ctinfo))
421 nf_conntrack_tcp_update(*pskb, ip_hdrlen(*pskb), ct, dir);
425 EXPORT_SYMBOL(nf_nat_seq_adjust);
427 /* Setup NAT on this expected conntrack so it follows master. */
428 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
429 void nf_nat_follow_master(struct nf_conn *ct,
430 struct nf_conntrack_expect *exp)
432 struct nf_nat_range range;
434 /* This must be a fresh one. */
435 BUG_ON(ct->status & IPS_NAT_DONE_MASK);
437 /* Change src to where master sends to */
438 range.flags = IP_NAT_RANGE_MAP_IPS;
439 range.min_ip = range.max_ip
440 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
441 /* hook doesn't matter, but it has to do source manip */
442 nf_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
444 /* For DST manip, map port here to where it's expected. */
445 range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
446 range.min = range.max = exp->saved_proto;
447 range.min_ip = range.max_ip
448 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
449 /* hook doesn't matter, but it has to do destination manip */
450 nf_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
452 EXPORT_SYMBOL(nf_nat_follow_master);