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 *skb, unsigned int extra)
116 if (skb->len + extra > 65535)
119 if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
125 /* Generic function for mangling variable-length address changes inside
126 * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
129 * Takes care about all the nasty sequence number changes, checksumming,
130 * skb enlargement, ...
134 nf_nat_mangle_tcp_packet(struct sk_buff *skb,
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)
142 struct rtable *rt = (struct rtable *)skb->dst;
147 if (!skb_make_writable(skb, skb->len))
150 if (rep_len > match_len &&
151 rep_len - match_len > skb_tailroom(skb) &&
152 !enlarge_skb(skb, rep_len - match_len))
155 SKB_LINEAR_ASSERT(skb);
158 tcph = (void *)iph + iph->ihl*4;
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);
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) +
172 skb->csum_offset = offsetof(struct tcphdr, check);
173 tcph->check = ~tcp_v4_check(datalen,
174 iph->saddr, iph->daddr, 0);
177 tcph->check = tcp_v4_check(datalen,
178 iph->saddr, iph->daddr,
183 nf_proto_csum_replace2(&tcph->check, skb,
184 htons(oldlen), htons(datalen), 1);
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,
191 /* Tell TCP window tracking about seq change */
192 nf_conntrack_tcp_update(skb, ip_hdrlen(skb),
193 ct, CTINFO2DIR(ctinfo));
197 EXPORT_SYMBOL(nf_nat_mangle_tcp_packet);
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)
203 * Takes care about all the nasty sequence number changes, checksumming,
204 * skb enlargement, ...
206 * XXX - This function could be merged with nf_nat_mangle_tcp_packet which
207 * should be fairly easy to do.
210 nf_nat_mangle_udp_packet(struct sk_buff *skb,
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)
218 struct rtable *rt = (struct rtable *)skb->dst;
223 /* UDP helpers might accidentally mangle the wrong packet */
225 if (skb->len < iph->ihl*4 + sizeof(*udph) +
226 match_offset + match_len)
229 if (!skb_make_writable(skb, skb->len))
232 if (rep_len > match_len &&
233 rep_len - match_len > skb_tailroom(skb) &&
234 !enlarge_skb(skb, rep_len - match_len))
238 udph = (void *)iph + iph->ihl*4;
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);
244 /* update the length of the UDP packet */
245 datalen = skb->len - iph->ihl*4;
246 udph->len = htons(datalen);
248 /* fix udp checksum if udp checksum was previously calculated */
249 if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
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) +
259 skb->csum_offset = offsetof(struct udphdr, check);
260 udph->check = ~csum_tcpudp_magic(iph->saddr, iph->daddr,
261 datalen, IPPROTO_UDP,
265 udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
266 datalen, IPPROTO_UDP,
270 udph->check = CSUM_MANGLED_0;
273 nf_proto_csum_replace2(&udph->check, skb,
274 htons(oldlen), htons(datalen), 1);
278 EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
280 /* Adjust one found SACK option including checksum correction */
282 sack_adjust(struct sk_buff *skb,
284 unsigned int sackoff,
285 unsigned int sackend,
286 struct nf_nat_seq *natseq)
288 while (sackoff < sackend) {
289 struct tcp_sack_block_wire *sack;
290 __be32 new_start_seq, new_end_seq;
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);
298 new_start_seq = htonl(ntohl(sack->start_seq)
299 - natseq->offset_before);
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);
306 new_end_seq = htonl(ntohl(sack->end_seq)
307 - natseq->offset_before);
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);
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);
323 /* TCP SACK sequence number adjustment */
324 static inline unsigned int
325 nf_nat_sack_adjust(struct sk_buff *skb,
328 enum ip_conntrack_info ctinfo)
330 unsigned int dir, optoff, optend;
331 struct nf_conn_nat *nat = nfct_nat(ct);
333 optoff = ip_hdrlen(skb) + sizeof(struct tcphdr);
334 optend = ip_hdrlen(skb) + tcph->doff * 4;
336 if (!skb_make_writable(skb, optend))
339 dir = CTINFO2DIR(ctinfo);
341 while (optoff < optend) {
342 /* Usually: option, length. */
343 unsigned char *op = skb->data + optoff;
352 /* no partial options */
353 if (optoff + 1 == optend ||
354 optoff + op[1] > optend ||
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]);
368 /* TCP sequence number adjustment. Returns 1 on success, 0 on failure */
370 nf_nat_seq_adjust(struct sk_buff *skb,
372 enum ip_conntrack_info ctinfo)
376 __be32 newseq, newack;
377 struct nf_conn_nat *nat = nfct_nat(ct);
378 struct nf_nat_seq *this_way, *other_way;
380 dir = CTINFO2DIR(ctinfo);
382 this_way = &nat->seq[dir];
383 other_way = &nat->seq[!dir];
385 if (!skb_make_writable(skb, ip_hdrlen(skb) + sizeof(*tcph)))
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);
392 newseq = htonl(ntohl(tcph->seq) + this_way->offset_before);
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);
398 newack = htonl(ntohl(tcph->ack_seq) - other_way->offset_before);
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);
403 pr_debug("Adjusting sequence number from %u->%u, ack from %u->%u\n",
404 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
408 tcph->ack_seq = newack;
410 if (!nf_nat_sack_adjust(skb, tcph, ct, ctinfo))
413 nf_conntrack_tcp_update(skb, ip_hdrlen(skb), ct, dir);
417 EXPORT_SYMBOL(nf_nat_seq_adjust);
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)
424 struct nf_nat_range range;
426 /* This must be a fresh one. */
427 BUG_ON(ct->status & IPS_NAT_DONE_MASK);
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_IP_POST_ROUTING);
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_IP_PRE_ROUTING);
444 EXPORT_SYMBOL(nf_nat_follow_master);