1 /* (C) 1999-2001 Paul `Rusty' Russell
2 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
7 */
8
9 #include <linux/types.h>
10 #include <linux/init.h>
11 #include <linux/export.h>
12 #include <linux/ip.h>
13 #include <linux/tcp.h>
14
15 #include <linux/netfilter.h>
16 #include <linux/netfilter/nfnetlink_conntrack.h>
17 #include <net/netfilter/nf_nat.h>
18 #include <net/netfilter/nf_nat_rule.h>
19 #include <net/netfilter/nf_nat_protocol.h>
20 #include <net/netfilter/nf_nat_core.h>
21
22 static u_int16_t tcp_port_rover;
23
24 static void
tcp_unique_tuple(struct nf_conntrack_tuple * tuple,const struct nf_nat_ipv4_range * range,enum nf_nat_manip_type maniptype,const struct nf_conn * ct)25 tcp_unique_tuple(struct nf_conntrack_tuple *tuple,
26 const struct nf_nat_ipv4_range *range,
27 enum nf_nat_manip_type maniptype,
28 const struct nf_conn *ct)
29 {
30 nf_nat_proto_unique_tuple(tuple, range, maniptype, ct, &tcp_port_rover);
31 }
32
33 static bool
tcp_manip_pkt(struct sk_buff * skb,unsigned int iphdroff,const struct nf_conntrack_tuple * tuple,enum nf_nat_manip_type maniptype)34 tcp_manip_pkt(struct sk_buff *skb,
35 unsigned int iphdroff,
36 const struct nf_conntrack_tuple *tuple,
37 enum nf_nat_manip_type maniptype)
38 {
39 const struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff);
40 struct tcphdr *hdr;
41 unsigned int hdroff = iphdroff + iph->ihl*4;
42 __be32 oldip, newip;
43 __be16 *portptr, newport, oldport;
44 int hdrsize = 8; /* TCP connection tracking guarantees this much */
45
46 /* this could be a inner header returned in icmp packet; in such
47 cases we cannot update the checksum field since it is outside of
48 the 8 bytes of transport layer headers we are guaranteed */
49 if (skb->len >= hdroff + sizeof(struct tcphdr))
50 hdrsize = sizeof(struct tcphdr);
51
52 if (!skb_make_writable(skb, hdroff + hdrsize))
53 return false;
54
55 iph = (struct iphdr *)(skb->data + iphdroff);
56 hdr = (struct tcphdr *)(skb->data + hdroff);
57
58 if (maniptype == NF_NAT_MANIP_SRC) {
59 /* Get rid of src ip and src pt */
60 oldip = iph->saddr;
61 newip = tuple->src.u3.ip;
62 newport = tuple->src.u.tcp.port;
63 portptr = &hdr->source;
64 } else {
65 /* Get rid of dst ip and dst pt */
66 oldip = iph->daddr;
67 newip = tuple->dst.u3.ip;
68 newport = tuple->dst.u.tcp.port;
69 portptr = &hdr->dest;
70 }
71
72 oldport = *portptr;
73 *portptr = newport;
74
75 if (hdrsize < sizeof(*hdr))
76 return true;
77
78 inet_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1);
79 inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
80 return true;
81 }
82
83 const struct nf_nat_protocol nf_nat_protocol_tcp = {
84 .protonum = IPPROTO_TCP,
85 .manip_pkt = tcp_manip_pkt,
86 .in_range = nf_nat_proto_in_range,
87 .unique_tuple = tcp_unique_tuple,
88 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
89 .nlattr_to_range = nf_nat_proto_nlattr_to_range,
90 #endif
91 };
92