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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/tcp.h> |
13 | |
14 | #include <linux/netfilter.h> |
15 | #include <linux/netfilter/nfnetlink_conntrack.h> |
16 | #include <net/netfilter/nf_nat.h> |
17 | #include <net/netfilter/nf_nat_l3proto.h> |
18 | #include <net/netfilter/nf_nat_l4proto.h> |
19 | #include <net/netfilter/nf_nat_core.h> |
20 | |
21 | static u16 tcp_port_rover; |
22 | |
23 | static void |
24 | tcp_unique_tuple(const struct nf_nat_l3proto *l3proto, |
25 | struct nf_conntrack_tuple *tuple, |
26 | const struct nf_nat_range *range, |
27 | enum nf_nat_manip_type maniptype, |
28 | const struct nf_conn *ct) |
29 | { |
30 | nf_nat_l4proto_unique_tuple(l3proto, tuple, range, maniptype, ct, |
31 | &tcp_port_rover); |
32 | } |
33 | |
34 | static bool |
35 | tcp_manip_pkt(struct sk_buff *skb, |
36 | const struct nf_nat_l3proto *l3proto, |
37 | unsigned int iphdroff, unsigned int hdroff, |
38 | const struct nf_conntrack_tuple *tuple, |
39 | enum nf_nat_manip_type maniptype) |
40 | { |
41 | struct tcphdr *hdr; |
42 | __be16 *portptr, newport, oldport; |
43 | int hdrsize = 8; /* TCP connection tracking guarantees this much */ |
44 | |
45 | /* this could be a inner header returned in icmp packet; in such |
46 | cases we cannot update the checksum field since it is outside of |
47 | the 8 bytes of transport layer headers we are guaranteed */ |
48 | if (skb->len >= hdroff + sizeof(struct tcphdr)) |
49 | hdrsize = sizeof(struct tcphdr); |
50 | |
51 | if (!skb_make_writable(skb, hdroff + hdrsize)) |
52 | return false; |
53 | |
54 | hdr = (struct tcphdr *)(skb->data + hdroff); |
55 | |
56 | if (maniptype == NF_NAT_MANIP_SRC) { |
57 | /* Get rid of src port */ |
58 | newport = tuple->src.u.tcp.port; |
59 | portptr = &hdr->source; |
60 | } else { |
61 | /* Get rid of dst port */ |
62 | newport = tuple->dst.u.tcp.port; |
63 | portptr = &hdr->dest; |
64 | } |
65 | |
66 | oldport = *portptr; |
67 | *portptr = newport; |
68 | |
69 | if (hdrsize < sizeof(*hdr)) |
70 | return true; |
71 | |
72 | l3proto->csum_update(skb, iphdroff, &hdr->check, tuple, maniptype); |
73 | inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0); |
74 | return true; |
75 | } |
76 | |
77 | const struct nf_nat_l4proto nf_nat_l4proto_tcp = { |
78 | .l4proto = IPPROTO_TCP, |
79 | .manip_pkt = tcp_manip_pkt, |
80 | .in_range = nf_nat_l4proto_in_range, |
81 | .unique_tuple = tcp_unique_tuple, |
82 | #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE) |
83 | .nlattr_to_range = nf_nat_l4proto_nlattr_to_range, |
84 | #endif |
85 | }; |
86 |
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