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5b1158e9 JK |
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> | |
41f4689a | 11 | #include <linux/random.h> |
5b1158e9 JK |
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 int | |
23 | tcp_in_range(const struct nf_conntrack_tuple *tuple, | |
24 | enum nf_nat_manip_type maniptype, | |
25 | const union nf_conntrack_man_proto *min, | |
26 | const union nf_conntrack_man_proto *max) | |
27 | { | |
28 | __be16 port; | |
29 | ||
30 | if (maniptype == IP_NAT_MANIP_SRC) | |
31 | port = tuple->src.u.tcp.port; | |
32 | else | |
33 | port = tuple->dst.u.tcp.port; | |
34 | ||
35 | return ntohs(port) >= ntohs(min->tcp.port) && | |
36 | ntohs(port) <= ntohs(max->tcp.port); | |
37 | } | |
38 | ||
39 | static int | |
40 | tcp_unique_tuple(struct nf_conntrack_tuple *tuple, | |
41 | const struct nf_nat_range *range, | |
42 | enum nf_nat_manip_type maniptype, | |
43 | const struct nf_conn *ct) | |
44 | { | |
45 | static u_int16_t port; | |
46 | __be16 *portptr; | |
47 | unsigned int range_size, min, i; | |
48 | ||
49 | if (maniptype == IP_NAT_MANIP_SRC) | |
50 | portptr = &tuple->src.u.tcp.port; | |
51 | else | |
52 | portptr = &tuple->dst.u.tcp.port; | |
53 | ||
54 | /* If no range specified... */ | |
55 | if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) { | |
56 | /* If it's dst rewrite, can't change port */ | |
57 | if (maniptype == IP_NAT_MANIP_DST) | |
58 | return 0; | |
59 | ||
60 | /* Map privileged onto privileged. */ | |
61 | if (ntohs(*portptr) < 1024) { | |
62 | /* Loose convention: >> 512 is credential passing */ | |
63 | if (ntohs(*portptr)<512) { | |
64 | min = 1; | |
65 | range_size = 511 - min + 1; | |
66 | } else { | |
67 | min = 600; | |
68 | range_size = 1023 - min + 1; | |
69 | } | |
70 | } else { | |
71 | min = 1024; | |
72 | range_size = 65535 - 1024 + 1; | |
73 | } | |
74 | } else { | |
75 | min = ntohs(range->min.tcp.port); | |
76 | range_size = ntohs(range->max.tcp.port) - min + 1; | |
77 | } | |
78 | ||
41f4689a EL |
79 | if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) |
80 | port = net_random(); | |
81 | ||
5b1158e9 JK |
82 | for (i = 0; i < range_size; i++, port++) { |
83 | *portptr = htons(min + port % range_size); | |
84 | if (!nf_nat_used_tuple(tuple, ct)) | |
85 | return 1; | |
86 | } | |
87 | return 0; | |
88 | } | |
89 | ||
90 | static int | |
3db05fea | 91 | tcp_manip_pkt(struct sk_buff *skb, |
5b1158e9 JK |
92 | unsigned int iphdroff, |
93 | const struct nf_conntrack_tuple *tuple, | |
94 | enum nf_nat_manip_type maniptype) | |
95 | { | |
3db05fea | 96 | struct iphdr *iph = (struct iphdr *)(skb->data + iphdroff); |
5b1158e9 JK |
97 | struct tcphdr *hdr; |
98 | unsigned int hdroff = iphdroff + iph->ihl*4; | |
99 | __be32 oldip, newip; | |
100 | __be16 *portptr, newport, oldport; | |
101 | int hdrsize = 8; /* TCP connection tracking guarantees this much */ | |
102 | ||
103 | /* this could be a inner header returned in icmp packet; in such | |
104 | cases we cannot update the checksum field since it is outside of | |
105 | the 8 bytes of transport layer headers we are guaranteed */ | |
3db05fea | 106 | if (skb->len >= hdroff + sizeof(struct tcphdr)) |
5b1158e9 JK |
107 | hdrsize = sizeof(struct tcphdr); |
108 | ||
3db05fea | 109 | if (!skb_make_writable(skb, hdroff + hdrsize)) |
5b1158e9 JK |
110 | return 0; |
111 | ||
3db05fea HX |
112 | iph = (struct iphdr *)(skb->data + iphdroff); |
113 | hdr = (struct tcphdr *)(skb->data + hdroff); | |
5b1158e9 JK |
114 | |
115 | if (maniptype == IP_NAT_MANIP_SRC) { | |
116 | /* Get rid of src ip and src pt */ | |
117 | oldip = iph->saddr; | |
118 | newip = tuple->src.u3.ip; | |
119 | newport = tuple->src.u.tcp.port; | |
120 | portptr = &hdr->source; | |
121 | } else { | |
122 | /* Get rid of dst ip and dst pt */ | |
123 | oldip = iph->daddr; | |
124 | newip = tuple->dst.u3.ip; | |
125 | newport = tuple->dst.u.tcp.port; | |
126 | portptr = &hdr->dest; | |
127 | } | |
128 | ||
129 | oldport = *portptr; | |
130 | *portptr = newport; | |
131 | ||
132 | if (hdrsize < sizeof(*hdr)) | |
133 | return 1; | |
134 | ||
3db05fea HX |
135 | nf_proto_csum_replace4(&hdr->check, skb, oldip, newip, 1); |
136 | nf_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0); | |
5b1158e9 JK |
137 | return 1; |
138 | } | |
139 | ||
140 | struct nf_nat_protocol nf_nat_protocol_tcp = { | |
141 | .name = "TCP", | |
142 | .protonum = IPPROTO_TCP, | |
143 | .me = THIS_MODULE, | |
144 | .manip_pkt = tcp_manip_pkt, | |
145 | .in_range = tcp_in_range, | |
146 | .unique_tuple = tcp_unique_tuple, | |
e281db5c | 147 | #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE) |
fdf70832 PM |
148 | .range_to_nlattr = nf_nat_port_range_to_nlattr, |
149 | .nlattr_to_range = nf_nat_port_nlattr_to_range, | |
5b1158e9 JK |
150 | #endif |
151 | }; |