1 /* (C) 1999-2001 Paul `Rusty' Russell
2 * (C) 2002-2004 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/netfilter.h>
12 #include <linux/ip.h>
13 #include <linux/tcp.h>
14 #include <linux/if.h>
15 #include <linux/netfilter_ipv4/ip_nat.h>
16 #include <linux/netfilter_ipv4/ip_nat_rule.h>
17 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
18 #include <linux/netfilter_ipv4/ip_nat_core.h>
19
20 static int
21 tcp_in_range(const struct ip_conntrack_tuple *tuple,
22 enum ip_nat_manip_type maniptype,
23 const union ip_conntrack_manip_proto *min,
24 const union ip_conntrack_manip_proto *max)
25 {
26 u_int16_t port;
27
28 if (maniptype == IP_NAT_MANIP_SRC)
29 port = tuple->src.u.tcp.port;
30 else
31 port = tuple->dst.u.tcp.port;
32
33 return ntohs(port) >= ntohs(min->tcp.port)
34 && ntohs(port) <= ntohs(max->tcp.port);
35 }
36
37 static int
38 tcp_unique_tuple(struct ip_conntrack_tuple *tuple,
39 const struct ip_nat_range *range,
40 enum ip_nat_manip_type maniptype,
41 const struct ip_conntrack *conntrack)
42 {
43 static u_int16_t port, *portptr;
44 unsigned int range_size, min, i;
45
46 if (maniptype == IP_NAT_MANIP_SRC)
47 portptr = &tuple->src.u.tcp.port;
48 else
49 portptr = &tuple->dst.u.tcp.port;
50
51 /* If no range specified... */
52 if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
53 /* If it's dst rewrite, can't change port */
54 if (maniptype == IP_NAT_MANIP_DST)
55 return 0;
56
57 /* Map privileged onto privileged. */
58 if (ntohs(*portptr) < 1024) {
59 /* Loose convention: >> 512 is credential passing */
60 if (ntohs(*portptr)<512) {
61 min = 1;
62 range_size = 511 - min + 1;
63 } else {
64 min = 600;
65 range_size = 1023 - min + 1;
66 }
67 } else {
68 min = 1024;
69 range_size = 65535 - 1024 + 1;
70 }
71 } else {
72 min = ntohs(range->min.tcp.port);
73 range_size = ntohs(range->max.tcp.port) - min + 1;
74 }
75
76 for (i = 0; i < range_size; i++, port++) {
77 *portptr = htons(min + port % range_size);
78 if (!ip_nat_used_tuple(tuple, conntrack)) {
79 return 1;
80 }
81 }
82 return 0;
83 }
84
85 static int
86 tcp_manip_pkt(struct sk_buff **pskb,
87 unsigned int iphdroff,
88 const struct ip_conntrack_tuple *tuple,
89 enum ip_nat_manip_type maniptype)
90 {
91 struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
92 struct tcphdr *hdr;
93 unsigned int hdroff = iphdroff + iph->ihl*4;
94 u32 oldip, newip;
95 u16 *portptr, newport, oldport;
96 int hdrsize = 8; /* TCP connection tracking guarantees this much */
97
98 /* this could be a inner header returned in icmp packet; in such
99 cases we cannot update the checksum field since it is outside of
100 the 8 bytes of transport layer headers we are guaranteed */
101 if ((*pskb)->len >= hdroff + sizeof(struct tcphdr))
102 hdrsize = sizeof(struct tcphdr);
103
104 if (!skb_ip_make_writable(pskb, hdroff + hdrsize))
105 return 0;
106
107 iph = (struct iphdr *)((*pskb)->data + iphdroff);
108 hdr = (struct tcphdr *)((*pskb)->data + hdroff);
109
110 if (maniptype == IP_NAT_MANIP_SRC) {
111 /* Get rid of src ip and src pt */
112 oldip = iph->saddr;
113 newip = tuple->src.ip;
114 newport = tuple->src.u.tcp.port;
115 portptr = &hdr->source;
116 } else {
117 /* Get rid of dst ip and dst pt */
118 oldip = iph->daddr;
119 newip = tuple->dst.ip;
120 newport = tuple->dst.u.tcp.port;
121 portptr = &hdr->dest;
122 }
123
124 oldport = *portptr;
125 *portptr = newport;
126
127 if (hdrsize < sizeof(*hdr))
128 return 1;
129
130 hdr->check = ip_nat_cheat_check(~oldip, newip,
131 ip_nat_cheat_check(oldport ^ 0xFFFF,
132 newport,
133 hdr->check));
134 return 1;
135 }
136
137 static unsigned int
138 tcp_print(char *buffer,
139 const struct ip_conntrack_tuple *match,
140 const struct ip_conntrack_tuple *mask)
141 {
142 unsigned int len = 0;
143
144 if (mask->src.u.tcp.port)
145 len += sprintf(buffer + len, "srcpt=%u ",
146 ntohs(match->src.u.tcp.port));
147
148
149 if (mask->dst.u.tcp.port)
150 len += sprintf(buffer + len, "dstpt=%u ",
151 ntohs(match->dst.u.tcp.port));
152
153 return len;
154 }
155
156 static unsigned int
157 tcp_print_range(char *buffer, const struct ip_nat_range *range)
158 {
159 if (range->min.tcp.port != 0 || range->max.tcp.port != 0xFFFF) {
160 if (range->min.tcp.port == range->max.tcp.port)
161 return sprintf(buffer, "port %u ",
162 ntohs(range->min.tcp.port));
163 else
164 return sprintf(buffer, "ports %u-%u ",
165 ntohs(range->min.tcp.port),
166 ntohs(range->max.tcp.port));
167 }
168 else return 0;
169 }
170
171 struct ip_nat_protocol ip_nat_protocol_tcp
172 = { "TCP", IPPROTO_TCP,
173 tcp_manip_pkt,
174 tcp_in_range,
175 tcp_unique_tuple,
176 tcp_print,
177 tcp_print_range
178 };
179
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