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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Transparent proxy support for Linux/iptables
4 *
5 * Copyright (C) 2007-2008 BalaBit IT Ltd.
6 * Author: Krisztian Kovacs
7 */
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9#include <linux/module.h>
10#include <linux/skbuff.h>
11#include <linux/netfilter/x_tables.h>
12#include <linux/netfilter_ipv4/ip_tables.h>
13#include <net/tcp.h>
14#include <net/udp.h>
15#include <net/icmp.h>
16#include <net/sock.h>
17#include <net/inet_sock.h>
18#include <net/netfilter/ipv4/nf_defrag_ipv4.h>
19
20#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
21#include <linux/netfilter_ipv6/ip6_tables.h>
22#include <net/inet6_hashtables.h>
23#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
24#endif
25
26#include <net/netfilter/nf_socket.h>
27#include <linux/netfilter/xt_socket.h>
28
29/* "socket" match based redirection (no specific rule)
30 * ===================================================
31 *
32 * There are connections with dynamic endpoints (e.g. FTP data
33 * connection) that the user is unable to add explicit rules
34 * for. These are taken care of by a generic "socket" rule. It is
35 * assumed that the proxy application is trusted to open such
36 * connections without explicit iptables rule (except of course the
37 * generic 'socket' rule). In this case the following sockets are
38 * matched in preference order:
39 *
40 * - match: if there's a fully established connection matching the
41 * _packet_ tuple
42 *
43 * - match: if there's a non-zero bound listener (possibly with a
44 * non-local address) We don't accept zero-bound listeners, since
45 * then local services could intercept traffic going through the
46 * box.
47 */
48static bool
49socket_match(const struct sk_buff *skb, struct xt_action_param *par,
50 const struct xt_socket_mtinfo1 *info)
51{
52 struct sk_buff *pskb = (struct sk_buff *)skb;
53 struct sock *sk = skb->sk;
54
55 if (sk && !net_eq(xt_net(par), sock_net(sk)))
56 sk = NULL;
57
58 if (!sk)
59 sk = nf_sk_lookup_slow_v4(xt_net(par), skb, xt_in(par));
60
61 if (sk) {
62 bool wildcard;
63 bool transparent = true;
64
65 /* Ignore sockets listening on INADDR_ANY,
66 * unless XT_SOCKET_NOWILDCARD is set
67 */
68 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
69 sk_fullsock(sk) &&
70 inet_sk(sk)->inet_rcv_saddr == 0);
71
72 /* Ignore non-transparent sockets,
73 * if XT_SOCKET_TRANSPARENT is used
74 */
75 if (info->flags & XT_SOCKET_TRANSPARENT)
76 transparent = inet_sk_transparent(sk);
77
78 if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
79 transparent && sk_fullsock(sk))
80 pskb->mark = READ_ONCE(sk->sk_mark);
81
82 if (sk != skb->sk)
83 sock_gen_put(sk);
84
85 if (wildcard || !transparent)
86 sk = NULL;
87 }
88
89 return sk != NULL;
90}
91
92static bool
93socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
94{
95 static struct xt_socket_mtinfo1 xt_info_v0 = {
96 .flags = 0,
97 };
98
99 return socket_match(skb, par, &xt_info_v0);
100}
101
102static bool
103socket_mt4_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
104{
105 return socket_match(skb, par, par->matchinfo);
106}
107
108#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
109static bool
110socket_mt6_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
111{
112 const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
113 struct sk_buff *pskb = (struct sk_buff *)skb;
114 struct sock *sk = skb->sk;
115
116 if (sk && !net_eq(xt_net(par), sock_net(sk)))
117 sk = NULL;
118
119 if (!sk)
120 sk = nf_sk_lookup_slow_v6(xt_net(par), skb, xt_in(par));
121
122 if (sk) {
123 bool wildcard;
124 bool transparent = true;
125
126 /* Ignore sockets listening on INADDR_ANY
127 * unless XT_SOCKET_NOWILDCARD is set
128 */
129 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
130 sk_fullsock(sk) &&
131 ipv6_addr_any(&sk->sk_v6_rcv_saddr));
132
133 /* Ignore non-transparent sockets,
134 * if XT_SOCKET_TRANSPARENT is used
135 */
136 if (info->flags & XT_SOCKET_TRANSPARENT)
137 transparent = inet_sk_transparent(sk);
138
139 if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
140 transparent && sk_fullsock(sk))
141 pskb->mark = READ_ONCE(sk->sk_mark);
142
143 if (sk != skb->sk)
144 sock_gen_put(sk);
145
146 if (wildcard || !transparent)
147 sk = NULL;
148 }
149
150 return sk != NULL;
151}
152#endif
153
154static int socket_mt_enable_defrag(struct net *net, int family)
155{
156 switch (family) {
157 case NFPROTO_IPV4:
158 return nf_defrag_ipv4_enable(net);
159#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
160 case NFPROTO_IPV6:
161 return nf_defrag_ipv6_enable(net);
162#endif
163 }
164 WARN_ONCE(1, "Unknown family %d\n", family);
165 return 0;
166}
167
168static int socket_mt_v1_check(const struct xt_mtchk_param *par)
169{
170 const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
171
172 if (info->flags & ~XT_SOCKET_FLAGS_V1) {
173 pr_info_ratelimited("unknown flags 0x%x\n",
174 info->flags & ~XT_SOCKET_FLAGS_V1);
175 return -EINVAL;
176 }
177
178 return socket_mt_enable_defrag(par->net, par->family);
179}
180
181static int socket_mt_v2_check(const struct xt_mtchk_param *par)
182{
183 const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
184
185 if (info->flags & ~XT_SOCKET_FLAGS_V2) {
186 pr_info_ratelimited("unknown flags 0x%x\n",
187 info->flags & ~XT_SOCKET_FLAGS_V2);
188 return -EINVAL;
189 }
190
191 return socket_mt_enable_defrag(par->net, par->family);
192}
193
194static int socket_mt_v3_check(const struct xt_mtchk_param *par)
195{
196 const struct xt_socket_mtinfo3 *info =
197 (struct xt_socket_mtinfo3 *)par->matchinfo;
198
199 if (info->flags & ~XT_SOCKET_FLAGS_V3) {
200 pr_info_ratelimited("unknown flags 0x%x\n",
201 info->flags & ~XT_SOCKET_FLAGS_V3);
202 return -EINVAL;
203 }
204
205 return socket_mt_enable_defrag(par->net, par->family);
206}
207
208static void socket_mt_destroy(const struct xt_mtdtor_param *par)
209{
210 if (par->family == NFPROTO_IPV4)
211 nf_defrag_ipv4_disable(par->net);
212#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
213 else if (par->family == NFPROTO_IPV6)
214 nf_defrag_ipv6_disable(par->net);
215#endif
216}
217
218static struct xt_match socket_mt_reg[] __read_mostly = {
219 {
220 .name = "socket",
221 .revision = 0,
222 .family = NFPROTO_IPV4,
223 .match = socket_mt4_v0,
224 .hooks = (1 << NF_INET_PRE_ROUTING) |
225 (1 << NF_INET_LOCAL_IN),
226 .me = THIS_MODULE,
227 },
228 {
229 .name = "socket",
230 .revision = 1,
231 .family = NFPROTO_IPV4,
232 .match = socket_mt4_v1_v2_v3,
233 .destroy = socket_mt_destroy,
234 .checkentry = socket_mt_v1_check,
235 .matchsize = sizeof(struct xt_socket_mtinfo1),
236 .hooks = (1 << NF_INET_PRE_ROUTING) |
237 (1 << NF_INET_LOCAL_IN),
238 .me = THIS_MODULE,
239 },
240#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
241 {
242 .name = "socket",
243 .revision = 1,
244 .family = NFPROTO_IPV6,
245 .match = socket_mt6_v1_v2_v3,
246 .checkentry = socket_mt_v1_check,
247 .matchsize = sizeof(struct xt_socket_mtinfo1),
248 .destroy = socket_mt_destroy,
249 .hooks = (1 << NF_INET_PRE_ROUTING) |
250 (1 << NF_INET_LOCAL_IN),
251 .me = THIS_MODULE,
252 },
253#endif
254 {
255 .name = "socket",
256 .revision = 2,
257 .family = NFPROTO_IPV4,
258 .match = socket_mt4_v1_v2_v3,
259 .checkentry = socket_mt_v2_check,
260 .destroy = socket_mt_destroy,
261 .matchsize = sizeof(struct xt_socket_mtinfo1),
262 .hooks = (1 << NF_INET_PRE_ROUTING) |
263 (1 << NF_INET_LOCAL_IN),
264 .me = THIS_MODULE,
265 },
266#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
267 {
268 .name = "socket",
269 .revision = 2,
270 .family = NFPROTO_IPV6,
271 .match = socket_mt6_v1_v2_v3,
272 .checkentry = socket_mt_v2_check,
273 .destroy = socket_mt_destroy,
274 .matchsize = sizeof(struct xt_socket_mtinfo1),
275 .hooks = (1 << NF_INET_PRE_ROUTING) |
276 (1 << NF_INET_LOCAL_IN),
277 .me = THIS_MODULE,
278 },
279#endif
280 {
281 .name = "socket",
282 .revision = 3,
283 .family = NFPROTO_IPV4,
284 .match = socket_mt4_v1_v2_v3,
285 .checkentry = socket_mt_v3_check,
286 .destroy = socket_mt_destroy,
287 .matchsize = sizeof(struct xt_socket_mtinfo1),
288 .hooks = (1 << NF_INET_PRE_ROUTING) |
289 (1 << NF_INET_LOCAL_IN),
290 .me = THIS_MODULE,
291 },
292#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
293 {
294 .name = "socket",
295 .revision = 3,
296 .family = NFPROTO_IPV6,
297 .match = socket_mt6_v1_v2_v3,
298 .checkentry = socket_mt_v3_check,
299 .destroy = socket_mt_destroy,
300 .matchsize = sizeof(struct xt_socket_mtinfo1),
301 .hooks = (1 << NF_INET_PRE_ROUTING) |
302 (1 << NF_INET_LOCAL_IN),
303 .me = THIS_MODULE,
304 },
305#endif
306};
307
308static int __init socket_mt_init(void)
309{
310 return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
311}
312
313static void __exit socket_mt_exit(void)
314{
315 xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
316}
317
318module_init(socket_mt_init);
319module_exit(socket_mt_exit);
320
321MODULE_LICENSE("GPL");
322MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
323MODULE_DESCRIPTION("x_tables socket match module");
324MODULE_ALIAS("ipt_socket");
325MODULE_ALIAS("ip6t_socket");