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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 = 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 = 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 int err;
172
173 err = socket_mt_enable_defrag(par->net, par->family);
174 if (err)
175 return err;
176
177 if (info->flags & ~XT_SOCKET_FLAGS_V1) {
178 pr_info_ratelimited("unknown flags 0x%x\n",
179 info->flags & ~XT_SOCKET_FLAGS_V1);
180 return -EINVAL;
181 }
182 return 0;
183}
184
185static int socket_mt_v2_check(const struct xt_mtchk_param *par)
186{
187 const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
188 int err;
189
190 err = socket_mt_enable_defrag(par->net, par->family);
191 if (err)
192 return err;
193
194 if (info->flags & ~XT_SOCKET_FLAGS_V2) {
195 pr_info_ratelimited("unknown flags 0x%x\n",
196 info->flags & ~XT_SOCKET_FLAGS_V2);
197 return -EINVAL;
198 }
199 return 0;
200}
201
202static int socket_mt_v3_check(const struct xt_mtchk_param *par)
203{
204 const struct xt_socket_mtinfo3 *info =
205 (struct xt_socket_mtinfo3 *)par->matchinfo;
206 int err;
207
208 err = socket_mt_enable_defrag(par->net, par->family);
209 if (err)
210 return err;
211 if (info->flags & ~XT_SOCKET_FLAGS_V3) {
212 pr_info_ratelimited("unknown flags 0x%x\n",
213 info->flags & ~XT_SOCKET_FLAGS_V3);
214 return -EINVAL;
215 }
216 return 0;
217}
218
219static void socket_mt_destroy(const struct xt_mtdtor_param *par)
220{
221 if (par->family == NFPROTO_IPV4)
222 nf_defrag_ipv4_disable(par->net);
223 else if (par->family == NFPROTO_IPV6)
224 nf_defrag_ipv4_disable(par->net);
225}
226
227static struct xt_match socket_mt_reg[] __read_mostly = {
228 {
229 .name = "socket",
230 .revision = 0,
231 .family = NFPROTO_IPV4,
232 .match = socket_mt4_v0,
233 .hooks = (1 << NF_INET_PRE_ROUTING) |
234 (1 << NF_INET_LOCAL_IN),
235 .me = THIS_MODULE,
236 },
237 {
238 .name = "socket",
239 .revision = 1,
240 .family = NFPROTO_IPV4,
241 .match = socket_mt4_v1_v2_v3,
242 .destroy = socket_mt_destroy,
243 .checkentry = socket_mt_v1_check,
244 .matchsize = sizeof(struct xt_socket_mtinfo1),
245 .hooks = (1 << NF_INET_PRE_ROUTING) |
246 (1 << NF_INET_LOCAL_IN),
247 .me = THIS_MODULE,
248 },
249#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
250 {
251 .name = "socket",
252 .revision = 1,
253 .family = NFPROTO_IPV6,
254 .match = socket_mt6_v1_v2_v3,
255 .checkentry = socket_mt_v1_check,
256 .matchsize = sizeof(struct xt_socket_mtinfo1),
257 .destroy = socket_mt_destroy,
258 .hooks = (1 << NF_INET_PRE_ROUTING) |
259 (1 << NF_INET_LOCAL_IN),
260 .me = THIS_MODULE,
261 },
262#endif
263 {
264 .name = "socket",
265 .revision = 2,
266 .family = NFPROTO_IPV4,
267 .match = socket_mt4_v1_v2_v3,
268 .checkentry = socket_mt_v2_check,
269 .destroy = socket_mt_destroy,
270 .matchsize = sizeof(struct xt_socket_mtinfo1),
271 .hooks = (1 << NF_INET_PRE_ROUTING) |
272 (1 << NF_INET_LOCAL_IN),
273 .me = THIS_MODULE,
274 },
275#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
276 {
277 .name = "socket",
278 .revision = 2,
279 .family = NFPROTO_IPV6,
280 .match = socket_mt6_v1_v2_v3,
281 .checkentry = socket_mt_v2_check,
282 .destroy = socket_mt_destroy,
283 .matchsize = sizeof(struct xt_socket_mtinfo1),
284 .hooks = (1 << NF_INET_PRE_ROUTING) |
285 (1 << NF_INET_LOCAL_IN),
286 .me = THIS_MODULE,
287 },
288#endif
289 {
290 .name = "socket",
291 .revision = 3,
292 .family = NFPROTO_IPV4,
293 .match = socket_mt4_v1_v2_v3,
294 .checkentry = socket_mt_v3_check,
295 .destroy = socket_mt_destroy,
296 .matchsize = sizeof(struct xt_socket_mtinfo1),
297 .hooks = (1 << NF_INET_PRE_ROUTING) |
298 (1 << NF_INET_LOCAL_IN),
299 .me = THIS_MODULE,
300 },
301#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
302 {
303 .name = "socket",
304 .revision = 3,
305 .family = NFPROTO_IPV6,
306 .match = socket_mt6_v1_v2_v3,
307 .checkentry = socket_mt_v3_check,
308 .destroy = socket_mt_destroy,
309 .matchsize = sizeof(struct xt_socket_mtinfo1),
310 .hooks = (1 << NF_INET_PRE_ROUTING) |
311 (1 << NF_INET_LOCAL_IN),
312 .me = THIS_MODULE,
313 },
314#endif
315};
316
317static int __init socket_mt_init(void)
318{
319 return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
320}
321
322static void __exit socket_mt_exit(void)
323{
324 xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
325}
326
327module_init(socket_mt_init);
328module_exit(socket_mt_exit);
329
330MODULE_LICENSE("GPL");
331MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
332MODULE_DESCRIPTION("x_tables socket match module");
333MODULE_ALIAS("ipt_socket");
334MODULE_ALIAS("ip6t_socket");