1 /*
2 * Transparent proxy support for Linux/iptables
3 *
4 * Copyright (C) 2007-2008 BalaBit IT Ltd.
5 * Author: Krisztian Kovacs
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 *
11 */
12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13 #include <linux/module.h>
14 #include <linux/skbuff.h>
15 #include <linux/netfilter/x_tables.h>
16 #include <linux/netfilter_ipv4/ip_tables.h>
17 #include <net/tcp.h>
18 #include <net/udp.h>
19 #include <net/icmp.h>
20 #include <net/sock.h>
21 #include <net/inet_sock.h>
22 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
23
24 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
25 #define XT_SOCKET_HAVE_IPV6 1
26 #include <linux/netfilter_ipv6/ip6_tables.h>
27 #include <net/inet6_hashtables.h>
28 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
29 #endif
30
31 #include <linux/netfilter/xt_socket.h>
32
33 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
34 #define XT_SOCKET_HAVE_CONNTRACK 1
35 #include <net/netfilter/nf_conntrack.h>
36 #endif
37
38 static int
extract_icmp4_fields(const struct sk_buff * skb,u8 * protocol,__be32 * raddr,__be32 * laddr,__be16 * rport,__be16 * lport)39 extract_icmp4_fields(const struct sk_buff *skb,
40 u8 *protocol,
41 __be32 *raddr,
42 __be32 *laddr,
43 __be16 *rport,
44 __be16 *lport)
45 {
46 unsigned int outside_hdrlen = ip_hdrlen(skb);
47 struct iphdr *inside_iph, _inside_iph;
48 struct icmphdr *icmph, _icmph;
49 __be16 *ports, _ports[2];
50
51 icmph = skb_header_pointer(skb, outside_hdrlen,
52 sizeof(_icmph), &_icmph);
53 if (icmph == NULL)
54 return 1;
55
56 switch (icmph->type) {
57 case ICMP_DEST_UNREACH:
58 case ICMP_SOURCE_QUENCH:
59 case ICMP_REDIRECT:
60 case ICMP_TIME_EXCEEDED:
61 case ICMP_PARAMETERPROB:
62 break;
63 default:
64 return 1;
65 }
66
67 inside_iph = skb_header_pointer(skb, outside_hdrlen +
68 sizeof(struct icmphdr),
69 sizeof(_inside_iph), &_inside_iph);
70 if (inside_iph == NULL)
71 return 1;
72
73 if (inside_iph->protocol != IPPROTO_TCP &&
74 inside_iph->protocol != IPPROTO_UDP)
75 return 1;
76
77 ports = skb_header_pointer(skb, outside_hdrlen +
78 sizeof(struct icmphdr) +
79 (inside_iph->ihl << 2),
80 sizeof(_ports), &_ports);
81 if (ports == NULL)
82 return 1;
83
84 /* the inside IP packet is the one quoted from our side, thus
85 * its saddr is the local address */
86 *protocol = inside_iph->protocol;
87 *laddr = inside_iph->saddr;
88 *lport = ports[0];
89 *raddr = inside_iph->daddr;
90 *rport = ports[1];
91
92 return 0;
93 }
94
95 /* "socket" match based redirection (no specific rule)
96 * ===================================================
97 *
98 * There are connections with dynamic endpoints (e.g. FTP data
99 * connection) that the user is unable to add explicit rules
100 * for. These are taken care of by a generic "socket" rule. It is
101 * assumed that the proxy application is trusted to open such
102 * connections without explicit iptables rule (except of course the
103 * generic 'socket' rule). In this case the following sockets are
104 * matched in preference order:
105 *
106 * - match: if there's a fully established connection matching the
107 * _packet_ tuple
108 *
109 * - match: if there's a non-zero bound listener (possibly with a
110 * non-local address) We don't accept zero-bound listeners, since
111 * then local services could intercept traffic going through the
112 * box.
113 */
114 static struct sock *
xt_socket_get_sock_v4(struct net * net,const u8 protocol,const __be32 saddr,const __be32 daddr,const __be16 sport,const __be16 dport,const struct net_device * in)115 xt_socket_get_sock_v4(struct net *net, const u8 protocol,
116 const __be32 saddr, const __be32 daddr,
117 const __be16 sport, const __be16 dport,
118 const struct net_device *in)
119 {
120 switch (protocol) {
121 case IPPROTO_TCP:
122 return __inet_lookup(net, &tcp_hashinfo,
123 saddr, sport, daddr, dport,
124 in->ifindex);
125 case IPPROTO_UDP:
126 return udp4_lib_lookup(net, saddr, sport, daddr, dport,
127 in->ifindex);
128 }
129 return NULL;
130 }
131
xt_socket_sk_is_transparent(struct sock * sk)132 static bool xt_socket_sk_is_transparent(struct sock *sk)
133 {
134 switch (sk->sk_state) {
135 case TCP_TIME_WAIT:
136 return inet_twsk(sk)->tw_transparent;
137
138 case TCP_NEW_SYN_RECV:
139 return inet_rsk(inet_reqsk(sk))->no_srccheck;
140
141 default:
142 return inet_sk(sk)->transparent;
143 }
144 }
145
xt_socket_lookup_slow_v4(const struct sk_buff * skb,const struct net_device * indev)146 static struct sock *xt_socket_lookup_slow_v4(const struct sk_buff *skb,
147 const struct net_device *indev)
148 {
149 const struct iphdr *iph = ip_hdr(skb);
150 __be32 uninitialized_var(daddr), uninitialized_var(saddr);
151 __be16 uninitialized_var(dport), uninitialized_var(sport);
152 u8 uninitialized_var(protocol);
153 #ifdef XT_SOCKET_HAVE_CONNTRACK
154 struct nf_conn const *ct;
155 enum ip_conntrack_info ctinfo;
156 #endif
157
158 if (iph->protocol == IPPROTO_UDP || iph->protocol == IPPROTO_TCP) {
159 struct udphdr _hdr, *hp;
160
161 hp = skb_header_pointer(skb, ip_hdrlen(skb),
162 sizeof(_hdr), &_hdr);
163 if (hp == NULL)
164 return NULL;
165
166 protocol = iph->protocol;
167 saddr = iph->saddr;
168 sport = hp->source;
169 daddr = iph->daddr;
170 dport = hp->dest;
171
172 } else if (iph->protocol == IPPROTO_ICMP) {
173 if (extract_icmp4_fields(skb, &protocol, &saddr, &daddr,
174 &sport, &dport))
175 return NULL;
176 } else {
177 return NULL;
178 }
179
180 #ifdef XT_SOCKET_HAVE_CONNTRACK
181 /* Do the lookup with the original socket address in
182 * case this is a reply packet of an established
183 * SNAT-ted connection.
184 */
185 ct = nf_ct_get(skb, &ctinfo);
186 if (ct && !nf_ct_is_untracked(ct) &&
187 ((iph->protocol != IPPROTO_ICMP &&
188 ctinfo == IP_CT_ESTABLISHED_REPLY) ||
189 (iph->protocol == IPPROTO_ICMP &&
190 ctinfo == IP_CT_RELATED_REPLY)) &&
191 (ct->status & IPS_SRC_NAT_DONE)) {
192
193 daddr = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip;
194 dport = (iph->protocol == IPPROTO_TCP) ?
195 ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.tcp.port :
196 ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.udp.port;
197 }
198 #endif
199
200 return xt_socket_get_sock_v4(dev_net(skb->dev), protocol, saddr, daddr,
201 sport, dport, indev);
202 }
203
204 static bool
socket_match(const struct sk_buff * skb,struct xt_action_param * par,const struct xt_socket_mtinfo1 * info)205 socket_match(const struct sk_buff *skb, struct xt_action_param *par,
206 const struct xt_socket_mtinfo1 *info)
207 {
208 struct sock *sk = skb->sk;
209
210 if (!sk)
211 sk = xt_socket_lookup_slow_v4(skb, par->in);
212 if (sk) {
213 bool wildcard;
214 bool transparent = true;
215
216 /* Ignore sockets listening on INADDR_ANY,
217 * unless XT_SOCKET_NOWILDCARD is set
218 */
219 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
220 sk_fullsock(sk) &&
221 inet_sk(sk)->inet_rcv_saddr == 0);
222
223 /* Ignore non-transparent sockets,
224 * if XT_SOCKET_TRANSPARENT is used
225 */
226 if (info->flags & XT_SOCKET_TRANSPARENT)
227 transparent = xt_socket_sk_is_transparent(sk);
228
229 if (sk != skb->sk)
230 sock_gen_put(sk);
231
232 if (wildcard || !transparent)
233 sk = NULL;
234 }
235
236 return sk != NULL;
237 }
238
239 static bool
socket_mt4_v0(const struct sk_buff * skb,struct xt_action_param * par)240 socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
241 {
242 static struct xt_socket_mtinfo1 xt_info_v0 = {
243 .flags = 0,
244 };
245
246 return socket_match(skb, par, &xt_info_v0);
247 }
248
249 static bool
socket_mt4_v1_v2(const struct sk_buff * skb,struct xt_action_param * par)250 socket_mt4_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
251 {
252 return socket_match(skb, par, par->matchinfo);
253 }
254
255 #ifdef XT_SOCKET_HAVE_IPV6
256
257 static int
extract_icmp6_fields(const struct sk_buff * skb,unsigned int outside_hdrlen,int * protocol,const struct in6_addr ** raddr,const struct in6_addr ** laddr,__be16 * rport,__be16 * lport,struct ipv6hdr * ipv6_var)258 extract_icmp6_fields(const struct sk_buff *skb,
259 unsigned int outside_hdrlen,
260 int *protocol,
261 const struct in6_addr **raddr,
262 const struct in6_addr **laddr,
263 __be16 *rport,
264 __be16 *lport,
265 struct ipv6hdr *ipv6_var)
266 {
267 const struct ipv6hdr *inside_iph;
268 struct icmp6hdr *icmph, _icmph;
269 __be16 *ports, _ports[2];
270 u8 inside_nexthdr;
271 __be16 inside_fragoff;
272 int inside_hdrlen;
273
274 icmph = skb_header_pointer(skb, outside_hdrlen,
275 sizeof(_icmph), &_icmph);
276 if (icmph == NULL)
277 return 1;
278
279 if (icmph->icmp6_type & ICMPV6_INFOMSG_MASK)
280 return 1;
281
282 inside_iph = skb_header_pointer(skb, outside_hdrlen + sizeof(_icmph),
283 sizeof(*ipv6_var), ipv6_var);
284 if (inside_iph == NULL)
285 return 1;
286 inside_nexthdr = inside_iph->nexthdr;
287
288 inside_hdrlen = ipv6_skip_exthdr(skb, outside_hdrlen + sizeof(_icmph) +
289 sizeof(*ipv6_var),
290 &inside_nexthdr, &inside_fragoff);
291 if (inside_hdrlen < 0)
292 return 1; /* hjm: Packet has no/incomplete transport layer headers. */
293
294 if (inside_nexthdr != IPPROTO_TCP &&
295 inside_nexthdr != IPPROTO_UDP)
296 return 1;
297
298 ports = skb_header_pointer(skb, inside_hdrlen,
299 sizeof(_ports), &_ports);
300 if (ports == NULL)
301 return 1;
302
303 /* the inside IP packet is the one quoted from our side, thus
304 * its saddr is the local address */
305 *protocol = inside_nexthdr;
306 *laddr = &inside_iph->saddr;
307 *lport = ports[0];
308 *raddr = &inside_iph->daddr;
309 *rport = ports[1];
310
311 return 0;
312 }
313
314 static struct sock *
xt_socket_get_sock_v6(struct net * net,const u8 protocol,const struct in6_addr * saddr,const struct in6_addr * daddr,const __be16 sport,const __be16 dport,const struct net_device * in)315 xt_socket_get_sock_v6(struct net *net, const u8 protocol,
316 const struct in6_addr *saddr, const struct in6_addr *daddr,
317 const __be16 sport, const __be16 dport,
318 const struct net_device *in)
319 {
320 switch (protocol) {
321 case IPPROTO_TCP:
322 return inet6_lookup(net, &tcp_hashinfo,
323 saddr, sport, daddr, dport,
324 in->ifindex);
325 case IPPROTO_UDP:
326 return udp6_lib_lookup(net, saddr, sport, daddr, dport,
327 in->ifindex);
328 }
329
330 return NULL;
331 }
332
xt_socket_lookup_slow_v6(const struct sk_buff * skb,const struct net_device * indev)333 static struct sock *xt_socket_lookup_slow_v6(const struct sk_buff *skb,
334 const struct net_device *indev)
335 {
336 __be16 uninitialized_var(dport), uninitialized_var(sport);
337 const struct in6_addr *daddr = NULL, *saddr = NULL;
338 struct ipv6hdr *iph = ipv6_hdr(skb);
339 int thoff = 0, tproto;
340
341 tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
342 if (tproto < 0) {
343 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
344 return NULL;
345 }
346
347 if (tproto == IPPROTO_UDP || tproto == IPPROTO_TCP) {
348 struct udphdr _hdr, *hp;
349
350 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
351 if (hp == NULL)
352 return NULL;
353
354 saddr = &iph->saddr;
355 sport = hp->source;
356 daddr = &iph->daddr;
357 dport = hp->dest;
358
359 } else if (tproto == IPPROTO_ICMPV6) {
360 struct ipv6hdr ipv6_var;
361
362 if (extract_icmp6_fields(skb, thoff, &tproto, &saddr, &daddr,
363 &sport, &dport, &ipv6_var))
364 return NULL;
365 } else {
366 return NULL;
367 }
368
369 return xt_socket_get_sock_v6(dev_net(skb->dev), tproto, saddr, daddr,
370 sport, dport, indev);
371 }
372
373 static bool
socket_mt6_v1_v2(const struct sk_buff * skb,struct xt_action_param * par)374 socket_mt6_v1_v2(const struct sk_buff *skb, struct xt_action_param *par)
375 {
376 const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
377 struct sock *sk = skb->sk;
378
379 if (!sk)
380 sk = xt_socket_lookup_slow_v6(skb, par->in);
381 if (sk) {
382 bool wildcard;
383 bool transparent = true;
384
385 /* Ignore sockets listening on INADDR_ANY
386 * unless XT_SOCKET_NOWILDCARD is set
387 */
388 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
389 sk_fullsock(sk) &&
390 ipv6_addr_any(&sk->sk_v6_rcv_saddr));
391
392 /* Ignore non-transparent sockets,
393 * if XT_SOCKET_TRANSPARENT is used
394 */
395 if (info->flags & XT_SOCKET_TRANSPARENT)
396 transparent = xt_socket_sk_is_transparent(sk);
397
398 if (sk != skb->sk)
399 sock_gen_put(sk);
400
401 if (wildcard || !transparent)
402 sk = NULL;
403 }
404
405 return sk != NULL;
406 }
407 #endif
408
socket_mt_v1_check(const struct xt_mtchk_param * par)409 static int socket_mt_v1_check(const struct xt_mtchk_param *par)
410 {
411 const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
412
413 if (info->flags & ~XT_SOCKET_FLAGS_V1) {
414 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V1);
415 return -EINVAL;
416 }
417 return 0;
418 }
419
socket_mt_v2_check(const struct xt_mtchk_param * par)420 static int socket_mt_v2_check(const struct xt_mtchk_param *par)
421 {
422 const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
423
424 if (info->flags & ~XT_SOCKET_FLAGS_V2) {
425 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V2);
426 return -EINVAL;
427 }
428 return 0;
429 }
430
431 static struct xt_match socket_mt_reg[] __read_mostly = {
432 {
433 .name = "socket",
434 .revision = 0,
435 .family = NFPROTO_IPV4,
436 .match = socket_mt4_v0,
437 .hooks = (1 << NF_INET_PRE_ROUTING) |
438 (1 << NF_INET_LOCAL_IN),
439 .me = THIS_MODULE,
440 },
441 {
442 .name = "socket",
443 .revision = 1,
444 .family = NFPROTO_IPV4,
445 .match = socket_mt4_v1_v2,
446 .checkentry = socket_mt_v1_check,
447 .matchsize = sizeof(struct xt_socket_mtinfo1),
448 .hooks = (1 << NF_INET_PRE_ROUTING) |
449 (1 << NF_INET_LOCAL_IN),
450 .me = THIS_MODULE,
451 },
452 #ifdef XT_SOCKET_HAVE_IPV6
453 {
454 .name = "socket",
455 .revision = 1,
456 .family = NFPROTO_IPV6,
457 .match = socket_mt6_v1_v2,
458 .checkentry = socket_mt_v1_check,
459 .matchsize = sizeof(struct xt_socket_mtinfo1),
460 .hooks = (1 << NF_INET_PRE_ROUTING) |
461 (1 << NF_INET_LOCAL_IN),
462 .me = THIS_MODULE,
463 },
464 #endif
465 {
466 .name = "socket",
467 .revision = 2,
468 .family = NFPROTO_IPV4,
469 .match = socket_mt4_v1_v2,
470 .checkentry = socket_mt_v2_check,
471 .matchsize = sizeof(struct xt_socket_mtinfo1),
472 .hooks = (1 << NF_INET_PRE_ROUTING) |
473 (1 << NF_INET_LOCAL_IN),
474 .me = THIS_MODULE,
475 },
476 #ifdef XT_SOCKET_HAVE_IPV6
477 {
478 .name = "socket",
479 .revision = 2,
480 .family = NFPROTO_IPV6,
481 .match = socket_mt6_v1_v2,
482 .checkentry = socket_mt_v2_check,
483 .matchsize = sizeof(struct xt_socket_mtinfo1),
484 .hooks = (1 << NF_INET_PRE_ROUTING) |
485 (1 << NF_INET_LOCAL_IN),
486 .me = THIS_MODULE,
487 },
488 #endif
489 };
490
socket_mt_init(void)491 static int __init socket_mt_init(void)
492 {
493 nf_defrag_ipv4_enable();
494 #ifdef XT_SOCKET_HAVE_IPV6
495 nf_defrag_ipv6_enable();
496 #endif
497
498 return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
499 }
500
socket_mt_exit(void)501 static void __exit socket_mt_exit(void)
502 {
503 xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
504 }
505
506 module_init(socket_mt_init);
507 module_exit(socket_mt_exit);
508
509 MODULE_LICENSE("GPL");
510 MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
511 MODULE_DESCRIPTION("x_tables socket match module");
512 MODULE_ALIAS("ipt_socket");
513 MODULE_ALIAS("ip6t_socket");
514