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Linux/net/netfilter/xt_socket.c

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  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
 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 *
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 
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 
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
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
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
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
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 *
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 
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
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 
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 
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 
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 
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 

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