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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 sk_buff *pskb = (struct sk_buff *)skb;
209         struct sock *sk = skb->sk;
210 
211         if (!sk)
212                 sk = xt_socket_lookup_slow_v4(skb, par->in);
213         if (sk) {
214                 bool wildcard;
215                 bool transparent = true;
216 
217                 /* Ignore sockets listening on INADDR_ANY,
218                  * unless XT_SOCKET_NOWILDCARD is set
219                  */
220                 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
221                             sk_fullsock(sk) &&
222                             inet_sk(sk)->inet_rcv_saddr == 0);
223 
224                 /* Ignore non-transparent sockets,
225                  * if XT_SOCKET_TRANSPARENT is used
226                  */
227                 if (info->flags & XT_SOCKET_TRANSPARENT)
228                         transparent = xt_socket_sk_is_transparent(sk);
229 
230                 if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
231                     transparent)
232                         pskb->mark = sk->sk_mark;
233 
234                 if (sk != skb->sk)
235                         sock_gen_put(sk);
236 
237                 if (wildcard || !transparent)
238                         sk = NULL;
239         }
240 
241         return sk != NULL;
242 }
243 
244 static bool
245 socket_mt4_v0(const struct sk_buff *skb, struct xt_action_param *par)
246 {
247         static struct xt_socket_mtinfo1 xt_info_v0 = {
248                 .flags = 0,
249         };
250 
251         return socket_match(skb, par, &xt_info_v0);
252 }
253 
254 static bool
255 socket_mt4_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
256 {
257         return socket_match(skb, par, par->matchinfo);
258 }
259 
260 #ifdef XT_SOCKET_HAVE_IPV6
261 
262 static int
263 extract_icmp6_fields(const struct sk_buff *skb,
264                      unsigned int outside_hdrlen,
265                      int *protocol,
266                      const struct in6_addr **raddr,
267                      const struct in6_addr **laddr,
268                      __be16 *rport,
269                      __be16 *lport,
270                      struct ipv6hdr *ipv6_var)
271 {
272         const struct ipv6hdr *inside_iph;
273         struct icmp6hdr *icmph, _icmph;
274         __be16 *ports, _ports[2];
275         u8 inside_nexthdr;
276         __be16 inside_fragoff;
277         int inside_hdrlen;
278 
279         icmph = skb_header_pointer(skb, outside_hdrlen,
280                                    sizeof(_icmph), &_icmph);
281         if (icmph == NULL)
282                 return 1;
283 
284         if (icmph->icmp6_type & ICMPV6_INFOMSG_MASK)
285                 return 1;
286 
287         inside_iph = skb_header_pointer(skb, outside_hdrlen + sizeof(_icmph),
288                                         sizeof(*ipv6_var), ipv6_var);
289         if (inside_iph == NULL)
290                 return 1;
291         inside_nexthdr = inside_iph->nexthdr;
292 
293         inside_hdrlen = ipv6_skip_exthdr(skb, outside_hdrlen + sizeof(_icmph) +
294                                               sizeof(*ipv6_var),
295                                          &inside_nexthdr, &inside_fragoff);
296         if (inside_hdrlen < 0)
297                 return 1; /* hjm: Packet has no/incomplete transport layer headers. */
298 
299         if (inside_nexthdr != IPPROTO_TCP &&
300             inside_nexthdr != IPPROTO_UDP)
301                 return 1;
302 
303         ports = skb_header_pointer(skb, inside_hdrlen,
304                                    sizeof(_ports), &_ports);
305         if (ports == NULL)
306                 return 1;
307 
308         /* the inside IP packet is the one quoted from our side, thus
309          * its saddr is the local address */
310         *protocol = inside_nexthdr;
311         *laddr = &inside_iph->saddr;
312         *lport = ports[0];
313         *raddr = &inside_iph->daddr;
314         *rport = ports[1];
315 
316         return 0;
317 }
318 
319 static struct sock *
320 xt_socket_get_sock_v6(struct net *net, const u8 protocol,
321                       const struct in6_addr *saddr, const struct in6_addr *daddr,
322                       const __be16 sport, const __be16 dport,
323                       const struct net_device *in)
324 {
325         switch (protocol) {
326         case IPPROTO_TCP:
327                 return inet6_lookup(net, &tcp_hashinfo,
328                                     saddr, sport, daddr, dport,
329                                     in->ifindex);
330         case IPPROTO_UDP:
331                 return udp6_lib_lookup(net, saddr, sport, daddr, dport,
332                                        in->ifindex);
333         }
334 
335         return NULL;
336 }
337 
338 static struct sock *xt_socket_lookup_slow_v6(const struct sk_buff *skb,
339                                              const struct net_device *indev)
340 {
341         __be16 uninitialized_var(dport), uninitialized_var(sport);
342         const struct in6_addr *daddr = NULL, *saddr = NULL;
343         struct ipv6hdr *iph = ipv6_hdr(skb);
344         int thoff = 0, tproto;
345 
346         tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
347         if (tproto < 0) {
348                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
349                 return NULL;
350         }
351 
352         if (tproto == IPPROTO_UDP || tproto == IPPROTO_TCP) {
353                 struct udphdr _hdr, *hp;
354 
355                 hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
356                 if (hp == NULL)
357                         return NULL;
358 
359                 saddr = &iph->saddr;
360                 sport = hp->source;
361                 daddr = &iph->daddr;
362                 dport = hp->dest;
363 
364         } else if (tproto == IPPROTO_ICMPV6) {
365                 struct ipv6hdr ipv6_var;
366 
367                 if (extract_icmp6_fields(skb, thoff, &tproto, &saddr, &daddr,
368                                          &sport, &dport, &ipv6_var))
369                         return NULL;
370         } else {
371                 return NULL;
372         }
373 
374         return xt_socket_get_sock_v6(dev_net(skb->dev), tproto, saddr, daddr,
375                                      sport, dport, indev);
376 }
377 
378 static bool
379 socket_mt6_v1_v2_v3(const struct sk_buff *skb, struct xt_action_param *par)
380 {
381         const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
382         struct sk_buff *pskb = (struct sk_buff *)skb;
383         struct sock *sk = skb->sk;
384 
385         if (!sk)
386                 sk = xt_socket_lookup_slow_v6(skb, par->in);
387         if (sk) {
388                 bool wildcard;
389                 bool transparent = true;
390 
391                 /* Ignore sockets listening on INADDR_ANY
392                  * unless XT_SOCKET_NOWILDCARD is set
393                  */
394                 wildcard = (!(info->flags & XT_SOCKET_NOWILDCARD) &&
395                             sk_fullsock(sk) &&
396                             ipv6_addr_any(&sk->sk_v6_rcv_saddr));
397 
398                 /* Ignore non-transparent sockets,
399                  * if XT_SOCKET_TRANSPARENT is used
400                  */
401                 if (info->flags & XT_SOCKET_TRANSPARENT)
402                         transparent = xt_socket_sk_is_transparent(sk);
403 
404                 if (info->flags & XT_SOCKET_RESTORESKMARK && !wildcard &&
405                     transparent)
406                         pskb->mark = sk->sk_mark;
407 
408                 if (sk != skb->sk)
409                         sock_gen_put(sk);
410 
411                 if (wildcard || !transparent)
412                         sk = NULL;
413         }
414 
415         return sk != NULL;
416 }
417 #endif
418 
419 static int socket_mt_v1_check(const struct xt_mtchk_param *par)
420 {
421         const struct xt_socket_mtinfo1 *info = (struct xt_socket_mtinfo1 *) par->matchinfo;
422 
423         if (info->flags & ~XT_SOCKET_FLAGS_V1) {
424                 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V1);
425                 return -EINVAL;
426         }
427         return 0;
428 }
429 
430 static int socket_mt_v2_check(const struct xt_mtchk_param *par)
431 {
432         const struct xt_socket_mtinfo2 *info = (struct xt_socket_mtinfo2 *) par->matchinfo;
433 
434         if (info->flags & ~XT_SOCKET_FLAGS_V2) {
435                 pr_info("unknown flags 0x%x\n", info->flags & ~XT_SOCKET_FLAGS_V2);
436                 return -EINVAL;
437         }
438         return 0;
439 }
440 
441 static int socket_mt_v3_check(const struct xt_mtchk_param *par)
442 {
443         const struct xt_socket_mtinfo3 *info =
444                                     (struct xt_socket_mtinfo3 *)par->matchinfo;
445 
446         if (info->flags & ~XT_SOCKET_FLAGS_V3) {
447                 pr_info("unknown flags 0x%x\n",
448                         info->flags & ~XT_SOCKET_FLAGS_V3);
449                 return -EINVAL;
450         }
451         return 0;
452 }
453 
454 static struct xt_match socket_mt_reg[] __read_mostly = {
455         {
456                 .name           = "socket",
457                 .revision       = 0,
458                 .family         = NFPROTO_IPV4,
459                 .match          = socket_mt4_v0,
460                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
461                                   (1 << NF_INET_LOCAL_IN),
462                 .me             = THIS_MODULE,
463         },
464         {
465                 .name           = "socket",
466                 .revision       = 1,
467                 .family         = NFPROTO_IPV4,
468                 .match          = socket_mt4_v1_v2_v3,
469                 .checkentry     = socket_mt_v1_check,
470                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
471                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
472                                   (1 << NF_INET_LOCAL_IN),
473                 .me             = THIS_MODULE,
474         },
475 #ifdef XT_SOCKET_HAVE_IPV6
476         {
477                 .name           = "socket",
478                 .revision       = 1,
479                 .family         = NFPROTO_IPV6,
480                 .match          = socket_mt6_v1_v2_v3,
481                 .checkentry     = socket_mt_v1_check,
482                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
483                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
484                                   (1 << NF_INET_LOCAL_IN),
485                 .me             = THIS_MODULE,
486         },
487 #endif
488         {
489                 .name           = "socket",
490                 .revision       = 2,
491                 .family         = NFPROTO_IPV4,
492                 .match          = socket_mt4_v1_v2_v3,
493                 .checkentry     = socket_mt_v2_check,
494                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
495                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
496                                   (1 << NF_INET_LOCAL_IN),
497                 .me             = THIS_MODULE,
498         },
499 #ifdef XT_SOCKET_HAVE_IPV6
500         {
501                 .name           = "socket",
502                 .revision       = 2,
503                 .family         = NFPROTO_IPV6,
504                 .match          = socket_mt6_v1_v2_v3,
505                 .checkentry     = socket_mt_v2_check,
506                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
507                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
508                                   (1 << NF_INET_LOCAL_IN),
509                 .me             = THIS_MODULE,
510         },
511 #endif
512         {
513                 .name           = "socket",
514                 .revision       = 3,
515                 .family         = NFPROTO_IPV4,
516                 .match          = socket_mt4_v1_v2_v3,
517                 .checkentry     = socket_mt_v3_check,
518                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
519                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
520                                   (1 << NF_INET_LOCAL_IN),
521                 .me             = THIS_MODULE,
522         },
523 #ifdef XT_SOCKET_HAVE_IPV6
524         {
525                 .name           = "socket",
526                 .revision       = 3,
527                 .family         = NFPROTO_IPV6,
528                 .match          = socket_mt6_v1_v2_v3,
529                 .checkentry     = socket_mt_v3_check,
530                 .matchsize      = sizeof(struct xt_socket_mtinfo1),
531                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
532                                   (1 << NF_INET_LOCAL_IN),
533                 .me             = THIS_MODULE,
534         },
535 #endif
536 };
537 
538 static int __init socket_mt_init(void)
539 {
540         nf_defrag_ipv4_enable();
541 #ifdef XT_SOCKET_HAVE_IPV6
542         nf_defrag_ipv6_enable();
543 #endif
544 
545         return xt_register_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
546 }
547 
548 static void __exit socket_mt_exit(void)
549 {
550         xt_unregister_matches(socket_mt_reg, ARRAY_SIZE(socket_mt_reg));
551 }
552 
553 module_init(socket_mt_init);
554 module_exit(socket_mt_exit);
555 
556 MODULE_LICENSE("GPL");
557 MODULE_AUTHOR("Krisztian Kovacs, Balazs Scheidler");
558 MODULE_DESCRIPTION("x_tables socket match module");
559 MODULE_ALIAS("ipt_socket");
560 MODULE_ALIAS("ip6t_socket");
561 

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