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TOMOYO Linux Cross Reference
Linux/net/netfilter/xt_TPROXY.c

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  1 /*
  2  * Transparent proxy support for Linux/iptables
  3  *
  4  * Copyright (c) 2006-2010 BalaBit IT Ltd.
  5  * Author: Balazs Scheidler, 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/ip.h>
 16 #include <net/checksum.h>
 17 #include <net/udp.h>
 18 #include <net/inet_sock.h>
 19 #include <linux/inetdevice.h>
 20 #include <linux/netfilter/x_tables.h>
 21 #include <linux/netfilter_ipv4/ip_tables.h>
 22 
 23 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
 24 
 25 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
 26 #define XT_TPROXY_HAVE_IPV6 1
 27 #include <net/if_inet6.h>
 28 #include <net/addrconf.h>
 29 #include <linux/netfilter_ipv6/ip6_tables.h>
 30 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 31 #endif
 32 
 33 #include <net/netfilter/nf_tproxy_core.h>
 34 #include <linux/netfilter/xt_TPROXY.h>
 35 
 36 static bool tproxy_sk_is_transparent(struct sock *sk)
 37 {
 38         if (sk->sk_state != TCP_TIME_WAIT) {
 39                 if (inet_sk(sk)->transparent)
 40                         return true;
 41                 sock_put(sk);
 42         } else {
 43                 if (inet_twsk(sk)->tw_transparent)
 44                         return true;
 45                 inet_twsk_put(inet_twsk(sk));
 46         }
 47         return false;
 48 }
 49 
 50 static inline __be32
 51 tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
 52 {
 53         struct in_device *indev;
 54         __be32 laddr;
 55 
 56         if (user_laddr)
 57                 return user_laddr;
 58 
 59         laddr = 0;
 60         rcu_read_lock();
 61         indev = __in_dev_get_rcu(skb->dev);
 62         for_primary_ifa(indev) {
 63                 laddr = ifa->ifa_local;
 64                 break;
 65         } endfor_ifa(indev);
 66         rcu_read_unlock();
 67 
 68         return laddr ? laddr : daddr;
 69 }
 70 
 71 /**
 72  * tproxy_handle_time_wait4() - handle IPv4 TCP TIME_WAIT reopen redirections
 73  * @skb:        The skb being processed.
 74  * @laddr:      IPv4 address to redirect to or zero.
 75  * @lport:      TCP port to redirect to or zero.
 76  * @sk:         The TIME_WAIT TCP socket found by the lookup.
 77  *
 78  * We have to handle SYN packets arriving to TIME_WAIT sockets
 79  * differently: instead of reopening the connection we should rather
 80  * redirect the new connection to the proxy if there's a listener
 81  * socket present.
 82  *
 83  * tproxy_handle_time_wait4() consumes the socket reference passed in.
 84  *
 85  * Returns the listener socket if there's one, the TIME_WAIT socket if
 86  * no such listener is found, or NULL if the TCP header is incomplete.
 87  */
 88 static struct sock *
 89 tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport,
 90                         struct sock *sk)
 91 {
 92         const struct iphdr *iph = ip_hdr(skb);
 93         struct tcphdr _hdr, *hp;
 94 
 95         hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 96         if (hp == NULL) {
 97                 inet_twsk_put(inet_twsk(sk));
 98                 return NULL;
 99         }
100 
101         if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
102                 /* SYN to a TIME_WAIT socket, we'd rather redirect it
103                  * to a listener socket if there's one */
104                 struct sock *sk2;
105 
106                 sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
107                                             iph->saddr, laddr ? laddr : iph->daddr,
108                                             hp->source, lport ? lport : hp->dest,
109                                             skb->dev, NFT_LOOKUP_LISTENER);
110                 if (sk2) {
111                         inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
112                         inet_twsk_put(inet_twsk(sk));
113                         sk = sk2;
114                 }
115         }
116 
117         return sk;
118 }
119 
120 static unsigned int
121 tproxy_tg4(struct sk_buff *skb, __be32 laddr, __be16 lport,
122            u_int32_t mark_mask, u_int32_t mark_value)
123 {
124         const struct iphdr *iph = ip_hdr(skb);
125         struct udphdr _hdr, *hp;
126         struct sock *sk;
127 
128         hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
129         if (hp == NULL)
130                 return NF_DROP;
131 
132         /* check if there's an ongoing connection on the packet
133          * addresses, this happens if the redirect already happened
134          * and the current packet belongs to an already established
135          * connection */
136         sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
137                                    iph->saddr, iph->daddr,
138                                    hp->source, hp->dest,
139                                    skb->dev, NFT_LOOKUP_ESTABLISHED);
140 
141         laddr = tproxy_laddr4(skb, laddr, iph->daddr);
142         if (!lport)
143                 lport = hp->dest;
144 
145         /* UDP has no TCP_TIME_WAIT state, so we never enter here */
146         if (sk && sk->sk_state == TCP_TIME_WAIT)
147                 /* reopening a TIME_WAIT connection needs special handling */
148                 sk = tproxy_handle_time_wait4(skb, laddr, lport, sk);
149         else if (!sk)
150                 /* no, there's no established connection, check if
151                  * there's a listener on the redirected addr/port */
152                 sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
153                                            iph->saddr, laddr,
154                                            hp->source, lport,
155                                            skb->dev, NFT_LOOKUP_LISTENER);
156 
157         /* NOTE: assign_sock consumes our sk reference */
158         if (sk && tproxy_sk_is_transparent(sk)) {
159                 /* This should be in a separate target, but we don't do multiple
160                    targets on the same rule yet */
161                 skb->mark = (skb->mark & ~mark_mask) ^ mark_value;
162 
163                 pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
164                          iph->protocol, &iph->daddr, ntohs(hp->dest),
165                          &laddr, ntohs(lport), skb->mark);
166 
167                 nf_tproxy_assign_sock(skb, sk);
168                 return NF_ACCEPT;
169         }
170 
171         pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
172                  iph->protocol, &iph->saddr, ntohs(hp->source),
173                  &iph->daddr, ntohs(hp->dest), skb->mark);
174         return NF_DROP;
175 }
176 
177 static unsigned int
178 tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
179 {
180         const struct xt_tproxy_target_info *tgi = par->targinfo;
181 
182         return tproxy_tg4(skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value);
183 }
184 
185 static unsigned int
186 tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
187 {
188         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
189 
190         return tproxy_tg4(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value);
191 }
192 
193 #ifdef XT_TPROXY_HAVE_IPV6
194 
195 static inline const struct in6_addr *
196 tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr,
197               const struct in6_addr *daddr)
198 {
199         struct inet6_dev *indev;
200         struct inet6_ifaddr *ifa;
201         struct in6_addr *laddr;
202 
203         if (!ipv6_addr_any(user_laddr))
204                 return user_laddr;
205         laddr = NULL;
206 
207         rcu_read_lock();
208         indev = __in6_dev_get(skb->dev);
209         if (indev)
210                 list_for_each_entry(ifa, &indev->addr_list, if_list) {
211                         if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED))
212                                 continue;
213 
214                         laddr = &ifa->addr;
215                         break;
216                 }
217         rcu_read_unlock();
218 
219         return laddr ? laddr : daddr;
220 }
221 
222 /**
223  * tproxy_handle_time_wait6() - handle IPv6 TCP TIME_WAIT reopen redirections
224  * @skb:        The skb being processed.
225  * @tproto:     Transport protocol.
226  * @thoff:      Transport protocol header offset.
227  * @par:        Iptables target parameters.
228  * @sk:         The TIME_WAIT TCP socket found by the lookup.
229  *
230  * We have to handle SYN packets arriving to TIME_WAIT sockets
231  * differently: instead of reopening the connection we should rather
232  * redirect the new connection to the proxy if there's a listener
233  * socket present.
234  *
235  * tproxy_handle_time_wait6() consumes the socket reference passed in.
236  *
237  * Returns the listener socket if there's one, the TIME_WAIT socket if
238  * no such listener is found, or NULL if the TCP header is incomplete.
239  */
240 static struct sock *
241 tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
242                          const struct xt_action_param *par,
243                          struct sock *sk)
244 {
245         const struct ipv6hdr *iph = ipv6_hdr(skb);
246         struct tcphdr _hdr, *hp;
247         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
248 
249         hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
250         if (hp == NULL) {
251                 inet_twsk_put(inet_twsk(sk));
252                 return NULL;
253         }
254 
255         if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
256                 /* SYN to a TIME_WAIT socket, we'd rather redirect it
257                  * to a listener socket if there's one */
258                 struct sock *sk2;
259 
260                 sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
261                                             &iph->saddr,
262                                             tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr),
263                                             hp->source,
264                                             tgi->lport ? tgi->lport : hp->dest,
265                                             skb->dev, NFT_LOOKUP_LISTENER);
266                 if (sk2) {
267                         inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
268                         inet_twsk_put(inet_twsk(sk));
269                         sk = sk2;
270                 }
271         }
272 
273         return sk;
274 }
275 
276 static unsigned int
277 tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
278 {
279         const struct ipv6hdr *iph = ipv6_hdr(skb);
280         const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
281         struct udphdr _hdr, *hp;
282         struct sock *sk;
283         const struct in6_addr *laddr;
284         __be16 lport;
285         int thoff;
286         int tproto;
287 
288         tproto = ipv6_find_hdr(skb, &thoff, -1, NULL);
289         if (tproto < 0) {
290                 pr_debug("unable to find transport header in IPv6 packet, dropping\n");
291                 return NF_DROP;
292         }
293 
294         hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
295         if (hp == NULL) {
296                 pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
297                 return NF_DROP;
298         }
299 
300         /* check if there's an ongoing connection on the packet
301          * addresses, this happens if the redirect already happened
302          * and the current packet belongs to an already established
303          * connection */
304         sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
305                                    &iph->saddr, &iph->daddr,
306                                    hp->source, hp->dest,
307                                    par->in, NFT_LOOKUP_ESTABLISHED);
308 
309         laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
310         lport = tgi->lport ? tgi->lport : hp->dest;
311 
312         /* UDP has no TCP_TIME_WAIT state, so we never enter here */
313         if (sk && sk->sk_state == TCP_TIME_WAIT)
314                 /* reopening a TIME_WAIT connection needs special handling */
315                 sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk);
316         else if (!sk)
317                 /* no there's no established connection, check if
318                  * there's a listener on the redirected addr/port */
319                 sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
320                                            &iph->saddr, laddr,
321                                            hp->source, lport,
322                                            par->in, NFT_LOOKUP_LISTENER);
323 
324         /* NOTE: assign_sock consumes our sk reference */
325         if (sk && tproxy_sk_is_transparent(sk)) {
326                 /* This should be in a separate target, but we don't do multiple
327                    targets on the same rule yet */
328                 skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
329 
330                 pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
331                          tproto, &iph->saddr, ntohs(hp->source),
332                          laddr, ntohs(lport), skb->mark);
333 
334                 nf_tproxy_assign_sock(skb, sk);
335                 return NF_ACCEPT;
336         }
337 
338         pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
339                  tproto, &iph->saddr, ntohs(hp->source),
340                  &iph->daddr, ntohs(hp->dest), skb->mark);
341 
342         return NF_DROP;
343 }
344 
345 static int tproxy_tg6_check(const struct xt_tgchk_param *par)
346 {
347         const struct ip6t_ip6 *i = par->entryinfo;
348 
349         if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
350             && !(i->flags & IP6T_INV_PROTO))
351                 return 0;
352 
353         pr_info("Can be used only in combination with "
354                 "either -p tcp or -p udp\n");
355         return -EINVAL;
356 }
357 #endif
358 
359 static int tproxy_tg4_check(const struct xt_tgchk_param *par)
360 {
361         const struct ipt_ip *i = par->entryinfo;
362 
363         if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
364             && !(i->invflags & IPT_INV_PROTO))
365                 return 0;
366 
367         pr_info("Can be used only in combination with "
368                 "either -p tcp or -p udp\n");
369         return -EINVAL;
370 }
371 
372 static struct xt_target tproxy_tg_reg[] __read_mostly = {
373         {
374                 .name           = "TPROXY",
375                 .family         = NFPROTO_IPV4,
376                 .table          = "mangle",
377                 .target         = tproxy_tg4_v0,
378                 .revision       = 0,
379                 .targetsize     = sizeof(struct xt_tproxy_target_info),
380                 .checkentry     = tproxy_tg4_check,
381                 .hooks          = 1 << NF_INET_PRE_ROUTING,
382                 .me             = THIS_MODULE,
383         },
384         {
385                 .name           = "TPROXY",
386                 .family         = NFPROTO_IPV4,
387                 .table          = "mangle",
388                 .target         = tproxy_tg4_v1,
389                 .revision       = 1,
390                 .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
391                 .checkentry     = tproxy_tg4_check,
392                 .hooks          = 1 << NF_INET_PRE_ROUTING,
393                 .me             = THIS_MODULE,
394         },
395 #ifdef XT_TPROXY_HAVE_IPV6
396         {
397                 .name           = "TPROXY",
398                 .family         = NFPROTO_IPV6,
399                 .table          = "mangle",
400                 .target         = tproxy_tg6_v1,
401                 .revision       = 1,
402                 .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
403                 .checkentry     = tproxy_tg6_check,
404                 .hooks          = 1 << NF_INET_PRE_ROUTING,
405                 .me             = THIS_MODULE,
406         },
407 #endif
408 
409 };
410 
411 static int __init tproxy_tg_init(void)
412 {
413         nf_defrag_ipv4_enable();
414 #ifdef XT_TPROXY_HAVE_IPV6
415         nf_defrag_ipv6_enable();
416 #endif
417 
418         return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
419 }
420 
421 static void __exit tproxy_tg_exit(void)
422 {
423         xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
424 }
425 
426 module_init(tproxy_tg_init);
427 module_exit(tproxy_tg_exit);
428 MODULE_LICENSE("GPL");
429 MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
430 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
431 MODULE_ALIAS("ipt_TPROXY");
432 MODULE_ALIAS("ip6t_TPROXY");
433 

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