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l2tp_ip.c
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1 /*
2  * L2TPv3 IP encapsulation support
3  *
4  * Copyright (c) 2008,2009,2010 Katalix Systems Ltd
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License
8  * as published by the Free Software Foundation; either version
9  * 2 of the License, or (at your option) any later version.
10  */
11 
12 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
13 
14 #include <linux/icmp.h>
15 #include <linux/module.h>
16 #include <linux/skbuff.h>
17 #include <linux/random.h>
18 #include <linux/socket.h>
19 #include <linux/l2tp.h>
20 #include <linux/in.h>
21 #include <net/sock.h>
22 #include <net/ip.h>
23 #include <net/icmp.h>
24 #include <net/udp.h>
25 #include <net/inet_common.h>
26 #include <net/inet_hashtables.h>
27 #include <net/tcp_states.h>
28 #include <net/protocol.h>
29 #include <net/xfrm.h>
30 
31 #include "l2tp_core.h"
32 
33 struct l2tp_ip_sock {
34  /* inet_sock has to be the first member of l2tp_ip_sock */
35  struct inet_sock inet;
36 
39 };
40 
41 static DEFINE_RWLOCK(l2tp_ip_lock);
42 static struct hlist_head l2tp_ip_table;
43 static struct hlist_head l2tp_ip_bind_table;
44 
45 static inline struct l2tp_ip_sock *l2tp_ip_sk(const struct sock *sk)
46 {
47  return (struct l2tp_ip_sock *)sk;
48 }
49 
50 static struct sock *__l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
51 {
52  struct hlist_node *node;
53  struct sock *sk;
54 
55  sk_for_each_bound(sk, node, &l2tp_ip_bind_table) {
56  struct inet_sock *inet = inet_sk(sk);
57  struct l2tp_ip_sock *l2tp = l2tp_ip_sk(sk);
58 
59  if (l2tp == NULL)
60  continue;
61 
62  if ((l2tp->conn_id == tunnel_id) &&
63  net_eq(sock_net(sk), net) &&
64  !(inet->inet_rcv_saddr && inet->inet_rcv_saddr != laddr) &&
65  !(sk->sk_bound_dev_if && sk->sk_bound_dev_if != dif))
66  goto found;
67  }
68 
69  sk = NULL;
70 found:
71  return sk;
72 }
73 
74 static inline struct sock *l2tp_ip_bind_lookup(struct net *net, __be32 laddr, int dif, u32 tunnel_id)
75 {
76  struct sock *sk = __l2tp_ip_bind_lookup(net, laddr, dif, tunnel_id);
77  if (sk)
78  sock_hold(sk);
79 
80  return sk;
81 }
82 
83 /* When processing receive frames, there are two cases to
84  * consider. Data frames consist of a non-zero session-id and an
85  * optional cookie. Control frames consist of a regular L2TP header
86  * preceded by 32-bits of zeros.
87  *
88  * L2TPv3 Session Header Over IP
89  *
90  * 0 1 2 3
91  * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
92  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
93  * | Session ID |
94  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
95  * | Cookie (optional, maximum 64 bits)...
96  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
97  * |
98  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
99  *
100  * L2TPv3 Control Message Header Over IP
101  *
102  * 0 1 2 3
103  * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
104  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
105  * | (32 bits of zeros) |
106  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
107  * |T|L|x|x|S|x|x|x|x|x|x|x| Ver | Length |
108  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
109  * | Control Connection ID |
110  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
111  * | Ns | Nr |
112  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
113  *
114  * All control frames are passed to userspace.
115  */
116 static int l2tp_ip_recv(struct sk_buff *skb)
117 {
118  struct sock *sk;
119  u32 session_id;
120  u32 tunnel_id;
121  unsigned char *ptr, *optr;
122  struct l2tp_session *session;
123  struct l2tp_tunnel *tunnel = NULL;
124  int length;
125 
126  /* Point to L2TP header */
127  optr = ptr = skb->data;
128 
129  if (!pskb_may_pull(skb, 4))
130  goto discard;
131 
132  session_id = ntohl(*((__be32 *) ptr));
133  ptr += 4;
134 
135  /* RFC3931: L2TP/IP packets have the first 4 bytes containing
136  * the session_id. If it is 0, the packet is a L2TP control
137  * frame and the session_id value can be discarded.
138  */
139  if (session_id == 0) {
140  __skb_pull(skb, 4);
141  goto pass_up;
142  }
143 
144  /* Ok, this is a data packet. Lookup the session. */
145  session = l2tp_session_find(&init_net, NULL, session_id);
146  if (session == NULL)
147  goto discard;
148 
149  tunnel = session->tunnel;
150  if (tunnel == NULL)
151  goto discard;
152 
153  /* Trace packet contents, if enabled */
154  if (tunnel->debug & L2TP_MSG_DATA) {
155  length = min(32u, skb->len);
156  if (!pskb_may_pull(skb, length))
157  goto discard;
158 
159  pr_debug("%s: ip recv\n", tunnel->name);
160  print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
161  }
162 
163  l2tp_recv_common(session, skb, ptr, optr, 0, skb->len, tunnel->recv_payload_hook);
164 
165  return 0;
166 
167 pass_up:
168  /* Get the tunnel_id from the L2TP header */
169  if (!pskb_may_pull(skb, 12))
170  goto discard;
171 
172  if ((skb->data[0] & 0xc0) != 0xc0)
173  goto discard;
174 
175  tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
176  tunnel = l2tp_tunnel_find(&init_net, tunnel_id);
177  if (tunnel != NULL)
178  sk = tunnel->sock;
179  else {
180  struct iphdr *iph = (struct iphdr *) skb_network_header(skb);
181 
182  read_lock_bh(&l2tp_ip_lock);
183  sk = __l2tp_ip_bind_lookup(&init_net, iph->daddr, 0, tunnel_id);
184  read_unlock_bh(&l2tp_ip_lock);
185  }
186 
187  if (sk == NULL)
188  goto discard;
189 
190  sock_hold(sk);
191 
192  if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
193  goto discard_put;
194 
195  nf_reset(skb);
196 
197  return sk_receive_skb(sk, skb, 1);
198 
199 discard_put:
200  sock_put(sk);
201 
202 discard:
203  kfree_skb(skb);
204  return 0;
205 }
206 
207 static int l2tp_ip_open(struct sock *sk)
208 {
209  /* Prevent autobind. We don't have ports. */
210  inet_sk(sk)->inet_num = IPPROTO_L2TP;
211 
212  write_lock_bh(&l2tp_ip_lock);
213  sk_add_node(sk, &l2tp_ip_table);
214  write_unlock_bh(&l2tp_ip_lock);
215 
216  return 0;
217 }
218 
219 static void l2tp_ip_close(struct sock *sk, long timeout)
220 {
221  write_lock_bh(&l2tp_ip_lock);
222  hlist_del_init(&sk->sk_bind_node);
223  sk_del_node_init(sk);
224  write_unlock_bh(&l2tp_ip_lock);
225  sk_common_release(sk);
226 }
227 
228 static void l2tp_ip_destroy_sock(struct sock *sk)
229 {
230  struct sk_buff *skb;
231 
232  while ((skb = __skb_dequeue_tail(&sk->sk_write_queue)) != NULL)
233  kfree_skb(skb);
234 
236 }
237 
238 static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
239 {
240  struct inet_sock *inet = inet_sk(sk);
241  struct sockaddr_l2tpip *addr = (struct sockaddr_l2tpip *) uaddr;
242  int ret;
243  int chk_addr_ret;
244 
245  if (!sock_flag(sk, SOCK_ZAPPED))
246  return -EINVAL;
247  if (addr_len < sizeof(struct sockaddr_l2tpip))
248  return -EINVAL;
249  if (addr->l2tp_family != AF_INET)
250  return -EINVAL;
251 
252  ret = -EADDRINUSE;
253  read_lock_bh(&l2tp_ip_lock);
254  if (__l2tp_ip_bind_lookup(&init_net, addr->l2tp_addr.s_addr, sk->sk_bound_dev_if, addr->l2tp_conn_id))
255  goto out_in_use;
256 
257  read_unlock_bh(&l2tp_ip_lock);
258 
259  lock_sock(sk);
260  if (sk->sk_state != TCP_CLOSE || addr_len < sizeof(struct sockaddr_l2tpip))
261  goto out;
262 
263  chk_addr_ret = inet_addr_type(&init_net, addr->l2tp_addr.s_addr);
264  ret = -EADDRNOTAVAIL;
265  if (addr->l2tp_addr.s_addr && chk_addr_ret != RTN_LOCAL &&
266  chk_addr_ret != RTN_MULTICAST && chk_addr_ret != RTN_BROADCAST)
267  goto out;
268 
269  if (addr->l2tp_addr.s_addr)
270  inet->inet_rcv_saddr = inet->inet_saddr = addr->l2tp_addr.s_addr;
271  if (chk_addr_ret == RTN_MULTICAST || chk_addr_ret == RTN_BROADCAST)
272  inet->inet_saddr = 0; /* Use device */
273  sk_dst_reset(sk);
274 
275  l2tp_ip_sk(sk)->conn_id = addr->l2tp_conn_id;
276 
277  write_lock_bh(&l2tp_ip_lock);
278  sk_add_bind_node(sk, &l2tp_ip_bind_table);
279  sk_del_node_init(sk);
280  write_unlock_bh(&l2tp_ip_lock);
281  ret = 0;
282  sock_reset_flag(sk, SOCK_ZAPPED);
283 
284 out:
285  release_sock(sk);
286 
287  return ret;
288 
289 out_in_use:
290  read_unlock_bh(&l2tp_ip_lock);
291 
292  return ret;
293 }
294 
295 static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
296 {
297  struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *) uaddr;
298  int rc;
299 
300  if (sock_flag(sk, SOCK_ZAPPED)) /* Must bind first - autobinding does not work */
301  return -EINVAL;
302 
303  if (addr_len < sizeof(*lsa))
304  return -EINVAL;
305 
306  if (ipv4_is_multicast(lsa->l2tp_addr.s_addr))
307  return -EINVAL;
308 
309  rc = ip4_datagram_connect(sk, uaddr, addr_len);
310  if (rc < 0)
311  return rc;
312 
313  lock_sock(sk);
314 
315  l2tp_ip_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
316 
317  write_lock_bh(&l2tp_ip_lock);
318  hlist_del_init(&sk->sk_bind_node);
319  sk_add_bind_node(sk, &l2tp_ip_bind_table);
320  write_unlock_bh(&l2tp_ip_lock);
321 
322  release_sock(sk);
323  return rc;
324 }
325 
326 static int l2tp_ip_disconnect(struct sock *sk, int flags)
327 {
328  if (sock_flag(sk, SOCK_ZAPPED))
329  return 0;
330 
331  return udp_disconnect(sk, flags);
332 }
333 
334 static int l2tp_ip_getname(struct socket *sock, struct sockaddr *uaddr,
335  int *uaddr_len, int peer)
336 {
337  struct sock *sk = sock->sk;
338  struct inet_sock *inet = inet_sk(sk);
339  struct l2tp_ip_sock *lsk = l2tp_ip_sk(sk);
340  struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *)uaddr;
341 
342  memset(lsa, 0, sizeof(*lsa));
343  lsa->l2tp_family = AF_INET;
344  if (peer) {
345  if (!inet->inet_dport)
346  return -ENOTCONN;
347  lsa->l2tp_conn_id = lsk->peer_conn_id;
348  lsa->l2tp_addr.s_addr = inet->inet_daddr;
349  } else {
350  __be32 addr = inet->inet_rcv_saddr;
351  if (!addr)
352  addr = inet->inet_saddr;
353  lsa->l2tp_conn_id = lsk->conn_id;
354  lsa->l2tp_addr.s_addr = addr;
355  }
356  *uaddr_len = sizeof(*lsa);
357  return 0;
358 }
359 
360 static int l2tp_ip_backlog_recv(struct sock *sk, struct sk_buff *skb)
361 {
362  int rc;
363 
364  /* Charge it to the socket, dropping if the queue is full. */
365  rc = sock_queue_rcv_skb(sk, skb);
366  if (rc < 0)
367  goto drop;
368 
369  return 0;
370 
371 drop:
373  kfree_skb(skb);
374  return -1;
375 }
376 
377 /* Userspace will call sendmsg() on the tunnel socket to send L2TP
378  * control frames.
379  */
380 static int l2tp_ip_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg, size_t len)
381 {
382  struct sk_buff *skb;
383  int rc;
384  struct inet_sock *inet = inet_sk(sk);
385  struct rtable *rt = NULL;
386  struct flowi4 *fl4;
387  int connected = 0;
388  __be32 daddr;
389 
390  lock_sock(sk);
391 
392  rc = -ENOTCONN;
393  if (sock_flag(sk, SOCK_DEAD))
394  goto out;
395 
396  /* Get and verify the address. */
397  if (msg->msg_name) {
398  struct sockaddr_l2tpip *lip = (struct sockaddr_l2tpip *) msg->msg_name;
399  rc = -EINVAL;
400  if (msg->msg_namelen < sizeof(*lip))
401  goto out;
402 
403  if (lip->l2tp_family != AF_INET) {
404  rc = -EAFNOSUPPORT;
405  if (lip->l2tp_family != AF_UNSPEC)
406  goto out;
407  }
408 
409  daddr = lip->l2tp_addr.s_addr;
410  } else {
411  rc = -EDESTADDRREQ;
412  if (sk->sk_state != TCP_ESTABLISHED)
413  goto out;
414 
415  daddr = inet->inet_daddr;
416  connected = 1;
417  }
418 
419  /* Allocate a socket buffer */
420  rc = -ENOMEM;
421  skb = sock_wmalloc(sk, 2 + NET_SKB_PAD + sizeof(struct iphdr) +
422  4 + len, 0, GFP_KERNEL);
423  if (!skb)
424  goto error;
425 
426  /* Reserve space for headers, putting IP header on 4-byte boundary. */
427  skb_reserve(skb, 2 + NET_SKB_PAD);
428  skb_reset_network_header(skb);
429  skb_reserve(skb, sizeof(struct iphdr));
430  skb_reset_transport_header(skb);
431 
432  /* Insert 0 session_id */
433  *((__be32 *) skb_put(skb, 4)) = 0;
434 
435  /* Copy user data into skb */
436  rc = memcpy_fromiovec(skb_put(skb, len), msg->msg_iov, len);
437  if (rc < 0) {
438  kfree_skb(skb);
439  goto error;
440  }
441 
442  fl4 = &inet->cork.fl.u.ip4;
443  if (connected)
444  rt = (struct rtable *) __sk_dst_check(sk, 0);
445 
446  rcu_read_lock();
447  if (rt == NULL) {
448  const struct ip_options_rcu *inet_opt;
449 
450  inet_opt = rcu_dereference(inet->inet_opt);
451 
452  /* Use correct destination address if we have options. */
453  if (inet_opt && inet_opt->opt.srr)
454  daddr = inet_opt->opt.faddr;
455 
456  /* If this fails, retransmit mechanism of transport layer will
457  * keep trying until route appears or the connection times
458  * itself out.
459  */
460  rt = ip_route_output_ports(sock_net(sk), fl4, sk,
461  daddr, inet->inet_saddr,
462  inet->inet_dport, inet->inet_sport,
463  sk->sk_protocol, RT_CONN_FLAGS(sk),
464  sk->sk_bound_dev_if);
465  if (IS_ERR(rt))
466  goto no_route;
467  if (connected) {
468  sk_setup_caps(sk, &rt->dst);
469  } else {
470  skb_dst_set(skb, &rt->dst);
471  goto xmit;
472  }
473  }
474 
475  /* We dont need to clone dst here, it is guaranteed to not disappear.
476  * __dev_xmit_skb() might force a refcount if needed.
477  */
478  skb_dst_set_noref(skb, &rt->dst);
479 
480 xmit:
481  /* Queue the packet to IP for output */
482  rc = ip_queue_xmit(skb, &inet->cork.fl);
483  rcu_read_unlock();
484 
485 error:
486  if (rc >= 0)
487  rc = len;
488 
489 out:
490  release_sock(sk);
491  return rc;
492 
493 no_route:
494  rcu_read_unlock();
495  IP_INC_STATS(sock_net(sk), IPSTATS_MIB_OUTNOROUTES);
496  kfree_skb(skb);
497  rc = -EHOSTUNREACH;
498  goto out;
499 }
500 
501 static int l2tp_ip_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
502  size_t len, int noblock, int flags, int *addr_len)
503 {
504  struct inet_sock *inet = inet_sk(sk);
505  size_t copied = 0;
506  int err = -EOPNOTSUPP;
507  struct sockaddr_in *sin = (struct sockaddr_in *)msg->msg_name;
508  struct sk_buff *skb;
509 
510  if (flags & MSG_OOB)
511  goto out;
512 
513  if (addr_len)
514  *addr_len = sizeof(*sin);
515 
516  skb = skb_recv_datagram(sk, flags, noblock, &err);
517  if (!skb)
518  goto out;
519 
520  copied = skb->len;
521  if (len < copied) {
522  msg->msg_flags |= MSG_TRUNC;
523  copied = len;
524  }
525 
526  err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
527  if (err)
528  goto done;
529 
530  sock_recv_timestamp(msg, sk, skb);
531 
532  /* Copy the address. */
533  if (sin) {
534  sin->sin_family = AF_INET;
535  sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
536  sin->sin_port = 0;
537  memset(&sin->sin_zero, 0, sizeof(sin->sin_zero));
538  }
539  if (inet->cmsg_flags)
540  ip_cmsg_recv(msg, skb);
541  if (flags & MSG_TRUNC)
542  copied = skb->len;
543 done:
544  skb_free_datagram(sk, skb);
545 out:
546  return err ? err : copied;
547 }
548 
549 static struct proto l2tp_ip_prot = {
550  .name = "L2TP/IP",
551  .owner = THIS_MODULE,
552  .init = l2tp_ip_open,
553  .close = l2tp_ip_close,
554  .bind = l2tp_ip_bind,
555  .connect = l2tp_ip_connect,
556  .disconnect = l2tp_ip_disconnect,
557  .ioctl = udp_ioctl,
558  .destroy = l2tp_ip_destroy_sock,
559  .setsockopt = ip_setsockopt,
560  .getsockopt = ip_getsockopt,
561  .sendmsg = l2tp_ip_sendmsg,
562  .recvmsg = l2tp_ip_recvmsg,
563  .backlog_rcv = l2tp_ip_backlog_recv,
564  .hash = inet_hash,
565  .unhash = inet_unhash,
566  .obj_size = sizeof(struct l2tp_ip_sock),
567 #ifdef CONFIG_COMPAT
568  .compat_setsockopt = compat_ip_setsockopt,
569  .compat_getsockopt = compat_ip_getsockopt,
570 #endif
571 };
572 
573 static const struct proto_ops l2tp_ip_ops = {
574  .family = PF_INET,
575  .owner = THIS_MODULE,
576  .release = inet_release,
577  .bind = inet_bind,
578  .connect = inet_dgram_connect,
579  .socketpair = sock_no_socketpair,
580  .accept = sock_no_accept,
581  .getname = l2tp_ip_getname,
582  .poll = datagram_poll,
583  .ioctl = inet_ioctl,
584  .listen = sock_no_listen,
585  .shutdown = inet_shutdown,
586  .setsockopt = sock_common_setsockopt,
587  .getsockopt = sock_common_getsockopt,
588  .sendmsg = inet_sendmsg,
589  .recvmsg = sock_common_recvmsg,
590  .mmap = sock_no_mmap,
591  .sendpage = sock_no_sendpage,
592 #ifdef CONFIG_COMPAT
593  .compat_setsockopt = compat_sock_common_setsockopt,
594  .compat_getsockopt = compat_sock_common_getsockopt,
595 #endif
596 };
597 
598 static struct inet_protosw l2tp_ip_protosw = {
599  .type = SOCK_DGRAM,
600  .protocol = IPPROTO_L2TP,
601  .prot = &l2tp_ip_prot,
602  .ops = &l2tp_ip_ops,
603  .no_check = 0,
604 };
605 
606 static struct net_protocol l2tp_ip_protocol __read_mostly = {
607  .handler = l2tp_ip_recv,
608 };
609 
610 static int __init l2tp_ip_init(void)
611 {
612  int err;
613 
614  pr_info("L2TP IP encapsulation support (L2TPv3)\n");
615 
616  err = proto_register(&l2tp_ip_prot, 1);
617  if (err != 0)
618  goto out;
619 
620  err = inet_add_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
621  if (err)
622  goto out1;
623 
624  inet_register_protosw(&l2tp_ip_protosw);
625  return 0;
626 
627 out1:
628  proto_unregister(&l2tp_ip_prot);
629 out:
630  return err;
631 }
632 
633 static void __exit l2tp_ip_exit(void)
634 {
635  inet_unregister_protosw(&l2tp_ip_protosw);
636  inet_del_protocol(&l2tp_ip_protocol, IPPROTO_L2TP);
637  proto_unregister(&l2tp_ip_prot);
638 }
639 
640 module_init(l2tp_ip_init);
641 module_exit(l2tp_ip_exit);
642 
643 MODULE_LICENSE("GPL");
644 MODULE_AUTHOR("James Chapman <[email protected]>");
645 MODULE_DESCRIPTION("L2TP over IP");
646 MODULE_VERSION("1.0");
647 
648 /* Use the value of SOCK_DGRAM (2) directory, because __stringify doesn't like
649  * enums
650  */