l2tp: fix oops in L2TP IP sockets for connect() AF_UNSPEC case

[ Upstream commit c51ce49735c183ef2592db70f918ee698716276b ]

An application may call connect() to disconnect a socket using an
address with family AF_UNSPEC. The L2TP IP sockets were not handling
this case when the socket is not bound and an attempt to connect()
using AF_UNSPEC in such cases would result in an oops. This patch
addresses the problem by protecting the sk_prot->disconnect() call
against trying to unhash the socket before it is bound.

The patch also adds more checks that the sockaddr supplied to bind()
and connect() calls is valid.

 RIP: 0010:[<ffffffff82e133b0>]  [<ffffffff82e133b0>] inet_unhash+0x50/0xd0
 RSP: 0018:ffff88001989be28  EFLAGS: 00010293
 Stack:
  ffff8800407a8000 0000000000000000 ffff88001989be78 ffffffff82e3a249
  ffffffff82e3a050 ffff88001989bec8 ffff88001989be88 ffff8800407a8000
  0000000000000010 ffff88001989bec8 ffff88001989bea8 ffffffff82e42639
 Call Trace:
 [<ffffffff82e3a249>] udp_disconnect+0x1f9/0x290
 [<ffffffff82e42639>] inet_dgram_connect+0x29/0x80
 [<ffffffff82d012fc>] sys_connect+0x9c/0x100

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 2a2a3e7..2fbbe1f 100644 (file)
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -251,9 +251,16 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {
        struct inet_sock *inet = inet_sk(sk);
        struct sockaddr_l2tpip *addr = (struct sockaddr_l2tpip *) uaddr;
-       int ret = -EINVAL;
+       int ret;
        int chk_addr_ret;
 
+       if (!sock_flag(sk, SOCK_ZAPPED))
+               return -EINVAL;
+       if (addr_len < sizeof(struct sockaddr_l2tpip))
+               return -EINVAL;
+       if (addr->l2tp_family != AF_INET)
+               return -EINVAL;
+
        ret = -EADDRINUSE;
        read_lock_bh(&l2tp_ip_lock);
        if (__l2tp_ip_bind_lookup(&init_net, addr->l2tp_addr.s_addr, sk->sk_bound_dev_if, addr->l2tp_conn_id))
@@ -283,6 +290,8 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
        sk_del_node_init(sk);
        write_unlock_bh(&l2tp_ip_lock);
        ret = 0;
+       sock_reset_flag(sk, SOCK_ZAPPED);
+
 out:
        release_sock(sk);
 
@@ -303,13 +312,14 @@ static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
        __be32 saddr;
        int oif, rc;
 
-       rc = -EINVAL;
+       if (sock_flag(sk, SOCK_ZAPPED)) /* Must bind first - autobinding does not work */
+               return -EINVAL;
+
        if (addr_len < sizeof(*lsa))
-               goto out;
+               return -EINVAL;
 
-       rc = -EAFNOSUPPORT;
        if (lsa->l2tp_family != AF_INET)
-               goto out;
+               return -EAFNOSUPPORT;
 
        lock_sock(sk);
 
@@ -363,6 +373,14 @@ out:
        return rc;
 }
 
+static int l2tp_ip_disconnect(struct sock *sk, int flags)
+{
+       if (sock_flag(sk, SOCK_ZAPPED))
+               return 0;
+
+       return udp_disconnect(sk, flags);
+}
+
 static int l2tp_ip_getname(struct socket *sock, struct sockaddr *uaddr,
                           int *uaddr_len, int peer)
 {
@@ -598,7 +616,7 @@ static struct proto l2tp_ip_prot = {
        .close             = l2tp_ip_close,
        .bind              = l2tp_ip_bind,
        .connect           = l2tp_ip_connect,
-       .disconnect        = udp_disconnect,
+       .disconnect        = l2tp_ip_disconnect,
        .ioctl             = udp_ioctl,
        .destroy           = l2tp_ip_destroy_sock,
        .setsockopt        = ip_setsockopt,