l2tp: lock socket before checking flags in connect()

BugLink: https://bugs.launchpad.net/bugs/1883916

commit 0382a25a upstream.

Socket flags aren't updated atomically, so the socket must be locked
while reading the SOCK_ZAPPED flag.

This issue exists for both l2tp_ip and l2tp_ip6. For IPv6, this patch
also brings error handling for __ip6_datagram_connect() failures.
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

include/net/ipv6.h

@@ -915,6 +915,8 @@ int compat_ipv6_setsockopt(struct sock *sk, int level, int optname,
 int compat_ipv6_getsockopt(struct sock *sk, int level, int optname,
 			   char __user *optval, int __user *optlen);
 
+int __ip6_datagram_connect(struct sock *sk, struct sockaddr *addr,
+			   int addr_len);
 int ip6_datagram_connect(struct sock *sk, struct sockaddr *addr, int addr_len);
 int ip6_datagram_connect_v6_only(struct sock *sk, struct sockaddr *addr,
 				 int addr_len);

net/ipv6/datagram.c

@@ -40,7 +40,8 @@ static bool ipv6_mapped_addr_any(const struct in6_addr *a)
 	return ipv6_addr_v4mapped(a) && (a->s6_addr32[3] == 0);
 }
 
-static int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
+			   int addr_len)
 {
 	struct sockaddr_in6	*usin = (struct sockaddr_in6 *) uaddr;
 	struct inet_sock	*inet = inet_sk(sk);
@@ -213,6 +214,7 @@ static int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int a
 	fl6_sock_release(flowlabel);
 	return err;
 }
+EXPORT_SYMBOL_GPL(__ip6_datagram_connect);
 
 int ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 {

net/l2tp/l2tp_ip.c

@@ -321,21 +321,24 @@ static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 	struct sockaddr_l2tpip *lsa = (struct sockaddr_l2tpip *) uaddr;
 	int rc;
 
-	if (sock_flag(sk, SOCK_ZAPPED)) /* Must bind first - autobinding does not work */
-		return -EINVAL;
-
 	if (addr_len < sizeof(*lsa))
 		return -EINVAL;
 
 	if (ipv4_is_multicast(lsa->l2tp_addr.s_addr))
 		return -EINVAL;
 
-	rc = ip4_datagram_connect(sk, uaddr, addr_len);
-	if (rc < 0)
-		return rc;
-
 	lock_sock(sk);
 
+	/* Must bind first - autobinding does not work */
+	if (sock_flag(sk, SOCK_ZAPPED)) {
+		rc = -EINVAL;
+		goto out_sk;
+	}
+
+	rc = __ip4_datagram_connect(sk, uaddr, addr_len);
+	if (rc < 0)
+		goto out_sk;
+
 	l2tp_ip_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
 
 	write_lock_bh(&l2tp_ip_lock);
@@ -343,7 +346,9 @@ static int l2tp_ip_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 	sk_add_bind_node(sk, &l2tp_ip_bind_table);
 	write_unlock_bh(&l2tp_ip_lock);
 
+out_sk:
 	release_sock(sk);
+
 	return rc;
 }
 

net/l2tp/l2tp_ip6.c

@@ -383,9 +383,6 @@ static int l2tp_ip6_connect(struct sock *sk, struct sockaddr *uaddr,
 	int	addr_type;
 	int rc;
 
-	if (sock_flag(sk, SOCK_ZAPPED)) /* Must bind first - autobinding does not work */
-		return -EINVAL;
-
 	if (addr_len < sizeof(*lsa))
 		return -EINVAL;
 
@@ -402,10 +399,18 @@ static int l2tp_ip6_connect(struct sock *sk, struct sockaddr *uaddr,
 			return -EINVAL;
 	}
 
-	rc = ip6_datagram_connect(sk, uaddr, addr_len);
-
 	lock_sock(sk);
 
+	 /* Must bind first - autobinding does not work */
+	if (sock_flag(sk, SOCK_ZAPPED)) {
+		rc = -EINVAL;
+		goto out_sk;
+	}
+
+	rc = __ip6_datagram_connect(sk, uaddr, addr_len);
+	if (rc < 0)
+		goto out_sk;
+
 	l2tp_ip6_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
 
 	write_lock_bh(&l2tp_ip6_lock);
@@ -413,6 +418,7 @@ static int l2tp_ip6_connect(struct sock *sk, struct sockaddr *uaddr,
 	sk_add_bind_node(sk, &l2tp_ip6_bind_table);
 	write_unlock_bh(&l2tp_ip6_lock);
 
+out_sk:
 	release_sock(sk);
 
 	return rc;