net: ipv6: keep sk status consistent after datagram connect failure

On unsuccesful ip6_datagram_connect(), if the failure is caused by
ip6_datagram_dst_update(), the sk peer information are cleared, but
the sk->sk_state is preserved.

If the socket was already in an established status, the overall sk
status is inconsistent and fouls later checks in datagram code.

Fix this saving the old peer information and restoring them in
case of failure. This also aligns ipv6 datagram connect() behavior
with ipv4.

v1 -> v2:
 - added missing Fixes tag

Fixes: 85cb73ff ("net: ipv6: reset daddr and dport in sk if connect() fails")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/datagram.c

@@ -146,10 +146,12 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 	struct sockaddr_in6	*usin = (struct sockaddr_in6 *) uaddr;
 	struct inet_sock	*inet = inet_sk(sk);
 	struct ipv6_pinfo	*np = inet6_sk(sk);
-	struct in6_addr		*daddr;
+	struct in6_addr		*daddr, old_daddr;
+	__be32			fl6_flowlabel = 0;
+	__be32			old_fl6_flowlabel;
+	__be32			old_dport;
 	int			addr_type;
 	int			err;
-	__be32			fl6_flowlabel = 0;
 
 	if (usin->sin6_family == AF_INET) {
 		if (__ipv6_only_sock(sk))
@@ -238,9 +240,13 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 		}
 	}
 
+	/* save the current peer information before updating it */
+	old_daddr = sk->sk_v6_daddr;
+	old_fl6_flowlabel = np->flow_label;
+	old_dport = inet->inet_dport;
+
 	sk->sk_v6_daddr = *daddr;
 	np->flow_label = fl6_flowlabel;
-
 	inet->inet_dport = usin->sin6_port;
 
 	/*
@@ -250,11 +256,12 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 
 	err = ip6_datagram_dst_update(sk, true);
 	if (err) {
-		/* Reset daddr and dport so that udp_v6_early_demux()
-		 * fails to find this socket
+		/* Restore the socket peer info, to keep it consistent with
+		 * the old socket state
 		 */
-		memset(&sk->sk_v6_daddr, 0, sizeof(sk->sk_v6_daddr));
-		inet->inet_dport = 0;
+		sk->sk_v6_daddr = old_daddr;
+		np->flow_label = old_fl6_flowlabel;
+		inet->inet_dport = old_dport;
 		goto out;
 	}