4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: WANG Cong <redacted>

commit d747a7a51b00984127a88113cdbbc26f91e9d815 upstream.

We have to reset the sk->sk_rx_dst when we disconnect a TCP
connection, because otherwise when we re-connect it this
dst reference is simply overridden in tcp_finish_connect().

This fixes a dst leak which leads to a loopback dev refcnt
leak. It is a long-standing bug, Kevin reported a very similar
(if not same) bug before. Thanks to Andrei for providing such
a reliable reproducer which greatly narrows down the problem.

Fixes: 41063e9dd119 ("ipv4: Early TCP socket demux.")
Reported-by: Andrei Vagin <redacted>
Reported-by: Kevin Xu <redacted>
Signed-off-by: Cong Wang <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/ipv4/tcp.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c

@@ -2263,6 +2263,8 @@ int tcp_disconnect(struct sock *sk, int
 	tcp_init_send_head(sk);
 	memset(&tp->rx_opt, 0, sizeof(tp->rx_opt));
 	__sk_dst_reset(sk);
+	dst_release(sk->sk_rx_dst);
+	sk->sk_rx_dst = NULL;
 	tcp_saved_syn_free(tp);
 
 	WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);