nbd:fix memory leak in nbd_get_socket()

commit dff10bbea4be47bdb615b036c834a275b7c68133 upstream.

Before returning NULL, put the sock first.

Cc: stable@vger.kernel.org
Fixes: cf1b2326b734 ("nbd: verify socket is supported during setup")
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NMike Christie <mchristi@redhat.com>
Signed-off-by: NSun Ke <sunke32@huawei.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/block/nbd.c

@@ -945,6 +945,7 @@ static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
 	if (sock->ops->shutdown == sock_no_shutdown) {
 		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
 		*err = -EINVAL;
+		sockfd_put(sock);
 		return NULL;
 	}