net: sched: act_tunnel_key: fix NULL pointer dereference during init

Metadata pointer is only initialized for action TCA_TUNNEL_KEY_ACT_SET, but
it is unconditionally dereferenced in tunnel_key_init() error handler.
Verify that metadata pointer is not NULL before dereferencing it in
tunnel_key_init error handling code.

Fixes: ee28bb56 ("net/sched: fix memory leak in act_tunnel_key_init()")
Signed-off-by: NVlad Buslov <vladbu@mellanox.com>
Reviewed-by: NDavide Caratti <dcaratti@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/act_tunnel_key.c

@@ -377,7 +377,8 @@ static int tunnel_key_init(struct net *net, struct nlattr *nla,
 	return ret;
 
 release_tun_meta:
-	dst_release(&metadata->dst);
+	if (metadata)
+		dst_release(&metadata->dst);
 
 err_out:
 	if (exists)