nfp: refuse offloading filters that redirects to upper devices

Previously we did not ensure that a netdev is a representative netdev
before dereferencing its private data. This can occur when an upper netdev
is created on a representative netdev. This patch corrects this by first
ensuring that the netdev is a representative netdev before using it.
Checking only switchdev_port_same_parent_id is not sufficient to ensure
that we can safely use the netdev. Failing to check that the netdev is also
a representative netdev would result in incorrect dereferencing.

Fixes: 1a1e586f54bf ("nfp: add basic action capabilities to flower offloads")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/flower/action.c

@@ -110,6 +110,8 @@ nfp_fl_output(struct nfp_fl_output *output, const struct tc_action *action,
 	 */
 	if (!switchdev_port_same_parent_id(in_dev, out_dev))
 		return -EOPNOTSUPP;
+	if (!nfp_netdev_is_nfp_repr(out_dev))
+		return -EOPNOTSUPP;
 
 	output->port = cpu_to_be32(nfp_repr_get_port_id(out_dev));
 	if (!output->port)