netfilter: ip6t_rpfilter: Fix regression with VRF interfaces

BugLink: https://bugs.launchpad.net/bugs/2086242

commit efb056e upstream.

When calling ip6_route_lookup() for the packet arriving on the VRF
interface, the result is always the real (slave) interface. Expect this
when validating the result.

Fixes: acc641a ("netfilter: rpfilter/fib: Populate flowic_l3mdev field")
Signed-off-by: Phil Sutter <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Koichiro Den <[email protected]>
Signed-off-by: Roxana Nicolescu <[email protected]>

Author: Phil Sutter

net/ipv6/netfilter/ip6t_rpfilter.c

@@ -72,7 +72,9 @@ static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
 		goto out;
 	}
 
-	if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
+	if (rt->rt6i_idev->dev == dev ||
+	    l3mdev_master_ifindex_rcu(rt->rt6i_idev->dev) == dev->ifindex ||
+	    (flags & XT_RPFILTER_LOOSE))
 		ret = true;
  out:
 	ip6_rt_put(rt);