ipv6: fix panic when forwarding a pkt with no in6 dev

commit e3fa461 upstream.

kongweibin reported a kernel panic in ip6_forward() when input interface
has no in6 dev associated.

The following tc commands were used to reproduce this panic:
tc qdisc del dev vxlan100 root
tc qdisc add dev vxlan100 root netem corrupt 5%

CC: [email protected]
Fixes: ccd27f0 ("ipv6: fix 'disable_policy' for fwd packets")
Reported-by: kongweibin <[email protected]>
Signed-off-by: Nicolas Dichtel <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: NicolasDichtel

net/ipv6/ip6_output.c

@@ -485,7 +485,7 @@ int ip6_forward(struct sk_buff *skb)
 		goto drop;
 
 	if (!net->ipv6.devconf_all->disable_policy &&
-	    !idev->cnf.disable_policy &&
+	    (!idev || !idev->cnf.disable_policy) &&
 	    !xfrm6_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
 		__IP6_INC_STATS(net, idev, IPSTATS_MIB_INDISCARDS);
 		goto drop;