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

stable inclusion
from stable-4.19.239
commit 74b68f5249f16c5f7f675d0f604fa6ae20e3a151
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5A6BA
CVE: NA

--------------------------------

commit e3fa461d 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: stable@vger.kernel.org
Fixes: ccd27f05 ("ipv6: fix 'disable_policy' for fwd packets")
Reported-by: Nkongweibin <kongweibin2@huawei.com>
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: NDavid Ahern <dsahern@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/ipv6/ip6_output.c

@@ -460,7 +460,7 @@ 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;