netfilter: bridge: Fix non-untagged fragment packet

netfilter: bridge: Fix non-untagged fragment packet

ip netns exec ns1 ip a a dev eth0 10.0.0.7/24
ip netns exec ns2 ip link a link eth0 name vlan type vlan id 200
ip netns exec ns2 ip a a dev vlan 10.0.0.8/24

ip l add dev br0 type bridge vlan_filtering 1
brctl addif br0 veth1
brctl addif br0 veth2

bridge vlan add dev veth1 vid 200 pvid untagged
bridge vlan add dev veth2 vid 200

A two fragment packet sent from ns2 contains the vlan tag 200.  In the
bridge conntrack, this packet will defrag to one skb with fraglist.
When the packet is forwarded to ns1 through veth1, the first skb vlan
tag will be cleared by the "untagged" flags. But the vlan tag in the
second skb is still tagged, so the second fragment ends up with tag 200
to ns1. So if the first fragment packet doesn't contain the vlan tag,
all of the remain should not contain vlan tag.

Fixes: 3c171f496ef5 ("netfilter: bridge: add connection tracking system")
Signed-off-by: wenxu <wenxu@ucloud.cn>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>