Antoine Tenart <atenart@xxxxxxxxxx> wrote: > Netfilter changes PACKET_OTHERHOST to PACKET_HOST before invoking the > hooks as, while it's an expected value for a bridge, routing expects > PACKET_HOST. The change is undone later on after hook traversal. This > can be seen with pairs of functions updating skb>pkt_type and then > reverting it to its original value: > > For hook NF_INET_PRE_ROUTING: > setup_pre_routing / br_nf_pre_routing_finish > > For hook NF_INET_FORWARD: > br_nf_forward_ip / br_nf_forward_finish > > But the third case where netfilter does this, for hook > NF_INET_POST_ROUTING, the packet type is changed in br_nf_post_routing > but never reverted. A comment says: > > /* We assume any code from br_dev_queue_push_xmit onwards doesn't care > * about the value of skb->pkt_type. */ [..] > But when having a tunnel (say vxlan) attached to a bridge we have the > following call trace: > In this specific case, this creates issues such as when an ICMPv6 PTB > should be sent back. When CONFIG_BRIDGE_NETFILTER is enabled, the PTB > isn't sent (as skb_tunnel_check_pmtu checks if pkt_type is PACKET_HOST > and returns early). > > If the comment is right and no one cares about the value of > skb->pkt_type after br_dev_queue_push_xmit (which isn't true), resetting > it to its original value should be safe. That comment is 18 years old, safe bet noone thought of ipv6-in-tunnel-interface-added-as-bridge-port back then. Reviewed-by: Florian Westphal <fw@xxxxxxxxx>
