On Mon, 23 Nov 2020 19:32:53 +0100 Florian Westphal wrote: > 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> Sounds like a fix. Probably hard to pin point which commit to blame, but this should go to net, not net-next, right?
