From: Antoine Tenart atenart@kernel.org
[ Upstream commit 44f64f23bae2f0fad25503bc7ab86cd08d04cd47 ]
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:
br_nf_pre_routing br_nf_pre_routing_ipv6 br_nf_pre_routing_finish br_nf_forward_ip br_nf_forward_finish br_nf_post_routing <- pkt_type is updated to PACKET_HOST br_nf_dev_queue_xmit <- but not reverted to its original value vxlan_xmit vxlan_xmit_one skb_tunnel_check_pmtu <- a check on pkt_type is performed
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.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Antoine Tenart atenart@kernel.org Reviewed-by: Florian Westphal fw@strlen.de Link: https://lore.kernel.org/r/20201123174902.622102-1-atenart@kernel.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/bridge/br_netfilter_hooks.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/net/bridge/br_netfilter_hooks.c +++ b/net/bridge/br_netfilter_hooks.c @@ -716,6 +716,11 @@ static int br_nf_dev_queue_xmit(struct n mtu_reserved = nf_bridge_mtu_reduction(skb); mtu = skb->dev->mtu;
+ if (nf_bridge->pkt_otherhost) { + skb->pkt_type = PACKET_OTHERHOST; + nf_bridge->pkt_otherhost = false; + } + if (nf_bridge->frag_max_size && nf_bridge->frag_max_size < mtu) mtu = nf_bridge->frag_max_size;
@@ -809,8 +814,6 @@ static unsigned int br_nf_post_routing(v else return NF_ACCEPT;
- /* We assume any code from br_dev_queue_push_xmit onwards doesn't care - * about the value of skb->pkt_type. */ if (skb->pkt_type == PACKET_OTHERHOST) { skb->pkt_type = PACKET_HOST; nf_bridge->pkt_otherhost = true;