bpf: lxc: don't take RevDNAT tailcall for service backend's ICMP messages #32155
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…ages When tail_nodeport_rev_dnat_ingress_ipv*() is called by from-container to apply RevDNAT for a local backend's reply traffic, it drops all unhandled packets. This would mostly be traffic where the pod-level CT entry was flagged as .node_port = 1, but there is no corresponding nodeport-level CT entry to provide a rev_nat_index for RevDNAT. Essentially an unexpected error situation. But we didn't consider that from-container might also see ICMP error messages by a service backend, and the CT_RELATED entry for such traffic *also* has the .node_port flag set. As we don't have RevDNAT support for such traffic, there's no good reason to send it down the RevDNAT tailcall. Let it continue in the normal from-container flow instead. This avoids subsequent drops with DROP_NAT_NO_MAPPING. Alternative solutions would be to tolerate ICMP traffic in tail_nodeport_rev_dnat_ingress_ipv*(), or not propagate the .node_port flag into CT_RELATED entries. Fixes: 6936db5 ("bpf: nodeport: drop reply by local backend if revDNAT is skipped") Signed-off-by: Julian Wiedmann <jwi@isovalent.com>
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When tail_nodeport_rev_dnat_ingress_ipv*() is called by from-container to apply RevDNAT for a local backend's reply traffic, it drops all unhandled packets. This would mostly be traffic where the pod-level CT entry was flagged as .node_port = 1, but there is no corresponding nodeport-level CT entry to provide a rev_nat_index for RevDNAT. Essentially an unexpected error situation.
But we didn't consider that from-container might also see ICMP error messages by a service backend, and the CT_RELATED entry for such traffic also has the .node_port flag set. As we don't have RevDNAT support for such traffic, there's no good reason to send it down the RevDNAT tailcall. Let it continue in the normal from-container flow instead. This avoids subsequent drops with DROP_NAT_NO_MAPPING.
Alternative solutions would be to tolerate ICMP traffic in tail_nodeport_rev_dnat_ingress_ipv*(), or not propagate the .node_port flag into CT_RELATED entries.
Fixes: 6936db5 ("bpf: nodeport: drop reply by local backend if revDNAT is skipped")