bpf: nodeport: add RevDNAT-based FIB lookup for reply traffic #26638
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When moving the RevDNAT for backend replies from
bpf_lxcintobpf_host, we lost the routing based on the post-RevDNAT layout of the packet. Depending on the installed routing rules, we then end up sending the (RevDNATed) packet from the wrong egress interface.So as part of the RevDNAT processing in
to-netdev, do a FIB lookup that considers the desired source IP. And redirect the packet if it's currently on the wrong interface. We intentionally delay the actual RevDNAT rewrite until the packet has reached the correct interface, so that the packet looks as expected to components into-netdev(in particular HostFW).Long-term we would want
FIB_DONEmark on the packet (similar toSNAT_DONE), to skip additional lookups.from-container(for BPF Host Routing) to already consider service RevDNAT.The initial idea was to have this check at the very top of the to-netdev program (see #26635). But we're hitting program size limits in 4.19 there, and improving that is too much of a refactor for a fix PR.
Fixes: #26166