bpf: nodeport: only set outer src IP for tunnel encap in XDP

[julianwiedmann]

As part of introducing native tunnel support for XDP, we started passing a src_ip parameter to __encap_with_nodeid(). This was needed to manually build the packet's outer headers.

But for TC context we actually don't want to specify the outer src IP, and defer its selection to the kernel stack instead. Worse, specifying the outer src IP means that the skb implementation for ctx_set_encap_info() starts to use the local_ipv4 field in the bpf_tunnel_key. And that's not supported on older kernels, resulting in drops.

Fix this by only setting the src_ip parameter in XDP context.

Reported-by: Yusuke Suzuki yusuke-suzuki@cybozu.co.jp
Fixes: 43dffb2 ("bpf: encap: manually set src IP and port from nodeport XDP paths")

[julianwiedmann]

/test

[ysksuzuki]

Thank you for the fix!

I tested this fix with flatcar stable 3510.2.4 and confirmed that it's working.
https://www.flatcar.org/releases#release-3510.2.4

$ uname -a
Linux rack0-cs5 5.15.117-flatcar

$ cilium config view
agent-not-ready-taint-key                      node.cilium.io/agent-not-ready
arping-refresh-period                          30s
auto-direct-node-routes                        false
bgp-announce-lb-ip                             true
bpf-ct-timeout-regular-any                     1h0m0s
bpf-ct-timeout-service-any                     1h0m0s
bpf-lb-acceleration                            disabled
bpf-lb-algorithm                               maglev
bpf-lb-dsr-dispatch                            geneve
bpf-lb-dsr-l4-xlate                            backend
bpf-lb-external-clusterip                      false
bpf-lb-map-max                                 65536
bpf-lb-mode                                    dsr
bpf-lb-sock                                    true
bpf-lb-sock-hostns-only                        true
bpf-map-dynamic-size-ratio                     0.0025
bpf-policy-map-max                             65536
bpf-root                                       /sys/fs/bpf
cgroup-root                                    /sys/fs/cgroup