bpf: fix nodeport to avoid sending loopback address out to wire #10841
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borkmann
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While testing recently, I've noticed the case where we start to use the 169.254.42.1 loopback address for requests from outside: # tcpdump -i any port 30042 or 80 -n [...] 09:50:15.835618 IP 192.168.178.28.80 > 169.254.42.1.32882: Flags [S.], seq 689888661, ack 2221057376, win 65160, options [mss 1460,sackOK,TS val 3644467179 ecr 3644467179,nop,wscale 7], length 0 09:50:16.863069 IP 192.168.178.28.80 > 169.254.42.1.32882: Flags [S.], seq 689888661, ack 2221057376, win 65160, options [mss 1460,sackOK,TS val 3644468207 ecr 3644467179,nop,wscale 7], length 0 [...] This can happen if the backend IP (192.168.178.28) is the same IP that is doing the request to the frontend: # ./cilium/cilium service list ID Frontend Service Type Backend 1 192.168.178.29:30042 NodePort 1 => 192.168.178.28:80 Then we're hitting the codepath where we replace the 192.168.178.28 src address with 169.254.42.1 (IPV4_LOOPBACK) and try to send it back out the NodePort device, which is just wrong. That code was only intended for node local Pod to Pod ClusterIP handling we had before socket LB. For NodePort requests from outside the node this should not be done. We can handle this situation just fine in case of BPF-based SNAT, and in case of DSR it is expected to not work and we should not try to do any special NAT'ing or such. For east-west traffic on Cilium-managed nodes, we are simply using the socket LB anyway for everything, so we won't run into this corner case either. There is a unused DISABLE_LOOPBACK_LB define, to compile this out. Fix it by specifying this define from init.sh. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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brb
approved these changes
Apr 3, 2020
joestringer
moved this from Needs backport from master
to Backport done to v1.7
in 1.7.3
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