datapath: Fix double SNAT #25189
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datapath: Fix double SNAT #25189
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Please keep the IPv6 path in sync :) |
Unfortunately, atm no BPF-based SNAT for IPv6 😭 |
uh, what about host-originating connections vs Nodeport NAT ports? I believe we should add the same thing in |
We have observed, that the same packet can be handled multiple times by
the bpf_host's to-netdev. This can happen when the to-netdev is attached
to a bridge and to an outgoing netdev which is attached to the bridge.
This can result e.g., into multiple unnecessary SNATs for the same
packet which can break the host-firewall (the host-firewall for a reply
to such a packet is invoked after only the first rev-SNAT).
To fix that particular case set the SNAT done flag (an SKB mark).
Tested manually. On kind-worker node (172.18.0.3):
ip link add br0 type bridge
ip addr add 172.18.0.3/16 dev br0
ip addr del 172.18.0.3/16 dev eth0
ip link set dev br0 up
ip link set dev eth0 master br0
ip route replace 0.0.0.0/0 via 172.18.0.1
Make sure that Cilium attached to both:
cilium status | grep KubeProxy
KubeProxyReplacement: Strict [br0 172.18.0.3, eth0 172.18.0.3]
Then start any pod on kind-worker, and run tcpdump on kind-work. curl
1.1.1.1 from that pod.
tcpdump -i any -n 'dst port 80'
lxc2663158aafe1 In IP 10.244.1.161.43710 > 1.1.1.1.80: Flags [S]
br0 Out IP 172.18.0.3.43710 > 1.1.1.1.80: Flags [S]
eth0 Out IP 172.18.0.3.43710 > 1.1.1.1.80: Flags [S]
Redo the same test w/o the fix. The relevant tcpdump output:
tcpdump -i any -n 'dst host 1.1.1.1'
lxcbce3c2f349e1 In IP 10.244.1.120.57408 > 1.1.1.1.80: Flags [S]
br0 Out IP 172.18.0.3.57408 > 1.1.1.1.80: Flags [S]
eth0 Out IP 172.18.0.3.56763 > 1.1.1.1.80: Flags [S] <-- 2nd SNAT!
Suggested-by: Julian Wiedmann <jwi@isovalent.com>
Signed-off-by: Martynas Pumputis <m@lambda.lt>
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gentoo-root
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May 1, 2023
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We have observed, that the same packet can be handled multiple times by
the bpf_host's to-netdev. This can happen when the to-netdev is attached
to a bridge and to an outgoing netdev which is attached to the bridge.
This can result e.g., into multiple unnecessary SNATs for the same
packet which can break the host-firewall (the host-firewall for a reply
to such a packet is invoked after only the first rev-SNAT).
To fix that particular case set the SNAT done flag (an SKB mark).
Tested manually. On kind-worker node (172.18.0.3):
Make sure that Cilium attached to both:
Then start any pod on kind-worker, and run tcpdump on kind-work. curl
1.1.1.1 from that pod.
Redo the same test w/o the fix. The relevant tcpdump output:
Suggested-by: Julian Wiedmann jwi@isovalent.com
Fix #24916