ipsec: Safely delete Xfrm state #32450
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No functional change, just to make further revision easier. Signed-off-by: gray <[email protected]>
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This patch introduces a workaround to avoid kernel issue when deleting xfrm states. Let's start from the kernel issue. After installing two xfrm states on the same host using below commands (please note the differences on the mark, mask, src): ``` ip x s a src 10.244.1.43 dst 10.244.3.114 proto esp spi 0x00000003 reqid 1 mode tunnel replay-window 0 mark 0x2a450d00 mask 0xffff0f00 output-mark 0xd00 mask 0xffffff00 aead 'rfc4106(gcm(aes))' 0x42a89014074c49243219a20cc87cadd7b9c0d7d1 128 sel src 0.0.0.0/0 dst 0.0.0.0/0 ip x s a src 0.0.0.0 dst 10.244.3.114 proto esp spi 0x00000003 reqid 1 mode tunnel replay-window 0 mark 0xd00 mask 0xf00 output-mark 0xd00 mask 0xffffff00 aead 'rfc4106(gcm(aes))' 0x42a89014074c49243219a20cc87cadd7b9c0d7d1 128 sel src 0.0.0.0/0 dst 0.0.0.0/0 ``` When trying to delete the first xfrm state using the following command, Linux kernel will instead remove the second xfrm state but keep the first: ``` ip x s d src 10.244.1.43 dst 10.244.3.114 proto esp spi 0x00000003 mark 0x2a450d00 mask 0xffff0f00 ``` This causes troubles for cilium upgrade. A real world scenario for cilium upgrade from 1.13.12 to 1.13.14 could be like: 1. Before upgrade, the node has "old-style" xfrm state to catch mark "0xd00/0xf00" for ingress traffic; old bpf programs also set "0xd00" mark to ingress skbs; 2. Upgrade begins, bpf programs are reloaded to new version, thereafter ingress skbs are marked with "0xXXXX0d00"; 3. After a short while, cilium-agent installs new xfrm states to catch traffic with specific mark "0xXXXX0d00"; During window between step 2 and 3, cilium relies on "old-style" xfrm states "0xd00/0xf00" to catch traffic with specific mark "0xXXXX0d00". So far so good. However, in a large scale cluster it's inevitable to receive NodeDeletion events during upgrade due to node churn. Once seeing a NodeDeletion event, cilium-agent will remove the xfrm state for that gone-away remote node. Now we hit the aforementioned kernel issue: cilium-agent tries to delete the xfrm state catching more specific mark, but kernel wrongly removes the one catching general mark. This causing traffic disruption until upgrade completes with all new xfrm states installed. This patch provides an elegant solution at low cost: if cilium-agent wants to remove a xfrm state catching specific mark, it has to temporarily remove the xfrm state catching general mark first and add it back after: 1. Temporarily remove the xfrm states catching the general mark; 2. Remove the xfrm state we really care abot; 3. Add back the temporaily removed one on step 1; Indeed there will be a small window between temporary removing and adding back, but our past test shows the window lasts 200-900µs only, so short that we shoudn't see many drops. Suggested-by: Julian Wiedmann <[email protected]> Signed-off-by: gray <[email protected]>
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Commit messages elaborate details. Although this is to fix an upgrade issue from 1.13, it doesn't harm main.
If the cilium is upgraded from an old version, it's possible a latest version cilium cluster has the old xfrm states left over. In this case, this PR performs unnecessary xfrm churn, but won't affect any traffic.
If the cilium is installed from scratch, it indeed doesn't need this fix at all. In this situation, the
SafelyDeleteXfrmState()doesn't even cause xfrm churn because it can't find the old style xfrm state to delete.This can be removed along with https://github.com/cilium/cilium/blob/v1.15.4/pkg/datapath/linux/ipsec/ipsec_linux.go#L351.