Workaround dns kernel bug #95
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: aojea The full list of commands accepted by this bot can be found here. The pull request process is described here
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I tested this locally and it works, thanks @aojea! |
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see if @danwinship wants to take a look, otherwise I will merge end of the day, so we can have it in kind |
jglick
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Oct 7, 2024
do you mean in kubernetes/kubernetes? this showed up in this e2e #12 |
This was fixed in the kernel in 6.12 (commit 8af79d3edb5f) However, users need a workaround to avoid hitting this bugs in existing kernels. Add a feature flag enabled by default to implement the workaround, that consists in processing the DNS packets on the prerouting hook, after dnat happens, so we can have the resolved IPs of the DNS server, and avoid to process them in the postrouting hook.
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Add a workaround to the netfilter conntrack bug https://bugzilla.netfilter.org/show_bug.cgi?id=1766 fixed by torvalds/linux@8af79d3.
Since the race problem is caused by having two packets DNATed with the same tuple at the same time by different CPUs, it impact specially DNS resolvers that sends A and AAAA request in parallel (it seems is default glibc behavior), and this is very visible to users that notice DNS latency.
Instead of processing all packets on the POSROUTING hook, special case DNS and process them in PREROUTING after DNAT happens.
Services implementations that don't rely on conntrack can disable this behavior by setting the flag to false.