rec: Only check the netmask for subnet specific cache entries #5319
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We used to check the netmask for all entries for a qname if at least one of them was a subnet specific one. Since an empty `Netmask` doesn't match anything, we would effectively ignore every non subnet specific entries if we had at least one subnet specific one. This caused a very hard to reproduce issue with for example f.root-servers.net that includes an EDNS Client Subnet option in its answer for `NS .` if the query has an EDNS Client Subnet option. This caused the recursor to cache a subnet specific entry for `NS .`. When that entry expired, we retrieved and cached a non subnet specific one, but that new one was ignored as long as the subnet specific was not expunged from the cache. Under certain circumstances that could cause a root refresh loop using a lot of stack memory.
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just reading this... might want a test? |
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I just pushed a new commit adding unit tests for the |
pieterlexis
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pieterlexis
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Short description
We used to check the netmask for all entries for a qname if at least one of them was a subnet specific one. Since an empty
Netmaskdoesn't match anything, we would effectively ignore everynon subnet specific entries if we had at least one subnet specific one.
This was part of a very hard to reproduce issue with for example f.root-servers.net that includes an EDNS Client Subnet option in its answer for
NS .if the query has an EDNS Client Subnet option.This caused the recursor to cache a subnet specific entry for
NS .. When that entry expired, we retrieved and cached a non subnet specific one, but that new one was ignored as long as the subnet specific was not expunged from the cache.Checklist
I have: