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fix(cache): data race when updating the TTL of cached messages #7397

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Merged
yongtang merged 1 commit into from
Jul 3, 2025
Merged

fix(cache): data race when updating the TTL of cached messages #7397

yongtang merged 1 commit into from
Jul 3, 2025

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@bn-smayr
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@bn-smayr bn-smayr commented Jul 1, 2025 •
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1. Why is this pull request needed and what does it do?

This PR fixes a data race that occurs when a cached DNS message is served by multiple goroutines. In this case the TTL of resource records is accessed and modified concurrently and go's race detector reports the following:

WARNING: DATA RACE
Write at 0x00c000a7e344 by goroutine 1264:
  github.com/coredns/coredns/plugin/cache.filterRRSlice()
      coredns/plugin/cache/dnssec.go:15 +0x118
  github.com/coredns/coredns/plugin/cache.(*item).toMsg()
      coredns/plugin/cache/item.go:90 +0x668
  github.com/coredns/coredns/plugin/cache.(*Cache).ServeDNS()
      coredns/plugin/cache/handler.go:79 +0x1064
  github.com/coredns/coredns/core/dnsserver.(*Server).ServeDNS()
      coredns/core/dnsserver/server.go:364 +0xcf5
...

Previous read at 0x00c000a7e340 by goroutine 1265:
  github.com/miekg/dns.(*CNAME).copy()
      pkg/mod/github.com/miekg/[email protected]/ztypes.go:898 +0x46
  github.com/miekg/dns.Copy()
      pkg/mod/github.com/miekg/[email protected]/msg.go:1065 +0x1b8
  github.com/coredns/coredns/plugin/cache.filterRRSlice()
      coredns/plugin/cache/dnssec.go:17 +0x79
  github.com/coredns/coredns/plugin/cache.(*item).toMsg()
      coredns/plugin/cache/item.go:90 +0x668
  github.com/coredns/coredns/plugin/cache.(*Cache).ServeDNS()
      coredns/plugin/cache/handler.go:79 +0x1064
  github.com/coredns/coredns/core/dnsserver.(*Server).ServeDNS()
      coredns/core/dnsserver/server.go:364 +0xcf5
  ...

2. Which issues (if any) are related?

Fixes #6718, pretty much as suggested by @DmitriyMV.

3. Which documentation changes (if any) need to be made?

None

4. Does this introduce a backward incompatible change or deprecation?

No

@bn-smayr bn-smayr changed the title fix(cache): race condition when updating the TTL of cached messages fix(cache): data race when updating the TTL of cached messages Jul 1, 2025
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codecov bot commented Jul 3, 2025 •
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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.98%. Comparing base (93c57b6) to head (8cc431b).
Report is 1516 commits behind head on master.

Additional details and impacted files 
@@            Coverage Diff             @@
##           master    #7397      +/-   ##
==========================================
+ Coverage   55.70%   59.98%   +4.28%     
==========================================
  Files         224      273      +49     
  Lines       10016    17982    +7966     
==========================================
+ Hits         5579    10787    +5208     
- Misses       3978     6566    +2588     
- Partials      459      629     +170

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@yongtang yongtang merged commit 06da7dc into coredns:master Jul 3, 2025
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@BrewTestBot BrewTestBot mentioned this pull request Aug 5, 2025
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@yongtang yongtang yongtang approved these changes

@miekg miekg Awaiting requested review from miekg miekg is a code owner

@chrisohaver chrisohaver Awaiting requested review from chrisohaver chrisohaver is a code owner

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Successfully merging this pull request may close these issues.

data-race: filterRRSlice function mutates original which it got from the shared cache

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@bn-smayr @yongtang