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dnsdist: Increment the DOHUnit ref count when it's set in the IDState #8471

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merged 2 commits into from Oct 26, 2019

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rgacogne commented Oct 25, 2019

Short description

We need to increment the reference counter even before sending the
query to the backend, as soon as we copy a reference into the IDState.
Because:

  • that makes sense anyway, we are storing a new copy ;
  • otherwise, in the unlikely event where we reuse the IDState before the query has been sent to the backend we might free the DOHUnit before the reference counter has been incremented and cause a double-free.

This is why we love smart pointers, too bad that we need to deal with raw C pointers a bit in that code..

Checklist

I have:

  • read the CONTRIBUTING.md document
  • compiled this code
  • tested this code
  • included documentation (including possible behaviour changes)
  • documented the code
  • added or modified regression test(s)
  • added or modified unit test(s)
We need to increment the reference counter even before sending the
query to the backend, as soon as we copy a reference into the IDState.
Because:
- that makes sense anyway, we are storing a new copy ;
- otherwise, in the unlikely event where we reuse the IDState before
  the query has been sent to the backend we might free the DOHUnit
  before the reference counter has been incremented and cause a
  double-free.
@rgacogne rgacogne added this to the dnsdist-1.4.0 milestone Oct 25, 2019
It was based on the reference counter used for the DOHAcceptContext
where thread safety was never an issue because those objects are
not shared between threads, but DOHUnit are.
@rgacogne rgacogne merged commit 2393dd9 into PowerDNS:master Oct 26, 2019
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@rgacogne rgacogne deleted the rgacogne:ddist-du-refcount-ids branch Oct 26, 2019
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