cDAC: AccessViolation/FailFast releasing ICorDebug COM objects on Windows x64

[steveisok]

With DOTNET_ENABLE_CDAC=1 on Windows x64, releasing ICorDebug COM objects can crash the process with an access violation, escalating to a fail-fast (exit -1073740791 / 0xC0000409). In an observed case the debugging operation itself completed correctly (frames were retrieved and validated), but the process then crashed while finalizing/releasing the underlying COM objects:

Process terminated. Access Violation: Attempted to read or write protected memory...
   at IIUnknownCacheStrategy.Clear(IIUnknownStrategy)
   at ComObject.Finalize()
   at __Finalizer.DrainQueue() / ProcessFinalizers()
   -> RuntimeExceptionHelpers.FailFast(...)

The AV during Release on the cached IUnknown pointers suggests a lifetime/ownership problem in the cDAC-backed ICorDebug objects (a stale or already-freed native pointer being released).

Repro / signal

• Runtime: 11.0.0-preview.6.26311.113, Windows x64, DOTNET_ENABLE_CDAC=1
• Stackwalk scenario; the crash occurs on the finalizer thread during COM release, after the debugging operation succeeds. Does not reproduce with cDAC disabled.

Expected

Releasing/finalizing cDAC-backed ICorDebug objects does not access freed memory.

[dotnet-policy-service]

Tagging subscribers to this area: @steveisok, @tommcdon, @dotnet/dotnet-diag
See info in area-owners.md if you want to be subscribed.

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• [cDAC] SOS expects deterministic destruction of COM objects #117785