Fix COM wrapper weak-handle defensive copy in ReferenceTrackerNativeObjectWrapper#129668
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Fix COM wrapper weak-handle defensive copy in ReferenceTrackerNativeObjectWrapper#129668Copilot wants to merge 3 commits into
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Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
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[WIP] Fix potential double free in ComWrappers implementation
Fix COM wrapper weak-handle defensive copy in ReferenceTrackerNativeObjectWrapper
Jun 21, 2026
jkotas
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Jun 21, 2026
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Pull request overview
This PR addresses a correctness issue in CoreLib’s COM wrapper tracking path by ensuring _nativeObjectWrapperWeakHandle.Free() mutates the actual stored GCHandle field (avoiding readonly-field defensive copies) so cleanup becomes reliably idempotent.
Changes:
- Changed
ReferenceTrackerNativeObjectWrapper._nativeObjectWrapperWeakHandlefromreadonlyto mutable to preventGCHandle.Free()from operating on a defensive copy. - Ensures subsequent cleanup paths (e.g., re-release/finalizer flows) can observe the freed state.
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| private int _trackerObjectDisconnected; // Atomic boolean, so using int. | ||
| private readonly bool _releaseTrackerObject; | ||
| internal readonly GCHandle _nativeObjectWrapperWeakHandle; | ||
| internal GCHandle _nativeObjectWrapperWeakHandle; |
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I agree with this. These sorts of gotchas crop up and we've no tests that can help us know we've done something wrong.
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| private readonly bool _releaseTrackerObject; | ||
| internal readonly GCHandle _nativeObjectWrapperWeakHandle; | ||
| internal GCHandle _nativeObjectWrapperWeakHandle; |
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It is very difficult to add deterministic test that verifies there is no GC handle double-free.
Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
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This change addresses a COM wrapper lifetime bug where
GCHandle.Free()could execute on a defensive copy of_nativeObjectWrapperWeakHandle, making cleanup non-idempotent under finalization/release interleavings.The fix is surgical: remove
readonlysoFree()updates the actual field state.What changed
System.Runtime.InteropServices.ComWrappers.ReferenceTrackerNativeObjectWrapper, changed:internal readonly GCHandle _nativeObjectWrapperWeakHandle;internal GCHandle _nativeObjectWrapperWeakHandle;Why this matters
GCHandleis a mutable struct.readonlyfield can operate on a defensive copy.Release()/finalizer race handling, this can lead to staleIsAllocatedstate and duplicate free behavior.Code example