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Fix DefaultCOMImpl reference counting bugs in DAC #125231

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Fix DefaultCOMImpl reference counting bugs in DAC #125231

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40b08bd
Fix DefaultCOMImpl reference counting bugs in DAC
Mar 5, 2026
40e8bab
Remove intentional ref count leak from cDAC GetHandleEnum APIs
Mar 5, 2026
2e0b30b
Use CLRDATA_REQUEST_REVISION instead of SOS_BREAKING_CHANGE_VERSION
Mar 6, 2026
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2 changes: 1 addition & 1 deletion src/coreclr/debug/daccess/dacimpl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1574,7 +1574,7 @@ class DefaultCOMImpl : public T

ULONG STDMETHODCALLTYPE Release()
{
ULONG res = mRef--;
ULONG res = --mRef;
if (res == 0)
delete this;
return res;
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14 changes: 11 additions & 3 deletions src/coreclr/debug/daccess/request.cpp
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Expand Up @@ -443,14 +443,19 @@ ClrDataAccess::GetMethodTableSlotEnumerator(CLRDATA_ADDRESS mt, ISOSMethodEnum *
else
{
DacMethodTableSlotEnumerator *methodTableSlotEnumerator = new (nothrow) DacMethodTableSlotEnumerator();
*enumerator = methodTableSlotEnumerator;
if (*enumerator == NULL)
if (methodTableSlotEnumerator == NULL)
{
hr = E_OUTOFMEMORY;
}
else
{
hr = methodTableSlotEnumerator->Init(mTable);

if (SUCCEEDED(hr))
hr = methodTableSlotEnumerator->QueryInterface(__uuidof(ISOSMethodEnum), (void**)enumerator);

if (FAILED(hr))
delete methodTableSlotEnumerator;
}
}

Expand Down Expand Up @@ -3969,7 +3974,10 @@ ClrDataAccess::Request(IN ULONG32 reqCode,
}
else
{
*(ULONG32*)outBuffer = 9;
// Revision 10: Fixed DefaultCOMImpl::Release() to use pre-decrement (--mRef).
// Consumers that previously compensated for the broken ref counting (e.g., ClrMD)
// should check this revision to avoid double-freeing.
*(ULONG32*)outBuffer = 10;
status = S_OK;
}
break;
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6 changes: 0 additions & 6 deletions src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Legacy/SOSDacImpl.cs
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Expand Up @@ -1528,9 +1528,6 @@ int ISOSDacInterface.GetHandleEnum(DacComNullableByRef<ISOSHandleEnum> ppHandleE
}
#endif
ppHandleEnum.Interface = new SOSHandleEnum(_target, supportedHandleTypes, legacyHandleEnum);
// COMPAT: In the legacy DAC, this API leaks a ref-count of the returned enumerator.
// Manually leak a refcount here to match previous behavior and avoid breaking customer code.
ComInterfaceMarshaller<ISOSHandleEnum>.ConvertToUnmanaged(ppHandleEnum.Interface);
}
catch (System.Exception ex)
{
Expand Down Expand Up @@ -1558,9 +1555,6 @@ int ISOSDacInterface.GetHandleEnumForTypes([In, MarshalUsing(CountElementName =
IGC gc = _target.Contracts.GC;
HandleType[] handleTypes = gc.GetHandleTypes(types);
ppHandleEnum.Interface = new SOSHandleEnum(_target, handleTypes, legacyHandleEnum);
// COMPAT: In the legacy DAC, this API leaks a ref-count of the returned enumerator.
// Manually leak a refcount here to match previous behavior and avoid breaking customer code.
ComInterfaceMarshaller<ISOSHandleEnum>.ConvertToUnmanaged(ppHandleEnum.Interface);
}
catch (System.Exception ex)
{
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