Is CoreValidateHandle() safe?

["Andrew Fish" <afish@apple.com>]

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I just hit the CR ASSERT [1] in CoreValidateHandle(). It looks like the IHANDLE was a use after free as it was a Pool buffer that was to small to be an IHANDLE and it did not have a valid handle. 

I’m trying to understand why it is safe to walk the gHandleList without a lock? Seems like a local could cache a pointer and an event could remove a handle and Link would point to a stale handle?

Kind of feels like I’m missing something?

[1] https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Core/Dxe/Hand/Handle.c#L64
EFI_STATUS
CoreValidateHandle (
  IN  EFI_HANDLE                UserHandle
  )
{
  IHANDLE             *Handle;
  LIST_ENTRY          *Link;

  if (UserHandle == NULL) {
    return EFI_INVALID_PARAMETER;
  }

  for (Link = gHandleList.BackLink; Link != &gHandleList; Link = Link->BackLink) {
    Handle = CR (Link, IHANDLE, AllHandles, EFI_HANDLE_SIGNATURE);
    if (Handle == (IHANDLE *) UserHandle) {
      return EFI_SUCCESS;
    }
  }

  return EFI_INVALID_PARAMETER;
}

Thanks,

Andrew Fish

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