[libvirt] [PATCH 4/9] util: Add magic_marker for all virObjects

[Pavel Hrdina]

On Tue, May 30, 2017 at 07:38:16AM -0400, John Ferlan wrote:
> The virObject logic "assumes" that whatever is passed to its API's
> would be some sort of virObjectPtr; however, if it is not then some
> really bad things can happen.
> 
> So far there's been only virObject{Ref|Unref}, virObject{Lock|Unlock},
> and virObjectIsClass and the virObject and virObjectLockable class
> consumers have been well behaved and code well tested. Soon there will
> be more consumers and one such consumer tripped over this during testing
> by passing a virHashTablePtr to virObjectIsClass which ends up calling
> virClassIsDerivedFrom using "obj->klass", which wasn't really a klass
> object causing one of those bad things to happen.
> 
> To avoid the future possibility that a non virObject class memory was
> passed to some virObject* API, let's add a "magic_marker" to the base
> virObject class that contains a value "0xFEEDBEEF", then any place in
> the code which would accept or process the base opaque virObjectPtr,
> compare the magic_marker against 0xFEEDBEEF to make sure this is an
> object allocated by this code.
> 
> It is still left up to the caller to handle the failed API calls just
> as it would be if it passed a NULL opaque pointer anyobj.

I don't think that we need to guard this kind of programming error.
We've been able to cope with the current virObject code without hitting
this issue.

Pavel
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