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

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.