bug#28489: Acknowledgement (27.0.50; eieio-persistent slot type validation should be a bit smarter)

[Eric Abrahamsen]

Noam Postavsky <npostavs@users.sourceforge.net> writes:

> Eric Abrahamsen <eric@ericabrahamsen.net> writes:
>
>> Essentially it is validating twice, both before and after the actual
>> objects are created. I don't have a very firm grasp of all the code
>> involved, but in principle I would prefer just to eval all object
>> construction forms regardless, and then let it blow up at "real"
>> validation time -- it was going to blow up anyway.
>
> Hmm, yeah, it does look the prevalidation is mostly redundant work.  The
> docstring of eieio-persistent-convert-list-to-object mentions malicious
> code, perhaps the prevalidation should be with unsafep (i.e., don't try
> to typecheck anything, just make sure it's safe to eval).  This would
> require that object constructors could be marked safe though.

That sounds like the right solution. I've never looked at
unsafep.el, and don't know exactly how it works, but in principle I
think object creation should be "safe". Of note:

1. Strings read from the persistence file are already stripped of
   properties.
2. Slot values are simply validated by type. I don't think eval is
   called anywhere, though I'd be happy to try to make sure of this.
3. Object creation could run malicious code *if* someone had overridden
   `initialize-instance' or `shared-initialize', and injected random
   hard-drive-destroying code. But I don't think this malicious code
   could be included in a persistence file itself (that's worth looking
   in to).

I don't know how close that gets us to "safe".

>> But again, my patch or something like it would be enough to get
>> everything working as advertised.
>
> Right.  I think your patch is probably fine, though a few tests might a
> good idea too.

I might as well write tests that exercise the whole eieio-persistent
round-trip: create a few test objects, write them to a tmp file, and
read them back as objects.

Thanks,
Eric