Re: [PATCH RFC 0/6] ALSA: Fix UAF with delayed kobj release

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On Tue, 08 Aug 2023 21:26:55 +0200,
Curtis Malainey wrote:
> 
> On Mon, Aug 7, 2023 at 3:34 PM Curtis Malainey <cujomalainey@xxxxxxxxxx> wrote:
> >
> > > It's just a RFC and only lightly tested.
> >
> > Thanks for the series
> >
> > I will be hammering this in my test setup for next several hours
> 
> Testing has yielded 0 bugs overnight.
> 
> After discussion it seems like this might be more of a workaround for
> the APIs than properly using them. Adding Stephen for more input but
> having two kobj in the same allocation is technically not correct as
> you essentially refcounting the same thing twice. Also having an empty
> release function essentially nullifies the purpose of the refcounts.
> We should probably consider something that uses the API as intended
> rather than trying to fight their function.

Moving each PCM device and control device to own object and properly
release in the own device release could be another way to go.

OTOH, I'm still wondering whether how to assure synchronization if all
device releases are done asynchronously.  If there are some
dependencies between the resources (e.g. taking the parent's lock) at
release, and how can it be guaranteed to work?  Or, the release calls
must not touch anything outside its own?  If so, we'll still need to
two places to finish the stuff: quiesce and release.


thanks,

Takashi



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