Re: sound: use-after-free in hrtimer_cancel

[Takashi Iwai]

On Fri, 24 Jun 2016 15:33:35 +0200,
Dmitry Vyukov wrote:
> 
> On Fri, Jun 24, 2016 at 3:32 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > On Tue, 21 Jun 2016 20:26:48 +0200,
> > Dmitry Vyukov wrote:
> >>
> >> On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> > On Sat, 04 Jun 2016 20:27:50 +0200,
> >> > Dmitry Vyukov wrote:
> >> >>
> >> >> On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> >> >> > Hello,
> >> >> >
> >> >> > The following program triggers use-after-free:
> >> >>
> >> >> Forget to mention that you need to run it in a tight parallel loop. It
> >> >> takes around 5 minutes to reproduce for me.
> >> >
> >> > Hmm, this again is a bug that is difficult to trigger...  At least, I
> >> > couldn't reproduce locally.  How many processes are you running with
> >> > stress program?
> >> >
> >> > It seems that there is nothing more than opening /dev/audio and does
> >> > some mmap in the job.  Is there any other relevant thing there?
> >> >
> >> > Also, this assumes that the first sound card is Dummy driver, right?
> >> > Check /proc/asound/cards.
> >> >
> >> > If it's about snd-dummy driver, one blind shot would be a patch like
> >> > below.  But even if it would fix, it doesn't explain why it's
> >> > triggered in that way...
> >> >
> >> >
> >> > thanks,
> >> >
> >> > Takashi
> >> >
> >> > ---
> >> > diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
> >> > index c0f8f613f1f1..172dacd925f5 100644
> >> > --- a/sound/drivers/dummy.c
> >> > +++ b/sound/drivers/dummy.c
> >> > @@ -420,6 +420,7 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream)
> >> >
> >> >  static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm)
> >> >  {
> >> > +       hrtimer_cancel(&dpcm->timer);
> >> >         tasklet_kill(&dpcm->tasklet);
> >> >  }
> >>
> >>
> >> Yes, this seems to fix it. I've stressed it for an hour with several
> >> reproducers. If I am not mistaken, it also makes test cases run 15%
> >> faster.
> >
> > Interesting.  Possibly because it now syncs properly before other
> > restart of stream or such...
> >
> >> Please mail a patch.
> >
> > OK, below is the formal patch.
> > Let me know if I can give your tested-by tag.
> 
> Sure.
> 
> Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

Thanks, the patch queued with your tags, now.


Takashi