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Date: Mon, 06 Jun 2016 16:11:05 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
LKML <linux-kernel@...r.kernel.org>,
Sasha Levin <sasha.levin@...cle.com>,
Alexander Potapenko <glider@...gle.com>,
Kostya Serebryany <kcc@...gle.com>,
syzkaller <syzkaller@...glegroups.com>
Subject: Re: sound: use-after-free in hrtimer_cancel
On Sat, 04 Jun 2016 20:27:50 +0200,
Dmitry Vyukov wrote:
>
> On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov <dvyukov@...gle.com> 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);
}
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