linux-kernel - Re: sound: use-after-free in snd_timer

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Message-ID: <s5hwprbt8ei.wl-tiwai@suse.de>
Date:	Fri, 15 Jan 2016 12:00:05 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	alsa-devel@...a-project.org, Jie Yang <yang.jie@...el.com>,
	Mark Brown <broonie@...nel.org>,
	Jaroslav Kysela <perex@...ex.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Kostya Serebryany <kcc@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: sound: use-after-free in snd_timer_interrupt

On Fri, 15 Jan 2016 09:06:10 +0100,
Dmitry Vyukov wrote:
> 
> On Thu, Jan 14, 2016 at 5:09 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > On Wed, 13 Jan 2016 21:54:10 +0100,
> > Takashi Iwai wrote:
> >>
> >> OK, then this might be a possible race at the current snd_timer_stop()
> >> implementation.  There is no sync action there, so the ISR might be
> >> still alive after snd_timer_close() call.  Or might be another race.
> >> This pattern looks a bit different, as it's involved with hrtimer.
> >>
> >> I'll take a look at it tomorrow.
> >
> > I've audited the code today, but the open window doesn't look like
> > what I expected.  I found only some possible cases with slave timer
> > instances.
> >
> > In anyway, below is a test fix patch.  Since I couldn't reproduce the
> > issue on my local machines, it's hard to say whether this covers the
> > holes you fell.  Let's see...
> 
> 
> Hi Takashi,
> 
> I would be interested to understand why other people can't reproduce
> issues that I hit pretty reliably.
> I suspect that it can be due to .config. Please try with the following
> config values.

I guess rather other config, e.g. the kernel debug options.
I suppose you enabled KASAN and DEBUG_LIST.  What else?


> I also start qemu with "-soundhw all" arg.

OK, so you're testing with VM?  This makes easier to recheck.


Takashi