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

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Date:	Fri, 15 Jan 2016 12:03:17 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Takashi Iwai <tiwai@...e.de>
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, Jan 15, 2016 at 12:00 PM, Takashi Iwai <tiwai@...e.de> wrote:
> 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've attached my config (you will need to disable CONFIG_KCOV, it is
not upstreamed).


>> I also start qemu with "-soundhw all" arg.
>
> OK, so you're testing with VM?  This makes easier to recheck.

Yes, I start qemu as:

qemu-system-x86_64 -hda wheezy.img -net
user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
arch/x86/boot/bzImage -append "console=ttyS0 root=/dev/sda debug
earlyprintk=serial slub_debug=UZ" -enable-kvm -m 2G -numa
node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 -smp
sockets=2,cores=2,threads=1 -usb -usbdevice mouse -usbdevice tablet
-soundhw all

Download attachment ".config" of type "application/octet-stream" (137378 bytes)