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

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Date:	Fri, 15 Jan 2016 15:38:58 +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 2:51 PM, Takashi Iwai <tiwai@...e.de> wrote:
> On Fri, 15 Jan 2016 12:03:17 +0100,
> Dmitry Vyukov wrote:
>>
>> 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).
>
> Hm, that has lots of other drivers built-in...
>
>> >> 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
>
> And which test did trigger use-after-free, even with all previous
> patches?

I will try to extract a new reproducer now.
Meanwhile, can you try to reproduce this one:
https://groups.google.com/forum/#!msg/syzkaller/bbtG9_h1ONU/CPLblMC6FAAJ
? I run the program in a tight parallel loop.