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

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Date:	Fri, 15 Jan 2016 20:47:05 +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 8:18 PM, Takashi Iwai <tiwai@...e.de> wrote:
> On Fri, 15 Jan 2016 20:13:11 +0100,
> Dmitry Vyukov wrote:
>>
>> On Fri, Jan 15, 2016 at 3:38 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> > 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.
>>
>> Ok, I does not seem to see any crashes except the timer hangs below.
>> Let's consider all other bugs as fixed. I will report anything new
>> that I see separately.
>
> OK, good to hear.
>
>> > 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.
>
> I could reproduce this after your suggestion with parallel runs.
>
> This seems specific to hrtimer.  Possibly it's not about the snd-timer
> core itself.  Could you check whether this doesn't happen when
> CONFIG_SND_HRTIMER isn't set?


Does not happen without CONFIG_SND_HRTIMER.
Do you mean that this is hrtimer bug?