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

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Message-ID: <s5hfuxytu55.wl-tiwai@suse.de>
Date:	Fri, 15 Jan 2016 22:22:46 +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 20:47:05 +0100,
Dmitry Vyukov wrote:
> 
> 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?

I guess rather it's a bug in snd-hrtimer driver.
Will check it later.


Takashi