Re: sound: use-after-free in snd_timer_interrupt

[Takashi Iwai]

On Fri, 15 Jan 2016 20:13:11 +0100,
Dmitry Vyukov wrote:
> 
> On Fri, Jan 15, 2016 at 3:38 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> > On Fri, Jan 15, 2016 at 2:51 PM, Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxx> 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@xxxxxxx> 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?


thanks,

Takashi