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

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Message-ID: <s5hd1pkzoq0.wl-tiwai@suse.de>
Date:	Wed, 20 Apr 2016 10:08:55 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	alsa-devel@...a-project.org, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	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 Wed, 20 Apr 2016 09:56:04 +0200,
Dmitry Vyukov wrote:
> 
> On Sun, Apr 3, 2016 at 8:33 AM, Takashi Iwai <tiwai@...e.de> wrote:
> >> >> It is not easily reproducible. I've hit several times while running
> >> >> fuzzer for a week. Here is one of the logs for the record:
> >> >> https://gist.githubusercontent.com/dvyukov/c84798ee55721563ecb537c4d51dc9f5/raw/f00b865a85877656f13b41917f7321730f140d35/gistfile1.txt
> >> >
> >> > There are a few more fixes in sound/core/timer.c since 4.5, and they
> >> > possibly already cover this.
> >> >
> >> > Please let me know if this is still seen on the upcoming 4.6-rc2.
> >>
> >> Hi Takashi,
> >>
> >> I've updated fuzzer to 05cf8077e54b20dddb756eaa26f3aeb5c38dd3cf (Apr
> >> 1) yesterday. Let's see if it still happens.
> >>
> >> Out of curiosity, how was the bug found?
> >
> > Well, I'm not entirely sure whether they really cover.  It's just a
> > hope, as these are patches to close some possible races :)
> >
> > 9984d1b5835ca29fc7025186a891ee7398d21cc7
> >     ALSA: timer: Protect the whole snd_timer_close() with open race
> > f65e0d299807d8a11812845c972493c3f9a18e10
> >     ALSA: timer: Call notifier in the same spinlock
> > 4a07083ed613644c96c34a7dd2853dc5d7c70902
> >     ALSA: timer: Use mod_timer() for rearming the system timer
> 
> 
> Hi Takashi,
> 
> I've hit it again on 806fdcce017dc98c4dbf8ed001750a0d7d2bb0af (Apr
> 14), all 3 commits are already in my tree.
> 
> [  343.222218] ------------[ cut here ]------------
> [  343.222218] WARNING: CPU: 3 PID: 7040 at kernel/time/hrtimer.c:837
> hrtimer_forward+0x26a/0x3e0

This is a different warning.  The previous was use-after-free, and
this is a warning about re-arming the queued hrtimer.
Maybe there is a slightly remaining race about hrtimer_start() and the
interrupt handler in snd-hrtimer.


thanks,

Takashi

> [  343.222218] Modules linked in:
> [  343.222218] CPU: 3 PID: 7040 Comm: syz-executor Not tainted 4.6.0-rc3+ #349
> [  343.222218] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS Bochs 01/01/2011
> [  343.229525]  ffffffff87eb25c0 ffff88006d507ce0 ffffffff82c8fabf
> ffffffff86abac00
> [  343.229525]  fffffbfff0fd64b8 0000000000000000 0000000000000000
> ffffffff86abac00
> [  343.229525]  ffffffff814cfe1a 0000000000000009 ffff88006d507d28
> ffffffff8136639f
> [  343.229525] Call Trace:
> [  343.229525]  <IRQ>  [<ffffffff82c8fabf>] dump_stack+0x12e/0x18f
> [  343.229525]  [<ffffffff814cfe1a>] ? hrtimer_forward+0x26a/0x3e0
> [  343.229525]  [<ffffffff8136639f>] __warn+0x19f/0x1e0
> [  343.229525]  [<ffffffff813665ac>] warn_slowpath_null+0x2c/0x40
> [  343.229525]  [<ffffffff814cfe1a>] hrtimer_forward+0x26a/0x3e0
> [  343.229525]  [<ffffffff85382ceb>] snd_hrtimer_callback+0x11b/0x230
> [  343.229525]  [<ffffffff814d1091>] __hrtimer_run_queues+0x331/0xe90
> [  343.229525]  [<ffffffff85382bd0>] ? snd_hrtimer_close+0xa0/0xa0
> [  343.229525]  [<ffffffff814d0d60>] ? enqueue_hrtimer+0x3d0/0x3d0
> [  343.229525]  [<ffffffff814d3a62>] hrtimer_interrupt+0x182/0x430
> [  343.229525]  [<ffffffff8125aa52>] local_apic_timer_interrupt+0x72/0xe0
> [  343.229525]  [<ffffffff867bec99>] smp_apic_timer_interrupt+0x79/0xa0
> [  343.229525]  [<ffffffff867bcfec>] apic_timer_interrupt+0x8c/0xa0
> [  343.229525]  <EOI>  [<ffffffff813e2e00>] ? ___might_sleep+0x3a0/0x3a0
> [  343.229525]  [<ffffffff81710fbf>] ? __might_fault+0xaf/0x1d0
> [  343.229525]  [<ffffffff814d4f4d>] SyS_nanosleep+0x6d/0x100
> [  343.229525]  [<ffffffff814d4ee0>] ? hrtimer_nanosleep+0x730/0x730
> [  343.229525]  [<ffffffff81007b53>] ? syscall_trace_enter_phase2+0x143/0x740
> [  343.229525]  [<ffffffff81008758>] ? do_syscall_64+0x48/0x640
> [  343.229525]  [<ffffffff8100821b>] ? syscall_trace_enter+0xcb/0xf0
> [  343.229525]  [<ffffffff814d4ee0>] ? hrtimer_nanosleep+0x730/0x730
> [  343.229525]  [<ffffffff810088ef>] do_syscall_64+0x1df/0x640
> [  343.229525]  [<ffffffff8100501b>] ? trace_hardirqs_on_thunk+0x1b/0x1d
> [  343.229525]  [<ffffffff867bc443>] entry_SYSCALL64_slow_path+0x25/0x25
> [  343.229525] ---[ end trace f4fa4ed5ea230466 ]---
> 
> 
> For the record, here is syzkaller log:
> https://gist.githubusercontent.com/dvyukov/4c31022a284421020029c877561a99ed/raw/649ebe7c882d9b4611a311f279055b272bd5443b/gistfile1.txt
>