From: Takashi Iwai <tiwai@suse.de>
Date: Wed, 13 Jan 2016 20:35:06 +0000 (+0100)
Subject: ALSA: timer: Fix double unlink of active_list
X-Git-Tag: v3.16.35~591
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=4a7ff8dcf12fae2b2368ba89dffa3743a9996e39;p=thirdparty%2Fkernel%2Fstable.git

ALSA: timer: Fix double unlink of active_list

commit ee8413b01045c74340aa13ad5bdf905de32be736 upstream.

ALSA timer instance object has a couple of linked lists and they are
unlinked unconditionally at snd_timer_stop().  Meanwhile
snd_timer_interrupt() unlinks it, but it calls list_del() which leaves
the element list itself unchanged.  This ends up with unlinking twice,
and it was caught by syzkaller fuzzer.

The fix is to use list_del_init() variant properly there, too.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 777a45e08e539..222c549341c8f 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -694,7 +694,7 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left)
 		} else {
 			ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
 			if (--timer->running)
-				list_del(&ti->active_list);
+				list_del_init(&ti->active_list);
 		}
 		if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) ||
 		    (ti->flags & SNDRV_TIMER_IFLG_FAST))