[PATCH 3.19.y-ckt 104/210] ALSA: timer: Fix double unlink of active_list

From: Kamal Mostafa
Date: Thu Jan 28 2016 - 20:57:03 EST

3.19.8-ckt14 -stable review patch. If anyone has any objections, please let me know.


From: Takashi Iwai <tiwai@xxxxxxx>

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@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
sound/core/timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 777a45e..222c549 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 {
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))