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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 1d5461719e31f5ea2278f2bfebc199086db1521c..4e436fe53afac1e99bf21cd7063d259aef3d3bce 100644 (file)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -703,7 +703,7 @@ 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))