ALSA: timer: Fix leftover link at closing

In ALSA timer core, the active timer instance is managed in
active_list linked list.  Each element is added / removed dynamically
at timer start, stop and in timer interrupt.  The problem is that
snd_timer_interrupt() has a thinko and leaves the element in
active_list when it's the last opened element.  This eventually leads
to list corruption or use-after-free error.

This hasn't been revealed because we used to delete the list forcibly
in snd_timer_stop() in the past.  However, the recent fix avoids the
double-stop behavior (in commit [f784beb75ce8: ALSA: timer: Fix link
corruption due to double start or stop]), and this leak hits reality.

This patch fixes the link management in snd_timer_interrupt().  Now it
simply unlinks no matter which stream is.

BugLink: http://lkml.kernel.org/r/CACT4Y+Yy2aukHP-EDp8-ziNqNNmb-NTf=jDWXMP7jB8HDa2vng@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/timer.c b/sound/core/timer.c
index b419e612f98749db23c5919292e358ed3d3d4912..9b513a05765a10985d556b101918ed3783b9ae60 100644 (file)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -744,8 +744,8 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left)
                        ti->cticks = ti->ticks;
                } else {
                        ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
-                       if (--timer->running)
-                               list_del_init(&ti->active_list);
+                       --timer->running;
+                       list_del_init(&ti->active_list);
                }
                if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) ||
                    (ti->flags & SNDRV_TIMER_IFLG_FAST))