[PATCH 4.4 016/162] ALSA: timer: Unconditionally unlink slave instances, too

Greg Kroah-Hartman
2021-11-24T12:03:48Z

From: Takashi Iwai <tiwai@suse.de>

commit ffdd98277f0a1d15a67a74ae09bee713df4c0dbc upstream.

Like the previous fix (commit c0317c0e8709 "ALSA: timer: Fix
use-after-free problem"), we have to unlink slave timer instances
immediately at snd_timer_stop(), too. Otherwise it may leave a stale
entry in the list if the slave instance is freed before actually
running.

Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211105091517.21733-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/core/timer.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -566,23 +566,22 @@ static int snd_timer_stop1(struct snd_ti
static int snd_timer_stop_slave(struct snd_timer_instance *timeri, bool stop)
{
unsigned long flags;
+ bool running;

spin_lock_irqsave(&slave_active_lock, flags);
- if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) {
- spin_unlock_irqrestore(&slave_active_lock, flags);
- return -EBUSY;
- }
+ running = timeri->flags & SNDRV_TIMER_IFLG_RUNNING;
timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
if (timeri->timer) {
spin_lock(&timeri->timer->lock);
list_del_init(&timeri->ack_list);
list_del_init(&timeri->active_list);
- snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
- SNDRV_TIMER_EVENT_PAUSE);
+ if (running)
+ snd_timer_notify1(timeri, stop ? SNDRV_TIMER_EVENT_STOP :
+ SNDRV_TIMER_EVENT_PAUSE);
spin_unlock(&timeri->timer->lock);
}
spin_unlock_irqrestore(&slave_active_lock, flags);
- return 0;
+ return running ? 0 : -EBUSY;
}

/*