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ALSA: timer: Fix link corruption due to double start or stop

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Although ALSA timer code got hardening for races, it still causes
use-after-free error.  This is however rather a corrupted linked list,
not actually the concurrent accesses.  Namely, when timer start is
triggered twice, list_add_tail() is called twice, too.  This ends
up with the link corruption and triggers KASAN error.

The simplest fix would be replacing list_add_tail() with
list_move_tail(), but fundamentally it's the problem that we don't
check the double start/stop correctly.  So, the right fix here is to
add the proper checks to snd_timer_start() and snd_timer_stop() (and
their variants).

BugLink: http://lkml.kernel.org/r/CACT4Y+ZyPRoMQjmawbvmCEDrkBD2BQuH7R09=eOkf5ESK8kJAw@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2016-01-30 23:09:08 +01:00
parent 2cdc7b636d
commit f784beb75c
1 changed files with 28 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
sound/core/timer.c
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@ -451,6 +451,10 @@ static int snd_timer_start_slave(struct snd_timer_instance *timeri)
unsigned long flags;
spin_lock_irqsave(&slave_active_lock, flags);
if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) {
spin_unlock_irqrestore(&slave_active_lock, flags);
return -EBUSY;
}
timeri->flags |= SNDRV_TIMER_IFLG_RUNNING;
if (timeri->master && timeri->timer) {
spin_lock(&timeri->timer->lock);
@ -475,7 +479,8 @@ int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks)
return -EINVAL;
if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) {
result = snd_timer_start_slave(timeri);
snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
if (result >= 0)
snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
return result;
}
timer = timeri->timer;
@ -484,11 +489,18 @@ int snd_timer_start(struct snd_timer_instance *timeri, unsigned int ticks)
if (timer->card && timer->card->shutdown)
return -ENODEV;
spin_lock_irqsave(&timer->lock, flags);
if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING |
SNDRV_TIMER_IFLG_START)) {
result = -EBUSY;
goto unlock;
}
timeri->ticks = timeri->cticks = ticks;
timeri->pticks = 0;
result = snd_timer_start1(timer, timeri, ticks);
unlock:
spin_unlock_irqrestore(&timer->lock, flags);
snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
if (result >= 0)
snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START);
return result;
}
@ -502,6 +514,10 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event)
if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) {
spin_lock_irqsave(&slave_active_lock, flags);
if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) {
spin_unlock_irqrestore(&slave_active_lock, flags);
return -EBUSY;
}
timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
list_del_init(&timeri->ack_list);
list_del_init(&timeri->active_list);
@ -512,6 +528,11 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event)
if (!timer)
return -EINVAL;
spin_lock_irqsave(&timer->lock, flags);
if (!(timeri->flags & (SNDRV_TIMER_IFLG_RUNNING |
SNDRV_TIMER_IFLG_START))) {
spin_unlock_irqrestore(&timer->lock, flags);
return -EBUSY;
}
list_del_init(&timeri->ack_list);
list_del_init(&timeri->active_list);
if (timer->card && timer->card->shutdown) {
@ -581,10 +602,15 @@ int snd_timer_continue(struct snd_timer_instance *timeri)
if (timer->card && timer->card->shutdown)
return -ENODEV;
spin_lock_irqsave(&timer->lock, flags);
if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) {
result = -EBUSY;
goto unlock;
}
if (!timeri->cticks)
timeri->cticks = 1;
timeri->pticks = 0;
result = snd_timer_start1(timer, timeri, timer->sticks);
unlock:
spin_unlock_irqrestore(&timer->lock, flags);
snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_CONTINUE);
return result;