From: Takashi Iwai <tiwai@xxxxxxx> This patch has been added to the 3.18 stable tree. If you have any objections, please let us know. =============== [ Upstream commit f784beb75ce82f4136f8a0960d3ee872f7109e09 ] 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@xxxxxxxxxxxxxx Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx> --- sound/core/timer.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index 2545b69..9e8b709 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -444,6 +444,10 @@ 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); @@ -468,18 +472,26 @@ 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; if (timer == NULL) return -EINVAL; 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; } @@ -493,6 +505,10 @@ 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); @@ -503,6 +519,11 @@ 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 ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) && @@ -566,10 +587,15 @@ int snd_timer_continue(struct snd_timer_instance *timeri) if (! timer) return -EINVAL; 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; -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html