@@ -215,11 +215,13 @@ static void snd_timer_check_master(struct snd_timer_instance *master)
slave->slave_id == master->slave_id) {
list_move_tail(&slave->open_list, &master->slave_list_head);
spin_lock_irq(&slave_active_lock);
+ spin_lock(&master->timer->lock);
slave->master = master;
slave->timer = master->timer;
if (slave->flags & SNDRV_TIMER_IFLG_RUNNING)
list_add_tail(&slave->active_list,
&master->slave_active_head);
+ spin_unlock(&master->timer->lock);
spin_unlock_irq(&slave_active_lock);
}
}
@@ -346,15 +348,18 @@ int snd_timer_close(struct snd_timer_instance *timeri)
timer->hw.close)
timer->hw.close(timer);
/* remove slave links */
+ spin_lock_irq(&slave_active_lock);
+ spin_lock(&timer->lock);
list_for_each_entry_safe(slave, tmp, &timeri->slave_list_head,
open_list) {
- spin_lock_irq(&slave_active_lock);
- _snd_timer_stop(slave, 1, SNDRV_TIMER_EVENT_RESOLUTION);
list_move_tail(&slave->open_list, &snd_timer_slave_list);
slave->master = NULL;
slave->timer = NULL;
- spin_unlock_irq(&slave_active_lock);
+ list_del_init(&slave->ack_list);
+ list_del_init(&slave->active_list);
}
+ spin_unlock(&timer->lock);
+ spin_unlock_irq(&slave_active_lock);
mutex_unlock(®ister_mutex);
}
out:
@@ -441,9 +446,12 @@ static int snd_timer_start_slave(struct snd_timer_instance *timeri)
spin_lock_irqsave(&slave_active_lock, flags);
timeri->flags |= SNDRV_TIMER_IFLG_RUNNING;
- if (timeri->master)
+ if (timeri->master && timeri->timer) {
+ spin_lock(&timeri->timer->lock);
list_add_tail(&timeri->active_list,
&timeri->master->slave_active_head);
+ spin_unlock(&timeri->timer->lock);
+ }
spin_unlock_irqrestore(&slave_active_lock, flags);
return 1; /* delayed start */
}
@@ -489,6 +497,8 @@ static int _snd_timer_stop(struct snd_timer_instance * timeri,
if (!keep_flag) {
spin_lock_irqsave(&slave_active_lock, flags);
timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
+ list_del_init(&timeri->ack_list);
+ list_del_init(&timeri->active_list);
spin_unlock_irqrestore(&slave_active_lock, flags);
}
goto __end;
This is a note to let you know that I have just added a patch titled ALSA: timer: Harden slave timer list handling to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue This patch is scheduled to be released in version 4.2.8-ckt3. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 4.2.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ---8<------------------------------------------------------------ From 62462eeafe7c9188898b7bb3769f624010f0c171 Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@suse.de> Date: Thu, 14 Jan 2016 16:30:58 +0100 Subject: ALSA: timer: Harden slave timer list handling commit b5a663aa426f4884c71cd8580adae73f33570f0d upstream. A slave timer instance might be still accessible in a racy way while operating the master instance as it lacks of locking. Since the master operation is mostly protected with timer->lock, we should cope with it while changing the slave instance, too. Also, some linked lists (active_list and ack_list) of slave instances aren't unlinked immediately at stopping or closing, and this may lead to unexpected accesses. This patch tries to address these issues. It adds spin lock of timer->lock (either from master or slave, which is equivalent) in a few places. For avoiding a deadlock, we ensure that the global slave_active_lock is always locked at first before each timer lock. Also, ack and active_list of slave instances are properly unlinked at snd_timer_stop() and snd_timer_close(). Last but not least, remove the superfluous call of _snd_timer_stop() at removing slave links. This is a noop, and calling it may confuse readers wrt locking. Further cleanup will follow in a later patch. Actually we've got reports of use-after-free by syzkaller fuzzer, and this hopefully fixes these issues. Reported-by: Dmitry Vyukov <dvyukov@google.com> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- sound/core/timer.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) -- 1.9.1