This is a note to let you know that I've just added the patch titled ALSA: timer: Harden slave timer list handling to the 3.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: alsa-timer-harden-slave-timer-list-handling.patch and it can be found in the queue-3.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From b5a663aa426f4884c71cd8580adae73f33570f0d Mon Sep 17 00:00:00 2001 From: Takashi Iwai <tiwai@xxxxxxx> Date: Thu, 14 Jan 2016 16:30:58 +0100 Subject: ALSA: timer: Harden slave timer list handling From: Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- sound/core/timer.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -215,11 +215,13 @@ static void snd_timer_check_master(struc 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); } } @@ -345,15 +347,18 @@ int snd_timer_close(struct snd_timer_ins 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: @@ -440,9 +445,12 @@ static int snd_timer_start_slave(struct 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 */ } @@ -488,6 +496,8 @@ static int _snd_timer_stop(struct snd_ti 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; Patches currently in stable-queue which might be from tiwai@xxxxxxx are queue-3.10/alsa-hrtimer-fix-stall-by-hrtimer_cancel.patch queue-3.10/alsa-timer-harden-slave-timer-list-handling.patch queue-3.10/alsa-timer-fix-double-unlink-of-active_list.patch queue-3.10/alsa-control-avoid-kernel-warnings-from-tlv-ioctl-with-numid-0.patch queue-3.10/alsa-hda-realtek-fix-silent-headphone-output-on-macpro-4-1-v2.patch queue-3.10/alsa-rme96-fix-unexpected-volume-reset-after-rate-changes.patch queue-3.10/alsa-hda-set-skl-hda-controller-power-at-freeze-and-thaw.patch queue-3.10/alsa-hda-add-inverted-dmic-for-packard-bell-dots.patch queue-3.10/alsa-hda-add-intel-lewisburg-device-ids-audio.patch queue-3.10/alsa-seq-fix-race-at-timer-setup-and-close.patch queue-3.10/alsa-pcm-fix-snd_pcm_hw_params-struct-copy-in-compat-mode.patch queue-3.10/alsa-seq-fix-snd_seq_call_port_info_ioctl-in-compat-mode.patch queue-3.10/alsa-seq-fix-missing-null-check-at-remove_events-ioctl.patch queue-3.10/alsa-timer-fix-race-among-timer-ioctls.patch queue-3.10/alsa-hda-apply-pin-fixup-for-hp-probook-6550b.patch -- 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