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 4.4-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-4.4 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);
}
}
@@ -346,15 +348,18 @@ 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:
@@ -441,9 +446,12 @@ 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 */
}
@@ -489,6 +497,8 @@ 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-4.4/alsa-hrtimer-fix-stall-by-hrtimer_cancel.patch
queue-4.4/alsa-hda-fix-white-noise-on-dell-latitude-e5550.patch
queue-4.4/alsa-hda-fix-the-headset-mic-detection-problem-for-a-dell-laptop.patch
queue-4.4/alsa-timer-harden-slave-timer-list-handling.patch
queue-4.4/alsa-timer-fix-double-unlink-of-active_list.patch
queue-4.4/alsa-control-avoid-kernel-warnings-from-tlv-ioctl-with-numid-0.patch
queue-4.4/alsa-hda-flush-the-pending-probe-work-at-remove.patch
queue-4.4/alsa-hda-fixup-inverted-internal-mic-for-lenovo-e50-80.patch
queue-4.4/alsa-usb-add-native-dsd-support-for-oppo-ha-1.patch
queue-4.4/alsa-hda-fix-missing-module-loading-with-model-generic-option.patch
queue-4.4/alsa-seq-fix-race-at-timer-setup-and-close.patch
queue-4.4/alsa-pcm-fix-snd_pcm_hw_params-struct-copy-in-compat-mode.patch
queue-4.4/alsa-seq-fix-snd_seq_call_port_info_ioctl-in-compat-mode.patch
queue-4.4/alsa-seq-fix-missing-null-check-at-remove_events-ioctl.patch
queue-4.4/alsa-usb-audio-fix-mixer-ctl-regression-of-native-instrument-devices.patch
queue-4.4/alsa-timer-handle-disconnection-more-safely.patch
queue-4.4/alsa-hda-fix-bass-pin-fixup-for-asus-n550jx.patch
queue-4.4/alsa-timer-fix-race-among-timer-ioctls.patch
queue-4.4/alsa-hda-add-fixup-for-dell-latitidue-e6540.patch
queue-4.4/alsa-usb-audio-avoid-calling-usb_autopm_put_interface-at-disconnect.patch
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