Patch "ALSA: firewire-tascam: accessing to user space outside spinlock" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: firewire-tascam: accessing to user space outside spinlock

to the 4.7-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-firewire-tascam-accessing-to-user-space-outside-spinlock.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Sakamoto <[email protected]>
Date: Wed, 31 Aug 2016 20:15:32 +0900
Subject: ALSA: firewire-tascam: accessing to user space outside spinlock

From: Takashi Sakamoto <[email protected]>

commit 04b2d9c9c319277ad4fbbb71855c256a9f4d5f98 upstream.

In hwdep interface of firewire-tascam driver, accessing to user space is in a critical section with disabled local interrupt. Depending on architecture, accessing to user space can cause page fault exception. Then local processor stores machine status and handle the synchronous event. A handler corresponding to the event can call task scheduler to wait for preparing pages. In a case of usage of single core processor, the state to disable local interrupt is worse because it doesn't handle usual interrupts from hardware.

This commit fixes this bug, by performing the accessing outside spinlock.

---
 sound/firewire/tascam/tascam-hwdep.c |   33 +++++++++++----------------------
 1 file changed, 11 insertions(+), 22 deletions(-)

@@ -16,31 +16,14 @@
 
 #include "tascam.h"
 
-static long hwdep_read_locked(struct snd_tscm *tscm, char __user *buf,
-			      long count)
-{
-	union snd_firewire_event event;
-
-	memset(&event, 0, sizeof(event));
-
-	event.lock_status.type = SNDRV_FIREWIRE_EVENT_LOCK_STATUS;
-	event.lock_status.status = (tscm->dev_lock_count > 0);
-	tscm->dev_lock_changed = false;
-
-	count = min_t(long, count, sizeof(event.lock_status));
-
-	if (copy_to_user(buf, &event, count))
-		return -EFAULT;
-
-	return count;
-}
-
 static long hwdep_read(struct snd_hwdep *hwdep, char __user *buf, long count,
 		       loff_t *offset)
 {
 	struct snd_tscm *tscm = hwdep->private_data;
 	DEFINE_WAIT(wait);
-	union snd_firewire_event event;
+	union snd_firewire_event event = {
+		.lock_status.type = SNDRV_FIREWIRE_EVENT_LOCK_STATUS,
+	};
 
 	spin_lock_irq(&tscm->lock);
 

@@ -54,10 +37,16 @@ static long hwdep_read(struct snd_hwdep
 		spin_lock_irq(&tscm->lock);
 	}
 
-	memset(&event, 0, sizeof(event));
-	count = hwdep_read_locked(tscm, buf, count);
+	event.lock_status.status = (tscm->dev_lock_count > 0);
+	tscm->dev_lock_changed = false;
+
 	spin_unlock_irq(&tscm->lock);
 
+	count = min_t(long, count, sizeof(event.lock_status));
+
+	if (copy_to_user(buf, &event, count))
+		return -EFAULT;
+
 	return count;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/alsa-fireworks-accessing-to-user-space-outside-spinlock.patch queue-4.7/alsa-firewire-tascam-accessing-to-user-space-outside-spinlock.patch