Patch "ALSA: firewire-tascam: accessing to user space outside spinlock" has been added to the 4.4-stable tree

Patch "ALSA: firewire-tascam: accessing to user space outside spinlock" has been added to the 4.4-stable tree

[gregkh]

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 4.4-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-firewire-tascam-accessing-to-user-space-outside-spinlock.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@vger.kernel.org> know about it.


>From 04b2d9c9c319277ad4fbbb71855c256a9f4d5f98 Mon Sep 17 00:00:00 2001
From: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Date: Wed, 31 Aug 2016 20:15:32 +0900
Subject: ALSA: firewire-tascam: accessing to user space outside spinlock

From: Takashi Sakamoto <o-takashi@sakamocchi.jp>

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.

Reported-by: Vaishali Thakkar <vaishali.thakkar@oracle.com>
Fixes: e5e0c3dd257b('ALSA: firewire-tascam: add hwdep interface')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/sound/firewire/tascam/tascam-hwdep.c
+++ b/sound/firewire/tascam/tascam-hwdep.c
@@ -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 o-takashi@sakamocchi.jp are

queue-4.4/alsa-fireworks-accessing-to-user-space-outside-spinlock.patch
queue-4.4/alsa-firewire-tascam-accessing-to-user-space-outside-spinlock.patch