Patch "ALSA: timer: Add missing mutex lock for compat ioctls" has been added to the 4.13-stable tree

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

ALSA: timer: Add missing mutex lock for compat ioctls

to the 4.13-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-add-missing-mutex-lock-for-compat-ioctls.patch
and it can be found in the queue-4.13 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 Iwai <[email protected]>
Date: Sun, 29 Oct 2017 11:02:04 +0100
Subject: ALSA: timer: Add missing mutex lock for compat ioctls

From: Takashi Iwai <[email protected]>

commit 79fb0518fec8c8b4ea7f1729f54f293724b3dbb0 upstream.

The races among ioctl and other operations were protected by the commit af368027a49a ("ALSA: timer: Fix race among timer ioctls") and later fixes, but one code path was forgotten in the scenario: the 32bit compat ioctl. As syzkaller recently spotted, a very similar use-after-free may happen with the combination of compat ioctls.

The fix is simply to apply the same ioctl_lock to the compat_ioctl callback, too.

Reference: http://lkml.kernel.org/r/[email protected]

---
 sound/core/timer_compat.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

@@ -133,7 +133,8 @@ enum {
 #endif /* CONFIG_X86_X32 */
 };
 
-static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg)
+static long __snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd,
+					  unsigned long arg)
 {
 	void __user *argp = compat_ptr(arg);
 

@@ -153,7 +154,7 @@ static long snd_timer_user_ioctl_compat(
 	case SNDRV_TIMER_IOCTL_PAUSE:
 	case SNDRV_TIMER_IOCTL_PAUSE_OLD:
 	case SNDRV_TIMER_IOCTL_NEXT_DEVICE:
-		return snd_timer_user_ioctl(file, cmd, (unsigned long)argp);
+		return __snd_timer_user_ioctl(file, cmd, (unsigned long)argp);
 	case SNDRV_TIMER_IOCTL_GPARAMS32:
 		return snd_timer_user_gparams_compat(file, argp);
 	case SNDRV_TIMER_IOCTL_INFO32:

@@ -167,3 +168,15 @@ static long snd_timer_user_ioctl_compat(
 	}
 	return -ENOIOCTLCMD;
 }
+
+static long snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd,
+					unsigned long arg)
+{
+	struct snd_timer_user *tu = file->private_data;
+	long ret;
+
+	mutex_lock(&tu->ioctl_lock);
+	ret = __snd_timer_user_ioctl_compat(file, cmd, arg);
+	mutex_unlock(&tu->ioctl_lock);
+	return ret;
+}

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

queue-4.13/alsa-seq-fix-nested-rwsem-annotation-for-lockdep-splat.patch queue-4.13/alsa-timer-add-missing-mutex-lock-for-compat-ioctls.patch