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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org> know about it.


>From 79fb0518fec8c8b4ea7f1729f54f293724b3dbb0 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Sun, 29 Oct 2017 11:02:04 +0100
Subject: ALSA: timer: Add missing mutex lock for compat ioctls

From: Takashi Iwai <tiwai@suse.de>

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.

Fixes: af368027a49a ("ALSA: timer: Fix race among timer ioctls")
Reference: http://lkml.kernel.org/r/089e082686ac9b482e055c832617@google.com
Reported-by: syzbot <bot+e5f3c9783e7048a74233054febbe9f1bdf54b6da@syzkaller.appspotmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/sound/core/timer_compat.c
+++ b/sound/core/timer_compat.c
@@ -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 tiwai@suse.de 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