Patch "ALSA: timer: Fix race between read and ioctl" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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

    ALSA: timer: Fix race between read and ioctl

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-fix-race-between-read-and-ioctl.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 d11662f4f798b50d8c8743f433842c3e40fe3378 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Fri, 2 Jun 2017 15:03:38 +0200
Subject: ALSA: timer: Fix race between read and ioctl

From: Takashi Iwai <tiwai@suse.de>

commit d11662f4f798b50d8c8743f433842c3e40fe3378 upstream.

The read from ALSA timer device, the function snd_timer_user_tread(),
may access to an uninitialized struct snd_timer_user fields when the
read is concurrently performed while the ioctl like
snd_timer_user_tselect() is invoked.  We have already fixed the races
among ioctls via a mutex, but we seem to have forgotten the race
between read vs ioctl.

This patch simply applies (more exactly extends the already applied
range of) tu->ioctl_lock in snd_timer_user_tread() for closing the
race window.

Reported-by: Alexander Potapenko <glider@google.com>
Tested-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 sound/core/timer.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1958,6 +1958,7 @@ static ssize_t snd_timer_user_read(struc
 
 	tu = file->private_data;
 	unit = tu->tread ? sizeof(struct snd_timer_tread) : sizeof(struct snd_timer_read);
+	mutex_lock(&tu->ioctl_lock);
 	spin_lock_irq(&tu->qlock);
 	while ((long)count - result >= unit) {
 		while (!tu->qused) {
@@ -1973,7 +1974,9 @@ static ssize_t snd_timer_user_read(struc
 			add_wait_queue(&tu->qchange_sleep, &wait);
 
 			spin_unlock_irq(&tu->qlock);
+			mutex_unlock(&tu->ioctl_lock);
 			schedule();
+			mutex_lock(&tu->ioctl_lock);
 			spin_lock_irq(&tu->qlock);
 
 			remove_wait_queue(&tu->qchange_sleep, &wait);
@@ -1993,7 +1996,6 @@ static ssize_t snd_timer_user_read(struc
 		tu->qused--;
 		spin_unlock_irq(&tu->qlock);
 
-		mutex_lock(&tu->ioctl_lock);
 		if (tu->tread) {
 			if (copy_to_user(buffer, &tu->tqueue[qhead],
 					 sizeof(struct snd_timer_tread)))
@@ -2003,7 +2005,6 @@ static ssize_t snd_timer_user_read(struc
 					 sizeof(struct snd_timer_read)))
 				err = -EFAULT;
 		}
-		mutex_unlock(&tu->ioctl_lock);
 
 		spin_lock_irq(&tu->qlock);
 		if (err < 0)
@@ -2013,6 +2014,7 @@ static ssize_t snd_timer_user_read(struc
 	}
  _error:
 	spin_unlock_irq(&tu->qlock);
+	mutex_unlock(&tu->ioctl_lock);
 	return result > 0 ? result : err;
 }
 


Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.4/alsa-timer-fix-race-between-read-and-ioctl.patch
queue-4.4/alsa-timer-fix-missing-queue-indices-reset-at-sndrv_timer_ioctl_select.patch
queue-4.4/asoc-fix-use-after-free-at-card-unregistration.patch
queue-4.4/ptrace-properly-initialize-ptracer_cred-on-fork.patch