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Commit d11662f4 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: timer: Fix race between read and ioctl 



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: default avatarAlexander Potapenko <glider@google.com>
Tested-by: default avatarAlexander Potapenko <glider@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent dd8038ec

sound/core/timer.c

+4 −2
Original line number Diff line number Diff line
@@ -1959,6 +1959,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 


	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) {
@@ -1974,7 +1975,9 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 
			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);
@@ -1994,7 +1997,6 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 
		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)))
@@ -2004,7 +2006,6 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 
					 sizeof(struct snd_timer_read)))

				err = -EFAULT;

		}

		mutex_unlock(&tu->ioctl_lock);



		spin_lock_irq(&tu->qlock);

		if (err < 0)
@@ -2014,6 +2015,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, 
	}

 _error:

	spin_unlock_irq(&tu->qlock);

	mutex_unlock(&tu->ioctl_lock);

	return result > 0 ? result : err;

}