Commit 334e9205 authored by Takashi Iwai's avatar Takashi Iwai Committed by Ben Hutchings

ALSA: timer: Fix race between read and ioctl

commit d11662f4 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: default avatarAlexander Potapenko <glider@google.com>
Tested-by: default avatarAlexander Potapenko <glider@google.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent d7575b38
......@@ -1976,6 +1976,7 @@ 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) {
......@@ -1991,7 +1992,9 @@ 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);
......@@ -2011,7 +2014,6 @@ 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)))
......@@ -2021,7 +2023,6 @@ 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)
......@@ -2031,6 +2032,7 @@ 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;
}
......
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