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@xxxxxxxxxx>
Tested-by: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
This is the patch adapted to 3.18.y base that failed to apply.
sound/core/timer.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sound/core/timer.c b/sound/core/timer.c
index d448437df4b5..00a73ecfb4e9 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1948,6 +1948,7 @@ 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) {
@@ -1963,7 +1964,9 @@ 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);
@@ -2001,6 +2004,7 @@ 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;
}
--
2.13.1