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ALSA: timer: Fix race at concurrent reads 

snd_timer_user_read() has a potential race among parallel reads, as
qhead and qused are updated outside the critical section due to
copy_to_user() calls.  Move them into the critical section, and also
sanitize the relevant code a bit.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2016-02-08 17:26:58 +01:00
parent ed8b1d6d2c
commit 4dff5c7b70
1 changed files with 15 additions and 19 deletions
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34
sound/core/timer.c
View File

@ -1933,6 +1933,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
{
struct snd_timer_user *tu;
long result = 0, unit;
int qhead;
int err = 0;
tu = file->private_data;
@ -1944,7 +1945,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) {
err = -EAGAIN;
break;
goto _error;
}
set_current_state(TASK_INTERRUPTIBLE);
@ -1959,42 +1960,37 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
if (tu->disconnected) {
err = -ENODEV;
break;
goto _error;
}
if (signal_pending(current)) {
err = -ERESTARTSYS;
break;
goto _error;
}
}
qhead = tu->qhead++;
tu->qhead %= tu->queue_size;
spin_unlock_irq(&tu->qlock);
if (err < 0)
goto _error;
if (tu->tread) {
if (copy_to_user(buffer, &tu->tqueue[tu->qhead++],
sizeof(struct snd_timer_tread))) {
if (copy_to_user(buffer, &tu->tqueue[qhead],
sizeof(struct snd_timer_tread)))
err = -EFAULT;
goto _error;
}
} else {
if (copy_to_user(buffer, &tu->queue[tu->qhead++],
sizeof(struct snd_timer_read))) {
if (copy_to_user(buffer, &tu->queue[qhead],
sizeof(struct snd_timer_read)))
err = -EFAULT;
goto _error;
}
}
tu->qhead %= tu->queue_size;
result += unit;
buffer += unit;
spin_lock_irq(&tu->qlock);
tu->qused--;
if (err < 0)
goto _error;
result += unit;
buffer += unit;
}
spin_unlock_irq(&tu->qlock);
_error:
spin_unlock_irq(&tu->qlock);
return result > 0 ? result : err;
}