Commit 547d982b authored by Takashi Iwai's avatar Takashi Iwai Committed by Greg Kroah-Hartman

ALSA: timer: Fix negative queue usage by racy accesses

commit 3fa6993f upstream.

The user timer tu->qused counter may go to a negative value when
multiple concurrent reads are performed since both the check and the
decrement of tu->qused are done in two individual locked contexts.
This results in bogus read outs, and the endless loop in the
user-space side.

The fix is to move the decrement of the tu->qused counter into the
same spinlock context as the zero-check of the counter.
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 02a49fd9
......@@ -1961,6 +1961,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
qhead = tu->qhead++;
tu->qhead %= tu->queue_size;
tu->qused--;
spin_unlock_irq(&tu->qlock);
if (tu->tread) {
......@@ -1974,7 +1975,6 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer,
}
spin_lock_irq(&tu->qlock);
tu->qused--;
if (err < 0)
goto _error;
result += unit;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment