Skip to content

Commit

Permalink
ALSA: timer: Fix negative queue usage by racy accesses
Browse files Browse the repository at this point in the history
[ Upstream commit 3fa6993 ]

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
  • Loading branch information
Takashi Iwai authored and Sasha Levin committed Jul 19, 2016
1 parent b86ef7e commit a851e56
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion sound/core/timer.c
Original file line number Diff line number Diff line change
@@ -1959,6 +1959,7 @@ 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) {
@@ -1972,7 +1973,6 @@ 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;

0 comments on commit a851e56

Please sign in to comment.