blob: 99c1c02348f4a153f323ab956f7b73a52e4b9330 [file] [log] [blame]
From: Takashi Iwai <tiwai@suse.de>
Date: Mon, 4 Jul 2016 14:02:15 +0200
Subject: ALSA: timer: Fix negative queue usage by racy accesses
commit 3fa6993fef634e05d200d141a85df0b044572364 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: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
sound/core/timer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1923,6 +1923,7 @@ static ssize_t snd_timer_user_read(struc
qhead = tu->qhead++;
tu->qhead %= tu->queue_size;
+ tu->qused--;
spin_unlock_irq(&tu->qlock);
if (tu->tread) {
@@ -1936,7 +1937,6 @@ static ssize_t snd_timer_user_read(struc
}
spin_lock_irq(&tu->qlock);
- tu->qused--;
if (err < 0)
goto _error;
result += unit;