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authorTakashi Iwai <tiwai@suse.de>2016-07-04 14:02:15 +0200
committerTakashi Iwai <tiwai@suse.de>2016-07-04 14:02:15 +0200
commit3fa6993fef634e05d200d141a85df0b044572364 (patch)
treed42f578d6f7f0ef27f4f556a36afe643636e5ad1 /sound/core
parent046e9ceefab985a137fbd15b946497a88e5a6513 (diff)
ALSA: timer: Fix negative queue usage by racy accesses
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>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/timer.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/sound/core/timer.c b/sound/core/timer.c
index e722022d325d..9a6157ea6881 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -1955,6 +1955,7 @@ 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) {
@@ -1968,7 +1969,6 @@ 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;