From a851e568525bde7790c8a2bdd49a0258b02accf7 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Mon, 4 Jul 2016 14:02:15 +0200 Subject: ALSA: timer: Fix negative queue usage by racy accesses [ Upstream commit 3fa6993fef634e05d200d141a85df0b044572364 ] 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: Signed-off-by: Takashi Iwai Signed-off-by: Sasha Levin --- sound/core/timer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'sound') diff --git a/sound/core/timer.c b/sound/core/timer.c index 2fd0dccf8505..5c769ea59b68 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -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; -- cgit v1.2.3