| From 3fa6993fef634e05d200d141a85df0b044572364 Mon Sep 17 00:00:00 2001 |
| 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 |
| |
| From: Takashi Iwai <tiwai@suse.de> |
| |
| 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| sound/core/timer.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/sound/core/timer.c |
| +++ b/sound/core/timer.c |
| @@ -1961,6 +1961,7 @@ 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) { |
| @@ -1974,7 +1975,6 @@ static ssize_t snd_timer_user_read(struc |
| } |
| |
| spin_lock_irq(&tu->qlock); |
| - tu->qused--; |
| if (err < 0) |
| goto _error; |
| result += unit; |
