| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.6 171/203] ALSA: timer: Fix negative queue usage by racy accesses | Date | Mon, 25 Jul 2016 13:56:26 -0700 |
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4.6-stable review patch. If anyone has any objections, please let me know.
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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 @@ -1954,6 +1954,7 @@ 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) { @@ -1967,7 +1968,6 @@ static ssize_t snd_timer_user_read(struc } spin_lock_irq(&tu->qlock); - tu->qused--; if (err < 0) goto _error; result += unit;
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