From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934420AbcHNLhW (ORCPT ); Sun, 14 Aug 2016 07:37:22 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:52488 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934335AbcHNLhT (ORCPT ); Sun, 14 Aug 2016 07:37:19 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Takashi Iwai" Date: Sat, 13 Aug 2016 18:42:58 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 80/94] ALSA: timer: Fix negative queue usage by racy accesses In-Reply-To: X-SA-Exim-Connect-IP: 92.40.249.202 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.82-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai 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 Signed-off-by: Ben Hutchings --- 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;