From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755950AbcBWVzx (ORCPT ); Tue, 23 Feb 2016 16:55:53 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41672 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755580AbcBWVo4 (ORCPT ); Tue, 23 Feb 2016 16:44:56 -0500 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" , "Dmitry Vyukov" Date: Tue, 23 Feb 2016 21:42:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 35/67] ALSA: timer: Fix link corruption due to double start or stop In-Reply-To: X-SA-Exim-Connect-IP: 92.40.248.141 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 3.2.78-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit f784beb75ce82f4136f8a0960d3ee872f7109e09 upstream. Although ALSA timer code got hardening for races, it still causes use-after-free error. This is however rather a corrupted linked list, not actually the concurrent accesses. Namely, when timer start is triggered twice, list_add_tail() is called twice, too. This ends up with the link corruption and triggers KASAN error. The simplest fix would be replacing list_add_tail() with list_move_tail(), but fundamentally it's the problem that we don't check the double start/stop correctly. So, the right fix here is to add the proper checks to snd_timer_start() and snd_timer_stop() (and their variants). BugLink: http://lkml.kernel.org/r/CACT4Y+ZyPRoMQjmawbvmCEDrkBD2BQuH7R09=eOkf5ESK8kJAw@mail.gmail.com Reported-by: Dmitry Vyukov Signed-off-by: Takashi Iwai [bwh: Backported to 3.2: adjust context, indentation] Signed-off-by: Ben Hutchings --- sound/core/timer.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -443,6 +443,10 @@ static int snd_timer_start_slave(struct unsigned long flags; spin_lock_irqsave(&slave_active_lock, flags); + if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) { + spin_unlock_irqrestore(&slave_active_lock, flags); + return -EBUSY; + } timeri->flags |= SNDRV_TIMER_IFLG_RUNNING; if (timeri->master && timeri->timer) { spin_lock(&timeri->timer->lock); @@ -467,18 +471,26 @@ int snd_timer_start(struct snd_timer_ins return -EINVAL; if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { result = snd_timer_start_slave(timeri); - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); + if (result >= 0) + snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); return result; } timer = timeri->timer; if (timer == NULL) return -EINVAL; spin_lock_irqsave(&timer->lock, flags); + if (timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | + SNDRV_TIMER_IFLG_START)) { + result = -EBUSY; + goto unlock; + } timeri->ticks = timeri->cticks = ticks; timeri->pticks = 0; result = snd_timer_start1(timer, timeri, ticks); + unlock: spin_unlock_irqrestore(&timer->lock, flags); - snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); + if (result >= 0) + snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_START); return result; } @@ -494,6 +506,10 @@ static int _snd_timer_stop(struct snd_ti if (timeri->flags & SNDRV_TIMER_IFLG_SLAVE) { if (!keep_flag) { spin_lock_irqsave(&slave_active_lock, flags); + if (!(timeri->flags & SNDRV_TIMER_IFLG_RUNNING)) { + spin_unlock_irqrestore(&slave_active_lock, flags); + return -EBUSY; + } timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING; list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); @@ -505,6 +521,11 @@ static int _snd_timer_stop(struct snd_ti if (!timer) return -EINVAL; spin_lock_irqsave(&timer->lock, flags); + if (!(timeri->flags & (SNDRV_TIMER_IFLG_RUNNING | + SNDRV_TIMER_IFLG_START))) { + spin_unlock_irqrestore(&timer->lock, flags); + return -EBUSY; + } list_del_init(&timeri->ack_list); list_del_init(&timeri->active_list); if ((timeri->flags & SNDRV_TIMER_IFLG_RUNNING) && @@ -570,10 +591,15 @@ int snd_timer_continue(struct snd_timer_ if (! timer) return -EINVAL; spin_lock_irqsave(&timer->lock, flags); + if (timeri->flags & SNDRV_TIMER_IFLG_RUNNING) { + result = -EBUSY; + goto unlock; + } if (!timeri->cticks) timeri->cticks = 1; timeri->pticks = 0; result = snd_timer_start1(timer, timeri, timer->sticks); + unlock: spin_unlock_irqrestore(&timer->lock, flags); snd_timer_notify1(timeri, SNDRV_TIMER_EVENT_CONTINUE); return result;