linux-kernel - [PATCH 2.6.32 47/55] ALSA: timer: Fix leftover link at closing

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Date:	Fri, 04 Mar 2016 16:30:47 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Dmitry Vyukov <dvyukov@...gle.com>, Takashi Iwai <tiwai@...e.de>,
	Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>
Subject: [PATCH 2.6.32 47/55] ALSA: timer: Fix leftover link at closing

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 094fd3be87b0f102589e2d5c3fa5d06b7e20496d upstream.

In ALSA timer core, the active timer instance is managed in
active_list linked list.  Each element is added / removed dynamically
at timer start, stop and in timer interrupt.  The problem is that
snd_timer_interrupt() has a thinko and leaves the element in
active_list when it's the last opened element.  This eventually leads
to list corruption or use-after-free error.

This hasn't been revealed because we used to delete the list forcibly
in snd_timer_stop() in the past.  However, the recent fix avoids the
double-stop behavior (in commit [f784beb75ce8: ALSA: timer: Fix link
corruption due to double start or stop]), and this leak hits reality.

This patch fixes the link management in snd_timer_interrupt().  Now it
simply unlinks no matter which stream is.

BugLink: http://lkml.kernel.org/r/CACT4Y+Yy2aukHP-EDp8-ziNqNNmb-NTf=jDWXMP7jB8HDa2vng@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Willy Tarreau <w@....eu>
---
 sound/core/timer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index fb29803..2383874 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -723,8 +723,8 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left)
 			ti->cticks = ti->ticks;
 		} else {
 			ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
-			if (--timer->running)
-				list_del_init(&ti->active_list);
+			--timer->running;
+			list_del_init(&ti->active_list);
 		}
 		if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) ||
 		    (ti->flags & SNDRV_TIMER_IFLG_FAST))
-- 
1.7.12.2.21.g234cd45.dirty