[3.13.y-ckt stable] Patch "ALSA: timer: Fix leftover link at closing" has been added to the 3.13.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ALSA: timer: Fix leftover link at closing

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt36.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 03cb8ef9c1c4edb81c9d986a2e0379e2983ab3b1 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai at suse.de>
Date: Thu, 4 Feb 2016 17:06:13 +0100
Subject: ALSA: timer: Fix leftover link at closing

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 at google.com>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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 2c2d3d1..79e57a7 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -728,8 +728,8 @@ 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))
--
2.7.0