[34-longterm 152/179] ALSA: timer - Fix Oops at closing slave timer

[Paul Gortmaker]

From: Takashi Iwai <tiwai@xxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 0584ffa548b6e59aceb027112f23a55f0133400e upstream.

A slave-timer instance has no timer reference, and this results in
NULL-dereference at stopping the timer, typically called at closing
the device.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=40682

Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 sound/core/timer.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 5040c7b..ecb2dd5 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -530,6 +530,8 @@ int snd_timer_stop(struct snd_timer_instance *timeri)
 	if (err < 0)
 		return err;
 	timer = timeri->timer;
+	if (!timer)
+		return -EINVAL;
 	spin_lock_irqsave(&timer->lock, flags);
 	timeri->cticks = timeri->ticks;
 	timeri->pticks = 0;
-- 
1.7.9.6

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