From d45da2e291b904332ac155ec15f5b85500b66ff8 Mon Sep 17 00:00:00 2001
From: z00208928 <zhangwei519@huawei.com>
Date: Tue, 23 May 2017 11:02:10 +0800
Subject: [PATCH] ALSA: pcm : Call kill_fasync() in stream lock

CVE-2016-9794

commit 3aa02cb664c5fb1042958c8d1aa8c35055a2ebc4 upstream.

Currently kill_fasync() is called outside the stream lock in
snd_pcm_period_elapsed().  This is potentially racy, since the stream
may get released even during the irq handler is running.  Although
snd_pcm_release_substream() calls snd_pcm_drop(), this doesn't
guarantee that the irq handler finishes, thus the kill_fasync() call
outside the stream spin lock may be invoked after the substream is
detached, as recently reported by KASAN.

As a quick workaround, move kill_fasync() call inside the stream
lock.  The fasync is rarely used interface, so this shouldn't have a
big impact from the performance POV.

Ideally, we should implement some sync mechanism for the proper finish
of stream and irq handler.  But this oneliner should suffice for most
cases, so far.

Change-Id: I8ff3ce388aaf2d5e0d942b53183144932525efa0
Reported-by: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 sound/core/pcm_lib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index f26e71cbe551..868ae20d9042 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1868,10 +1868,10 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
 	if (substream->timer_running)
 		snd_timer_interrupt(substream->timer, 1);
  _end:
+	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
 	snd_pcm_stream_unlock_irqrestore(substream, flags);
 	if (runtime->transfer_ack_end)
 		runtime->transfer_ack_end(substream);
-	kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
 }
 
 EXPORT_SYMBOL(snd_pcm_period_elapsed);
-- 
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