[PATCH] ASoC: dpcm: fix race condition to dpcm links in dpcm_be_dai_trigger

["Gyeongtaek Lee" <gt82.lee@samsung.com>]

If routing change and underrun stop is run at the same time,
data abort can be occurred by the following sequence.

CPU0: Processing underrun 	CPU1: Processing routing change
dpcm_be_dai_trigger():		dpcm_be_disconnect():

for_each_dpcm_be(fe, stream, dpcm) {

				spin_lock_irqsave(&fe->card->dpcm_lock, flags);
				list_del(&dpcm->list_be);
				list_del(&dpcm->list_fe);
				spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
				kfree(dpcm);

struct snd_soc_pcm_runtime *be = dpcm->be; <-- Accessing freed memory

To prevent this situation, dpcm_lock is needed during accessing
the lists for dpcm links.

Signed-off-by: Gyeongtaek Lee <gt82.lee@samsung.com>
Cc: stable@vger.kernel.org
---
 sound/soc/soc-pcm.c | 53 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 50 insertions(+), 3 deletions(-)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 48f71bb81a2f..df2cd4c0dabe 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1993,17 +1993,63 @@ static int dpcm_fe_dai_hw_params(struct snd_pcm_substream *substream,
 	return ret;
 }
 
+struct dpcm_be_list {
+	unsigned int num;
+	struct snd_soc_pcm_runtime *be[];
+};
+
+static int dpcm_create_be_list(struct snd_soc_pcm_runtime *fe, int stream,
+		struct dpcm_be_list **be_list)
+{
+	struct snd_soc_dpcm *dpcm;
+	struct dpcm_be_list *be;
+	int size = 0;
+	int ret = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&fe->card->dpcm_lock, flags);
+
+	for_each_dpcm_be(fe, stream, dpcm)
+		size++;
+
+	be = kzalloc(struct_size(be, be, size), GFP_ATOMIC);
+	if (!be) {
+		ret = -ENOMEM;
+	} else {
+		unsigned int i = 0;
+
+		for_each_dpcm_be(fe, stream, dpcm)
+			be->be[i++] = dpcm->be;
+
+		*be_list = be;
+	}
+
+	spin_unlock_irqrestore(&fe->card->dpcm_lock, flags);
+
+	return ret;
+}
+
+static void dpcm_free_be_list(struct dpcm_be_list *be_list)
+{
+	kfree(be_list);
+}
+
 int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 			       int cmd)
 {
 	struct snd_soc_pcm_runtime *be;
-	struct snd_soc_dpcm *dpcm;
+	struct dpcm_be_list *be_list;
 	int ret = 0;
+	int i;
 
-	for_each_dpcm_be(fe, stream, dpcm) {
+	ret = dpcm_create_be_list(fe, stream, &be_list);
+	if (ret < 0)
+		return ret;
+
+	for(i = 0; i < be_list->num; i++) {
 		struct snd_pcm_substream *be_substream;
 
-		be = dpcm->be;
+		be = be_list->be[i];
 		be_substream = snd_soc_dpcm_get_substream(be, stream);
 
 		/* is this op for this BE ? */
@@ -2092,6 +2138,7 @@ int dpcm_be_dai_trigger(struct snd_soc_pcm_runtime *fe, int stream,
 	if (ret < 0)
 		dev_err(fe->dev, "ASoC: %s() failed at %s (%d)\n",
 			__func__, be->dai_link->name, ret);
+	dpcm_free_be_list(be_list);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dpcm_be_dai_trigger);

base-commit: 4ac6d90867a4de2e12117e755dbd76e08d88697f
-- 
2.21.0