[alsa-devel] [PATCH] ASoC: dapm: Fix empty list check in dapm_new_mux()

[Lars-Peter Clausen]

list_first_entry() will always return a valid pointer, even if the list is
empty. So the check whether path is NULL will always be false. So we end up
calling dapm_create_or_share_mixmux_kcontrol() with a path struct that points
right in the middle of the widget struct and by trying to modify the path the
widgets memory will become corrupted. Fix this by using list_emtpy() to check if
the widget doesn't have any paths.

Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>

---
This is the real fix for the rt5640 crash.
---
 sound/soc/soc-dapm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/sound/soc/soc-dapm.c b/sound/soc/soc-dapm.c
index 5f64c16..196cea7 100644
--- a/sound/soc/soc-dapm.c
+++ b/sound/soc/soc-dapm.c
@@ -747,13 +747,14 @@ static int dapm_new_mux(struct snd_soc_dapm_widget *w)
 		return -EINVAL;
 	}
 
-	path = list_first_entry(&w->sources, struct snd_soc_dapm_path,
-				list_sink);
-	if (!path) {
+	if (list_empty(&w->sources)) {
 		dev_err(dapm->dev, "ASoC: mux %s has no paths\n", w->name);
 		return -EINVAL;
 	}
 
+	path = list_first_entry(&w->sources, struct snd_soc_dapm_path,
+				list_sink);
+
 	ret = dapm_create_or_share_mixmux_kcontrol(w, 0, path);
 	if (ret < 0)
 		return ret;
-- 
1.8.0