[alsa-devel] [PATCH] sound/usb: fix to release stream resources from media_snd_device_delete()

[Shuah Khan]

Fix to release stream resources from media_snd_device_delete() before
media device is unregistered. Without this change, stream resource free
is attempted after the media device is unregistered which would result
in use-after-free errors.

Signed-off-by: Shuah Khan <shuahkh at osg.samsung.com>
---

- Ran bind/unbind loop (1000 iteration) test on snd-usb-audio
  while running mc_nextgen_test loop (1000 iterations) in parallel.
- Ran bind/unbind and rmmod/modprobe tests on both drivers. Also
  generated graphs when after bind/unbind, rmmod/modprobe. Graphs
  look good.
- Note: Please apply the following patch to fix memory leak:
  sound/usb: Fix memory leak in media_snd_stream_delete() during unbind
  https://lkml.org/lkml/2016/3/16/1050

 sound/usb/media.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/usb/media.c b/sound/usb/media.c
index de4a815..e35af88 100644
--- a/sound/usb/media.c
+++ b/sound/usb/media.c
@@ -301,6 +301,13 @@ int media_snd_device_create(struct snd_usb_audio *chip,
 void media_snd_device_delete(struct snd_usb_audio *chip)
 {
 	struct media_device *mdev = chip->media_dev;
+	struct snd_usb_stream *stream;
+
+	/* release resources */
+	list_for_each_entry(stream, &chip->pcm_list, list) {
+		media_snd_stream_delete(&stream->substream[0]);
+		media_snd_stream_delete(&stream->substream[1]);
+	}
 
 	media_snd_mixer_delete(chip);
 
-- 
2.5.0