[PATCH v4 03/15] ALSA: usb-audio: prevent NULL dereference on stop trigger

[Eldad Zack <eldad@fogrefinery.com>]

If an endpoint uses another endpoint for synchronization, and the
other endpoint is stopped, an oops will occur on NULL dereference.
Clearing the prepare/retire callbacks solves this issue.

v2: Thanks to Daniel Mack, fixed (an ironic) NULL dereference when
the pcm substream is opened and closed immediately.

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>
---
 sound/usb/pcm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 1a9a018..525bc8c 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1205,6 +1205,11 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream, int direction)
 		subs->interface = -1;
 	}
 
+	if (subs->data_endpoint) {
+		subs->data_endpoint->prepare_data_urb = NULL;
+		subs->data_endpoint->retire_data_urb = NULL;
+	}
+
 	subs->pcm_substream = NULL;
 	snd_usb_autosuspend(subs->stream->chip);
 
@@ -1535,6 +1540,8 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
 		subs->running = 1;
 		return 0;
 	case SNDRV_PCM_TRIGGER_STOP:
+		subs->data_endpoint->prepare_data_urb = NULL;
+		subs->data_endpoint->retire_data_urb = NULL;
 		stop_endpoints(subs, false);
 		subs->running = 0;
 		return 0;
@@ -1565,6 +1572,7 @@ static int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream
 		subs->running = 1;
 		return 0;
 	case SNDRV_PCM_TRIGGER_STOP:
+		subs->data_endpoint->retire_data_urb = NULL;
 		stop_endpoints(subs, false);
 		subs->running = 0;
 		return 0;
-- 
1.8.1.5