Re: [PATCH 1/2] ALSA: usb: fix corrupted pointers due to interface setting change

[Takashi Iwai <tiwai@suse.de>]

On Fri, 14 Aug 2015 00:42:32 +0200,
Pierre-Louis Bossart wrote:
> 
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -395,6 +395,19 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
>  	if (err < 0)
>  		return err;
>  
> +	if ((is_playback && (attr != USB_ENDPOINT_SYNC_ASYNC)) ||
> +		(!is_playback && (attr != USB_ENDPOINT_SYNC_ADAPTIVE))) {
> +
> +		/*
> +		 * Clean-up subs pointers to make sure sync_endpoint is never
> +		 * configured. This is needed in case of a transition between
> +		 * alternate settings using different synchronization modes
> +		 * where the previous sync_endpoint may no longer be valid.
> +		 */
> +		subs->sync_endpoint = NULL;
> +		subs->data_endpoint->sync_master = NULL;
> +	}

I think this initialization can be put unconditionally on top, not in
a separate like below, as this is just overlooked leaks.
The comment can be better in more details, of course.


Takashi

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index b4ef410e5a98..0d935369d641 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -391,6 +391,10 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
 	 */
 	attr = fmt->ep_attr & USB_ENDPOINT_SYNCTYPE;
 
+	/* Clean-up subs sync and master pointers at first */
+	subs->sync_endpoint = NULL;
+	subs->data_endpoint->sync_master = NULL;
+
 	err = set_sync_ep_implicit_fb_quirk(subs, dev, altsd, attr);
 	if (err < 0)
 		return err;