Re: [PATCH] ALSA: control: confirm to return all identical information in 'activate' event data

[Takashi Iwai <tiwai@suse.de>]

At Tue, 10 Feb 2015 00:02:06 +0900,
Takashi Sakamoto wrote:
> 
> When event originator doesn't set numerical ID in identical information,
> the event data includes no numerical ID, thus userspace applications
> cannot identify the control just by unique ID in event data.
> 
> This commit fix this bug so as the event data includes all of identical
> information.
> 
> Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

You can't overwrite id pointer in this case.  It's a caller's object.

One way to fix would be to copy the id instance.  Another way would be
to change up/down_write() with _read(), and include snd_ctl_notify()
call with kctl->id inside the semaphore lock.

The former would be less changes but consume the stack significantly.


thanks,

Takashi


> ---
>  sound/core/control.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/sound/core/control.c b/sound/core/control.c
> index 6a72b3e..884fddd 100644
> --- a/sound/core/control.c
> +++ b/sound/core/control.c
> @@ -587,6 +587,7 @@ int snd_ctl_activate_id(struct snd_card *card, struct snd_ctl_elem_id *id,
>  	}
>  	ret = 1;
>   unlock:
> +	*id = kctl->id;
>  	up_write(&card->controls_rwsem);
>  	if (ret > 0)
>  		snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_INFO, id);
> -- 
> 2.1.0
>