Re: [patch] Fix snd-usb-audio in 32-bit compat environemt

[Takashi Iwai]

At Sun, 19 Feb 2006 20:02:03 +0100,
Juergen Kreileder wrote:
> 
> Alexey Dobriyan <adobriyan@xxxxxxxxx> writes:
> 
> > On Sat, Feb 18, 2006 at 07:50:37PM +0100, Juergen Kreileder wrote:
> >> I'm getting oopses with snd-usb-audio in 32-bit compat
> >> environments: control_compat.c:get_ctl_type() doesn't initialize
> >> 'info', so
> >> 'itemlist[uinfo->value.enumerated.item]' in
> >> usbmixer.c:mixer_ctl_selector_info() might access random memory
> >> (The 'if ((int)uinfo->value.enumerated.item >= cval->max)' doesn't fix
> >> all problems because of the unsigned -> signed conversion.)
> >
> > IMO, what you did is an overkill.
> 
> The advantage of the longer fix is reduced stack usage.

But it also introduces a kmalloc overhead.
Let's fix the problem first with a simpler patch.

> > Does this patch fixes your problem?
> 
> Yes but you can have that even simpler:
> 
> --- linux-mm-vanilla/sound/core/control_compat.c	2006-02-18 17:00:17.000000000 +0100
> +++ linux-mm/sound/core/control_compat.c	2006-02-19 19:41:51.000000000 +0100
> @@ -167,7 +167,7 @@ static int get_ctl_type(struct snd_card 
>  			int *countp)
>  {
>  	struct snd_kcontrol *kctl;
> -	struct snd_ctl_elem_info info;
> +	struct snd_ctl_elem_info info = {0};
>  	int err;
>  
>  	down_read(&card->controls_rwsem);

I prefer Alexey's patch sicne it's clearer that the
zero-initialization is done just before the usage.

But = {0} might result in a better code because of compiler
optimization...


Thanks!

Takashi
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