Re: [PATCH] ALSA: usb-audio: Fix missing error handling for get_min_max*()

[Takashi Iwai <tiwai@suse.de>]

On Tue, 14 Apr 2026 14:17:28 +0200,
Rong Zhang wrote:
> 
> Hi Takashi,
> 
> On Tue, 2026-04-14 at 11:33 +0200, Takashi Iwai wrote:
> > The recent fix to add the error return value check from get_min_max*()
> > missed one case in build_audio_procunit() where no error value is set.
> > This may lead to an uninitialized variable and confuse the caller
> > (although this wouldn't happen practically because err is set for the
> > loop of num_ins at the beginning of the funciton).
> > 
> > Fix it by setting "err = 0" properly at the missing case, too.
> > 
> > Fixes: 4f55a85cd4fc ("ALSA: usb-audio: Add error checks against get_min_max*()")
> > Reported-by: Dan Carpenter <error27@gmail.com>
> > Closes: https://lore.kernel.org/ad36dGpCBTGsyFr_@stanley.mountain
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > ---
> >  sound/usb/mixer.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> > index d4ef45bf53d7..aa6ea3be100a 100644
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -2687,6 +2687,7 @@ static int build_audio_procunit(struct mixer_build *state, int unitid,
> >  				cval->max = control_spec[0];
> >  				cval->res = 1;
> >  				cval->initialized = 1;
> > +				err = 0;
> 
> Whoops, it's my fault that I didn't noticed the code path.
> 
> I think we can make the UAC_PROCESS_UP_DOWNMIX case fall through the
> default case so that we can move the error check into the latter and get
> rid of all `err = 0'. Doing so also improves readability and prevents
> similar mistakes in future changes. Perhaps I should have done this in
> my previous refactoring patch...
> 
> I just noticed that you've applied this patch to your tree. If my
> proposed refactor makes sense to you, I will send a patch for it.

That was my another idea, too.  OTOH, I thought handling the success
error code explicitly makes it clearer that the code handles it.

It's pretty nuance, and I'm open for either option, so feel free to
submit a cleanup patch on the top.


thanks,

Takashi