linux-kernel - Re: [PATCH] vgaswitcheroo: Fix error checking in vga_switcheroo_register_audio

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Message-ID: <8e161bf8-70f6-4557-8fa8-81d4bbfab91f@stanley.mountain>
Date: Mon, 24 Feb 2025 22:26:47 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Jim Qu <Jim.Qu@....com>, Lukas Wunner <lukas@...ner.de>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Takashi Iwai <tiwai@...e.de>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	Su Hui <suhui@...china.com>
Subject: Re: [PATCH] vgaswitcheroo: Fix error checking in
 vga_switcheroo_register_audio_client()

On Mon, Feb 24, 2025 at 03:14:33PM +0200, Jani Nikula wrote:
> On Wed, 19 Feb 2025, Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > The "id" variable is an enum and in this context it's treated as an
> > unsigned int so the error handling can never trigger.  The
> > ->get_client_id() functions do not currently return any errors but
> > I imagine that if they did, then the intention was to return
> > VGA_SWITCHEROO_UNKNOWN_ID on error.  Let's check for both negatives
> > and UNKNOWN_ID so we'll catch it either way.
> >
> > Reported-by: Su Hui <suhui@...china.com>
> > Closes: https://lore.kernel.org/all/20231026021056.850680-1-suhui@nfschina.com/
> > Fixes: 4aaf448fa975 ("vga_switcheroo: set audio client id according to bound GPU id")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> > ---
> >  drivers/gpu/vga/vga_switcheroo.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
> > index 18f2c92beff8..216fb208eb31 100644
> > --- a/drivers/gpu/vga/vga_switcheroo.c
> > +++ b/drivers/gpu/vga/vga_switcheroo.c
> > @@ -375,7 +375,7 @@ int vga_switcheroo_register_audio_client(struct pci_dev *pdev,
> >  	mutex_lock(&vgasr_mutex);
> >  	if (vgasr_priv.active) {
> >  		id = vgasr_priv.handler->get_client_id(vga_dev);
> > -		if (id < 0) {
> > +		if ((int)id < 0 || id == VGA_SWITCHEROO_UNKNOWN_ID) {
> 
> Maybe we want to do something else here... see [1].
> 
> BR,
> Jani.
> 
> 
> [1] https://lore.kernel.org/r/CAHk-=wgg2A_iHNwf_JDjYJF=XHnKVGOjGp50FzVWniA2Z010bw@mail.gmail.com
> 

I feel like my patch is good enough...  I guess the concern here is that
GCC could change enums to something else.  I don't think that's likely as
it would break a lot of code.  The other option, which is a good option,
is to change the function signature for vgasr_priv.handler->get_client_id()
so that we do:

	ret = vgasr_priv.handler->get_client_id(vga_dev, &id);
	if (ret)
		return;

That's better code, honestly.  But I can't find motivation enough to do
the work.

regards,
dan carpenter