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

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Message-ID: <87zfiim09n.fsf@intel.com>
Date: Wed, 19 Feb 2025 17:17:56 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Dan Carpenter <dan.carpenter@...aro.org>, Jim Qu <Jim.Qu@....com>
Cc: 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 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.

When would that be true with GCC?

BR,
Jani.

> 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) {
>  			mutex_unlock(&vgasr_mutex);
>  			return -EINVAL;
>  		}

-- 
Jani Nikula, Intel