linux-kernel - Re: [PATCH] media: v4l2-tpg: Fix division by zero error in color_to

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Date: Mon, 8 Apr 2024 11:13:34 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Mikhail Lobanov <m.lobanov@...alinux.ru>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: v4l2-tpg: Fix division by zero error in
 color_to_hsv

On 01/03/2024 18:08, Mikhail Lobanov wrote:
> In the color_to_hsv function, division by zero is possible due to
> attributes r,g,b are equal so diff_rgb = 0.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 54fb15348385 ("[media] vivid: Add support for HSV formats")
> Signed-off-by: Mikhail Lobanov <m.lobanov@...alinux.ru>

With this patch I get this compiler warning:

drivers/media/common/v4l2-tpg/v4l2-tpg-core.c: In function 'precalculate_color':
drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:1004:35: warning: 'h' may be used uninitialized [-Wmaybe-uninitialized]
 1004 |                 tpg->colors[k][0] = h;
      |                 ~~~~~~~~~~~~~~~~~~^~~
drivers/media/common/v4l2-tpg/v4l2-tpg-core.c:1001:21: note: 'h' was declared here
 1001 |                 int h, s, v;
      |                     ^

In any case, I think this patch is wrong.

Based on this formula:

https://www.rapidtables.com/convert/color/rgb-to-hsv.html

The bug is in:

        *s = aux;
        if (!aux) {
                *h = 0;
                return;
        }

'if (!aux)' should be 'if (!diff_rgb)'.

Regards,

	Hans

> ---
>  drivers/media/common/v4l2-tpg/v4l2-tpg-core.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> index a366566f22c3..943aab3ad97c 100644
> --- a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> +++ b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> @@ -597,6 +597,11 @@ static void color_to_hsv(struct tpg_data *tpg, int r, int g, int b,
>  		third = third_size * 2;
>  	}
>  
> +	if (!diff_rgb) {
> +		*s = 0;
> +		return;
> +	}
> +
>  	aux *= third_size / 2;
>  	aux += diff_rgb / 2;
>  	aux /= diff_rgb;