linux-kernel - Re: [PATCH 02/13] media: v4l2-tpg: prevent the risk of a division by zero

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Message-ID: <2bffad36-efc1-44a2-861a-5d6afb7e5b38@xs4all.nl>
Date: Wed, 16 Oct 2024 12:49:14 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Zhipeng Lu <alexious@....edu.cn>, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 02/13] media: v4l2-tpg: prevent the risk of a division by
 zero

On 16/10/2024 12:22, Mauro Carvalho Chehab wrote:
> The logic at tpg_precalculate_line() blindly rescales the
> buffer even when scaled_witdh is equal to zero. If this ever

scaled_witdh -> scaled_width

> happens, this will cause a division by zero.
> 
> Instead, add a WARN_ON() to trigger such cases and return
> without doing any precalculation.
> 
> Fixes: 63881df94d3e ("[media] vivid: add the Test Pattern Generator")
> Cc: stable@...r.kernel.org
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> ---
>  drivers/media/common/v4l2-tpg/v4l2-tpg-core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> index c86343a4d0bf..a22f31515d7e 100644
> --- a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> +++ b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
> @@ -1795,6 +1795,9 @@ static void tpg_precalculate_line(struct tpg_data *tpg)
>  	unsigned p;
>  	unsigned x;
>  
> +	if (WARN_ON(tpg->src_width == 0))

You need to check for both src_width and scaled_width.

Also replace this by WARN_ON_ONCE.

Regards,

	Hans

> +		return;
> +
>  	switch (tpg->pattern) {
>  	case TPG_PAT_GREEN:
>  		contrast = TPG_COLOR_100_RED;