linux-kernel - Re: [PATCH] fbdev: tgafb: Fix potential divide by zero

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Date:   Wed, 8 Mar 2023 23:05:54 +0100
From:   Helge Deller <deller@....de>
To:     harperchen <harperchen1110@...il.com>
Cc:     javierm@...hat.com, tzimmermann@...e.de,
        wsa+renesas@...g-engineering.com, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fbdev: tgafb: Fix potential divide by zero

On 3/7/23 14:08, harperchen wrote:
> fb_set_var would by called when user invokes ioctl with cmd
> FBIOPUT_VSCREENINFO. User-provided data would finally reach
> tgafb_check_var. In case var->pixclock is assigned to zero,
> divide by zero would occur when checking whether reciprocal
> of var->pixclock is too high.
>
> Similar crashes have happened in other fbdev drivers. There
> is no check and modification on var->pixclock along the call
> chain to tgafb_check_var. We believe it could also be triggered
> in driver tgafb from user site.
>
> Signed-off-by: harperchen <harperchen1110@...il.com>

Could you provide a real name?
Otherwise applied to fbdev git tree.

Thanks!
Helge

> ---
>   drivers/video/fbdev/tgafb.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/video/fbdev/tgafb.c b/drivers/video/fbdev/tgafb.c
> index 14d37c49633c..b44004880f0d 100644
> --- a/drivers/video/fbdev/tgafb.c
> +++ b/drivers/video/fbdev/tgafb.c
> @@ -173,6 +173,9 @@ tgafb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
>   {
>   	struct tga_par *par = (struct tga_par *)info->par;
>
> +	if (!var->pixclock)
> +		return -EINVAL;
> +
>   	if (par->tga_type == TGA_TYPE_8PLANE) {
>   		if (var->bits_per_pixel != 8)
>   			return -EINVAL;