linux-kernel - Re: [PATCH] fbdev: au1200fb: Fix potential divide by zero

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Date:   Wed, 15 Mar 2023 11:25:52 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Wei Chen <harperchen1110@...il.com>, deller@....de
Cc:     linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] fbdev: au1200fb: Fix potential divide by zero

Hi,

thanks for looking through these drivers.

Am 15.03.23 um 10:22 schrieb Wei Chen:
> var->pixclock can be assigned to zero by user. Without
> proper check, divide by zero would occur when invoking
> macro PICOS2KHZ in au1200fb_fb_check_var.
> 
> Error out if var->pixclock is zero.
> 
> Signed-off-by: Wei Chen <harperchen1110@...il.com>
> ---
>   drivers/video/fbdev/au1200fb.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/video/fbdev/au1200fb.c b/drivers/video/fbdev/au1200fb.c
> index 81c315454428..b6b22fa4a8a0 100644
> --- a/drivers/video/fbdev/au1200fb.c
> +++ b/drivers/video/fbdev/au1200fb.c
> @@ -1040,6 +1040,9 @@ static int au1200fb_fb_check_var(struct fb_var_screeninfo *var,
>   	u32 pixclock;
>   	int screen_size, plane;
>   
> +	if (!var->pixclock)
> +		return -EINVAL;
> +

Instead of the whale-a-mole approach of fixing individual drivers, could 
this be solved by testing in fb_set_var [1] and fb_try_mode.? [2]

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/core/fbmem.c#L958
[2] 
https://elixir.bootlin.com/linux/latest/source/drivers/video/fbdev/core/modedb.c#L567

>   	plane = fbdev->plane;
>   
>   	/* Make sure that the mode respect all LCD controller and

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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