[PATCH] fbdev: au1200fb: Fix potential divide by zero

[PATCH] fbdev: au1200fb: Fix potential divide by zero

[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@gmail.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;
+
 	plane = fbdev->plane;
 
 	/* Make sure that the mode respect all LCD controller and
-- 
2.25.1

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

[Thomas Zimmermann]

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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@gmail.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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Re: [PATCH] fbdev: au1200fb: Fix potential divide by zero

[Wei Chen]

Dear Thomas,

Thank you for the kind advice.

In fact, I notice there was a discussion regarding whether to put the
check in each individual driver or solve this problem as a whole as
you suggested. The conclusion is that it is better to keep the check per
driver rather than in the caller.

Related discussions are here:
https://lore.kernel.org/all/YXclZQGFTr1NFjbc@ravnborg.org/
https://lore.kernel.org/all/YPgbHMtLQqb1kP0l@ravnborg.org/
https://lore.kernel.org/all/20220404084723.79089-1-zheyuma97@gmail.com/

Thanks,
Wei

------ Original Message ------
From "Thomas Zimmermann" <tzimmermann@suse.de>
To "Wei Chen" <harperchen1110@gmail.com>; deller@gmx.de
Cc linux-fbdev@vger.kernel.org; linux-kernel@vger.kernel.org;
dri-devel@lists.freedesktop.org
Date 2023/3/15 18:25:52
Subject Re: [PATCH] fbdev: au1200fb: Fix potential divide by zero


On Wed, 15 Mar 2023 at 18:25, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> 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@gmail.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