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

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Date:   Thu, 9 Mar 2023 14:11:14 +0800
From:   Wei Chen <harperchen1110@...il.com>
To:     Helge Deller <deller@....de>
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

Dear Helge,

Thank you for the kind words. My real name is Wei Chen.

Please apply this patch to fbdev git tree if it is correct.

Best,
Wei

On Thu, 9 Mar 2023 at 06:05, Helge Deller <deller@....de> wrote:
>
> 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;
>