[PATCH v3 4/4] fbmem: Prevent invalid virtual screen sizes

[Daniel Vetter]

On Sun, Jun 26, 2022 at 12:06:30AM +0200, Helge Deller wrote:
> Prevent that drivers or the user sets the virtual screen resolution
> smaller than the physical screen resolution.  This is important, because
> otherwise we may get accesses outside of the graphics memory area.
> 
> Signed-off-by: Helge Deller <deller at gmx.de>
> Cc: stable at vger.kernel.org # v5.4+

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> ---
>  drivers/video/fbdev/core/fbmem.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 160389365a36..b6e1d0f2b974 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1006,6 +1006,12 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
>  	if (var->xres < 8 || var->yres < 8)
>  		return -EINVAL;
> 
> +	/* make sure virtual resolution >= physical resolution */
> +	if (var->xres_virtual < var->xres)
> +		return -EINVAL;
> +	if (var->yres_virtual < var->yres)
> +		return -EINVAL;
> +
>  	/* Too huge resolution causes multiplication overflow. */
>  	if (check_mul_overflow(var->xres, var->yres, &unused) ||
>  	    check_mul_overflow(var->xres_virtual, var->yres_virtual, &unused))
> --
> 2.35.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch