[PATCHv2] fbcon: Check font dimension limits

[Miko Larsson]

On Sun, 2023-01-29 at 16:17 +0100, Samuel Thibault wrote:
> blit_x and blit_y are u32, so fbcon currently cannot support fonts
> larger than 32x32.
> 
> The 32x32 case also needs shifting an unsigned int, to properly set
> bit
> 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font",
> as reported on:
> 
> http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com
> Kernel Branch: 6.2.0-rc5-next-20230124
> Kernel config:
> https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing
> Reproducer:
> https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing
> 
> Reported-by: Sanan Hasanov <sanan.hasanov at Knights.ucf.edu>
> Signed-off-by: Samuel Thibault <samuel.thibault at ens-lyon.org>
> Fixes: 2d2699d98492 ("fbcon: font setting should check limitation of
> driver")
> Cc: stable at vger.kernel.org
> 
> ---
> v1 -> v2:
> - Use BIT macro instead of fixing bit test by hand.
> - Add Fixes and Cc: stable headers.
> 
> Index: linux-6.0/drivers/video/fbdev/core/fbcon.c
> ===================================================================
> --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c
> +++ linux-6.0/drivers/video/fbdev/core/fbcon.c
> @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data
>             h > FBCON_SWAP(info->var.rotate, info->var.yres, info-
> >var.xres))
>                 return -EINVAL;
>  
> +       if (font->width > 32 || font->height > 32)
> +               return -EINVAL;
> +
>         /* Make sure drawing engine can handle the font */
> -       if (!(info->pixmap.blit_x & (1 << (font->width - 1))) ||
> -           !(info->pixmap.blit_y & (1 << (font->height - 1))))
> +       if (!(info->pixmap.blit_x & BIT(font->width - 1)) ||
> +           !(info->pixmap.blit_y & BIT(font->height - 1)))
>                 return -EINVAL;
>  
>         /* Make sure driver can handle the font length */

Tested-by: Miko Larsson <mikoxyzzz at gmail.com>
-- 
~miko