[PATCH 2/5] fbcon: Fix up user-provided virtual screen size

[Geert Uytterhoeven]

Hi Helge,

On Wed, Jun 29, 2022 at 10:00 PM Helge Deller <deller at gmx.de> wrote:
> The virtual screen size can't be smaller than the physical screen size.
> Based on the general rule that we round up user-provided input if
> neccessary, adjust the virtual screen size as well if needed.
>
> Signed-off-by: Helge Deller <deller at gmx.de>
> Cc: stable at vger.kernel.org # v5.4+

Thanks for your patch!

> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1106,6 +1106,11 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>                         return -EFAULT;
>                 console_lock();
>                 lock_fb_info(info);
> +               /* adjust virtual screen size if user missed it */
> +               if (var.xres_virtual < var.xres)
> +                       var.xres_virtual = var.xres;
> +               if (var.yres_virtual < var.yres)
> +                       var.yres_virtual = var.yres;
>                 ret = fb_set_var(info, &var);
>                 if (!ret)
>                         fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);

Given "[PATCH 4/5] fbmem: Prevent invalid virtual screen sizes in
fb_set_var", I don't think we need this patch.  Moreover, this
patch will prevent triggering the WARN_ON()s in [PATCH 4/5] in the
most common buggy case of drivers plainly ignoring var.[xy]res_virtual.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds