Hi Helge,
On Sun, Jun 26, 2022 at 12:33 PM Helge Deller <deller@xxxxxx> wrote:
> We need to prevent that users configure a screen size which is smaller than the
> currently selected font size. Otherwise rendering chars on the screen will
> access memory outside the graphics memory region.
>
> This patch adds a new function fbcon_modechange_possible() which
> implements this check and which later may be extended with other checks
> if necessary. The new function is called from the FBIOPUT_VSCREENINFO
> ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
> for a too small screen size.
>
> Signed-off-by: Helge Deller <deller@xxxxxx>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.4+
Thanks for your patch, which is now commit f0b6a66d33ca6e7e ("fbcon:
Prevent that screen size is smaller than font size") in fbdev/for-next
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1112,7 +1112,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> return -EFAULT;
> console_lock();
> lock_fb_info(info);
> - ret = fb_set_var(info, &var);
> + ret = fbcon_modechange_possible(info, &var);
Again, this should be done (if done at all) after the call to
fb_ops.check_var(), as it breaks the FBIOPUT_VSCREENINFO rounding rule.
What if the user just wants to display graphics, not text?
Can't the text console be disabled instead?
> + if (!ret)
> + ret = fb_set_var(info, &var);
> if (!ret)
> fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
> unlock_fb_info(info);
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
