Re: [PATCH v6 3/4] fbcon: Prevent that screen size is smaller than font size
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: 2022-06-28 08:40:15
Also in:
dri-devel
Hi Helge, On Sun, Jun 26, 2022 at 12:33 PM Helge Deller [off-list ref] 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@gmx.de> Reviewed-by: Daniel Vetter <redacted> Cc: stable@vger.kernel.org # 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
quoted hunk ↗ jump to hunk
--- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c
quoted hunk ↗ jump to hunk
--- 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@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