Hi Helge,

On Thu, Jun 30, 2022 at 9:46 PM Helge Deller [off-list ref] wrote:

On 6/30/22 21:36, Geert Uytterhoeven wrote:

quoted

On Thu, Jun 30, 2022 at 9:31 PM Helge Deller [off-list ref] wrote:

quoted

On 6/30/22 21:00, Geert Uytterhoeven wrote:

quoted

On Wed, Jun 29, 2022 at 10:00 PM Helge Deller [off-list ref] wrote:

quoted

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@gmx.de>
Cc: stable@vger.kernel.org # v5.4+

Thanks for your patch!

quoted

--- 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.

We do.

Why? It will be caught by [PATCH 4/5].

Right, it will be caught by patch #4.
But if you drop this part, then everytime a user runs
        fbset -xres 800 -yres 600 -xvres 200
users will get the KERNEL BUG WARNING (from patch #4) including
a kernel backtrace in their syslogs.

No, they will only see that warning if they are using a broken fbdev
driver that implements .fb_check_var(), but fails to validate or
update the passed geometry.

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