[PATCH] fbdev: Don't spam dmesg on bad userspace ioctl input

[Michel Dänzer]

On 4/4/23 14:36, Daniel Vetter wrote:
> There's a few reasons the kernel should not spam dmesg on bad
> userspace ioctl input:
> - at warning level it results in CI false positives
> - it allows userspace to drown dmesg output, potentially hiding real
>   issues.
> 
> None of the other generic EINVAL checks report in the
> FBIOPUT_VSCREENINFO ioctl do this, so it's also inconsistent.
> 
> I guess the intent of the patch which introduced this warning was that
> the drivers ->fb_check_var routine should fail in that case. Reality
> is that there's too many fbdev drivers and not enough people
> maintaining them by far, and so over the past few years we've simply
> handled all these validation gaps by tighning the checks in the core,
> because that's realistically really all that will ever happen.
> 
> Reported-by: syzbot+20dcf81733d43ddff661 at syzkaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=c5faf983bfa4a607de530cd3bb008888bf06cefc
> Fixes: 6c11df58fd1a ("fbmem: Check virtual screen sizes in fb_set_var()")
> Cc: Helge Deller <deller at gmx.de>
> Cc: Geert Uytterhoeven <geert at linux-m68k.org>
> Cc: stable at vger.kernel.org # v5.4+
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Javier Martinez Canillas <javierm at redhat.com>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/video/fbdev/core/fbmem.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 875541ff185b..9757f4bcdf57 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1021,10 +1021,6 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
>  	/* verify that virtual resolution >= physical resolution */
>  	if (var->xres_virtual < var->xres ||
>  	    var->yres_virtual < var->yres) {
> -		pr_warn("WARNING: fbcon: Driver '%s' missed to adjust virtual screen size (%ux%u vs. %ux%u)\n",
> -			info->fix.id,
> -			var->xres_virtual, var->yres_virtual,
> -			var->xres, var->yres);
>  		return -EINVAL;
>  	}
>  

Make it pr_warn_once? 99.9...% of the benefit, without spam.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer