Re: [PATCH stable 4.19 4.14 0/2] add fix patch for CVE-2021-3365

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, Jul 29, 2022 at 03:11:38AM +0000, Chen Jun wrote:
> refer to https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
> 3 patches are provided to fix CVE-2021-3365 (When sending malicous data
> to kernel by ioctl cmd FBIOPUT_VSCREENINFO,kernel will write memory out
> of bounds. https://nvd.nist.gov/vuln/detail/CVE-2021-33655) in mainline.
> 
> But only
> commit 65a01e601dbb ("fbcon: Disallow setting font bigger than screen size")
> was backported to stable (4.19,4.14).
> 
> without other two commit
> commit e64242caef18 ("fbcon: Prevent that screen size is smaller than font size")
> commit 6c11df58fd1a ("fbmem: Check virtual screen sizes in fb_set_var()")
> The problem still exists.
> 
> static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, unsigned long arg)
> 	fb_set_var(info, &var);
> 		fb_notifier_call_chain(evnt, &event); // evnt = FB_EVENT_MODE_CHANGE
> 
> static int fbcon_event_notify(struct notifier_block *self,
> 			      unsigned long action, void *data)
> 	fbcon_modechanged(info);
> 		updatescrollmode(p, info, vc);
> 			...
> 			p->vrows = vyres/fh;
> 			if (yres > (fh * (vc->vc_rows + 1)))
> 				p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
> 			if ((yres % fh) && (vyres % fh < yres % fh))
> 				p->vrows--;	[1]
> [1]: p->vrows could be -1, like what CVE-2021-3365 described.
> 
> I think, the two commits should be backported to 4.19 and 4.14.
> 
> Helge Deller (2):
>   fbcon: Prevent that screen size is smaller than font size
>   fbmem: Check virtual screen sizes in fb_set_var()
> 
>  drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
>  drivers/video/fbdev/core/fbmem.c | 20 +++++++++++++++++---
>  include/linux/fbcon.h            |  4 ++++
>  3 files changed, 49 insertions(+), 3 deletions(-)
> 
> -- 
> 2.17.1
> 

This breaks the build on 4.14.y, did you test it there?

The error is:
	ERROR: "is_console_locked" [drivers/video/fbdev/core/fb.ko] undefined!

Can you please fix this up and also do a 4.9.y version?

thanks,

greg k-h