Re: [video] dc13cac486: BUG:KASAN:stack-out-of-bounds_in_hgafb_open

[Anirudh Rayabharam]

On Sun, May 16, 2021 at 11:00:19PM +0800, kernel test robot wrote:
> 
> 
> Greeting,
> 
> FYI, we noticed the following commit (built with gcc-9):
> 
> commit: dc13cac4862cc68ec74348a80b6942532b7735fa ("video: hgafb: fix potential NULL pointer dereference")
> https://git.kernel.org/cgit/linux/kernel/git/gregkh/char-misc.git char-misc-linus
> 
> 
> in testcase: trinity
> version: trinity-static-x86_64-x86_64-f93256fb_2019-08-28
> with following parameters:
> 
> 	number: 99999
> 	group: group-02
> 
> test-description: Trinity is a linux system call fuzz tester.
> test-url: http://codemonkey.org.uk/projects/trinity/
> 
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> 
> 
> +---------------------------------------------+------------+------------+
> |                                             | 58c0cc2d90 | dc13cac486 |
> +---------------------------------------------+------------+------------+
> | boot_successes                              | 42         | 14         |
> | boot_failures                               | 0          | 34         |
> | BUG:KASAN:stack-out-of-bounds_in_hgafb_open | 0          | 34         |
> +---------------------------------------------+------------+------------+
> 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> 
> 
> [  419.568887] BUG: KASAN: stack-out-of-bounds in hgafb_open (kbuild/src/consumer/drivers/video/fbdev/hgafb.c:375) 

Looks like the return value of hga_card_detect() is not properly
handled causing the probe function to succeed even though
hga_card_detect() has failed. Since probe has succeeded, hgafb_open()
can be called which will end up operating on an unmapped hga_vram.

Patch on the way.

Thanks!

	- Anirudh.