Re: [PATCH V4] fbcon: fix fbcon out-of-bounds write in sys_imageblit

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Aug 30, 2021 at 11:30:23AM +0800, tcs.kernel@gmail.com wrote:
> From: Haimin Zhang <tcs_kernel@tencent.com>
> 
> yres and vyres can be controlled by user mode parameters, and cause
> p->vrows to become a negative value. While this value be passed to real_y
> function, the ypos will be out of screen range.This is an out-of-bounds
> write bug.
> some driver will check xres and yres in fb_check_var callback,but some not
> so we add a common check after that callback.
> 
> Signed-off-by: Haimin Zhang <tcs_kernel@tencent.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
> ---
>  drivers/video/fbdev/core/fbmem.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 1c85514..5599372 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1013,6 +1013,10 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
>  	if (ret)
>  		return ret;
>  
> +	/* virtual resolution cannot be smaller than visible resolution. */
> +	if (var->yres_virtual < var->yres || var->xres_virtual < var->xres)
> +		return -EINVAL;
> +
>  	if ((var->activate & FB_ACTIVATE_MASK) != FB_ACTIVATE_NOW)
>  		return 0;
>  
> -- 
> 1.8.3.1
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
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