[PATCH v6] fbdev: fbmem: Fix the implicit type casting

[Sam Ravnborg]

Hi Daniel,

I assume you will take this.

Patch is:
Reviewed-by: Sam Ravnborg <sam at ravnborg.org>

	Sam

On Wed, Feb 02, 2022 at 03:58:08PM -0800, Yizhuo Zhai wrote:
> In function do_fb_ioctl(), the "arg" is the type of unsigned long,
> and in "case FBIOBLANK:" this argument is casted into an int before
> passig to fb_blank(). In fb_blank(), the comparision
> if (blank > FB_BLANK_POWERDOWN) would be bypass if the original
> "arg" is a large number, which is possible because it comes from
> the user input. Fix this by adding the check before the function
> call.
> 
> Signed-off-by: Yizhuo Zhai <yzhai003 at ucr.edu>
> ---
>  drivers/video/fbdev/core/fbmem.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 0fa7ede94fa6..13083ad8d751 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1160,6 +1160,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>  		ret = fbcon_set_con2fb_map_ioctl(argp);
>  		break;
>  	case FBIOBLANK:
> +		if (arg > FB_BLANK_POWERDOWN)
> +			return -EINVAL;
>  		console_lock();
>  		lock_fb_info(info);
>  		ret = fb_blank(info, arg);
> -- 
> 2.25.1