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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Yizhuo Zhai' <yzhai003@ucr.edu>
CC:     Helge Deller <deller@gmx.de>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Matthew Wilcox <willy@infradead.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        "Zhen Lei" <thunder.leizhen@huawei.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Zheyu Ma <zheyuma97@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2] fbdev: fbmem: Fix the implicit type casting
Thread-Topic: [PATCH v2] fbdev: fbmem: Fix the implicit type casting
Thread-Index: AQHYFxVn+cS+fUmzMESHo6Syg/F7Wqx/+Mmg
Date:   Wed, 2 Feb 2022 09:02:52 +0000
Message-ID: <5286c6acac7c4ee598f6fa4a7ea04b86@AcuMS.aculab.com>
References: <202201311943.VXU6K1gH-lkp@intel.com>
 <20220201023559.2622144-1-yzhai003@ucr.edu>
In-Reply-To: <20220201023559.2622144-1-yzhai003@ucr.edu>
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From: Yizhuo Zhai
> Sent: 01 February 2022 02:36
> 
> 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.

Doesn't this convert invalid values (> FB_BLANK_POWERDOWN)
that should generate errors into valid requests?

	David

> 
> Signed-off-by: Yizhuo Zhai <yzhai003@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..f08326efff54 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1162,6 +1162,8 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>  	case FBIOBLANK:
>  		console_lock();
>  		lock_fb_info(info);
> +		if (blank > FB_BLANK_POWERDOWN)
> +			blank = FB_BLANK_POWERDOWN;
>  		ret = fb_blank(info, arg);
>  		/* might again call into fb_blank */
>  		fbcon_fb_blanked(info, arg);
> --
> 2.25.1

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