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

From: Yizhuo Zhai <yzhai003@ucr.edu>
To: unlisted-recipients:; (no To-header on input)
Cc: Yizhuo Zhai <yzhai003@ucr.edu>, Helge Deller <deller@gmx.de>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Sam Ravnborg <sam@ravnborg.org>,
	Matthew Wilcox <willy@infradead.org>,
	Alex Deucher <alexander.deucher@amd.com>,
	Xin Tan <tanxin.ctf@gmail.com>,
	Xiyu Yang <xiyuyang19@fudan.edu.cn>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	Zheyu Ma <zheyuma97@gmail.com>,
	Guenter Roeck <linux@roeck-us.net>,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v6] fbdev: fbmem: Fix the implicit type casting
Date: Wed,  2 Feb 2022 15:58:08 -0800	[thread overview]
Message-ID: <20220202235811.1621017-1-yzhai003@ucr.edu> (raw)
In-Reply-To: <f3b28143-5f59-ad77-f2b8-6274a6edbfdc@roeck-us.net>

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@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

