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From:   Yizhuo Zhai <yzhai003@ucr.edu>
Cc:     Yizhuo Zhai <yzhai003@ucr.edu>, Helge Deller <deller@gmx.de>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Matthew Wilcox <willy@infradead.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Zhen Lei <thunder.leizhen@huawei.com>,
        Zheyu Ma <zheyuma97@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Guenter Roeck <linux@roeck-us.net>,
        linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v5] fbdev: fbmem: Fix the implicit type casting
Date:   Wed,  2 Feb 2022 15:33:58 -0800
Message-Id: <20220202233402.1477864-1-yzhai003@ucr.edu>
In-Reply-To: <83e46d8d-ec7a-6cbd-010e-7f50f88dcf96@I-love.SAKURA.ne.jp>
References: <83e46d8d-ec7a-6cbd-010e-7f50f88dcf96@I-love.SAKURA.ne.jp>
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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 | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 0fa7ede94fa6..d5dec24c4d16 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1162,6 +1162,11 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 	case FBIOBLANK:
 		console_lock();
 		lock_fb_info(info);
+		if (arg > FB_BLANK_POWERDOWN) {
+			unlock_fb_info(info);
+			console_unlock();
+			return -EINVAL;
+		}
 		ret = fb_blank(info, arg);
 		/* might again call into fb_blank */
 		fbcon_fb_blanked(info, arg);
-- 
2.25.1