linux-kernel - [PATCH v3] fbdev: fbmem: Fix the implicit type casting

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Date:   Tue,  1 Feb 2022 02:56:07 -0800
From:   Yizhuo Zhai <yzhai003@....edu>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Yizhuo Zhai <yzhai003@....edu>, Helge Deller <deller@....de>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Matthew Wilcox <willy@...radead.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Zheyu Ma <zheyuma97@...il.com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Alex Deucher <alexander.deucher@....com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3] fbdev: fbmem: Fix the implicit type casting

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@....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..991711bfd647 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 (arg > FB_BLANK_POWERDOWN)
+			arg = FB_BLANK_POWERDOWN;
 		ret = fb_blank(info, arg);
 		/* might again call into fb_blank */
 		fbcon_fb_blanked(info, arg);
-- 
2.25.1