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

[Yizhuo Zhai]

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@xxxxxxx>
---
 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