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

On Thu, Feb 03, 2022 at 09:18:30AM +0100, Helge Deller wrote:

On 2/3/22 07:39, Sam Ravnborg wrote:

quoted

Hi Daniel,

I assume you will take this.

Patch is:
Reviewed-by: Sam Ravnborg <redacted>

Acked-by: Helge Deller <deller@gmx.de>

Pushed to drm-misc-fixes, thanks for patch&review.
-Daniel

Helge

quoted

	Sam

On Wed, Feb 02, 2022 at 03:58:08PM -0800, Yizhuo Zhai wrote:

quoted

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 <redacted>
---
 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

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch