RE: [PATCH v2] fbdev: fbmem: Fix the implicit type casting

From: Yizhuo Zhai

Sent: 01 February 2022 02:36

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.

Doesn't this convert invalid values (> FB_BLANK_POWERDOWN) that should generate errors into valid requests?

David

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..f08326efff54 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 (blank > FB_BLANK_POWERDOWN)
  

• 	blank = FB_BLANK_POWERDOWN;
  

  ret = fb_blank(info, arg); /* might again call into fb_blank */ fbcon_fb_blanked(info, arg);

-- 2.25.1

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