Code: static int get_bitmap_file(struct mddev *mddev, void __user * arg)
{
	mdu_bitmap_file_t *file = NULL; /* too big for stack allocation */
 	char *ptr;
 	int err;
 
	file = kmalloc(sizeof(*file), GFP_NOIO);
 	if (!file)
 		return -ENOMEM;
 
	err = 0;
	spin_lock(&mddev->lock);
	/* bitmap disabled, zero the first byte and copy out */
	if (!mddev->bitmap_info.file)
		file->pathname[0] = '\0';
	else if ((ptr = file_path(mddev->bitmap_info.file,
			       file->pathname, sizeof(file->pathname))),
		 IS_ERR(ptr))
		err = PTR_ERR(ptr);
	else
		memmove(file->pathname, ptr,
			sizeof(file->pathname)-(ptr-file->pathname));
	spin_unlock(&mddev->lock);

	if (err == 0 &&
	    copy_to_user(arg, file, sizeof(*file)))
		err = -EFAULT;

	kfree(file);
	return err;
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The get_bitmap_file function in drivers/md/md.c in the Linux kernel before 4.1.6 does not initialize a certain bitmap data structure, which allows local users to obtain sensitive information from kernel memory via a GET_BITMAP_FILE ioctl call.
Commit Message: md: use kzalloc() when bitmap is disabled

In drivers/md/md.c get_bitmap_file() uses kmalloc() for creating a
mdu_bitmap_file_t called "file".

5769         file = kmalloc(sizeof(*file), GFP_NOIO);
5770         if (!file)
5771                 return -ENOMEM;

This structure is copied to user space at the end of the function.

5786         if (err == 0 &&
5787             copy_to_user(arg, file, sizeof(*file)))
5788                 err = -EFAULT

But if bitmap is disabled only the first byte of "file" is initialized
with zero, so it's possible to read some bytes (up to 4095) of kernel
space memory from user space. This is an information leak.

5775         /* bitmap disabled, zero the first byte and copy out */
5776         if (!mddev->bitmap_info.file)
5777                 file->pathname[0] = '\0';

Signed-off-by: Benjamin Randazzo <benjamin@randazzo.fr>
Signed-off-by: NeilBrown <neilb@suse.com>