kcm: remove a useless copy_from_user()

struct kcm_clone only contains fd, and kcm_clone() only
writes this struct, so there is no need to copy it from user.

Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/kcm/kcmsock.c

@@ -1707,11 +1707,7 @@ static int kcm_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 		struct kcm_clone info;
 		struct socket *newsock = NULL;
 
-		if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
-			return -EFAULT;
-
 		err = kcm_clone(sock, &info, &newsock);
-
 		if (!err) {
 			if (copy_to_user((void __user *)arg, &info,
 					 sizeof(info))) {