xfrm_user_policy(): don't open-code memdup_user()

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

net/xfrm/xfrm_state.c

@@ -2023,13 +2023,9 @@ int xfrm_user_policy(struct sock *sk, int optname, u8 __user *optval, int optlen
 	if (optlen <= 0 || optlen > PAGE_SIZE)
 		return -EMSGSIZE;
 
-	data = kmalloc(optlen, GFP_KERNEL);
-	if (!data)
-		return -ENOMEM;
-
-	err = -EFAULT;
-	if (copy_from_user(data, optval, optlen))
-		goto out;
+	data = memdup_user(optval, optlen);
+	if (IS_ERR(data))
+		return PTR_ERR(data);
 
 	err = -EINVAL;
 	rcu_read_lock();
@@ -2047,7 +2043,6 @@ int xfrm_user_policy(struct sock *sk, int optname, u8 __user *optval, int optlen
 		err = 0;
 	}
 
-out:
 	kfree(data);
 	return err;
 }