selinux: correct return values in selinux_socket_getpeersec_dgram()

Instead of returning -EINVAL if any type of error occurs, limit
-EINVAL to only those errors caused by passing a bad/invalid socket
or packet/skb.  In other cases where everything is correct but there
isn't a valid peer label we return -ENOPROTOOPT.

This helps make selinux_socket_getpeersec_dgram() more consistent
with selinux_socket_getpeersec_stream().
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -5193,11 +5193,11 @@ static int selinux_socket_getpeersec_stream(struct socket *sock,
 	return err;
 }
 
-static int selinux_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, u32 *secid)
+static int selinux_socket_getpeersec_dgram(struct socket *sock,
+					   struct sk_buff *skb, u32 *secid)
 {
 	u32 peer_secid = SECSID_NULL;
 	u16 family;
-	struct inode_security_struct *isec;
 
 	if (skb && skb->protocol == htons(ETH_P_IP))
 		family = PF_INET;
@@ -5205,19 +5205,21 @@ static int selinux_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *
 		family = PF_INET6;
 	else if (sock)
 		family = sock->sk->sk_family;
-	else
-		goto out;
+	else {
+		*secid = SECSID_NULL;
+		return -EINVAL;
+	}
 
 	if (sock && family == PF_UNIX) {
+		struct inode_security_struct *isec;
 		isec = inode_security_novalidate(SOCK_INODE(sock));
 		peer_secid = isec->sid;
 	} else if (skb)
 		selinux_skb_peerlbl_sid(skb, family, &peer_secid);
 
-out:
 	*secid = peer_secid;
 	if (peer_secid == SECSID_NULL)
-		return -EINVAL;
+		return -ENOPROTOOPT;
 	return 0;
 }