udp: empty address is different from uninitialized address

* instead teach getpeername that family is to be checked.
* fix #19652

Change-Id: I0e2150820687ca08e339adaf111918adc83b9e6b
Reviewed-on: https://review.haiku-os.org/c/haiku/+/9397
Reviewed-by: waddlesplash <[email protected]>

src/add-ons/kernel/network/protocols/ipv4/ipv4_address.cpp

@@ -402,7 +402,7 @@ ipv4_set_to_empty_address(sockaddr *address)
 		return B_BAD_VALUE;
 
 	memset(address, 0, sizeof(sockaddr_in));
-	address->sa_len = 0;
+	address->sa_len = sizeof(sockaddr_in);
 	address->sa_family = AF_INET;
 	return B_OK;
 }

src/add-ons/kernel/network/protocols/udp/udp.cpp

@@ -362,6 +362,7 @@ UdpDomainSupport::ConnectEndpoint(UdpEndpoint *endpoint,
 		// [Stevens-UNP1, p226]: specifying AF_UNSPEC requests a "disconnect",
 		// so we reset the peer address:
 		endpoint->PeerAddress().SetToEmpty();
+		(*endpoint->PeerAddress())->sa_family = AF_UNSPEC;
 	} else {
 		if (!AddressModule()->is_same_family(address))
 			return EAFNOSUPPORT;

src/add-ons/kernel/network/stack/net_socket.cpp

@@ -965,8 +965,10 @@ socket_getpeername(net_socket* _socket, struct sockaddr* address,
 	net_socket_private* socket = (net_socket_private*)_socket;
 	BReference<net_socket_private> parent = socket->parent.GetReference();
 
-	if ((!parent.IsSet() && !socket->is_connected) || socket->peer.ss_len == 0)
+	if ((!parent.IsSet() && !socket->is_connected) || socket->peer.ss_len == 0
+		|| socket->peer.ss_family == AF_UNSPEC) {
 		return ENOTCONN;
+	}
 
 	memcpy(address, &socket->peer, min_c(*_addressLength, socket->peer.ss_len));
 	*_addressLength = socket->peer.ss_len;