[dhcp] Verify DHCP server source port

Verifying server ID and DHCP transaction ID is insufficient to
differentiate between DHCPACK and ProxyDHCPACK when the DHCP server and
Proxy DHCP server are the same machine.

src/net/udp/dhcp.c

  * Receive new data
  *
  * @v xfer 		Data transfer interface
- * @v data		Received data
- * @v len		Length of received data
+ * @v iobuf		I/O buffer
+ * @v meta		Transfer metadata
  * @ret rc		Return status code
  */
-static int dhcp_deliver_raw ( struct xfer_interface *xfer,
-			      const void *data, size_t len ) {
+static int dhcp_deliver_iob ( struct xfer_interface *xfer,
+			      struct io_buffer *iobuf,
+			      struct xfer_metadata *meta ) {
 	struct dhcp_session *dhcp =
 		container_of ( xfer, struct dhcp_session, xfer );
+	struct sockaddr_tcpip *st_src;
+	unsigned int src_port;
 	struct dhcp_settings *dhcpset;
 	struct dhcphdr *dhcphdr;
 	uint8_t msgtype = 0;
+	int rc = 0;
+
+	/* Sanity checks */
+	if ( ! meta ) {
+		DBGC ( dhcp, "DHCP %p received packet without metadata\n",
+		       dhcp );
+		rc = -EINVAL;
+		goto err_no_meta;
+	}
+	if ( ! meta->src ) {
+		DBGC ( dhcp, "DHCP %p received packet without source port\n",
+		       dhcp );
+		rc = -EINVAL;
+		goto err_no_src;
+	}
+	st_src = ( struct sockaddr_tcpip * ) meta->src;
+	src_port = st_src->st_port;
 
 	/* Convert packet into a DHCP settings block */
-	dhcpset = dhcpset_create ( data, len );
+	dhcpset = dhcpset_create ( iobuf->data, iob_len ( iobuf ) );
 	if ( ! dhcpset ) {
 		DBGC ( dhcp, "DHCP %p could not store DHCP packet\n", dhcp );
-		return -ENOMEM;
+		rc = -ENOMEM;
+		goto err_dhcpset_create;
 	}
 	dhcphdr = dhcpset->dhcppkt.dhcphdr;
 
 	/* Identify message type */
 	dhcppkt_fetch ( &dhcpset->dhcppkt, DHCP_MESSAGE_TYPE, &msgtype,
 			sizeof ( msgtype ) );
-	DBGC ( dhcp, "DHCP %p received %s %p\n",
-	       dhcp, dhcp_msgtype_name ( msgtype ), dhcpset );
+	DBGC ( dhcp, "DHCP %p received %s %p from port %d\n", dhcp,
+	       dhcp_msgtype_name ( msgtype ), dhcpset, ntohs ( src_port ) );
 
 	/* Check for matching transaction ID */
 	if ( dhcphdr->xid != dhcp_xid ( dhcp->netdev ) ) {
 		DBGC ( dhcp, "DHCP %p received %s %p has bad transaction ID\n",
 		       dhcp, dhcp_msgtype_name ( msgtype ), dhcpset );
-		goto out;
+		rc = -EINVAL;
+		goto err_xid;
 	};
 
 	/* Handle packet based on current state */
 	switch ( dhcp->state ) {
 	case DHCP_STATE_DISCOVER:
-		if ( msgtype == DHCPOFFER )
+		if ( ( msgtype == DHCPOFFER ) &&
+		     ( src_port == htons ( BOOTPS_PORT ) ) )
 			dhcp_rx_dhcpoffer ( dhcp, dhcpset );
 		break;
 	case DHCP_STATE_REQUEST:
-		if ( msgtype == DHCPACK )
+		if ( ( msgtype == DHCPACK ) &&
+		     ( src_port == htons ( BOOTPS_PORT ) ) )
 			dhcp_rx_dhcpack ( dhcp, dhcpset );
 		break;
 	case DHCP_STATE_PROXYREQUEST:
-		if ( msgtype == DHCPACK )
+		if ( ( msgtype == DHCPACK ) &&
+		     ( src_port == htons ( PROXYDHCP_PORT ) ) )
 			dhcp_rx_proxydhcpack ( dhcp, dhcpset );
 		break;
 	default:
 		break;
 	}
 
- out:
+ err_xid:
 	dhcpset_put ( dhcpset );
-	return 0;
+ err_dhcpset_create:
+ err_no_src:
+ err_no_meta:
+	free_iob ( iobuf );
+	return rc;
 }
 
 /** DHCP data transfer interface operations */
 	.vredirect	= xfer_vopen,
 	.window		= unlimited_xfer_window,
 	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= dhcp_deliver_raw,
+	.deliver_iob	= dhcp_deliver_iob,
+	.deliver_raw	= xfer_deliver_as_iob,
 };
 
 /**