bgpd: Assign explicit-null for default-originate according to the AFI

RFC 3032 defines:

A value of 2 represents the "IPv6 Explicit NULL Label".
This label value is only legal at the bottom of the label
stack.  It indicates that the label stack must be popped,
and the forwarding of the packet must then be based on the
IPv6 header.

Before this patch we set 128, but it was even more wrong, because it was sent
in host-byte order, not the network-byte.

Signed-off-by: Donatas Abraitis <[email protected]>

Author: ton31337

bgpd/bgp_updgrp_packet.c

@@ -1080,8 +1080,7 @@ void subgroup_default_update_packet(struct update_subgroup *subgrp,
 	safi_t safi;
 	struct bpacket_attr_vec_arr vecarr;
 	bool addpath_capable = false;
-	uint8_t default_originate_label[4] = {0x80, 0x00, 0x00};
-	mpls_label_t *label = NULL;
+	mpls_label_t label = MPLS_LABEL_IMPLICIT_NULL;
 	uint32_t num_labels = 0;
 
 	if (DISABLE_BGP_ANNOUNCE)
@@ -1097,7 +1096,11 @@ void subgroup_default_update_packet(struct update_subgroup *subgrp,
 	addpath_capable = bgp_addpath_encode_tx(peer, afi, safi);
 
 	if (safi == SAFI_LABELED_UNICAST) {
-		label = (mpls_label_t *)default_originate_label;
+		label = mpls_lse_encode((afi == AFI_IP)
+						? MPLS_LABEL_IPV4_EXPLICIT_NULL
+						: MPLS_LABEL_IPV6_EXPLICIT_NULL,
+					0, 0, 1);
+		bgp_set_valid_label(&label);
 		num_labels = 1;
 	}
 
@@ -1142,10 +1145,12 @@ void subgroup_default_update_packet(struct update_subgroup *subgrp,
 	/* Make place for total attribute length.  */
 	pos = stream_get_endp(s);
 	stream_putw(s, 0);
-	total_attr_len = bgp_packet_attribute(
-		NULL, peer, s, attr, &vecarr, &p, afi, safi, from, NULL, label,
-		num_labels, addpath_capable,
-		BGP_ADDPATH_TX_ID_FOR_DEFAULT_ORIGINATE, NULL);
+	total_attr_len =
+		bgp_packet_attribute(NULL, peer, s, attr, &vecarr, &p, afi,
+				     safi, from, NULL, &label, num_labels,
+				     addpath_capable,
+				     BGP_ADDPATH_TX_ID_FOR_DEFAULT_ORIGINATE,
+				     NULL);
 
 	/* Set Total Path Attribute Length. */
 	stream_putw_at(s, pos, total_attr_len);