bgpd: authorise to select bgp self peer prefix on rr case

This commit addresses an issue that happens when using bgp
peering with a rr client, with a received prefix which is the
local ip address of the bgp session.

When using bgp ipv4 unicast session, the local prefix is
received by a peer, and finds out that the proposed prefix
and its next-hop are the same. To avoid a route loop locally,
no nexthop entry is referenced for that prefix, and the route
will not be selected.

When the received peer is a route reflector, the prefix has
to be selected, even if the route can not be installed locally.

Fixes: ("fb8ae704615c") bgpd: prevent routes loop through itself

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
(cherry picked from commit f874552)

bgpd/bgp_route.c

@@ -3874,6 +3874,7 @@ int bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 	int vnc_implicit_withdraw = 0;
 #endif
 	int same_attr = 0;
+	const struct prefix *bgp_nht_param_prefix;
 
 	/* Special case for BGP-LU - map LU safi to ordinary unicast safi */
 	if (orig_safi == SAFI_LABELED_UNICAST)
@@ -3937,6 +3938,11 @@ int bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 		if (aspath_get_last_as(attr->aspath) == bgp->as)
 			do_loop_check = 0;
 
+	if (CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_REFLECTOR_CLIENT))
+		bgp_nht_param_prefix = NULL;
+	else
+		bgp_nht_param_prefix = p;
+
 	/* AS path loop check. */
 	if (do_loop_check) {
 		if (aspath_loop_check(attr->aspath, bgp->as)
@@ -4445,8 +4451,8 @@ int bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 
 			if (bgp_find_or_add_nexthop(bgp, bgp_nexthop, nh_afi,
 						    safi, pi, NULL, connected,
-						    p)
-			    || CHECK_FLAG(peer->flags, PEER_FLAG_IS_RFAPI_HD))
+						    bgp_nht_param_prefix) ||
+			    CHECK_FLAG(peer->flags, PEER_FLAG_IS_RFAPI_HD))
 				bgp_path_info_set_flag(dest, pi,
 						       BGP_PATH_VALID);
 			else {
@@ -4604,8 +4610,8 @@ int bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 		nh_afi = BGP_ATTR_NH_AFI(afi, new->attr);
 
 		if (bgp_find_or_add_nexthop(bgp, bgp, nh_afi, safi, new, NULL,
-					    connected, p)
-		    || CHECK_FLAG(peer->flags, PEER_FLAG_IS_RFAPI_HD))
+					    connected, bgp_nht_param_prefix) ||
+		    CHECK_FLAG(peer->flags, PEER_FLAG_IS_RFAPI_HD))
 			bgp_path_info_set_flag(dest, new, BGP_PATH_VALID);
 		else {
 			if (BGP_DEBUG(nht, NHT)) {