bgpd: Validate both nexthop information (NEXTHOP and NLRI)

If we receive an IPv6 prefix e.g.: 2001:db8:100::/64 with nextop: 0.0.0.0, and
mp_nexthop: fc00::2, we should not treat this with an invalid nexthop because
of 0.0.0.0. We MUST check for MP_REACH attribute also and decide later if we
have at least one a valid nexthop.

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

bgpd/bgp_route.c

@@ -4459,7 +4459,7 @@ bool bgp_update_martian_nexthop(struct bgp *bgp, afi_t afi, safi_t safi,
 				uint8_t type, uint8_t stype, struct attr *attr,
 				struct bgp_dest *dest)
 {
-	bool ret = false;
+	bool mp_nh_invalid = false;
 	bool is_bgp_static_route =
 		(type == ZEBRA_ROUTE_BGP && stype == BGP_ROUTE_STATIC) ? true
 								       : false;
@@ -4481,14 +4481,6 @@ bool bgp_update_martian_nexthop(struct bgp *bgp, afi_t afi, safi_t safi,
 	    (safi != SAFI_UNICAST && safi != SAFI_MULTICAST && safi != SAFI_EVPN))
 		return false;
 
-	/* If NEXT_HOP is present, validate it. */
-	if (CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_NEXT_HOP))) {
-		if (attr->nexthop.s_addr == INADDR_ANY ||
-		    !ipv4_unicast_nexthop_valid(&attr->nexthop) ||
-		    bgp_nexthop_self(bgp, afi, type, stype, attr, dest))
-			return true;
-	}
-
 	/* If MP_NEXTHOP is present, validate it. */
 	/* Note: For IPv6 nexthops, we only validate the global (1st) nexthop;
 	 * there is code in bgp_attr.c to ignore the link-local (2nd) nexthop if
@@ -4502,36 +4494,42 @@ bool bgp_update_martian_nexthop(struct bgp *bgp, afi_t afi, safi_t safi,
 		switch (attr->mp_nexthop_len) {
 		case BGP_ATTR_NHLEN_IPV4:
 		case BGP_ATTR_NHLEN_VPNV4:
-			ret = (attr->mp_nexthop_global_in.s_addr == INADDR_ANY ||
-			       !ipv4_unicast_nexthop_valid(&attr->mp_nexthop_global_in) ||
-			       bgp_nexthop_self(bgp, afi, type, stype, attr, dest));
+			mp_nh_invalid = (attr->mp_nexthop_global_in.s_addr == INADDR_ANY ||
+					 !ipv4_unicast_nexthop_valid(&attr->mp_nexthop_global_in) ||
+					 bgp_nexthop_self(bgp, afi, type, stype, attr, dest));
 			break;
 
 		case BGP_ATTR_NHLEN_IPV6_GLOBAL:
 		case BGP_ATTR_NHLEN_VPNV6_GLOBAL:
-			ret = (IN6_IS_ADDR_UNSPECIFIED(
-					&attr->mp_nexthop_global)
-			       || IN6_IS_ADDR_LOOPBACK(&attr->mp_nexthop_global)
-			       || IN6_IS_ADDR_MULTICAST(
-				       &attr->mp_nexthop_global)
-			       || bgp_nexthop_self(bgp, afi, type, stype, attr,
-						   dest));
+			mp_nh_invalid = (IN6_IS_ADDR_UNSPECIFIED(&attr->mp_nexthop_global) ||
+					 IN6_IS_ADDR_LOOPBACK(&attr->mp_nexthop_global) ||
+					 IN6_IS_ADDR_MULTICAST(&attr->mp_nexthop_global) ||
+					 bgp_nexthop_self(bgp, afi, type, stype, attr, dest));
 			break;
 		case BGP_ATTR_NHLEN_IPV6_GLOBAL_AND_LL:
-			ret = (IN6_IS_ADDR_LOOPBACK(&attr->mp_nexthop_global)
-			       || IN6_IS_ADDR_MULTICAST(
-				       &attr->mp_nexthop_global)
-			       || bgp_nexthop_self(bgp, afi, type, stype, attr,
-						   dest));
+			mp_nh_invalid = (IN6_IS_ADDR_LOOPBACK(&attr->mp_nexthop_global) ||
+					 IN6_IS_ADDR_MULTICAST(&attr->mp_nexthop_global) ||
+					 bgp_nexthop_self(bgp, afi, type, stype, attr, dest));
 			break;
 
 		default:
-			ret = true;
+			mp_nh_invalid = true;
 			break;
 		}
 	}
 
-	return ret;
+	/* If NEXT_HOP is present, validate it:
+	 * The route can have both nexthop + mp_nexthop encoded as multiple NLRIs,
+	 * and we MUST check if at least one of them is valid.
+	 * E.g.: IPv6 prefix can be with nexthop: 0.0.0.0, and mp_nexthop: fc00::1.
+	 */
+	if (CHECK_FLAG(attr->flag, ATTR_FLAG_BIT(BGP_ATTR_NEXT_HOP)) && mp_nh_invalid) {
+		return (attr->nexthop.s_addr == INADDR_ANY ||
+			!ipv4_unicast_nexthop_valid(&attr->nexthop) ||
+			bgp_nexthop_self(bgp, afi, type, stype, attr, dest));
+	}
+
+	return mp_nh_invalid;
 }
 
 static void bgp_attr_add_no_export_community(struct attr *attr)