bgpd: Ignore validating the attribute flags if path-attribute is conf…

…igured

E.g. Cisco sends AIGP attribute as transitive, but it's wrong. Hence, the session
is teared down, because of this bgp_attr_flag_invalid() test.

Relax this check if we have `neighbor X path-attribute <discard|treat-as-withdraw>`
configured.

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

bgpd/bgp_attr.c

@@ -1526,13 +1526,22 @@ static bool bgp_attr_flag_invalid(struct bgp_attr_parser_args *args)
 	uint8_t mask = BGP_ATTR_FLAG_EXTLEN;
 	const uint8_t flags = args->flags;
 	const uint8_t attr_code = args->type;
+	struct peer *peer = args->peer;
 
 	/* there may be attributes we don't know about */
 	if (attr_code > attr_flags_values_max)
 		return false;
 	if (attr_flags_values[attr_code] == 0)
 		return false;
 
+	/* If `neighbor X path-attribute <discard|treat-as-withdraw>` is
+	 * configured, then ignore checking optional, trasitive flags.
+	 * The attribute/route will be discarded/withdrawned later instead
+	 * of dropping the session.
+	 */
+	if (peer->discard_attrs[attr_code] || peer->withdraw_attrs[attr_code])
+		return false;
+
 	/* RFC4271, "For well-known attributes, the Transitive bit MUST be set
 	 * to
 	 * 1."