Improve performance when custom lists are not loaded

firewall/master.go

@@ -619,6 +619,11 @@ matchLoop:
 }
 
 func checkCustomFilterList(_ context.Context, conn *network.Connection, p *profile.LayeredProfile, _ packet.Packet) bool {
+	// Check if any custom list is loaded at all.
+	if !customlists.IsLoaded() {
+		return false
+	}
+
 	// block if the domain name appears in the custom filter list (check for subdomains if enabled)
 	if conn.Entity.Domain != "" {
 		if ok, match := customlists.LookupDomain(conn.Entity.Domain, p.FilterSubDomains()); ok {

intel/customlists/lists.go

@@ -36,6 +36,25 @@ func initFilterLists() {
 	domainsFilterList = make(map[string]struct{})
 }
 
+// IsLoaded returns whether a custom filter list is loaded.
+func IsLoaded() bool {
+	filterListLock.RLock()
+	defer filterListLock.RUnlock()
+
+	switch {
+	case len(domainsFilterList) > 0:
+		return true
+	case len(ipAddressesFilterList) > 0:
+		return true
+	case len(countryCodesFilterList) > 0:
+		return true
+	case len(autonomousSystemsFilterList) > 0:
+		return true
+	default:
+		return false
+	}
+}
+
 func parseFile(filePath string) error {
 	// Reset all maps, previous (if any) settings will be lost.
 	for key := range countryCodesFilterList {