[client] Set up networkd to ignore ip rules (#4730)

client/cmd/service_installer.go

@@ -10,6 +10,8 @@ import (
 	"path/filepath"
 	"runtime"
 
+	log "github.com/sirupsen/logrus"
+
 	"github.com/kardianos/service"
 	"github.com/spf13/cobra"
 
@@ -81,6 +83,10 @@ func configurePlatformSpecificSettings(svcConfig *service.Config) error {
 				svcConfig.Option["LogDirectory"] = dir
 			}
 		}
+
+		if err := configureSystemdNetworkd(); err != nil {
+			log.Warnf("failed to configure systemd-networkd: %v", err)
+		}
 	}
 
 	if runtime.GOOS == "windows" {
@@ -160,6 +166,12 @@ var uninstallCmd = &cobra.Command{
 			return fmt.Errorf("uninstall service: %w", err)
 		}
 
+		if runtime.GOOS == "linux" {
+			if err := cleanupSystemdNetworkd(); err != nil {
+				log.Warnf("failed to cleanup systemd-networkd configuration: %v", err)
+			}
+		}
+
 		cmd.Println("NetBird service has been uninstalled")
 		return nil
 	},
@@ -245,3 +257,45 @@ func isServiceRunning() (bool, error) {
 
 	return status == service.StatusRunning, nil
 }
+
+const (
+	networkdConfDir     = "/etc/systemd/networkd.conf.d"
+	networkdConfFile    = "/etc/systemd/networkd.conf.d/99-netbird.conf"
+	networkdConfContent = `# Created by NetBird to prevent systemd-networkd from removing
+# routes and policy rules managed by NetBird.
+
+[Network]
+ManageForeignRoutes=no
+ManageForeignRoutingPolicyRules=no
+`
+)
+
+// configureSystemdNetworkd creates a drop-in configuration file to prevent
+// systemd-networkd from removing NetBird's routes and policy rules.
+func configureSystemdNetworkd() error {
+	parentDir := filepath.Dir(networkdConfDir)
+	if _, err := os.Stat(parentDir); os.IsNotExist(err) {
+		log.Debug("systemd networkd.conf.d parent directory does not exist, skipping configuration")
+		return nil
+	}
+
+	// nolint:gosec // standard networkd permissions
+	if err := os.WriteFile(networkdConfFile, []byte(networkdConfContent), 0644); err != nil {
+		return fmt.Errorf("write networkd configuration: %w", err)
+	}
+
+	return nil
+}
+
+// cleanupSystemdNetworkd removes the NetBird systemd-networkd configuration file.
+func cleanupSystemdNetworkd() error {
+	if _, err := os.Stat(networkdConfFile); os.IsNotExist(err) {
+		return nil
+	}
+
+	if err := os.Remove(networkdConfFile); err != nil {
+		return fmt.Errorf("remove networkd configuration: %w", err)
+	}
+
+	return nil
+}