Add new CLI flag to disable TLS SAN CN filtering

pkg/cli/cmds/server.go

@@ -47,6 +47,7 @@ type Server struct {
 	KubeConfigMode           string
 	HelmJobImage             string
 	TLSSan                   cli.StringSlice
+	TLSSanSecurity           bool
 	BindAddress              string
 	EnablePProf              bool
 	ExtraAPIArgs             cli.StringSlice
@@ -202,6 +203,11 @@ var ServerFlags = []cli.Flag{
 		Usage: "(listener) Add additional hostnames or IPv4/IPv6 addresses as Subject Alternative Names on the server TLS cert",
 		Value: &ServerConfig.TLSSan,
 	},
+	&cli.BoolTFlag{
+		Name:        "tls-san-security",
+		Usage:       "(listener) Protect the server TLS cert by refusing to add Subject Alternative Names not associated with the kubernetes apiserver service, server nodes, or values of the tls-san option (default: true)",
+		Destination: &ServerConfig.TLSSanSecurity,
+	},
 	DataDirFlag,
 	ClusterCIDR,
 	ServiceCIDR,

pkg/cli/server/server.go

@@ -132,6 +132,7 @@ func run(app *cli.Context, cfg *cmds.Server, leaderControllers server.CustomCont
 	serverConfig.ControlConfig.Rootless = cfg.Rootless
 	serverConfig.ControlConfig.ServiceLBNamespace = cfg.ServiceLBNamespace
 	serverConfig.ControlConfig.SANs = util.SplitStringSlice(cfg.TLSSan)
+	serverConfig.ControlConfig.SANSecurity = cfg.TLSSanSecurity
 	serverConfig.ControlConfig.BindAddress = cfg.BindAddress
 	serverConfig.ControlConfig.SupervisorPort = cfg.SupervisorPort
 	serverConfig.ControlConfig.HTTPSPort = cfg.HTTPSPort

pkg/cluster/https.go

@@ -52,8 +52,10 @@ func (c *Cluster) newListener(ctx context.Context) (net.Listener, http.Handler,
 		return nil, nil, err
 	}
 	c.config.SANs = append(c.config.SANs, "kubernetes", "kubernetes.default", "kubernetes.default.svc", "kubernetes.default.svc."+c.config.ClusterDomain)
-	c.config.Runtime.ClusterControllerStarts["server-cn-filter"] = func(ctx context.Context) {
-		registerAddressHandlers(ctx, c)
+	if c.config.SANSecurity {
+		c.config.Runtime.ClusterControllerStarts["server-cn-filter"] = func(ctx context.Context) {
+			registerAddressHandlers(ctx, c)
+		}
 	}
 	storage := tlsStorage(ctx, c.config.DataDir, c.config.Runtime)
 	return wrapHandler(dynamiclistener.NewListenerWithChain(tcp, storage, certs, key, dynamiclistener.Config{

pkg/daemons/config/types.go

@@ -220,6 +220,7 @@ type Control struct {
 
 	BindAddress string
 	SANs        []string
+	SANSecurity bool
 	PrivateIP   string
 	Runtime     *ControlRuntime `json:"-"`
 }