advancedtls: Add system default CAs to config function (#3663)

* Add system default CAs to config function

security/advancedtls/advancedtls.go

@@ -81,6 +81,8 @@ type GetRootCAsResults struct {
 // RootCertificateOptions contains a field and a function for obtaining root
 // trust certificates.
 // It is used by both ClientOptions and ServerOptions.
+// If users want to use default verification, but did not provide a valid
+// RootCertificateOptions, we use the system default trust certificates.
 type RootCertificateOptions struct {
 	// If field RootCACerts is set, field GetRootCAs will be ignored. RootCACerts
 	// will be used every time when verifying the peer certificates, without
@@ -184,15 +186,26 @@ func (o *ClientOptions) config() (*tls.Config, error) {
 		return nil, fmt.Errorf(
 			"client needs to provide custom verification mechanism if choose to skip default verification")
 	}
+	rootCAs := o.RootCACerts
+	if o.VType != SkipVerification && o.RootCACerts == nil && o.GetRootCAs == nil {
+		// Set rootCAs to system default.
+		systemRootCAs, err := x509.SystemCertPool()
+		if err != nil {
+			return nil, err
+		}
+		rootCAs = systemRootCAs
+	}
 	// We have to set InsecureSkipVerify to true to skip the default checks and
 	// use the verification function we built from buildVerifyFunc.
 	config := &tls.Config{
 		ServerName:           o.ServerNameOverride,
 		Certificates:         o.Certificates,
 		GetClientCertificate: o.GetClientCertificate,
-		RootCAs:              o.RootCACerts,
 		InsecureSkipVerify:   true,
 	}
+	if rootCAs != nil {
+		config.RootCAs = rootCAs
+	}
 	return config, nil
 }
 
@@ -204,6 +217,15 @@ func (o *ServerOptions) config() (*tls.Config, error) {
 		return nil, fmt.Errorf(
 			"server needs to provide custom verification mechanism if choose to skip default verification, but require client certificate(s)")
 	}
+	clientCAs := o.RootCACerts
+	if o.VType != SkipVerification && o.RootCACerts == nil && o.GetRootCAs == nil && o.RequireClientCert {
+		// Set clientCAs to system default.
+		systemRootCAs, err := x509.SystemCertPool()
+		if err != nil {
+			return nil, err
+		}
+		clientCAs = systemRootCAs
+	}
 	clientAuth := tls.NoClientCert
 	if o.RequireClientCert {
 		// We have to set clientAuth to RequireAnyClientCert to force underlying
@@ -216,8 +238,8 @@ func (o *ServerOptions) config() (*tls.Config, error) {
 		Certificates:   o.Certificates,
 		GetCertificate: o.GetCertificate,
 	}
-	if o.RootCACerts != nil {
-		config.ClientCAs = o.RootCACerts
+	if clientCAs != nil {
+		config.ClientCAs = clientCAs
 	}
 	return config, nil
 }

security/advancedtls/advancedtls_test.go

@@ -623,3 +623,59 @@ func TestWrapSyscallConn(t *testing.T) {
 			wrapConn)
 	}
 }
+
+func TestOptionsConfig(t *testing.T) {
+	serverPeerCert, err := tls.LoadX509KeyPair(testdata.Path("server_cert_1.pem"),
+		testdata.Path("server_key_1.pem"))
+	if err != nil {
+		t.Fatalf("Server is unable to parse peer certificates. Error: %v", err)
+	}
+	tests := []struct {
+		desc            string
+		clientVType     VerificationType
+		serverMutualTLS bool
+		serverCert      []tls.Certificate
+		serverVType     VerificationType
+	}{
+		{
+			desc:            "Client uses system-provided RootCAs; server uses system-provided ClientCAs",
+			clientVType:     CertVerification,
+			serverMutualTLS: true,
+			serverCert:      []tls.Certificate{serverPeerCert},
+			serverVType:     CertAndHostVerification,
+		},
+	}
+	for _, test := range tests {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			serverOptions := &ServerOptions{
+				Certificates:      test.serverCert,
+				RequireClientCert: test.serverMutualTLS,
+				VType:             test.serverVType,
+			}
+			serverConfig, err := serverOptions.config()
+			if err != nil {
+				t.Fatalf("Unable to generate serverConfig. Error: %v", err)
+			}
+			// Verify that the system-provided certificates would be used
+			// when no verification method was set in serverOptions.
+			if serverOptions.RootCACerts == nil && serverOptions.GetRootCAs == nil &&
+				serverOptions.RequireClientCert && serverConfig.ClientCAs == nil {
+				t.Fatalf("Failed to assign system-provided certificates on the server side.")
+			}
+			clientOptions := &ClientOptions{
+				VType: test.clientVType,
+			}
+			clientConfig, err := clientOptions.config()
+			if err != nil {
+				t.Fatalf("Unable to generate clientConfig. Error: %v", err)
+			}
+			// Verify that the system-provided certificates would be used
+			// when no verification method was set in clientOptions.
+			if clientOptions.RootCACerts == nil && clientOptions.GetRootCAs == nil &&
+				clientConfig.RootCAs == nil {
+				t.Fatalf("Failed to assign system-provided certificates on the client side.")
+			}
+		})
+	}
+}