ftpd: advertise TLS support only if really enabled

if we don't have a global TLS configuration, advertise TLS only on the
bindings where it is configured instead of failing at runtime

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

docs/full-configuration.md

@@ -163,8 +163,8 @@ The configuration file contains the following sections:
     - `port`, integer. The port used for serving FTP requests. 0 means disabled. Default: 0.
     - `address`, string. Leave blank to listen on all available network interfaces. Default: "".
     - `apply_proxy_config`, boolean. If enabled the common proxy configuration, if any, will be applied. Please note that we expect the proxy header on control and data connections. Default `true`.
-    - `tls_mode`, integer. 0 means accept both cleartext and encrypted sessions. 1 means TLS is required for both control and data connection. 2 means implicit TLS. Do not enable this blindly, please check that a proper TLS config is in place if you set `tls_mode` is different from 0.
-    - `tls_session_reuse`, integer. 0 means session reuse is not checked, clients may or may not resume TLS sessions. 1 means TLS session reuse is required for explicit FTPS. Not supported for implicit TLS. Default: `0`.
+    - `tls_mode`, integer. 0 means accept both cleartext and encrypted sessions. 1 means TLS is required for both control and data connection. 2 means implicit TLS.Please check that a proper TLS config is in place if you set `tls_mode` is different from 0.
+    - `tls_session_reuse`, integer. 0 means session reuse is not checked, clients may or may not reuse TLS sessions. 1 means TLS session reuse is required for explicit FTPS. Legacy reuse method based on session IDs is not supported, clients must use session tickets. Session reuse is not supported for implicit TLS. Default: `0`.
     - `certificate_file`, string. Binding specific TLS certificate. This can be an absolute path or a path relative to the config dir.
     - `certificate_key_file`, string. Binding specific private key matching the above certificate. This can be an absolute path or a path relative to the config dir. If not set the global ones will be used, if any.
     - `min_tls_version`, integer. Defines the minimum version of TLS to be enabled. `12` means TLS 1.2 (and therefore TLS 1.2 and TLS 1.3 will be enabled),`13` means TLS 1.3. Default: `12`.

internal/common/tlsutils.go

@@ -108,6 +108,15 @@ func (m *CertManager) loadCertificates() error {
 	return nil
 }
 
+// HasCertificate returns true if there is a certificate for the specified certID
+func (m *CertManager) HasCertificate(certID string) bool {
+	m.RLock()
+	defer m.RUnlock()
+
+	_, ok := m.certs[certID]
+	return ok
+}
+
 // GetCertificateFunc returns the loaded certificate
 func (m *CertManager) GetCertificateFunc(certID string) func(*tls.ClientHelloInfo) (*tls.Certificate, error) {
 	return func(_ *tls.ClientHelloInfo) (*tls.Certificate, error) {
@@ -136,7 +145,7 @@ func (m *CertManager) IsRevoked(crt *x509.Certificate, caCrt *x509.Certificate)
 
 	for _, crl := range m.crls {
 		if crl.CheckSignatureFrom(caCrt) == nil {
-			for _, rc := range crl.RevokedCertificates {
+			for _, rc := range crl.RevokedCertificateEntries {
 				if rc.SerialNumber.Cmp(crt.SerialNumber) == 0 {
 					return true
 				}

internal/common/tlsutils_test.go

@@ -325,6 +325,8 @@ func TestLoadCertificate(t *testing.T) {
 
 	certManager, err = NewCertManager(keyPairs, configDir, logSenderTest)
 	assert.NoError(t, err)
+	assert.True(t, certManager.HasCertificate(DefaultTLSKeyPaidID))
+	assert.False(t, certManager.HasCertificate("unknownID"))
 	certFunc := certManager.GetCertificateFunc(DefaultTLSKeyPaidID)
 	if assert.NotNil(t, certFunc) {
 		hello := &tls.ClientHelloInfo{

internal/ftpd/ftpd.go

@@ -240,7 +240,10 @@ func (b *Binding) GetTLSDescription() string {
 		return "Implicit"
 	}
 
-	return "Plain and explicit"
+	if certMgr.HasCertificate(common.DefaultTLSKeyPaidID) || certMgr.HasCertificate(b.GetAddress()) {
+		return "Plain and explicit"
+	}
+	return "Disabled"
 }
 
 // PortRange defines a port range

internal/ftpd/internal_test.go

@@ -480,20 +480,37 @@ func TestInitialization(t *testing.T) {
 	err = ReloadCertificateMgr()
 	assert.NoError(t, err)
 
-	certMgr = oldMgr
-
 	binding = Binding{
 		Port:           2121,
 		ClientAuthType: 1,
 	}
+	assert.Equal(t, "Disabled", binding.GetTLSDescription())
+	certPath := filepath.Join(os.TempDir(), "test_ftpd.crt")
+	keyPath := filepath.Join(os.TempDir(), "test_ftpd.key")
+	binding.CertificateFile = certPath
+	binding.CertificateKeyFile = keyPath
+	keyPairs := []common.TLSKeyPair{
+		{
+			Cert: certPath,
+			Key:  keyPath,
+			ID:   binding.GetAddress(),
+		},
+	}
+	certMgr, err = common.NewCertManager(keyPairs, configDir, "")
+	require.NoError(t, err)
+
+	assert.Equal(t, "Plain and explicit", binding.GetTLSDescription())
 	server = NewServer(c, configDir, binding, 0)
 	cfg, err := server.GetTLSConfig()
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.Equal(t, tls.RequireAndVerifyClientCert, cfg.ClientAuth)
+
+	certMgr = oldMgr
 }
 
 func TestServerGetSettings(t *testing.T) {
 	oldConfig := common.Config
+	oldMgr := certMgr
 
 	binding := Binding{
 		Port:             2121,
@@ -518,7 +535,9 @@ func TestServerGetSettings(t *testing.T) {
 	assert.Error(t, err)
 	server.binding.Port = 8021
 
-	assert.Equal(t, "Plain and explicit", binding.GetTLSDescription())
+	assert.Equal(t, "Disabled", binding.GetTLSDescription())
+	_, err = server.GetTLSConfig()
+	assert.Error(t, err) // TLS configured but cert manager has no certificate
 
 	binding.TLSMode = 1
 	assert.Equal(t, "Explicit required", binding.GetTLSDescription())
@@ -526,13 +545,22 @@ func TestServerGetSettings(t *testing.T) {
 	binding.TLSMode = 2
 	assert.Equal(t, "Implicit", binding.GetTLSDescription())
 
-	certPath := filepath.Join(os.TempDir(), "test.crt")
-	keyPath := filepath.Join(os.TempDir(), "test.key")
+	certPath := filepath.Join(os.TempDir(), "test_ftpd.crt")
+	keyPath := filepath.Join(os.TempDir(), "test_ftpd.key")
 	err = os.WriteFile(certPath, []byte(ftpsCert), os.ModePerm)
 	assert.NoError(t, err)
 	err = os.WriteFile(keyPath, []byte(ftpsKey), os.ModePerm)
 	assert.NoError(t, err)
 
+	keyPairs := []common.TLSKeyPair{
+		{
+			Cert: certPath,
+			Key:  keyPath,
+			ID:   common.DefaultTLSKeyPaidID,
+		},
+	}
+	certMgr, err = common.NewCertManager(keyPairs, configDir, "")
+	require.NoError(t, err)
 	common.Config.ProxyAllowed = nil
 	c.CertificateFile = certPath
 	c.CertificateKeyFile = keyPath
@@ -550,12 +578,8 @@ func TestServerGetSettings(t *testing.T) {
 	_, ok := listener.(*proxyproto.Listener)
 	assert.True(t, ok)
 
-	err = os.Remove(certPath)
-	assert.NoError(t, err)
-	err = os.Remove(keyPath)
-	assert.NoError(t, err)
-
 	common.Config = oldConfig
+	certMgr = oldMgr
 }
 
 func TestUserInvalidParams(t *testing.T) {

internal/ftpd/server.go

@@ -280,6 +280,9 @@ func (s *Server) buildTLSConfig() {
 		if getConfigPath(s.binding.CertificateFile, "") != "" && getConfigPath(s.binding.CertificateKeyFile, "") != "" {
 			certID = s.binding.GetAddress()
 		}
+		if !certMgr.HasCertificate(certID) {
+			return
+		}
 		s.tlsConfig = &tls.Config{
 			GetCertificate: certMgr.GetCertificateFunc(certID),
 			MinVersion:     util.GetTLSVersion(s.binding.MinTLSVersion),