Configurable SSH key exchange algorithm and MAC suite (#2806)

conf/app.ini

@@ -128,6 +128,12 @@ SSH_ROOT_PATH =
 ; For built-in SSH server only, choose the ciphers to support for SSH connections,
 ; for system SSH this setting has no effect
 SSH_SERVER_CIPHERS = aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, arcfour256, arcfour128
+; For built-in SSH server only, choose the key exchange algorithms to support for SSH connections,
+; for system SSH this setting has no effect
+SSH_SERVER_KEY_EXCHANGES = diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, ecdh-sha2-nistp256, ecdh-sha2-nistp384, ecdh-sha2-nistp521, curve25519-sha256@libssh.org
+; For built-in SSH server only, choose the MACs to support for SSH connections,
+; for system SSH this setting has no effect
+SSH_SERVER_MACS = hmac-sha2-256-etm@openssh.com, hmac-sha2-256, hmac-sha1, hmac-sha1-96
 ; Directory to create temporary files when test public key using ssh-keygen,
 ; default is system temporary directory.
 SSH_KEY_TEST_PATH =

modules/setting/setting.go

@@ -98,6 +98,8 @@ var (
 		ListenPort           int            `ini:"SSH_LISTEN_PORT"`
 		RootPath             string         `ini:"SSH_ROOT_PATH"`
 		ServerCiphers        []string       `ini:"SSH_SERVER_CIPHERS"`
+		ServerKeyExchanges   []string       `ini:"SSH_SERVER_KEY_EXCHANGES"`
+		ServerMACs           []string       `ini:"SSH_SERVER_MACS"`
 		KeyTestPath          string         `ini:"SSH_KEY_TEST_PATH"`
 		KeygenPath           string         `ini:"SSH_KEYGEN_PATH"`
 		AuthorizedKeysBackup bool           `ini:"SSH_AUTHORIZED_KEYS_BACKUP"`
@@ -110,6 +112,8 @@ var (
 		Domain:             "",
 		Port:               22,
 		ServerCiphers:      []string{"aes128-ctr", "aes192-ctr", "aes256-ctr", "aes128-gcm@openssh.com", "arcfour256", "arcfour128"},
+		ServerKeyExchanges: []string{"diffie-hellman-group1-sha1", "diffie-hellman-group14-sha1", "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "curve25519-sha256@libssh.org"},
+		ServerMACs:         []string{"hmac-sha2-256-etm@openssh.com", "hmac-sha2-256", "hmac-sha1", "hmac-sha1-96"},
 		KeygenPath:         "ssh-keygen",
 	}
 
@@ -732,6 +736,14 @@ func NewContext() {
 	if len(serverCiphers) > 0 {
 		SSH.ServerCiphers = serverCiphers
 	}
+	serverKeyExchanges := sec.Key("SSH_SERVER_KEY_EXCHANGES").Strings(",")
+	if len(serverKeyExchanges) > 0 {
+		SSH.ServerKeyExchanges = serverKeyExchanges
+	}
+	serverMACs := sec.Key("SSH_SERVER_MACS").Strings(",")
+	if len(serverMACs) > 0 {
+		SSH.ServerMACs = serverMACs
+	}
 	SSH.KeyTestPath = os.TempDir()
 	if err = Cfg.Section("server").MapTo(&SSH); err != nil {
 		log.Fatal(4, "Failed to map SSH settings: %v", err)

modules/ssh/ssh.go

@@ -151,10 +151,12 @@ func listen(config *ssh.ServerConfig, host string, port int) {
 }
 
 // Listen starts a SSH server listens on given port.
-func Listen(host string, port int, ciphers []string) {
+func Listen(host string, port int, ciphers []string, keyExchanges []string, macs []string) {
 	config := &ssh.ServerConfig{
 		Config: ssh.Config{
-			Ciphers: ciphers,
+			Ciphers:      ciphers,
+			KeyExchanges: keyExchanges,
+			MACs:         macs,
 		},
 		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
 			pkey, err := models.SearchPublicKeyByContent(strings.TrimSpace(string(ssh.MarshalAuthorizedKey(key))))

routers/init.go

@@ -81,7 +81,7 @@ func GlobalInit() {
 	checkRunMode()
 
 	if setting.InstallLock && setting.SSH.StartBuiltinServer {
-		ssh.Listen(setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers)
-		log.Info("SSH server started on %s:%d. Cipher list (%v)", setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers)
+		ssh.Listen(setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers, setting.SSH.ServerKeyExchanges, setting.SSH.ServerMACs)
+		log.Info("SSH server started on %s:%d. Cipher list (%v), key exchange algorithms (%v), MACs (%v)", setting.SSH.ListenHost, setting.SSH.ListenPort, setting.SSH.ServerCiphers, setting.SSH.ServerKeyExchanges, setting.SSH.ServerMACs)
 	}
 }