disable self connections by default

now that the event manager can create files, self connections may create
even more issues than before

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

docs/full-configuration.md

@@ -78,6 +78,7 @@ The configuration file contains the following sections:
   - `max_total_connections`, integer. Maximum number of concurrent client connections. 0 means unlimited. Default: 0.
   - `max_per_host_connections`, integer.  Maximum number of concurrent client connections from the same host (IP). If the defender is enabled, exceeding this limit will generate `score_limit_exceeded` events and thus hosts that repeatedly exceed the max allowed connections can be automatically blocked. 0 means unlimited. Default: 20.
   - `whitelist_file`, string. Path to a file containing a list of IP addresses and/or networks to allow. Only the listed IPs/networks can access the configured services, all other client connections will be dropped before they even try to authenticate. The whitelist must be a JSON file with the same structure documented for the [defenders's list](./defender.md). The whitelist can be reloaded on demand sending a `SIGHUP` signal on Unix based systems and a `paramchange` request to the running service on Windows. Default: "".
+  - `allow_self_connections`, integer. Allow users on this instance to use other users/virtual folders on this instance as storage backend. Enable this setting if you know what you are doing. Set to `1` to enable. Default: `0`.
   - `defender`, struct containing the defender configuration. See [Defender](./defender.md) for more details.
     - `enabled`, boolean. Default `false`.
     - `driver`, string. Supported drivers are `memory` and `provider`. The `provider` driver will use the configured data provider to store defender events and it is supported for `MySQL`, `PostgreSQL` and `CockroachDB` data providers. Using the `provider` driver you can share the defender events among multiple SFTPGO instances. For a single instance the `memory` driver will be much faster. Default: `memory`.

internal/common/common.go

@@ -212,6 +212,8 @@ func Initialize(c Configuration, isShared int) error {
 	}
 	vfs.SetTempPath(c.TempPath)
 	dataprovider.SetTempPath(c.TempPath)
+	vfs.SetAllowSelfConnections(c.AllowSelfConnections)
+	dataprovider.SetAllowSelfConnections(c.AllowSelfConnections)
 	transfersChecker = getTransfersChecker(isShared)
 	return nil
 }
@@ -504,6 +506,9 @@ type Configuration struct {
 	// Only the listed IPs/networks can access the configured services, all other client connections
 	// will be dropped before they even try to authenticate.
 	WhiteListFile string `json:"whitelist_file" mapstructure:"whitelist_file"`
+	// Allow users on this instance to use other users/virtual folders on this instance as storage backend.
+	// Enable this setting if you know what you are doing.
+	AllowSelfConnections int `json:"allow_self_connections" mapstructure:"allow_self_connections"`
 	// Defender configuration
 	DefenderConfig DefenderConfig `json:"defender" mapstructure:"defender"`
 	// Rate limiter configurations

internal/common/protocol_test.go

@@ -93,6 +93,7 @@ func TestMain(m *testing.M) {
 	logger.InitLogger(logFilePath, 5, 1, 28, false, false, zerolog.DebugLevel)
 
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_COMMON__ALLOW_SELF_CONNECTIONS", "1")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")
 	err := config.LoadConfig(configDir, "")

internal/config/config.go

@@ -208,6 +208,7 @@ func Init() {
 			MaxTotalConnections:   0,
 			MaxPerHostConnections: 20,
 			WhiteListFile:         "",
+			AllowSelfConnections:  0,
 			DefenderConfig: common.DefenderConfig{
 				Enabled:            false,
 				Driver:             common.DefenderDriverMemory,
@@ -1862,6 +1863,7 @@ func setViperDefaults() {
 	viper.SetDefault("common.max_total_connections", globalConf.Common.MaxTotalConnections)
 	viper.SetDefault("common.max_per_host_connections", globalConf.Common.MaxPerHostConnections)
 	viper.SetDefault("common.whitelist_file", globalConf.Common.WhiteListFile)
+	viper.SetDefault("common.allow_self_connections", globalConf.Common.AllowSelfConnections)
 	viper.SetDefault("common.defender.enabled", globalConf.Common.DefenderConfig.Enabled)
 	viper.SetDefault("common.defender.driver", globalConf.Common.DefenderConfig.Driver)
 	viper.SetDefault("common.defender.ban_time", globalConf.Common.DefenderConfig.BanTime)

internal/dataprovider/dataprovider.go

@@ -195,6 +195,7 @@ var (
 	lastLoginMinDelay            = 10 * time.Minute
 	usernameRegex                = regexp.MustCompile("^[a-zA-Z0-9-_.~]+$")
 	tempPath                     string
+	allowSelfConnections         int
 	fnReloadRules                FnReloadRules
 	fnRemoveRule                 FnRemoveRule
 	fnHandleRuleForProviderEvent FnHandleRuleForProviderEvent
@@ -804,6 +805,11 @@ type Provider interface {
 	resetDatabase() error
 }
 
+// SetAllowSelfConnections sets the desired behaviour for self connections
+func SetAllowSelfConnections(value int) {
+	allowSelfConnections = value
+}
+
 // SetTempPath sets the path for temporary files
 func SetTempPath(fsPath string) {
 	tempPath = fsPath

internal/dataprovider/user.go

@@ -497,6 +497,9 @@ func (u *User) GetPermissionsForPath(p string) []string {
 }
 
 func (u *User) getForbiddenSFTPSelfUsers(username string) ([]string, error) {
+	if allowSelfConnections == 0 {
+		return nil, nil
+	}
 	sftpUser, err := UserExists(username)
 	if err == nil {
 		err = sftpUser.LoadAndApplyGroupSettings()

internal/ftpd/ftpd_test.go

@@ -277,6 +277,7 @@ func TestMain(m *testing.M) {
 	// work in non atomic mode too
 	os.Setenv("SFTPGO_COMMON__UPLOAD_MODE", "2")
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_COMMON__ALLOW_SELF_CONNECTIONS", "1")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")
 	err = config.LoadConfig(configDir, "")

internal/httpd/httpd_test.go

@@ -296,6 +296,7 @@ func TestMain(m *testing.M) {
 	logger.InitLogger(logfilePath, 5, 1, 28, false, false, zerolog.DebugLevel)
 	os.Setenv("SFTPGO_COMMON__UPLOAD_MODE", "2")
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_COMMON__ALLOW_SELF_CONNECTIONS", "1")
 	os.Setenv("SFTPGO_DATA_PROVIDER__NAMING_RULES", "0")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")

internal/sftpd/sftpd_test.go

@@ -189,6 +189,7 @@ func TestMain(m *testing.M) {
 	}
 	os.Setenv("SFTPGO_COMMON__UPLOAD_MODE", "2")
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_COMMON__ALLOW_SELF_CONNECTIONS", "1")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")
 	err = config.LoadConfig(configDir, "")

internal/vfs/sftpfs.go

@@ -843,8 +843,12 @@ func (fs *SFTPFs) createConnection() error {
 		HostKeyCallback: func(_ string, _ net.Addr, key ssh.PublicKey) error {
 			fp := ssh.FingerprintSHA256(key)
 			if util.Contains(sftpFingerprints, fp) {
+				if allowSelfConnections == 0 {
+					fsLog(fs, logger.LevelError, "SFTP self connections not allowed")
+					return ErrSFTPLoop
+				}
 				if util.Contains(fs.config.forbiddenSelfUsernames, fs.config.Username) {
-					fsLog(fs, logger.LevelError, "SFTP loop or nested local SFTP folders detected, mount path %#v, username %#v, forbidden usernames: %+v",
+					fsLog(fs, logger.LevelError, "SFTP loop or nested local SFTP folders detected, mount path %q, username %q, forbidden usernames: %+v",
 						fs.mountPath, fs.config.Username, fs.config.forbiddenSelfUsernames)
 					return ErrSFTPLoop
 				}

internal/vfs/vfs.go

@@ -48,8 +48,14 @@ var (
 	ErrVfsUnsupported    = errors.New("not supported")
 	tempPath             string
 	sftpFingerprints     []string
+	allowSelfConnections int
 )
 
+// SetAllowSelfConnections sets the desired behaviour for self connections
+func SetAllowSelfConnections(value int) {
+	allowSelfConnections = value
+}
+
 // SetTempPath sets the path for temporary files
 func SetTempPath(fsPath string) {
 	tempPath = fsPath

internal/webdavd/webdavd_test.go

@@ -268,6 +268,7 @@ func TestMain(m *testing.M) {
 	logFilePath = filepath.Join(configDir, "sftpgo_webdavd_test.log")
 	logger.InitLogger(logFilePath, 5, 1, 28, false, false, zerolog.DebugLevel)
 	os.Setenv("SFTPGO_DATA_PROVIDER__CREATE_DEFAULT_ADMIN", "1")
+	os.Setenv("SFTPGO_COMMON__ALLOW_SELF_CONNECTIONS", "1")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_USERNAME", "admin")
 	os.Setenv("SFTPGO_DEFAULT_ADMIN_PASSWORD", "password")
 	err := config.LoadConfig(configDir, "")

sftpgo.json

@@ -18,6 +18,7 @@
     "max_total_connections": 0,
     "max_per_host_connections": 20,
     "whitelist_file": "",
+    "allow_self_connections": 0,
     "defender": {
       "enabled": false,
       "driver": "memory",