Merge pull request 'Clarified and Split Apart Environment Variables that alter port binding behaviour.' (#47) from whonix into master

Reviewed-on: #47
Reviewed-by: Dan Ballard <dan@openprivacy.ca>

README.md

@@ -10,6 +10,8 @@ A library providing an ACN (Anonymous Communication Network
 ## Environment Variables
 
 - `TOR_LD_LIBRARY_PATH` - override the library path given to the Tor process as different from the one given to the parent process.
+- `CWTCH_RESTRICT_PORTS` - forces connectivity to bind to a subset of ports `15000-15378`
+- `CWTCH_BIND_EXTERNAL_WHONIX` - forces connectivity to bind to external interfaces (only supported/recommended on certain Whonix-based setups. Please open an issue if you think this should be expanded.)
 
 ## Requirements for ACN Support
 
@@ -54,4 +56,4 @@ service:
         acn.Restart()
 and
         
-        acn.Close()
+        acn.Close()

tor/torProvider.go

@@ -268,7 +268,28 @@ func (tp *torProvider) Listen(identity connectivity.PrivateKey, port int) (conne
 		localport += 1024
 	}
 
-	localListener, err := net.Listen("tcp", "127.0.0.1:"+strconv.Itoa(localport))
+	var localListener net.Listener
+	var err error
+
+	if cwtchRestrictPorts := os.Getenv("CWTCH_RESTRICT_PORTS"); strings.ToLower(cwtchRestrictPorts) == "true" {
+		// for whonix like systems we tightly restrict possible listen...
+		// pick a random port between 15000 and 15378
+		// cwtch = 63 *77 *74* 63* 68 = 1537844616
+		log.Infof("using restricted ports, CWTCH_RESTRICT_PORTS=true");
+		localport = 15000 + (localport % 378)
+	}
+	
+	if bindExternal := os.Getenv("CWTCH_BIND_EXTERNAL_WHONIX"); strings.ToLower(bindExternal) == "true" {
+		if _, ferr := os.Stat("/usr/share/anon-ws-base-files/workstation"); !os.IsNotExist(ferr) {
+			log.Infof("WARNING: binding to external interfaces. This is potentially unsafe outside of a containerized environment.");
+			localListener, err = net.Listen("tcp", "0.0.0.0:"+strconv.Itoa(localport))
+		} else {
+			log.Errorf("CWTCH_BIND_EXTERNAL_WHONIX flag set, but /usr/share/anon-ws-base-files/workstation does not exist. Defaulting to binding to local ports");
+			localListener, err = net.Listen("tcp", "127.0.0.1:"+strconv.Itoa(localport))
+		}
+	} else {
+		localListener, err = net.Listen("tcp", "127.0.0.1:"+strconv.Itoa(localport))
+	}
 
 	if err != nil {
 		return nil, err
@@ -290,6 +311,8 @@ func (tp *torProvider) Listen(identity connectivity.PrivateKey, port int) (conne
 		return nil, err
 	}
 
+	// We need to set os.ID here, otherwise os.Close() may not shut down the onion service properly...
+	os.ID = onion
 	os.CloseLocalListenerOnClose = true
 
 	ols := &onionListenService{os: os, tp: tp}