Android VpnService, packets forwarding

Question

I'm creating application based on ToyVPN to capture tcp/udp packets. After i get outgoing packets in my apllication i would like to forward them to original destination. I have managed to get destination ip and port from headers but i have no idea how to communicate with remote server and then write response back to the source. I think this is possible because there is this app. Here is my first first attempt:

private void runVpnConnection() throws Exception {
configure();

FileInputStream in = new FileInputStream(mInterface.getFileDescriptor());
FileOutputStream out = new FileOutputStream(
        mInterface.getFileDescriptor());

// Allocate the buffer for a single packet.
ByteBuffer packet = ByteBuffer.allocate(32767);
boolean ok = true;

while (ok) {
    Socket tcpSocket = SocketChannel.open().socket();
    try {
        // Read the outgoing packet from the input stream.
        int length = in.read(packet.array());
        if (length > 0) {

            Log.i(TAG, "-------------------New packet: " + length);
            packet.limit(length);

            // here i get destIP and destIP

            InetAddress serverAddr = InetAddress.getByName(destIP);
            SocketAddress socketadd = new InetSocketAddress(serverAddr,
                    destPort);

            protect(tcpSocket);

            OutputStream outBuffer = tcpSocket.getOutputStream();

            outBuffer.write(packet.array());
            outBuffer.flush();
            // outBuffer.close();
            packet.clear();
        }

        if (tcpSocket.isConnected()) {
            InputStream inBuffer = tcpSocket.getInputStream();
            DataInputStream inStream = new DataInputStream(inBuffer);
            Log.i(TAG, "Response length " + inStream.available());
            if (inStream.available() > 0) {
                Log.i(TAG, "Server says " + inStream.readUTF());
                inStream.readFully(packet.array());
                out.write(packet.array());
                inBuffer.close();
            }
            out.flush();
        }
        packet.clear();
        // Thread.sleep(50);
    } catch (Exception e) {
        e.printStackTrace();
        Log.e(TAG, e.toString());
        ok = false;
    }
    tcpSocket.close();
}
in.close();
out.close();
}

were you able to solve this problem? I am currently facing similar issues. Also how did you manage to get the destination ip and port from headers? Can you post more code ? — thedarkpassenger, Feb 21 '16 at 14:24

score 3 · Answer 1 · edited May 23 '17 at 11:44

3

Apparently tPacketCapture routes the traffice into another interface running on the phone and sends all of this traffic to the internet (this is the same as mobiwol, greyshirts and other apps that use VPNService).

If you run (and understand) ToyVPN, you know that all of the traffic from the phone goes into a server (your computer) in which you configure iptables to send all the traffic to the internet.

If you want to run without a server, yo have to do the same thing on the phone. From another question:

When I look at mobiwol's connection with "adb shell netcfg" it creates a tun0 interface with 10.2.3.4/32 address. It routes all packages to this private network and send to internet.

So basically from your app you will have to configure the phone to act as it's own server.

edited May 23 '17 at 11:44

Community

1
1

answered May 19 '14 at 18:26

brunorey

2,135
1
18
26

Any idea how i can create this server on android? – user2087932 May 20 '14 at 08:14
AFAIK, `iptables` runs on android. I'm not sure about the specific commands. Try logging into a shell and run `iptables -h` to get help about how to use it. It's pretty much the same commands as the ones you had to run on a pc to use toyvpn. – brunorey May 20 '14 at 14:50
2

Ok, I was wrong earlier, that's not how these appse work. To run iptables you need root privileges so it's probably not feasible. According to [this answer](http://stackoverflow.com/a/15440263/3271507) you need to open one socket for each connection that you read in the interface. Yo preety much have to implement most of the TCP protocol. It's not something trivial, it will involve a nice amount of work. – brunorey May 30 '14 at 19:40
@user2087932 not sure how far you got on this but if anyone else is reading this it is absolutely possible to do it on Android via a VPN service without root. Check out the Drony app. Traffic is intercepted, headers modified and packets forwarded. – skyjacks Sep 30 '15 at 17:11

Android VpnService, packets forwarding

1 Answers1

Linked