Add support for ARP packets

src/ethernet/arp/arp.go

@@ -0,0 +1,126 @@
+package arp
+
+import (
+	"fmt"
+	"github.com/fatih/color"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"log"
+	"net"
+)
+
+var (
+	arpStatsList []arpStats
+	devices []arpDevice
+)
+
+// Called on every ARP packet
+func ProcessARPPacket(packet gopacket.Packet) error {
+	var arppacket layers.ARP
+
+	// Decode raw packet into ARP
+	decodeErr := arppacket.DecodeFromBytes(packet.Layer(layers.LayerTypeARP).LayerContents(), gopacket.NilDecodeFeedback)
+	if decodeErr != nil {
+		// Encountered an error during decoding, most likely a broken packet
+		return decodeErr
+	}
+
+	// Convert MAC address byte array to string
+	sourceAddr := net.HardwareAddr(arppacket.SourceHwAddress).String()
+	participant := getStatOrCreate(sourceAddr)
+
+	// Raise stats
+	if arppacket.Operation == layers.ARPRequest {
+		// Request packet
+		participant.asked++
+		appendIfUnique(net.IP(arppacket.DstProtAddress).String(), participant.askedList)
+	} else {
+		// Response packet
+		participant.answered++
+		appendIfUnique(net.IP(arppacket.SourceProtAddress).String(), participant.answeredList)
+
+		// Add device entry
+		addDeviceEntry(sourceAddr, net.IP(arppacket.SourceProtAddress).String())
+	}
+
+	return nil
+}
+
+// Print a summary after all packets are processed
+func PrintARPSummary() {
+	headline := color.New(color.FgRed, color.Bold)
+	headline.Println("ARP traffic summary")
+	printTrafficStats()
+	headline.Println("ARP LAN overview")
+	printLANOverview()
+}
+
+// Constructs an answer regarding the ARP traffic
+func printTrafficStats() {
+	var tmparr []string
+
+	// Iterate over all participants
+	for _, p := range arpStatsList {
+		tmparr = append(tmparr, fmt.Sprintf("%s asked for %d addresses and answered %d requests", p.macaddr, p.asked, p.answered))
+	}
+
+	// And print it as a tree
+	printTree(tmparr)
+}
+
+// Prints an overview over all connected devices in the LAN
+func printLANOverview() {
+	var tmparr []string
+
+	// iterate over all devices
+	for _, d := range devices {
+		tmparr = append(tmparr, fmt.Sprintf("%s got address %s", d.macaddr, d.ipaddr))
+	}
+
+	// And print it as a tree
+	printTree(tmparr)
+}
+
+// Returns the arpStats object for the given MAC address, or creates a new one
+func getStatOrCreate(macaddr string) *arpStats {
+	// Try to find the given macaddr
+	for i := 0; i < len(arpStatsList); i++ {
+		if arpStatsList[i].macaddr == macaddr {
+			// Found, return it
+			return &arpStatsList[i]
+		}
+	}
+
+	// None found yet, we need to create a new one
+	arpStatsList = append(arpStatsList, arpStats{
+		macaddr:  macaddr,
+	})
+
+	// And return it
+	return &arpStatsList[len(arpStatsList)-1]
+}
+
+// Adds a new entry to the devices array, checking if there may be a collision (=ARP Spoofing)
+func addDeviceEntry(macaddr string, ipaddr string) {
+	for i := 0; i < len(devices); i++ {
+		// check if we found a collision (possible ARP spoofing)
+		if (devices[i].macaddr == macaddr) != (devices[i].ipaddr == ipaddr) {
+			// this operation is practically XOR (which golang doesn't provide e.g. with ^)
+			log.Printf("Found possible ARP spoofing! Old: (MAC=%s, IP=%s), New: (MAC=%s, IP=%s). Overriding...", devices[i].macaddr, devices[i].ipaddr, macaddr, ipaddr)
+			devices[i].macaddr = macaddr
+			devices[i].ipaddr = ipaddr
+			return
+		}
+
+		if devices[i].macaddr == macaddr && devices[i].ipaddr == ipaddr {
+			// Found collision, but no ARP spoofing (both values are identical)
+			return
+		}
+	}
+
+	// No device found, add a new entry
+	devices = append(devices, arpDevice{
+		macaddr: macaddr,
+		ipaddr:  ipaddr,
+	})
+}

src/ethernet/arp/arpDevice.go

@@ -0,0 +1,6 @@
+package arp
+
+type arpDevice struct {
+	macaddr string
+	ipaddr string
+}

src/ethernet/arp/arpStats.go

@@ -0,0 +1,9 @@
+package arp
+
+type arpStats struct {
+	macaddr string
+	asked int
+	answered int
+	askedList []string
+	answeredList []string
+}

src/ethernet/arp/common.go

@@ -0,0 +1,30 @@
+package arp
+
+import "fmt"
+
+// Appends the appendee to the array if it does not contain appendee yet
+func appendIfUnique(appendee string, array []string) []string {
+	// Iterate over all elements and check values
+	for _, elem := range array {
+		if elem == appendee {
+			// ... found. Stop here
+			return array
+		}
+	}
+
+	// None found, append
+	return append(array, appendee)
+}
+
+// Prints each element, along with a small ASCII tree
+func printTree(strarr []string) {
+	// iterate over each element
+	for iter, elem := range strarr {
+		// check if we got the last element
+		if iter < len(strarr) - 1 {
+			fmt.Printf("|- %s\n", elem)
+		} else {
+			fmt.Printf("'- %s\n\n", elem)
+		}
+	}
+}

src/ethernet/ethernet.go

@@ -4,6 +4,7 @@ import (
 	"github.com/google/gopacket"
 	"github.com/google/gopacket/layers"
 	"log"
+	"./arp"
 	"./dns"
 )
 
@@ -20,14 +21,14 @@ func Analyze(source *gopacket.PacketSource) error {
 			continue
 		}
 
-		// Check if we can do some Application Layer statistics with this packet
-		if packet.ApplicationLayer() != nil {
-			// We can, switch over the type
-			switch packet.ApplicationLayer().LayerType() {
-			case layers.LayerTypeDNS:
+		if packet.Layer(layers.LayerTypeDNS) != nil {
 			// Handle DNS packet
 			dns.ProcessDNSPacket(packet)
 		}
+
+		if packet.Layer(layers.LayerTypeARP) != nil {
+			// Handle ARP packet
+			arp.ProcessARPPacket(packet)
 		}
 	}
 
@@ -39,5 +40,6 @@ func Analyze(source *gopacket.PacketSource) error {
 
 // Prints all the summaries.
 func printSummary() {
+	arp.PrintARPSummary()
 	dns.PrintDNSSummary()
 }