Get rid of LinkType-style branching: different LinkTypes may use the same Protocol modules.

protocol/dhcpv4/dhcp.go

@@ -0,0 +1,74 @@
+package dhcpv4
+
+import (
+	"git.darknebu.la/maride/pancap/output"
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+)
+
+type Protocol struct {
+	hostnames []hostname
+	networkSetup map[layers.DHCPOpt][]byte
+	requestMAC []string
+	responses []dhcpResponse
+}
+
+// Checks if the given packet is a DHCP packet we can process
+func (p *Protocol) CanAnalyze(packet gopacket.Packet) bool {
+	return packet.Layer(layers.LayerTypeDHCPv4) != nil && packet.Layer(layers.LayerTypeEthernet) != nil && packet.Layers()[2].LayerPayload() != nil
+}
+
+// Analyzes the given DHCP packet
+func (p *Protocol) Analyze(packet gopacket.Packet) error {
+	var dhcppacket layers.DHCPv4
+	var ethernetpacket layers.Ethernet
+
+	// Check if it's the first run - init networkSetup map then
+	if p.networkSetup == nil {
+		p.networkSetup = make(map[layers.DHCPOpt][]byte)
+	}
+
+	// For some reason I can't find an explanation for,
+	// 	packet.Layer(layers.LayerTypeDHCPv4).LayerContents(), which effectively is
+	// 	packet.Layers()[3].layerContents(), is empty, but
+	//  packet.Layers()[2].layerPayload() contains the correct DHCP packet.
+	// ... although both calls should return the same bytes.
+	// TODO: Open an Issue on github.com/google/gopacket
+
+	// Decode raw packet into DHCPv4
+	decodeDHCPErr := dhcppacket.DecodeFromBytes(packet.Layers()[2].LayerPayload(), gopacket.NilDecodeFeedback)
+	if decodeDHCPErr != nil {
+		// Encountered an error during decoding, most likely a broken packet
+		return decodeDHCPErr
+	}
+
+	// And decode raw packet into Ethernet
+	decodeEthernetErr := ethernetpacket.DecodeFromBytes(packet.Layer(layers.LayerTypeEthernet).LayerContents(), gopacket.NilDecodeFeedback)
+	if decodeEthernetErr != nil {
+		// Encountered an error during decoding, most likely a broken packet
+		return decodeEthernetErr
+	}
+
+	// Examine packet further
+	if dhcppacket.Operation == layers.DHCPOpRequest {
+		// Request packet
+		p.processRequestPacket(dhcppacket)
+	} else {
+		// Response/Offer packet
+		p.processResponsePacket(dhcppacket, ethernetpacket)
+	}
+
+	// Check for Hostname DHCP option (12)
+	p.checkForHostname(dhcppacket)
+	p.checkForNetworkInfos(dhcppacket)
+
+	return nil
+}
+
+// Print summary after all packets are processed
+func (p *Protocol) PrintSummary() {
+	output.PrintBlock("DHCP Network Overview", p.generateNetworkSummary())
+	output.PrintBlock("DHCP Requests", p.generateRequestSummary())
+	output.PrintBlock("DHCP Responses/Offers", p.generateResponseSummary())
+	output.PrintBlock("DHCP Hostnames", p.generateHostnamesSummary())
+}

protocol/dhcpv4/dhcpResponse.go

@@ -0,0 +1,9 @@
+package dhcpv4
+
+type dhcpResponse struct {
+	destMACAddr string
+	newIPAddr string
+	serverMACAddr string
+	askedFor bool
+}
+

protocol/dhcpv4/hostname.go

@@ -0,0 +1,8 @@
+package dhcpv4
+
+type hostname struct {
+	hostname string
+	requestedByMAC string
+	granted bool
+	deniedHostname string
+}

protocol/dhcpv4/hostnames.go

@@ -0,0 +1,114 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"git.darknebu.la/maride/pancap/common"
+	"github.com/google/gopacket/layers"
+	"log"
+)
+
+func (p *Protocol) checkForHostname(dhcppacket layers.DHCPv4) {
+	// Search for "Hostname" option (ID 12) in DHCP Packet Options
+	for _, o := range dhcppacket.Options {
+		if o.Type == layers.DHCPOptHostname {
+			// found it. Let's see if it's a request or response
+			if dhcppacket.Operation == layers.DHCPOpRequest {
+				// request, not granted yet.
+				p.addHostname(hostname{
+					hostname:       string(o.Data),
+					requestedByMAC: dhcppacket.ClientHWAddr.String(),
+					granted:        false,
+				})
+			} else {
+				// Response, DHCP issued this hostname
+				p.addHostname(hostname{
+					hostname:       string(o.Data),
+					requestedByMAC: "",
+					granted:        true,
+				})
+			}
+
+			return
+		}
+	}
+
+	// None found, means client or server doesn't support Hostname option field. Ignore.
+}
+
+// Generates the list of all hostnames encountered.
+func (p *Protocol) generateHostnamesSummary() string {
+	var tmparr []string
+
+	// Construct meaningful text
+	for _, h := range p.hostnames {
+		answer := ""
+
+		// check what kind of answer we need to construct
+		if h.deniedHostname == "" {
+			// Hostname was not denied, let's check if it was officially accepted
+			if h.granted {
+				// it was. Yay.
+				answer = fmt.Sprintf("%s has hostname %s, granted by the DHCP server", h.requestedByMAC, h.hostname)
+			} else {
+				// it was neither denied nor accepted, either missing the DHCP answer in capture file or misconfigured DHCP server
+				answer = fmt.Sprintf("%s has hostname %s, without a response from DHCP server", h.requestedByMAC, h.hostname)
+			}
+		} else {
+			// Hostname was denied, let's check if we captured the request
+			if h.hostname == "" {
+				// we didn't.
+				answer = fmt.Sprintf("%s was forced to have hostname %s by DHCP server,", h.requestedByMAC, h.hostname)
+			} else {
+				// we did, print desired and de-facto hostname
+				answer = fmt.Sprintf("%s asked for hostname %s, but got hostname %s from DHCP server.", h.requestedByMAC, h.deniedHostname, h.hostname)
+			}
+		}
+
+		tmparr = append(tmparr, answer)
+	}
+
+	// and print it as a tree.
+	return common.GenerateTree(tmparr)
+}
+
+// Adds the given hostname to the hostname array, or patches an existing entry if found
+func (p *Protocol) addHostname(tmph hostname) {
+	// see if we have an existing entry for this hostname
+	for i := 0; i < len(p.hostnames); i++ {
+		// get ith hostname in the list
+		h := p.hostnames[i]
+
+		// ... and check if it's the one requested
+		if h.hostname == tmph.hostname {
+			// Found hostname, check different possible cases
+			if tmph.requestedByMAC != "" {
+				// Already got that hostname in the list, but received another request for it
+				if tmph.requestedByMAC == h.requestedByMAC {
+					// Same client asked for the same hostname - that's ok. Ignore.
+				} else {
+					// Different devices asked for the same hostname - log it.
+					log.Printf("Multiple clients (%s, %s) asked for the same hostname (%s)", h.requestedByMAC, tmph.requestedByMAC, h.hostname)
+				}
+			} else {
+				// Received a response for this hostname, check if it was granted
+				if h.hostname == tmph.hostname {
+					// granted, everything is fine.
+					p.hostnames[i].granted = true
+				} else {
+					// Received a different hostname than the one requested by the MAC. Report that.
+					log.Printf("Client %s asked for hostname '%s' but was given '%s' by DHCP server", h.requestedByMAC, tmph.hostname, h.hostname)
+					p.hostnames[i].deniedHostname = p.hostnames[i].hostname
+					p.hostnames[i].hostname = tmph.hostname
+					p.hostnames[i].granted = false
+				}
+				// in either case, it's a response by the DHCP server - hostname is granted in this context
+
+			}
+
+			return
+		}
+	}
+
+	// We didn't find the desired hostname, append given object to the list
+	p.hostnames = append(p.hostnames, tmph)
+}

protocol/dhcpv4/network.go

@@ -0,0 +1,153 @@
+package dhcpv4
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"github.com/fatih/color"
+	"github.com/google/gopacket/layers"
+	"log"
+	"net"
+)
+
+var (
+	watchedOpts = []layers.DHCPOpt{
+		layers.DHCPOptSubnetMask, // Option 1
+		layers.DHCPOptRouter, // Option 3
+		layers.DHCPOptDNS, // Option 6
+		layers.DHCPOptBroadcastAddr, // Option 28
+		layers.DHCPOptNTPServers, // Option 42
+		layers.DHCPOptLeaseTime, // Option 51
+		layers.DHCPOptT1, // Option 58
+	}
+)
+
+// Generates the summary of relevant DHCP options
+func (p *Protocol) generateNetworkSummary() string {
+	// It's also possible to use strings.Builder here, but it produces code which is longer than this solution :shrug:
+	summary := fmt.Sprintf("Subnet Mask: %s\n", formatIP(p.networkSetup[layers.DHCPOptSubnetMask]))
+	summary = fmt.Sprintf("%sBroadcast: %s\n", summary, formatIP(p.networkSetup[layers.DHCPOptBroadcastAddr]))
+	summary = fmt.Sprintf("%sRouter: %s\n", summary, formatIP(p.networkSetup[layers.DHCPOptRouter]))
+	summary = fmt.Sprintf("%sDNS Server: %s\n", summary, formatIP(p.networkSetup[layers.DHCPOptDNS]))
+	summary = fmt.Sprintf("%sNTP Server: %s\n", summary, formatIP(p.networkSetup[layers.DHCPOptNTPServers]))
+	summary = fmt.Sprintf( "%sLease Time: %s\n", summary, formatDate(p.networkSetup[layers.DHCPOptLeaseTime]))
+	summary = fmt.Sprintf("%sRenewal Time: %s\n", summary, formatDate(p.networkSetup[layers.DHCPOptT1]))
+	return summary
+}
+
+// Looks for information specifying the setup of the network. This includes
+//  - Option  1: Subnet Mask
+//  - Option  3: Router address
+//  - Option  6: Domain Name Server address
+//  - Option 28: Broadcast address
+//  - Option 42: NTP Server address
+//  - Option 51: IP Address Lease time
+//  - Option 58: IP Renewal time
+func (p *Protocol) checkForNetworkInfos(dhcppacket layers.DHCPv4) {
+	// Check if it is a DHCP request
+	if dhcppacket.Operation == layers.DHCPOpRequest {
+		// We can ignore requests, they won't help us here
+		return
+	}
+
+	// Search for different options (1, 3, 6, 28, 42, 51, 58) in DHCP Packet Options
+	for _, o := range dhcppacket.Options {
+		if isRelevantOption(o) {
+			// Found DHCP option to be watched, let's watch it
+			p.saveOption(o)
+		}
+	}
+
+}
+
+// Saves the given option in the networkSetup map, and informs the user if the value changes
+func (p *Protocol) saveOption(opt layers.DHCPOption) {
+	// check if we already stored this value
+	if p.networkSetup[opt.Type] != nil {
+		// We already stored a value, let's check if it's the same as the new one
+		if !bytes.Equal(p.networkSetup[opt.Type], opt.Data) {
+			// Already stored a value and it's different from our new value - inform user and overwrite value later
+			log.Printf("Received different values for DHCP Option %s (ID %d). (Old: %s, New. %s)", opt.Type.String(), opt.Type, p.networkSetup[opt.Type], opt.Data)
+		} else {
+			// Exactly this value was already stored, no need to overwrite it
+			return
+		}
+	}
+
+	p.networkSetup[opt.Type] = opt.Data
+}
+
+// Checks if the given DHCPOption is part of the watchlist
+func isRelevantOption(opt layers.DHCPOption) bool {
+	// Iterate over all DHCP options in our watchlist
+	for _, o := range watchedOpts {
+		if o == opt.Type {
+			// Found.
+			return true
+		}
+	}
+
+	// This option is not on our watchlist.
+	return false
+}
+
+// Formats the given byte array as string representing the IP address, or returns an error (as string)
+func formatIP(rawIP []byte) string {
+	// Check if we even have an IP
+	if rawIP == nil {
+		// We don't have an IP, construct an error message (as string)
+		error := color.New(color.FgRed)
+		return error.Sprint("(not found)")
+	}
+
+	// Return formatted IP
+	return net.IP(rawIP).String()
+}
+
+func formatDate(rawDate []byte) string {
+	// Check if we even have a date
+	if rawDate == nil {
+		// We don't have a date, construct an error message (as string)
+		error := color.New(color.FgRed)
+		return error.Sprint("(not found)")
+	}
+
+	// Actually format date
+	intDate := binary.LittleEndian.Uint32(rawDate)
+	seconds := intDate % 60
+	minutes := intDate / 60 % 60
+	hours   := intDate / 60 / 60 % 60
+	formattedDate := ""
+
+	// Check which words we need to pick
+	// ... regarding hours
+	if hours > 0 {
+		formattedDate = fmt.Sprintf("%d hours", hours)
+	}
+
+	// ... regarding minutes
+	if minutes > 0 {
+		// check if we got a previous string we need to take care of
+		if len(formattedDate) > 0 {
+			// yes, append our information to existing string
+			formattedDate = fmt.Sprintf("%s, %d minutes", formattedDate, minutes)
+		} else {
+			// no, use our string
+			formattedDate = fmt.Sprintf("%d minutes", minutes)
+		}
+	}
+
+	// ... regarding seconds
+	if seconds > 0 {
+		// check if we got a previous string we need to take care of
+		if len(formattedDate) > 0 {
+			// yes, append our information to existing string
+			formattedDate = fmt.Sprintf("%s, %d seconds", formattedDate, seconds)
+		} else {
+			// no, use our string
+			formattedDate = fmt.Sprintf("%d seconds", seconds)
+		}
+	}
+
+	return formattedDate
+}

protocol/dhcpv4/request.go

@@ -0,0 +1,17 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"git.darknebu.la/maride/pancap/common"
+	"github.com/google/gopacket/layers"
+)
+
+// Processes the DHCP request packet handed over
+func (p *Protocol) processRequestPacket(dhcppacket layers.DHCPv4) {
+	p.requestMAC = common.AppendIfUnique(dhcppacket.ClientHWAddr.String(), p.requestMAC)
+}
+
+// Generates the summary of all DHCP request packets
+func (p *Protocol) generateRequestSummary() string {
+	return fmt.Sprintf("%d unique DHCP requests\n%s", len(p.requestMAC), common.GenerateTree(p.requestMAC))
+}

protocol/dhcpv4/response.go

@@ -0,0 +1,76 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"git.darknebu.la/maride/pancap/common"
+	"github.com/google/gopacket/layers"
+	"log"
+)
+
+func (p *Protocol) processResponsePacket(dhcppacket layers.DHCPv4, ethernetpacket layers.Ethernet) {
+	p.addResponseEntry(dhcppacket.ClientIP.String(), dhcppacket.YourClientIP.String(), dhcppacket.ClientHWAddr.String(), ethernetpacket.SrcMAC.String())
+}
+
+// Generates the summary of all DHCP offer packets
+func (p *Protocol) generateResponseSummary() string {
+	var tmpaddr []string
+
+	// Iterate over all responses
+	for _, r := range p.responses {
+		addition := ""
+
+		if r.askedFor {
+			addition = " which the client explicitly asked for."
+		}
+
+		tmpaddr = append(tmpaddr, fmt.Sprintf("%s offered %s IP address %s%s", r.serverMACAddr, r.destMACAddr, r.newIPAddr, addition))
+	}
+
+	// Draw as tree
+	return common.GenerateTree(tmpaddr)
+}
+
+// Adds a new response entry. If an IP address was already issued or a MAC asks multiple times for DNS, the case is examined further
+func (p *Protocol) addResponseEntry(newIP string, yourIP string, destMAC string, serverMAC string) {
+	// Check if client asked for a specific address (which was granted by the DHCP server)
+	askedFor := false
+	if newIP == "0.0.0.0" {
+		// Yes, client asked for a specific address. Most likely not the first time in this network.
+		newIP = yourIP
+		askedFor = true
+	}
+
+	for _, r := range p.responses {
+		// Check for interesting cases
+		if r.destMACAddr == destMAC {
+			// The same client device received multiple IP addresses, let's examine further
+			if r.newIPAddr == newIP {
+				// the handed IP is the same - this is ok, just badly configured
+				if r.serverMACAddr == serverMAC {
+					// Same DHCP server answered.
+					log.Printf("MAC address %s received the same IP address multiple times via DHCP by the same server.", destMAC)
+				} else {
+					// Different DHCP servers answered, but with the same address - strange network, but ok...
+					log.Printf("MAC address %s received the same IP address multiple times via DHCP by different servers.", destMAC)
+				}
+			} else {
+				// far more interesting - one client received multiple addresses
+				if r.serverMACAddr == serverMAC {
+					// Same DHCP server answered.
+					log.Printf("MAC address %s received different IP addresses (%s, %s) multiple times via DHCP by the same server.", destMAC, r.newIPAddr, newIP)
+				} else {
+					// Different DHCP servers answered, with different addresses - possibly an attempt to build up MitM
+					log.Printf("MAC address %s received different IP addresses (%s, %s) multiple times via DHCP by different servers (%s, %s).", destMAC, r.newIPAddr, newIP, r.serverMACAddr, serverMAC)
+				}
+			}
+		}
+	}
+
+	// Add a response entry - even if we found some "strange" behavior before.
+	p.responses = append(p.responses, dhcpResponse{
+		destMACAddr:   destMAC,
+		newIPAddr:     newIP,
+		serverMACAddr: serverMAC,
+		askedFor:      askedFor,
+	})
+}