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