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95 lines
2.1 KiB
Go
95 lines
2.1 KiB
Go
// We handle the checking as a lexing program.
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// We use the lexer like Rob Pike lectures about in this
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// clip: http://www.youtube.com/watch?v=HxaD_trXwRE
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package main
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import (
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"dns"
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)
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type itemType int
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type item struct {
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typ itemType
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val string
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}
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const (
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itemError itemType = iota
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itemVender // software vendor
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itemSoftware // the name of the DNS server software
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itemVersionMin // the minimum version of the software (empty if not determined)
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itemVersionMax // the maximum version of the software (empty if not determined)
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)
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// stateFn represents the state of the scanner as a function that returns the next state.
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type stateFn func(*lexer) stateFn
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type lexer struct {
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client *dns.Client // client used.
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addr string // addr of the server being scanned.
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fp *fingerprint // fingerprint to test.
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q dns.Question // question to ask.
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items chan item // channel of scanned items.
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state stateFn // the next function to enter.
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}
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func (l *lexer) probe() *fingerprint {
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return sendProbe(l.client, l.addr, l.fp, l.q)
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}
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func (l *lexer) emit(i *item) {
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l.items <- *i
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}
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func (l *lexer) setString(s string) {
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l.fp.setString(s)
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}
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func (l *lexer) setQuestion(name string, t uint16, c uint16) {
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l.q = dns.Question{name, t, c}
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}
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func (l *lexer) run() {
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go func() {
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for l.state != nil {
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l.state = l.state(l)
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}
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close(l.items)
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}()
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}
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// "Lexer" functions, prefixed with dns
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// Check if the server responds
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func dnsAlive(l *lexer) stateFn {
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println("lexAlive")
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l.setString("QUERY,NOERROR,qr,aa,tc,rd,ad,cd,z,1,0,0,0,do,0")
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l.setQuestion(".", dns.TypeNS, dns.ClassINET)
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f := l.probe()
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if f.ok() {
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return dnsDoBitMirror
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}
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l.emit(&item{itemError, f.error()})
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return nil
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}
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// Check if the server returns the DO-bit when set in the request.
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func dnsDoBitMirror(l *lexer) stateFn {
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println("lexDoBitMirror")
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// The important part here is that the DO bit is on
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l.setString("QUERY,NOERROR,qr,aa,tc,RD,ad,cd,z,1,0,0,0,DO,0")
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l.setQuestion(".", dns.TypeNS, dns.ClassINET)
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f := l.probe()
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if f.Do {
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l.emit(&item{itemSoftware, NSD})
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}
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l.emit(&item{itemSoftware, BIND})
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return nil
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}
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