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resolver-generic.go
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resolver-generic.go
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package dnsclient
/*
Sliver Implant Framework
Copyright (C) 2021 Bishop Fox
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
import (
"crypto/rand"
"encoding/binary"
"errors"
"strings"
"time"
// {{if .Config.Debug}}
"log"
// {{end}}
"github.com/starkzarn/glod/implant/sliver/encoders"
"github.com/miekg/dns"
)
var (
// ErrInvalidRcode - Returned when the response code is not a success
ErrInvalidRcode = errors.New("invalid rcode")
)
// NewGenericResolver - Instantiate a new generic resolver
func NewGenericResolver(address string, port string, retryWait time.Duration, retries int, timeout time.Duration) DNSResolver {
if retries < 1 {
retries = 1
}
return &GenericResolver{
address: address + ":" + port,
retries: retries,
retryWait: retryWait,
resolver: &dns.Client{
ReadTimeout: timeout,
WriteTimeout: timeout,
},
base64: encoders.Base64{},
}
}
// GenericResolver - Cross-platform Go DNS resolver
type GenericResolver struct {
address string
retries int
retryWait time.Duration
resolver *dns.Client
base64 encoders.Base64
}
// Address - Return the address of the resolver
func (r *GenericResolver) Address() string {
return r.address
}
// A - Query for A records
func (r *GenericResolver) A(domain string) ([]byte, time.Duration, error) {
var resp []byte
var rtt time.Duration
var err error
for attempt := 0; attempt < r.retries; attempt++ {
resp, rtt, err = r.a(domain)
if err == nil {
break
}
// {{if .Config.Debug}}
log.Printf("[dns] query error: %s (retry wait: %s)", err, r.retryWait)
// {{end}}
time.Sleep(r.retryWait)
}
return resp, rtt, err
}
func (r *GenericResolver) a(domain string) ([]byte, time.Duration, error) {
// {{if .Config.Debug}}
log.Printf("[dns] %s->A record of %s ?", r.address, domain)
// {{end}}
resp, rtt, err := r.localQuery(domain, dns.TypeA)
if err != nil {
return nil, rtt, err
}
if resp.Rcode != dns.RcodeSuccess {
// {{if .Config.Debug}}
log.Printf("[dns] error response status: %v", resp.Rcode)
// {{end}}
return nil, rtt, ErrInvalidRcode
}
records := []byte{}
for _, answer := range resp.Answer {
switch answer := answer.(type) {
case *dns.A:
// {{if .Config.Debug}}
log.Printf("[dns] answer (a): %v", answer.A)
// {{end}}
records = append(records, []byte(answer.A)...)
}
}
return records, rtt, err
}
// TXT - Query for TXT records
func (r *GenericResolver) TXT(domain string) ([]byte, time.Duration, error) {
var resp []byte
var rtt time.Duration
var err error
for attempt := 0; attempt < r.retries; attempt++ {
resp, rtt, err = r.txt(domain)
if err == nil {
break
}
// {{if .Config.Debug}}
log.Printf("[dns] query error: %s (retry wait: %s)", err, r.retryWait)
// {{end}}
time.Sleep(r.retryWait)
}
return resp, rtt, err
}
func (r *GenericResolver) txt(domain string) ([]byte, time.Duration, error) {
resp, rtt, err := r.localQuery(domain, dns.TypeTXT)
if err != nil {
return nil, rtt, err
}
if resp.Rcode != dns.RcodeSuccess {
// {{if .Config.Debug}}
log.Printf("[dns] error response status: %v", resp.Rcode)
// {{end}}
return nil, rtt, ErrInvalidRcode
}
records := ""
for _, answer := range resp.Answer {
switch answer := answer.(type) {
case *dns.TXT:
// {{if .Config.Debug}}
log.Printf("[dns] answer (txt): %v", answer.Txt)
// {{end}}
records += strings.Join(answer.Txt, "")
}
}
data := []byte{}
if 0 < len(records) {
data, err = r.base64.Decode([]byte(records))
}
return data, rtt, err
}
func (r *GenericResolver) localQuery(qName string, qType uint16) (*dns.Msg, time.Duration, error) {
msg := &dns.Msg{
MsgHdr: dns.MsgHdr{
Id: headerID(),
RecursionDesired: true,
Opcode: dns.OpcodeQuery,
},
}
msg.SetQuestion(qName, qType)
resp, rtt, err := r.resolver.Exchange(msg, r.address)
// {{if .Config.Debug}}
log.Printf("[dns] rtt->%s %s (err: %v)", r.address, rtt, err)
// {{end}}
if err != nil {
return nil, rtt, err
}
return resp, rtt, nil
}
func headerID() uint16 {
buf := make([]byte, 2)
rand.Read(buf)
return binary.LittleEndian.Uint16(buf)
}