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dns_server.go
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dns_server.go
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package nebula
import (
"fmt"
"net"
"strconv"
"strings"
"sync"
"github.com/miekg/dns"
"github.com/sirupsen/logrus"
"github.com/slackhq/nebula/config"
"github.com/slackhq/nebula/iputil"
)
// This whole thing should be rewritten to use context
var dnsR *dnsRecords
var dnsServer *dns.Server
var dnsAddr string
type dnsRecords struct {
sync.RWMutex
dnsMap map[string]string
hostMap *HostMap
}
func newDnsRecords(hostMap *HostMap) *dnsRecords {
return &dnsRecords{
dnsMap: make(map[string]string),
hostMap: hostMap,
}
}
func (d *dnsRecords) Query(data string) string {
d.RLock()
defer d.RUnlock()
if r, ok := d.dnsMap[strings.ToLower(data)]; ok {
return r
}
return ""
}
func (d *dnsRecords) QueryCert(data string) string {
ip := net.ParseIP(data[:len(data)-1])
if ip == nil {
return ""
}
iip := iputil.Ip2VpnIp(ip)
hostinfo := d.hostMap.QueryVpnIp(iip)
if hostinfo == nil {
return ""
}
q := hostinfo.GetCert()
if q == nil {
return ""
}
cert := q.Details
c := fmt.Sprintf("\"Name: %s\" \"Ips: %s\" \"Subnets %s\" \"Groups %s\" \"NotBefore %s\" \"NotAFter %s\" \"PublicKey %x\" \"IsCA %t\" \"Issuer %s\"", cert.Name, cert.Ips, cert.Subnets, cert.Groups, cert.NotBefore, cert.NotAfter, cert.PublicKey, cert.IsCA, cert.Issuer)
return c
}
func (d *dnsRecords) Add(host, data string) {
d.Lock()
defer d.Unlock()
d.dnsMap[strings.ToLower(host)] = data
}
func parseQuery(l *logrus.Logger, m *dns.Msg, w dns.ResponseWriter) {
for _, q := range m.Question {
switch q.Qtype {
case dns.TypeA:
l.Debugf("Query for A %s", q.Name)
ip := dnsR.Query(q.Name)
if ip != "" {
rr, err := dns.NewRR(fmt.Sprintf("%s A %s", q.Name, ip))
if err == nil {
m.Answer = append(m.Answer, rr)
}
}
case dns.TypeTXT:
a, _, _ := net.SplitHostPort(w.RemoteAddr().String())
b := net.ParseIP(a)
// We don't answer these queries from non nebula nodes or localhost
//l.Debugf("Does %s contain %s", b, dnsR.hostMap.vpnCIDR)
if !dnsR.hostMap.vpnCIDR.Contains(b) && a != "127.0.0.1" {
return
}
l.Debugf("Query for TXT %s", q.Name)
ip := dnsR.QueryCert(q.Name)
if ip != "" {
rr, err := dns.NewRR(fmt.Sprintf("%s TXT %s", q.Name, ip))
if err == nil {
m.Answer = append(m.Answer, rr)
}
}
}
}
}
func handleDnsRequest(l *logrus.Logger, w dns.ResponseWriter, r *dns.Msg) {
m := new(dns.Msg)
m.SetReply(r)
m.Compress = false
switch r.Opcode {
case dns.OpcodeQuery:
parseQuery(l, m, w)
}
w.WriteMsg(m)
}
func dnsMain(l *logrus.Logger, hostMap *HostMap, c *config.C) func() {
dnsR = newDnsRecords(hostMap)
// attach request handler func
dns.HandleFunc(".", func(w dns.ResponseWriter, r *dns.Msg) {
handleDnsRequest(l, w, r)
})
c.RegisterReloadCallback(func(c *config.C) {
reloadDns(l, c)
})
return func() {
startDns(l, c)
}
}
func getDnsServerAddr(c *config.C) string {
return c.GetString("lighthouse.dns.host", "") + ":" + strconv.Itoa(c.GetInt("lighthouse.dns.port", 53))
}
func startDns(l *logrus.Logger, c *config.C) {
dnsAddr = getDnsServerAddr(c)
dnsServer = &dns.Server{Addr: dnsAddr, Net: "udp"}
l.WithField("dnsListener", dnsAddr).Info("Starting DNS responder")
err := dnsServer.ListenAndServe()
defer dnsServer.Shutdown()
if err != nil {
l.Errorf("Failed to start server: %s\n ", err.Error())
}
}
func reloadDns(l *logrus.Logger, c *config.C) {
if dnsAddr == getDnsServerAddr(c) {
l.Debug("No DNS server config change detected")
return
}
l.Debug("Restarting DNS server")
dnsServer.Shutdown()
go startDns(l, c)
}