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package dns
import (
"fmt"
"net"
"strings"
"time"
"github.com/miekg/dns"
"github.com/lxc/incus/v6/shared/api"
"github.com/lxc/incus/v6/shared/logger"
)
type dnsHandler struct {
server *Server
}
func (d dnsHandler) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
// Don't allow concurrent queries.
d.server.mu.Lock()
defer d.server.mu.Unlock()
// Check if we're ready to serve queries.
if d.server.zoneRetriever == nil {
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeServerFailure)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
// Only allow a single request.
if len(r.Question) != 1 {
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeServerFailure)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
// Check that it's a supported request type.
if r.Question[0].Qtype != dns.TypeAXFR && r.Question[0].Qtype != dns.TypeIXFR && r.Question[0].Qtype != dns.TypeSOA {
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeNotImplemented)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
// Extract the request information.
name := strings.TrimSuffix(r.Question[0].Name, ".")
ip, _, err := net.SplitHostPort(w.RemoteAddr().String())
if err != nil {
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeServerFailure)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
// Prepare the response.
m := &dns.Msg{}
m.SetReply(r)
m.Authoritative = true
// Load the zone.
zone, err := d.server.zoneRetriever(name, r.Question[0].Qtype != dns.TypeSOA)
if err != nil {
// On failure, return NXDOMAIN.
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeNameError)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
// Check access.
if !isAllowed(zone.Info, ip, r.IsTsig(), w.TsigStatus() == nil) {
// On auth failure, return NXDOMAIN to avoid information leaks.
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeNameError)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
zoneRR := dns.NewZoneParser(strings.NewReader(zone.Content), "", "")
for {
rr, ok := zoneRR.Next()
if !ok {
err := zoneRR.Err()
if err != nil {
logger.Errorf("Bad DNS record in zone %q: %v", name, err)
m := &dns.Msg{}
m.SetRcode(r, dns.RcodeFormatError)
err := w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
return
}
break
}
m.Answer = append(m.Answer, rr)
}
tsig := r.IsTsig()
if tsig != nil && w.TsigStatus() == nil {
m.SetTsig(tsig.Hdr.Name, tsig.Algorithm, 300, time.Now().Unix())
}
err = w.WriteMsg(m)
if err != nil {
logger.Error("Unable to write message", logger.Ctx{"err": err})
}
}
func isAllowed(zone api.NetworkZone, ip string, tsig *dns.TSIG, tsigStatus bool) bool {
type peer struct {
address string
key string
}
// Build a list of peers.
peers := map[string]*peer{}
for k, v := range zone.Config {
if !strings.HasPrefix(k, "peers.") {
continue
}
// Extract the fields.
fields := strings.SplitN(k, ".", 3)
if len(fields) != 3 {
continue
}
peerName := fields[1]
if peers[peerName] == nil {
peers[peerName] = &peer{}
}
// Add the correct validation rule for the dynamic field based on last part of key.
switch fields[2] {
case "address":
peers[peerName].address = v
case "key":
peers[peerName].key = v
}
}
// Validate access.
for peerName, peer := range peers {
peerKeyName := fmt.Sprintf("%s_%s.", zone.Name, peerName)
if peer.address != "" && ip != peer.address {
// Bad IP address.
continue
}
if peer.key != "" && (tsig == nil || !tsigStatus) {
// Missing or invalid TSIG.
continue
}
if peer.key != "" && tsig.Hdr.Name != peerKeyName {
// Bad key name (valid TSIG but potentially for another domain).
continue
}
// We have a trusted peer.
return true
}
return false
}
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