AdGuardHome/dnsforward/msg.go

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package dnsforward
import (
"log"
"net"
"time"
"github.com/AdguardTeam/AdGuardHome/dnsfilter"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/miekg/dns"
)
// Create a DNS response by DNS request and set necessary flags
func (s *Server) makeResponse(req *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetReply(req)
resp.RecursionAvailable = true
resp.Compress = true
return &resp
}
// genDNSFilterMessage generates a DNS message corresponding to the filtering result
func (s *Server) genDNSFilterMessage(d *proxy.DNSContext, result *dnsfilter.Result) *dns.Msg {
m := d.Req
if m.Question[0].Qtype != dns.TypeA && m.Question[0].Qtype != dns.TypeAAAA {
return s.genNXDomain(m)
}
switch result.Reason {
case dnsfilter.FilteredSafeBrowsing:
return s.genBlockedHost(m, s.conf.SafeBrowsingBlockHost, d)
case dnsfilter.FilteredParental:
return s.genBlockedHost(m, s.conf.ParentalBlockHost, d)
default:
// If the query was filtered by "Safe search", dnsfilter also must return
// the IP address that must be used in response.
// In this case regardless of the filtering method, we should return it
if result.Reason == dnsfilter.FilteredSafeSearch && result.IP != nil {
return s.genResponseWithIP(m, result.IP)
}
if s.conf.BlockingMode == "null_ip" {
// it means that we should return 0.0.0.0 or :: for any blocked request
switch m.Question[0].Qtype {
case dns.TypeA:
return s.genARecord(m, []byte{0, 0, 0, 0})
case dns.TypeAAAA:
return s.genAAAARecord(m, net.IPv6zero)
}
} else if s.conf.BlockingMode == "custom_ip" {
// means that we should return custom IP for any blocked request
switch m.Question[0].Qtype {
case dns.TypeA:
return s.genARecord(m, s.conf.BlockingIPAddrv4)
case dns.TypeAAAA:
return s.genAAAARecord(m, s.conf.BlockingIPAddrv6)
}
} else if s.conf.BlockingMode == "nxdomain" {
// means that we should return NXDOMAIN for any blocked request
return s.genNXDomain(m)
}
// Default blocking mode
// If there's an IP specified in the rule, return it
// If there is no IP, return NXDOMAIN
if result.IP != nil {
return s.genResponseWithIP(m, result.IP)
}
return s.genNXDomain(m)
}
}
func (s *Server) genServerFailure(request *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeServerFailure)
resp.RecursionAvailable = true
return &resp
}
func (s *Server) genARecord(request *dns.Msg, ip net.IP) *dns.Msg {
resp := s.makeResponse(request)
resp.Answer = append(resp.Answer, s.genAAnswer(request, ip))
return resp
}
func (s *Server) genAAAARecord(request *dns.Msg, ip net.IP) *dns.Msg {
resp := s.makeResponse(request)
resp.Answer = append(resp.Answer, s.genAAAAAnswer(request, ip))
return resp
}
func (s *Server) genAAnswer(req *dns.Msg, ip net.IP) *dns.A {
answer := new(dns.A)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.A = ip
return answer
}
func (s *Server) genAAAAAnswer(req *dns.Msg, ip net.IP) *dns.AAAA {
answer := new(dns.AAAA)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeAAAA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.AAAA = ip
return answer
}
// generate DNS response message with an IP address
func (s *Server) genResponseWithIP(req *dns.Msg, ip net.IP) *dns.Msg {
if req.Question[0].Qtype == dns.TypeA && ip.To4() != nil {
return s.genARecord(req, ip.To4())
} else if req.Question[0].Qtype == dns.TypeAAAA &&
len(ip) == net.IPv6len && ip.To4() == nil {
return s.genAAAARecord(req, ip)
}
// empty response
resp := s.makeResponse(req)
return resp
}
func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, d *proxy.DNSContext) *dns.Msg {
ip := net.ParseIP(newAddr)
if ip != nil {
return s.genResponseWithIP(request, ip)
}
// look up the hostname, TODO: cache
replReq := dns.Msg{}
replReq.SetQuestion(dns.Fqdn(newAddr), request.Question[0].Qtype)
replReq.RecursionDesired = true
newContext := &proxy.DNSContext{
Proto: d.Proto,
Addr: d.Addr,
StartTime: time.Now(),
Req: &replReq,
}
err := s.dnsProxy.Resolve(newContext)
if err != nil {
log.Printf("Couldn't look up replacement host '%s': %s", newAddr, err)
return s.genServerFailure(request)
}
resp := s.makeResponse(request)
if newContext.Res != nil {
for _, answer := range newContext.Res.Answer {
answer.Header().Name = request.Question[0].Name
resp.Answer = append(resp.Answer, answer)
}
}
return resp
}
// Make a CNAME response
func (s *Server) genCNAMEAnswer(req *dns.Msg, cname string) *dns.CNAME {
answer := new(dns.CNAME)
answer.Hdr = dns.RR_Header{
Name: req.Question[0].Name,
Rrtype: dns.TypeCNAME,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
}
answer.Target = dns.Fqdn(cname)
return answer
}
func (s *Server) genNXDomain(request *dns.Msg) *dns.Msg {
resp := dns.Msg{}
resp.SetRcode(request, dns.RcodeNameError)
resp.RecursionAvailable = true
resp.Ns = s.genSOA(request)
return &resp
}
func (s *Server) genSOA(request *dns.Msg) []dns.RR {
zone := ""
if len(request.Question) > 0 {
zone = request.Question[0].Name
}
soa := dns.SOA{
// values copied from verisign's nonexistent .com domain
// their exact values are not important in our use case because they are used for domain transfers between primary/secondary DNS servers
Refresh: 1800,
Retry: 900,
Expire: 604800,
Minttl: 86400,
// copied from AdGuard DNS
Ns: "fake-for-negative-caching.adguard.com.",
Serial: 100500,
// rest is request-specific
Hdr: dns.RR_Header{
Name: zone,
Rrtype: dns.TypeSOA,
Ttl: s.conf.BlockedResponseTTL,
Class: dns.ClassINET,
},
Mbox: "hostmaster.", // zone will be appended later if it's not empty or "."
}
if soa.Hdr.Ttl == 0 {
soa.Hdr.Ttl = defaultValues.BlockedResponseTTL
}
if len(zone) > 0 && zone[0] != '.' {
soa.Mbox += zone
}
return []dns.RR{&soa}
}