package dnsforward import ( "encoding/binary" "net" "net/netip" "strconv" "strings" "time" "github.com/AdguardTeam/AdGuardHome/internal/filtering" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/dnsproxy/upstream" "github.com/AdguardTeam/golibs/errors" "github.com/AdguardTeam/golibs/log" "github.com/AdguardTeam/golibs/netutil" "github.com/AdguardTeam/golibs/stringutil" "github.com/miekg/dns" ) // To transfer information between modules // // TODO(s.chzhen): Add lowercased, non-FQDN version of the hostname from the // question of the request. Add persistent client. type dnsContext struct { proxyCtx *proxy.DNSContext // setts are the filtering settings for the client. setts *filtering.Settings result *filtering.Result // origResp is the response received from upstream. It is set when the // response is modified by filters. origResp *dns.Msg // unreversedReqIP stores an IP address obtained from a PTR request if it // was parsed successfully and belongs to one of the locally served IP // ranges. It is also filled with unmapped version of the address if it's // within DNS64 prefixes. // // TODO(e.burkov): Use netip.Addr when we switch to netip more fully. unreversedReqIP net.IP // err is the error returned from a processing function. err error // clientID is the ClientID from DoH, DoQ, or DoT, if provided. clientID string // startTime is the time at which the processing of the request has started. startTime time.Time // origQuestion is the question received from the client. It is set // when the request is modified by rewrites. origQuestion dns.Question // protectionEnabled shows if the filtering is enabled, and if the // server's DNS filter is ready. protectionEnabled bool // responseFromUpstream shows if the response is received from the // upstream servers. responseFromUpstream bool // responseAD shows if the response had the AD bit set. responseAD bool // isLocalClient shows if client's IP address is from locally served // network. isLocalClient bool // isDHCPHost is true if the request for a local domain name and the DHCP is // available for this request. isDHCPHost bool } // resultCode is the result of a request processing function. type resultCode int const ( // resultCodeSuccess is returned when a handler performed successfully, and // the next handler must be called. resultCodeSuccess resultCode = iota // resultCodeFinish is returned when a handler performed successfully, and // the processing of the request must be stopped. resultCodeFinish // resultCodeError is returned when a handler failed, and the processing of // the request must be stopped. resultCodeError ) // ddrHostFQDN is the FQDN used in Discovery of Designated Resolvers (DDR) requests. // See https://www.ietf.org/archive/id/draft-ietf-add-ddr-06.html. const ddrHostFQDN = "_dns.resolver.arpa." // handleDNSRequest filters the incoming DNS requests and writes them to the query log func (s *Server) handleDNSRequest(_ *proxy.Proxy, pctx *proxy.DNSContext) error { dctx := &dnsContext{ proxyCtx: pctx, result: &filtering.Result{}, startTime: time.Now(), } type modProcessFunc func(ctx *dnsContext) (rc resultCode) // Since (*dnsforward.Server).handleDNSRequest(...) is used as // proxy.(Config).RequestHandler, there is no need for additional index // out of range checking in any of the following functions, because the // (*proxy.Proxy).handleDNSRequest method performs it before calling the // appropriate handler. mods := []modProcessFunc{ s.processRecursion, s.processInitial, s.processDDRQuery, s.processDetermineLocal, s.processDHCPHosts, s.processRestrictLocal, s.processDHCPAddrs, s.processFilteringBeforeRequest, s.processLocalPTR, s.processUpstream, s.processFilteringAfterResponse, s.ipset.process, s.processQueryLogsAndStats, } for _, process := range mods { r := process(dctx) switch r { case resultCodeSuccess: // continue: call the next filter case resultCodeFinish: return nil case resultCodeError: return dctx.err } } if pctx.Res != nil { // Some devices require DNS message compression. pctx.Res.Compress = true } return nil } // processRecursion checks the incoming request and halts its handling by // answering NXDOMAIN if s has tried to resolve it recently. func (s *Server) processRecursion(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing recursion") defer log.Debug("dnsforward: finished processing recursion") pctx := dctx.proxyCtx if msg := pctx.Req; msg != nil && s.recDetector.check(*msg) { log.Debug("dnsforward: recursion detected resolving %q", msg.Question[0].Name) pctx.Res = s.genNXDomain(pctx.Req) return resultCodeFinish } return resultCodeSuccess } // mozillaFQDN is the domain used to signal the Firefox browser to not use its // own DoH server. // // See https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet. const mozillaFQDN = "use-application-dns.net." // healthcheckFQDN is a reserved domain-name used for healthchecking. // // [Section 6.2 of RFC 6761] states that DNS Registries/Registrars must not // grant requests to register test names in the normal way to any person or // entity, making domain names under the .test TLD free to use in internal // purposes. // // [Section 6.2 of RFC 6761]: https://www.rfc-editor.org/rfc/rfc6761.html#section-6.2 const healthcheckFQDN = "healthcheck.adguardhome.test." // processInitial terminates the following processing for some requests if // needed and enriches dctx with some client-specific information. // // TODO(e.burkov): Decompose into less general processors. func (s *Server) processInitial(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing initial") defer log.Debug("dnsforward: finished processing initial") pctx := dctx.proxyCtx s.processClientIP(pctx.Addr) q := pctx.Req.Question[0] qt := q.Qtype if s.conf.AAAADisabled && qt == dns.TypeAAAA { _ = proxy.CheckDisabledAAAARequest(pctx, true) return resultCodeFinish } if (qt == dns.TypeA || qt == dns.TypeAAAA) && q.Name == mozillaFQDN { pctx.Res = s.genNXDomain(pctx.Req) return resultCodeFinish } if q.Name == healthcheckFQDN { // Generate a NODATA negative response to make nslookup exit with 0. pctx.Res = s.makeResponse(pctx.Req) return resultCodeFinish } // Get the ClientID, if any, before getting client-specific filtering // settings. var key [8]byte binary.BigEndian.PutUint64(key[:], pctx.RequestID) dctx.clientID = string(s.clientIDCache.Get(key[:])) // Get the client-specific filtering settings. dctx.protectionEnabled, _ = s.UpdatedProtectionStatus() dctx.setts = s.clientRequestFilteringSettings(dctx) return resultCodeSuccess } // processClientIP sends the client IP address to s.addrProc, if needed. func (s *Server) processClientIP(addr net.Addr) { clientIP := netutil.NetAddrToAddrPort(addr).Addr() if clientIP == (netip.Addr{}) { log.Info("dnsforward: warning: bad client addr %q", addr) return } // Do not assign s.addrProc to a local variable to then use, since this lock // also serializes the closure of s.addrProc. s.serverLock.RLock() defer s.serverLock.RUnlock() s.addrProc.Process(clientIP) } // processDDRQuery responds to Discovery of Designated Resolvers (DDR) SVCB // queries. The response contains different types of encryption supported by // current user configuration. // // See https://www.ietf.org/archive/id/draft-ietf-add-ddr-10.html. func (s *Server) processDDRQuery(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing ddr") defer log.Debug("dnsforward: finished processing ddr") if !s.conf.HandleDDR { return resultCodeSuccess } pctx := dctx.proxyCtx q := pctx.Req.Question[0] if q.Name == ddrHostFQDN { pctx.Res = s.makeDDRResponse(pctx.Req) return resultCodeFinish } return resultCodeSuccess } // makeDDRResponse creates a DDR answer based on the server configuration. The // constructed SVCB resource records have the priority of 1 for each entry, // similar to examples provided by the [draft standard]. // // TODO(a.meshkov): Consider setting the priority values based on the protocol. // // [draft standard]: https://www.ietf.org/archive/id/draft-ietf-add-ddr-10.html. func (s *Server) makeDDRResponse(req *dns.Msg) (resp *dns.Msg) { resp = s.makeResponse(req) if req.Question[0].Qtype != dns.TypeSVCB { return resp } // TODO(e.burkov): Think about storing the FQDN version of the server's // name somewhere. domainName := dns.Fqdn(s.conf.ServerName) for _, addr := range s.conf.HTTPSListenAddrs { values := []dns.SVCBKeyValue{ &dns.SVCBAlpn{Alpn: []string{"h2"}}, &dns.SVCBPort{Port: uint16(addr.Port)}, &dns.SVCBDoHPath{Template: "/dns-query{?dns}"}, } ans := &dns.SVCB{ Hdr: s.hdr(req, dns.TypeSVCB), Priority: 1, Target: domainName, Value: values, } resp.Answer = append(resp.Answer, ans) } if s.conf.hasIPAddrs { // Only add DNS-over-TLS resolvers in case the certificate contains IP // addresses. // // See https://github.com/AdguardTeam/AdGuardHome/issues/4927. for _, addr := range s.dnsProxy.TLSListenAddr { values := []dns.SVCBKeyValue{ &dns.SVCBAlpn{Alpn: []string{"dot"}}, &dns.SVCBPort{Port: uint16(addr.Port)}, } ans := &dns.SVCB{ Hdr: s.hdr(req, dns.TypeSVCB), Priority: 1, Target: domainName, Value: values, } resp.Answer = append(resp.Answer, ans) } } for _, addr := range s.dnsProxy.QUICListenAddr { values := []dns.SVCBKeyValue{ &dns.SVCBAlpn{Alpn: []string{"doq"}}, &dns.SVCBPort{Port: uint16(addr.Port)}, } ans := &dns.SVCB{ Hdr: s.hdr(req, dns.TypeSVCB), Priority: 1, Target: domainName, Value: values, } resp.Answer = append(resp.Answer, ans) } return resp } // processDetermineLocal determines if the client's IP address is from locally // served network and saves the result into the context. func (s *Server) processDetermineLocal(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing local detection") defer log.Debug("dnsforward: finished processing local detection") rc = resultCodeSuccess var ip net.IP if ip, _ = netutil.IPAndPortFromAddr(dctx.proxyCtx.Addr); ip == nil { return rc } dctx.isLocalClient = s.privateNets.Contains(ip) return rc } // processDHCPHosts respond to A requests if the target hostname is known to // the server. It responds with a mapped IP address if the DNS64 is enabled and // the request is for AAAA. // // TODO(a.garipov): Adapt to AAAA as well. func (s *Server) processDHCPHosts(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing dhcp hosts") defer log.Debug("dnsforward: finished processing dhcp hosts") pctx := dctx.proxyCtx req := pctx.Req q := &req.Question[0] dhcpHost := s.dhcpHostFromRequest(q) if dctx.isDHCPHost = dhcpHost != ""; !dctx.isDHCPHost { return resultCodeSuccess } if !dctx.isLocalClient { log.Debug("dnsforward: %q requests for dhcp host %q", pctx.Addr, dhcpHost) pctx.Res = s.genNXDomain(req) // Do not even put into query log. return resultCodeFinish } ip := s.dhcpServer.IPByHost(dhcpHost) if ip == (netip.Addr{}) { // Go on and process them with filters, including dnsrewrite ones, and // possibly route them to a domain-specific upstream. log.Debug("dnsforward: no dhcp record for %q", dhcpHost) return resultCodeSuccess } log.Debug("dnsforward: dhcp record for %q is %s", dhcpHost, ip) resp := s.makeResponse(req) switch q.Qtype { case dns.TypeA: a := &dns.A{ Hdr: s.hdr(req, dns.TypeA), A: ip.AsSlice(), } resp.Answer = append(resp.Answer, a) case dns.TypeAAAA: if s.dns64Pref != (netip.Prefix{}) { // Respond with DNS64-mapped address for IPv4 host if DNS64 is // enabled. aaaa := &dns.AAAA{ Hdr: s.hdr(req, dns.TypeAAAA), AAAA: s.mapDNS64(ip), } resp.Answer = append(resp.Answer, aaaa) } default: // Go on. } dctx.proxyCtx.Res = resp return resultCodeSuccess } // indexFirstV4Label returns the index at which the reversed IPv4 address // starts, assuming the domain is pre-validated ARPA domain having in-addr and // arpa labels removed. func indexFirstV4Label(domain string) (idx int) { idx = len(domain) for labelsNum := 0; labelsNum < net.IPv4len && idx > 0; labelsNum++ { curIdx := strings.LastIndexByte(domain[:idx-1], '.') + 1 _, parseErr := strconv.ParseUint(domain[curIdx:idx-1], 10, 8) if parseErr != nil { return idx } idx = curIdx } return idx } // indexFirstV6Label returns the index at which the reversed IPv6 address // starts, assuming the domain is pre-validated ARPA domain having ip6 and arpa // labels removed. func indexFirstV6Label(domain string) (idx int) { idx = len(domain) for labelsNum := 0; labelsNum < net.IPv6len*2 && idx > 0; labelsNum++ { curIdx := idx - len("a.") if curIdx > 1 && domain[curIdx-1] != '.' { return idx } nibble := domain[curIdx] if (nibble < '0' || nibble > '9') && (nibble < 'a' || nibble > 'f') { return idx } idx = curIdx } return idx } // extractARPASubnet tries to convert a reversed ARPA address being a part of // domain to an IP network. domain must be an FQDN. // // TODO(e.burkov): Move to golibs. func extractARPASubnet(domain string) (pref netip.Prefix, err error) { err = netutil.ValidateDomainName(strings.TrimSuffix(domain, ".")) if err != nil { // Don't wrap the error since it's informative enough as is. return netip.Prefix{}, err } const ( v4Suffix = "in-addr.arpa." v6Suffix = "ip6.arpa." ) domain = strings.ToLower(domain) var idx int switch { case strings.HasSuffix(domain, v4Suffix): idx = indexFirstV4Label(domain[:len(domain)-len(v4Suffix)]) case strings.HasSuffix(domain, v6Suffix): idx = indexFirstV6Label(domain[:len(domain)-len(v6Suffix)]) default: return netip.Prefix{}, &netutil.AddrError{ Err: netutil.ErrNotAReversedSubnet, Kind: netutil.AddrKindARPA, Addr: domain, } } var subnet *net.IPNet subnet, err = netutil.SubnetFromReversedAddr(domain[idx:]) if err != nil { // Don't wrap the error since it's informative enough as is. return netip.Prefix{}, err } return netutil.IPNetToPrefixNoMapped(subnet) } // processRestrictLocal responds with NXDOMAIN to PTR requests for IP addresses // in locally served network from external clients. func (s *Server) processRestrictLocal(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing local restriction") defer log.Debug("dnsforward: finished processing local restriction") pctx := dctx.proxyCtx req := pctx.Req q := req.Question[0] if q.Qtype != dns.TypePTR { // No need for restriction. return resultCodeSuccess } subnet, err := extractARPASubnet(q.Name) if err != nil { if errors.Is(err, netutil.ErrNotAReversedSubnet) { log.Debug("dnsforward: request is not for arpa domain") return resultCodeSuccess } log.Debug("dnsforward: parsing reversed addr: %s", err) return resultCodeError } // Restrict an access to local addresses for external clients. We also // assume that all the DHCP leases we give are locally served or at least // shouldn't be accessible externally. subnetAddr := subnet.Addr() addrData := subnetAddr.AsSlice() if !s.privateNets.Contains(addrData) { return resultCodeSuccess } log.Debug("dnsforward: addr %s is from locally served network", subnetAddr) if !dctx.isLocalClient { log.Debug("dnsforward: %q requests an internal ip", pctx.Addr) pctx.Res = s.genNXDomain(req) // Do not even put into query log. return resultCodeFinish } // Do not perform unreversing ever again. dctx.unreversedReqIP = addrData // There is no need to filter request from external addresses since this // code is only executed when the request is for locally served ARPA // hostname so disable redundant filters. dctx.setts.ParentalEnabled = false dctx.setts.SafeBrowsingEnabled = false dctx.setts.SafeSearchEnabled = false dctx.setts.ServicesRules = nil // Nothing to restrict. return resultCodeSuccess } // processDHCPAddrs responds to PTR requests if the target IP is leased by the // DHCP server. func (s *Server) processDHCPAddrs(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing dhcp addrs") defer log.Debug("dnsforward: finished processing dhcp addrs") pctx := dctx.proxyCtx if pctx.Res != nil { return resultCodeSuccess } ip := dctx.unreversedReqIP if ip == nil { return resultCodeSuccess } // TODO(a.garipov): Remove once we switch to [netip.Addr] more fully. ipAddr, err := netutil.IPToAddrNoMapped(ip) if err != nil { log.Debug("dnsforward: bad reverse ip %v from dhcp: %s", ip, err) return resultCodeSuccess } host := s.dhcpServer.HostByIP(ipAddr) if host == "" { return resultCodeSuccess } log.Debug("dnsforward: dhcp client %s is %q", ip, host) req := pctx.Req resp := s.makeResponse(req) ptr := &dns.PTR{ Hdr: dns.RR_Header{ Name: req.Question[0].Name, Rrtype: dns.TypePTR, // TODO(e.burkov): Use [dhcpsvc.Lease.Expiry]. See // https://github.com/AdguardTeam/AdGuardHome/issues/3932. Ttl: s.dnsFilter.BlockedResponseTTL(), Class: dns.ClassINET, }, Ptr: dns.Fqdn(strings.Join([]string{host, s.localDomainSuffix}, ".")), } resp.Answer = append(resp.Answer, ptr) pctx.Res = resp return resultCodeSuccess } // processLocalPTR responds to PTR requests if the target IP is detected to be // inside the local network and the query was not answered from DHCP. func (s *Server) processLocalPTR(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing local ptr") defer log.Debug("dnsforward: finished processing local ptr") pctx := dctx.proxyCtx if pctx.Res != nil { return resultCodeSuccess } ip := dctx.unreversedReqIP if ip == nil { return resultCodeSuccess } s.serverLock.RLock() defer s.serverLock.RUnlock() if s.conf.UsePrivateRDNS { s.recDetector.add(*pctx.Req) if err := s.localResolvers.Resolve(pctx); err != nil { log.Debug("dnsforward: resolving private address: %s", err) // Generate the server failure if the private upstream configuration // is empty. // // TODO(e.burkov): Get rid of this crutch once the local resolvers // logic is moved to the dnsproxy completely. if errors.Is(err, upstream.ErrNoUpstreams) { pctx.Res = s.genServerFailure(pctx.Req) // Do not even put into query log. return resultCodeFinish } dctx.err = err return resultCodeError } } if pctx.Res == nil { pctx.Res = s.genNXDomain(pctx.Req) // Do not even put into query log. return resultCodeFinish } return resultCodeSuccess } // Apply filtering logic func (s *Server) processFilteringBeforeRequest(ctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing filtering before req") defer log.Debug("dnsforward: finished processing filtering before req") if ctx.proxyCtx.Res != nil { // Go on since the response is already set. return resultCodeSuccess } s.serverLock.RLock() defer s.serverLock.RUnlock() var err error if ctx.result, err = s.filterDNSRequest(ctx); err != nil { ctx.err = err return resultCodeError } return resultCodeSuccess } // ipStringFromAddr extracts an IP address string from net.Addr. func ipStringFromAddr(addr net.Addr) (ipStr string) { if ip, _ := netutil.IPAndPortFromAddr(addr); ip != nil { return ip.String() } return "" } // processUpstream passes request to upstream servers and handles the response. func (s *Server) processUpstream(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing upstream") defer log.Debug("dnsforward: finished processing upstream") pctx := dctx.proxyCtx req := pctx.Req if pctx.Res != nil { // The response has already been set. return resultCodeSuccess } else if dctx.isDHCPHost { // A DHCP client hostname query that hasn't been handled or filtered. // Respond with an NXDOMAIN. // // TODO(a.garipov): Route such queries to a custom upstream for the // local domain name if there is one. name := req.Question[0].Name log.Debug("dnsforward: dhcp client hostname %q was not filtered", name[:len(name)-1]) pctx.Res = s.genNXDomain(req) return resultCodeFinish } s.setCustomUpstream(pctx, dctx.clientID) reqWantsDNSSEC := s.setReqAD(req) // Process the request further since it wasn't filtered. prx := s.proxy() if prx == nil { dctx.err = srvClosedErr return resultCodeError } if err := prx.Resolve(pctx); err != nil { if errors.Is(err, upstream.ErrNoUpstreams) { // Do not even put into querylog. Currently this happens either // when the private resolvers enabled and the request is DNS64 PTR, // or when the client isn't considered local by prx. // // TODO(e.burkov): Make proxy detect local client the same way as // AGH does. pctx.Res = s.genNXDomain(req) return resultCodeFinish } dctx.err = err return resultCodeError } dctx.responseFromUpstream = true dctx.responseAD = pctx.Res.AuthenticatedData s.setRespAD(pctx, reqWantsDNSSEC) return resultCodeSuccess } // setReqAD changes the request based on the server settings. wantsDNSSEC is // false if the response should be cleared of the AD bit. // // TODO(a.garipov, e.burkov): This should probably be done in module dnsproxy. func (s *Server) setReqAD(req *dns.Msg) (wantsDNSSEC bool) { if !s.conf.EnableDNSSEC { return false } origReqAD := req.AuthenticatedData req.AuthenticatedData = true // Per [RFC 6840] says, validating resolvers should only set the AD bit when // the response has the AD bit set and the request contained either a set DO // bit or a set AD bit. So, if neither of these is true, clear the AD bits // in [Server.setRespAD]. // // [RFC 6840]: https://datatracker.ietf.org/doc/html/rfc6840#section-5.8 return origReqAD || hasDO(req) } // hasDO returns true if msg has EDNS(0) options and the DNSSEC OK flag is set // in there. // // TODO(a.garipov): Move to golibs/dnsmsg when it's there. func hasDO(msg *dns.Msg) (do bool) { o := msg.IsEdns0() if o == nil { return false } return o.Do() } // setRespAD changes the request and response based on the server settings and // the original request data. func (s *Server) setRespAD(pctx *proxy.DNSContext, reqWantsDNSSEC bool) { if s.conf.EnableDNSSEC && !reqWantsDNSSEC { pctx.Req.AuthenticatedData = false pctx.Res.AuthenticatedData = false } } // dhcpHostFromRequest returns a hostname from question, if the request is for a // DHCP client's hostname when DHCP is enabled, and an empty string otherwise. func (s *Server) dhcpHostFromRequest(q *dns.Question) (reqHost string) { if !s.dhcpServer.Enabled() { return "" } // Include AAAA here, because despite the fact that we don't support it yet, // the expected behavior here is to respond with an empty answer and not // NXDOMAIN. if qt := q.Qtype; qt != dns.TypeA && qt != dns.TypeAAAA { return "" } reqHost = strings.ToLower(q.Name[:len(q.Name)-1]) if !netutil.IsImmediateSubdomain(reqHost, s.localDomainSuffix) { return "" } return reqHost[:len(reqHost)-len(s.localDomainSuffix)-1] } // setCustomUpstream sets custom upstream settings in pctx, if necessary. func (s *Server) setCustomUpstream(pctx *proxy.DNSContext, clientID string) { customUpsByClient := s.conf.GetCustomUpstreamByClient if pctx.Addr == nil || customUpsByClient == nil { return } // Use the ClientID first, since it has a higher priority. id := stringutil.Coalesce(clientID, ipStringFromAddr(pctx.Addr)) upsConf, err := customUpsByClient(id) if err != nil { log.Error("dnsforward: getting custom upstreams for client %s: %s", id, err) return } if upsConf != nil { log.Debug("dnsforward: using custom upstreams for client %s", id) } pctx.CustomUpstreamConfig = upsConf } // Apply filtering logic after we have received response from upstream servers func (s *Server) processFilteringAfterResponse(dctx *dnsContext) (rc resultCode) { log.Debug("dnsforward: started processing filtering after resp") defer log.Debug("dnsforward: finished processing filtering after resp") pctx := dctx.proxyCtx switch res := dctx.result; res.Reason { case filtering.NotFilteredAllowList: return resultCodeSuccess case filtering.Rewritten, filtering.RewrittenRule: if dctx.origQuestion.Name == "" { // origQuestion is set in case we get only CNAME without IP from // rewrites table. return resultCodeSuccess } pctx.Req.Question[0], pctx.Res.Question[0] = dctx.origQuestion, dctx.origQuestion if len(pctx.Res.Answer) > 0 { rr := s.genAnswerCNAME(pctx.Req, res.CanonName) answer := append([]dns.RR{rr}, pctx.Res.Answer...) pctx.Res.Answer = answer } return resultCodeSuccess default: return s.filterAfterResponse(dctx, pctx) } } // filterAfterResponse returns the result of filtering the response that wasn't // explicitly allowed or rewritten. func (s *Server) filterAfterResponse(dctx *dnsContext, pctx *proxy.DNSContext) (res resultCode) { // Check the response only if it's from an upstream. Don't check the // response if the protection is disabled since dnsrewrite rules aren't // applied to it anyway. if !dctx.protectionEnabled || !dctx.responseFromUpstream { return resultCodeSuccess } result, err := s.filterDNSResponse(pctx, dctx.setts) if err != nil { dctx.err = err return resultCodeError } if result != nil { dctx.result = result dctx.origResp = pctx.Res } return resultCodeSuccess }