package dnsforward import ( "encoding/binary" "net" "strings" "time" "github.com/AdguardTeam/AdGuardHome/internal/dhcpd" "github.com/AdguardTeam/AdGuardHome/internal/filtering" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/golibs/log" "github.com/AdguardTeam/golibs/netutil" "github.com/AdguardTeam/golibs/stringutil" "github.com/miekg/dns" ) // To transfer information between modules 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 PTR request if it // parsed successfully and belongs to one of locally-served IP ranges as per // RFC 6303. 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 // origQuestion is the question received from the client. It is set // when the request is modified by rewrites. origQuestion dns.Question // startTime is the time at which the processing of the request has started. startTime time.Time // 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 } // 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 it's handling if s // have tried to resolve it recently. func (s *Server) processRecursion(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx if msg := pctx.Req; msg != nil && s.recDetector.check(*msg) { log.Debug("recursion detected resolving %q", msg.Question[0].Name) pctx.Res = s.genNXDomain(pctx.Req) return resultCodeFinish } return resultCodeSuccess } // processInitial terminates the following processing for some requests if // needed and enriches the ctx with some client-specific information. // // TODO(e.burkov): Decompose into less general processors. func (s *Server) processInitial(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx q := pctx.Req.Question[0] qt := q.Qtype if s.conf.AAAADisabled && qt == dns.TypeAAAA { _ = proxy.CheckDisabledAAAARequest(pctx, true) return resultCodeFinish } if s.conf.OnDNSRequest != nil { s.conf.OnDNSRequest(pctx) } // Disable Mozilla DoH. // // See https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet. if (qt == dns.TypeA || qt == dns.TypeAAAA) && q.Name == "use-application-dns.net." { pctx.Res = s.genNXDomain(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.conf.ProtectionEnabled dctx.setts = s.getClientRequestFilteringSettings(dctx) return resultCodeSuccess } func (s *Server) setTableHostToIP(t hostToIPTable) { s.tableHostToIPLock.Lock() defer s.tableHostToIPLock.Unlock() s.tableHostToIP = t } func (s *Server) setTableIPToHost(t *netutil.IPMap) { s.tableIPToHostLock.Lock() defer s.tableIPToHostLock.Unlock() s.tableIPToHost = t } func (s *Server) onDHCPLeaseChanged(flags int) { var err error add := true switch flags { case dhcpd.LeaseChangedAdded, dhcpd.LeaseChangedAddedStatic, dhcpd.LeaseChangedRemovedStatic: // Go on. case dhcpd.LeaseChangedRemovedAll: add = false default: return } var hostToIP hostToIPTable var ipToHost *netutil.IPMap if add { ll := s.dhcpServer.Leases(dhcpd.LeasesAll) hostToIP = make(hostToIPTable, len(ll)) ipToHost = netutil.NewIPMap(len(ll)) for _, l := range ll { // TODO(a.garipov): Remove this after we're finished with the client // hostname validations in the DHCP server code. err = netutil.ValidateDomainName(l.Hostname) if err != nil { log.Debug( "dns: skipping invalid hostname %q from dhcp: %s", l.Hostname, err, ) } lowhost := strings.ToLower(l.Hostname + "." + s.localDomainSuffix) ip := netutil.CloneIP(l.IP) ipToHost.Set(ip, lowhost) hostToIP[lowhost] = ip } log.Debug("dns: added %d A/PTR entries from DHCP", ipToHost.Len()) } s.setTableHostToIP(hostToIP) s.setTableIPToHost(ipToHost) } // 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) { pctx := dctx.proxyCtx q := pctx.Req.Question[0] if !s.conf.HandleDDR { return resultCodeSuccess } if q.Name == ddrHostFQDN { if s.dnsProxy.TLSListenAddr == nil && s.conf.HTTPSListenAddrs == nil && s.dnsProxy.QUICListenAddr == nil || q.Qtype != dns.TypeSVCB { pctx.Res = s.makeResponse(pctx.Req) return resultCodeFinish } 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) // 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) } 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) { 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 } // dhcpHostToIP tries to get an IP leased by DHCP and returns the copy of // address since the data inside the internal table may be changed while request // processing. It's safe for concurrent use. func (s *Server) dhcpHostToIP(host string) (ip net.IP, ok bool) { s.tableHostToIPLock.Lock() defer s.tableHostToIPLock.Unlock() if s.tableHostToIP == nil { return nil, false } var ipFromTable net.IP ipFromTable, ok = s.tableHostToIP[host] if !ok { return nil, false } ip = make(net.IP, len(ipFromTable)) copy(ip, ipFromTable) return ip, true } // processDHCPHosts respond to A requests if the target hostname is known to // the server. // // TODO(a.garipov): Adapt to AAAA as well. func (s *Server) processDHCPHosts(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx req := pctx.Req q := req.Question[0] reqHost, ok := s.isDHCPClientHostQ(q) if !ok { return resultCodeSuccess } if !dctx.isLocalClient { log.Debug("dns: %q requests for dhcp host %q", pctx.Addr, reqHost) pctx.Res = s.genNXDomain(req) // Do not even put into query log. return resultCodeFinish } ip, ok := s.dhcpHostToIP(reqHost) if !ok { // Go on and process them with filters, including dnsrewrite ones, and // possibly route them to a domain-specific upstream. log.Debug("dns: no dhcp record for %q", reqHost) return resultCodeSuccess } log.Debug("dns: dhcp record for %q is %s", reqHost, ip) resp := s.makeResponse(req) if q.Qtype == dns.TypeA { a := &dns.A{ Hdr: s.hdr(req, dns.TypeA), A: ip, } resp.Answer = append(resp.Answer, a) } dctx.proxyCtx.Res = resp return resultCodeSuccess } // 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) { pctx := dctx.proxyCtx req := pctx.Req q := req.Question[0] if q.Qtype != dns.TypePTR { // No need for restriction. return resultCodeSuccess } ip, err := netutil.IPFromReversedAddr(q.Name) if err != nil { log.Debug("dns: parsing reversed addr: %s", err) // DNS-Based Service Discovery uses PTR records having not an ARPA // format of the domain name in question. Those shouldn't be // invalidated. See http://www.dns-sd.org/ServerStaticSetup.html and // RFC 2782. name := strings.TrimSuffix(q.Name, ".") if err = netutil.ValidateSRVDomainName(name); err != nil { log.Debug("dns: validating service domain: %s", err) return resultCodeError } log.Debug("dns: request is for a service domain") return resultCodeSuccess } // 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 // don't need to be accessible externally. if !s.privateNets.Contains(ip) { log.Debug("dns: addr %s is not from locally-served network", ip) return resultCodeSuccess } if !dctx.isLocalClient { log.Debug("dns: %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 = ip // 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 } // ipToDHCPHost tries to get a hostname leased by DHCP. It's safe for // concurrent use. func (s *Server) ipToDHCPHost(ip net.IP) (host string, ok bool) { s.tableIPToHostLock.Lock() defer s.tableIPToHostLock.Unlock() if s.tableIPToHost == nil { return "", false } var v any v, ok = s.tableIPToHost.Get(ip) if !ok { return "", false } if host, ok = v.(string); !ok { log.Error("dns: bad type %T in tableIPToHost for %s", v, ip) return "", false } return host, true } // processDHCPAddrs responds to PTR requests if the target IP is leased by the // DHCP server. func (s *Server) processDHCPAddrs(dctx *dnsContext) (rc resultCode) { pctx := dctx.proxyCtx if pctx.Res != nil { return resultCodeSuccess } ip := dctx.unreversedReqIP if ip == nil { return resultCodeSuccess } host, ok := s.ipToDHCPHost(ip) if !ok { return resultCodeSuccess } log.Debug("dns: dhcp reverse record for %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, Ttl: s.conf.BlockedResponseTTL, Class: dns.ClassINET, }, Ptr: dns.Fqdn(host), } 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) { 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.privateNets.Contains(ip) { return resultCodeSuccess } if s.conf.UsePrivateRDNS { s.recDetector.add(*pctx.Req) if err := s.localResolvers.Resolve(pctx); err != nil { 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) { if ctx.proxyCtx.Res != nil { // Go on since the response is already set. return resultCodeSuccess } s.serverLock.RLock() defer s.serverLock.RUnlock() if s.dnsFilter == nil { return resultCodeSuccess } 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) { pctx := dctx.proxyCtx req := pctx.Req q := req.Question[0] if pctx.Res != nil { // The response has already been set. return resultCodeSuccess } else if reqHost, ok := s.isDHCPClientHostQ(q); ok { // 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. log.Debug("dns: dhcp client hostname %q was not filtered", reqHost) pctx.Res = s.genNXDomain(req) return resultCodeFinish } s.setCustomUpstream(pctx, dctx.clientID) origReqAD := false if s.conf.EnableDNSSEC { if req.AuthenticatedData { origReqAD = true } else { req.AuthenticatedData = true } } // Process the request further since it wasn't filtered. prx := s.proxy() if prx == nil { dctx.err = srvClosedErr return resultCodeError } if dctx.err = prx.Resolve(pctx); dctx.err != nil { return resultCodeError } dctx.responseFromUpstream = true dctx.responseAD = pctx.Res.AuthenticatedData if s.conf.EnableDNSSEC && !origReqAD { pctx.Req.AuthenticatedData = false pctx.Res.AuthenticatedData = false } return resultCodeSuccess } // isDHCPClientHostQ returns true if q is from a request for a DHCP client // hostname. If ok is true, reqHost contains the requested hostname. func (s *Server) isDHCPClientHostQ(q dns.Question) (reqHost string, ok bool) { if !s.dhcpServer.Enabled() { return "", false } // 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 "", false } reqHost = strings.ToLower(q.Name[:len(q.Name)-1]) if strings.HasSuffix(reqHost, s.localDomainSuffix) { return reqHost, true } return "", false } // 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("dns: getting custom upstreams for client %s: %s", id, err) return } if upsConf != nil { log.Debug("dns: 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) { 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 || s.dnsFilter == nil { 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 }