package dnsforward import ( "errors" "net" "strings" "time" "github.com/AdguardTeam/AdGuardHome/internal/aghnet" "github.com/AdguardTeam/AdGuardHome/internal/dhcpd" "github.com/AdguardTeam/AdGuardHome/internal/dnsfilter" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/golibs/log" "github.com/miekg/dns" ) // To transfer information between modules type dnsContext struct { // TODO(a.garipov): Remove this and rewrite processors to be methods of // *Server instead. srv *Server proxyCtx *proxy.DNSContext // setts are the filtering settings for the client. setts *dnsfilter.FilteringSettings startTime time.Time result *dnsfilter.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 // was successfully parsed. 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 // 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 // origReqDNSSEC shows if the DNSSEC flag in the original request from // the client is set. origReqDNSSEC 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 ) // handleDNSRequest filters the incoming DNS requests and writes them to the query log func (s *Server) handleDNSRequest(_ *proxy.Proxy, d *proxy.DNSContext) error { ctx := &dnsContext{ srv: s, proxyCtx: d, result: &dnsfilter.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{ processInitial, s.processInternalHosts, s.processRestrictLocal, s.processInternalIPAddrs, processClientID, processFilteringBeforeRequest, s.processLocalPTR, processUpstream, processDNSSECAfterResponse, processFilteringAfterResponse, s.ipset.process, processQueryLogsAndStats, } for _, process := range mods { r := process(ctx) switch r { case resultCodeSuccess: // continue: call the next filter case resultCodeFinish: return nil case resultCodeError: return ctx.err } } if d.Res != nil { d.Res.Compress = true // some devices require DNS message compression } return nil } // Perform initial checks; process WHOIS & rDNS func processInitial(ctx *dnsContext) (rc resultCode) { s := ctx.srv d := ctx.proxyCtx if s.conf.AAAADisabled && d.Req.Question[0].Qtype == dns.TypeAAAA { _ = proxy.CheckDisabledAAAARequest(d, true) return resultCodeFinish } if s.conf.OnDNSRequest != nil { s.conf.OnDNSRequest(d) } // disable Mozilla DoH // https://support.mozilla.org/en-US/kb/canary-domain-use-application-dnsnet if (d.Req.Question[0].Qtype == dns.TypeA || d.Req.Question[0].Qtype == dns.TypeAAAA) && d.Req.Question[0].Name == "use-application-dns.net." { d.Res = s.genNXDomain(d.Req) return resultCodeFinish } return resultCodeSuccess } // Return TRUE if host names doesn't contain disallowed characters func isHostnameOK(hostname string) bool { for _, c := range hostname { if !((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '.' || c == '-') { log.Debug("dns: skipping invalid hostname %s from DHCP", hostname) return false } } return true } func (s *Server) onDHCPLeaseChanged(flags int) { switch flags { case dhcpd.LeaseChangedAdded, dhcpd.LeaseChangedAddedStatic, dhcpd.LeaseChangedRemovedStatic: // default: return } hostToIP := make(map[string]net.IP) m := make(map[string]string) ll := s.dhcpServer.Leases(dhcpd.LeasesAll) for _, l := range ll { if len(l.Hostname) == 0 || !isHostnameOK(l.Hostname) { continue } lowhost := strings.ToLower(l.Hostname) m[l.IP.String()] = lowhost ip := make(net.IP, 4) copy(ip, l.IP.To4()) hostToIP[lowhost] = ip } log.Debug("dns: added %d A/PTR entries from DHCP", len(m)) s.tableHostToIPLock.Lock() s.tableHostToIP = hostToIP s.tableHostToIPLock.Unlock() s.tablePTRLock.Lock() s.tablePTR = m s.tablePTRLock.Unlock() } // hostToIP 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) hostToIP(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 } // processInternalHosts respond to A requests if the target hostname is known to // the server. // // TODO(a.garipov): Adapt to AAAA as well. func (s *Server) processInternalHosts(dctx *dnsContext) (rc resultCode) { req := dctx.proxyCtx.Req q := req.Question[0] // Go on processing the AAAA request despite the fact that we don't // support it yet. The expected behavior here is to respond with an // empty asnwer and not NXDOMAIN. if q.Qtype != dns.TypeA && q.Qtype != dns.TypeAAAA { return resultCodeSuccess } reqHost := strings.ToLower(q.Name) host := strings.TrimSuffix(reqHost, s.autohostSuffix) if host == reqHost { return resultCodeSuccess } // TODO(e.burkov): Restrict the access for external clients. ip, ok := s.hostToIP(host) if !ok { return resultCodeSuccess } log.Debug("dns: internal record: %s -> %s", q.Name, 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 empty answers to PTR requests for IP // addresses in locally-served network from external clients. func (s *Server) processRestrictLocal(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx req := d.Req q := req.Question[0] if q.Qtype != dns.TypePTR { // No need for restriction. return resultCodeSuccess } ip := aghnet.UnreverseAddr(q.Name) if ip == nil { // That's weird. // // TODO(e.burkov): Research the cases when it could happen. 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 unaccessable externally. if s.subnetDetector.IsLocallyServedNetwork(ip) { clientIP := IPFromAddr(d.Addr) if !s.subnetDetector.IsLocallyServedNetwork(clientIP) { log.Debug("dns: %q requests for internal ip", clientIP) d.Res = s.makeResponse(req) // Do not even put into query log. return resultCodeFinish } } // Do not perform unreversing ever again. ctx.unreversedReqIP = ip // Nothing to restrict. return resultCodeSuccess } // ipToHost tries to get a hostname leased by DHCP. It's safe for concurrent // use. func (s *Server) ipToHost(ip net.IP) (host string, ok bool) { s.tablePTRLock.Lock() defer s.tablePTRLock.Unlock() if s.tablePTR == nil { return "", false } host, ok = s.tablePTR[ip.String()] return host, ok } // Respond to PTR requests if the target IP is leased by our DHCP server and the // requestor is inside the local network. func (s *Server) processInternalIPAddrs(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess } ip := ctx.unreversedReqIP if ip == nil { return resultCodeSuccess } host, ok := s.ipToHost(ip) if !ok { return resultCodeSuccess } log.Debug("dns: reverse-lookup: %s -> %s", ip, host) req := d.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) d.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(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess } ip := ctx.unreversedReqIP if ip == nil { return resultCodeSuccess } if !s.subnetDetector.IsLocallyServedNetwork(ip) { return resultCodeSuccess } req := d.Req resp, err := s.localResolvers.Exchange(req) if err != nil { if errors.Is(err, aghnet.NoUpstreamsErr) { d.Res = s.genNXDomain(req) return resultCodeFinish } ctx.err = err return resultCodeError } d.Res = resp return resultCodeSuccess } // Apply filtering logic func processFilteringBeforeRequest(ctx *dnsContext) (rc resultCode) { s := ctx.srv d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess // response is already set - nothing to do } s.RLock() // Synchronize access to s.dnsFilter so it won't be suddenly uninitialized while in use. // This could happen after proxy server has been stopped, but its workers are not yet exited. // // A better approach is for proxy.Stop() to wait until all its workers exit, // but this would require the Upstream interface to have Close() function // (to prevent from hanging while waiting for unresponsive DNS server to respond). var err error ctx.protectionEnabled = s.conf.ProtectionEnabled && s.dnsFilter != nil if ctx.protectionEnabled { ctx.setts = s.getClientRequestFilteringSettings(ctx) ctx.result, err = s.filterDNSRequest(ctx) } s.RUnlock() if err != nil { ctx.err = err return resultCodeError } return resultCodeSuccess } // processUpstream passes request to upstream servers and handles the response. func processUpstream(ctx *dnsContext) (rc resultCode) { s := ctx.srv d := ctx.proxyCtx if d.Res != nil { return resultCodeSuccess // response is already set - nothing to do } if d.Addr != nil && s.conf.GetCustomUpstreamByClient != nil { clientIP := IPStringFromAddr(d.Addr) upstreamsConf := s.conf.GetCustomUpstreamByClient(clientIP) if upstreamsConf != nil { log.Debug("Using custom upstreams for %s", clientIP) d.CustomUpstreamConfig = upstreamsConf } } if s.conf.EnableDNSSEC { opt := d.Req.IsEdns0() if opt == nil { log.Debug("dns: Adding OPT record with DNSSEC flag") d.Req.SetEdns0(4096, true) } else if !opt.Do() { opt.SetDo(true) } else { ctx.origReqDNSSEC = true } } // request was not filtered so let it be processed further err := s.dnsProxy.Resolve(d) if err != nil { ctx.err = err return resultCodeError } ctx.responseFromUpstream = true return resultCodeSuccess } // Process DNSSEC after response from upstream server func processDNSSECAfterResponse(ctx *dnsContext) (rc resultCode) { d := ctx.proxyCtx if !ctx.responseFromUpstream || // don't process response if it's not from upstream servers !ctx.srv.conf.EnableDNSSEC { return resultCodeSuccess } if !ctx.origReqDNSSEC { optResp := d.Res.IsEdns0() if optResp != nil && !optResp.Do() { return resultCodeSuccess } // Remove RRSIG records from response // because there is no DO flag in the original request from client, // but we have EnableDNSSEC set, so we have set DO flag ourselves, // and now we have to clean up the DNS records our client didn't ask for. answers := []dns.RR{} for _, a := range d.Res.Answer { switch a.(type) { case *dns.RRSIG: log.Debug("Removing RRSIG record from response: %v", a) default: answers = append(answers, a) } } d.Res.Answer = answers answers = []dns.RR{} for _, a := range d.Res.Ns { switch a.(type) { case *dns.RRSIG: log.Debug("Removing RRSIG record from response: %v", a) default: answers = append(answers, a) } } d.Res.Ns = answers } return resultCodeSuccess } // Apply filtering logic after we have received response from upstream servers func processFilteringAfterResponse(ctx *dnsContext) (rc resultCode) { s := ctx.srv d := ctx.proxyCtx res := ctx.result var err error switch res.Reason { case dnsfilter.Rewritten, dnsfilter.RewrittenRule: if len(ctx.origQuestion.Name) == 0 { // origQuestion is set in case we get only CNAME without IP from rewrites table break } d.Req.Question[0] = ctx.origQuestion d.Res.Question[0] = ctx.origQuestion if len(d.Res.Answer) != 0 { answer := []dns.RR{} answer = append(answer, s.genAnswerCNAME(d.Req, res.CanonName)) answer = append(answer, d.Res.Answer...) d.Res.Answer = answer } case dnsfilter.NotFilteredAllowList: // nothing default: if !ctx.protectionEnabled || // filters are disabled: there's nothing to check for !ctx.responseFromUpstream { // only check response if it's from an upstream server break } origResp2 := d.Res ctx.result, err = s.filterDNSResponse(ctx) if err != nil { ctx.err = err return resultCodeError } if ctx.result != nil { ctx.origResp = origResp2 // matched by response } else { ctx.result = &dnsfilter.Result{} } } return resultCodeSuccess }