package dnsforward import ( "errors" "fmt" "log" "net" "strings" "sync" "time" "github.com/AdguardTeam/AdGuardHome/dnsfilter" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/dnsproxy/upstream" "github.com/joomcode/errorx" "github.com/miekg/dns" ) // DefaultTimeout is the default upstream timeout const DefaultTimeout = 10 * time.Second const ( safeBrowsingBlockHost = "standard-block.dns.adguard.com" parentalBlockHost = "family-block.dns.adguard.com" ) // Server is the main way to start a DNS server. // // Example: // s := dnsforward.Server{} // err := s.Start(nil) // will start a DNS server listening on default port 53, in a goroutine // err := s.Reconfigure(ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}}) // will reconfigure running DNS server to listen on UDP port 53535 // err := s.Stop() // will stop listening on port 53535 and cancel all goroutines // err := s.Start(nil) // will start listening again, on port 53535, in a goroutine // // The zero Server is empty and ready for use. type Server struct { dnsProxy *proxy.Proxy // DNS proxy instance dnsFilter *dnsfilter.Dnsfilter // DNS filter instance sync.RWMutex ServerConfig } // FilteringConfig represents the DNS filtering configuration of AdGuard Home type FilteringConfig struct { ProtectionEnabled bool `yaml:"protection_enabled"` // whether or not use any of dnsfilter features FilteringEnabled bool `yaml:"filtering_enabled"` // whether or not use filter lists BlockedResponseTTL uint32 `yaml:"blocked_response_ttl"` // if 0, then default is used (3600) QueryLogEnabled bool `yaml:"querylog_enabled"` Ratelimit int `yaml:"ratelimit"` RatelimitWhitelist []string `yaml:"ratelimit_whitelist"` RefuseAny bool `yaml:"refuse_any"` BootstrapDNS string `yaml:"bootstrap_dns"` dnsfilter.Config `yaml:",inline"` } // ServerConfig represents server configuration. // The zero ServerConfig is empty and ready for use. type ServerConfig struct { UDPListenAddr *net.UDPAddr // UDP listen address Upstreams []upstream.Upstream // Configured upstreams Filters []dnsfilter.Filter // A list of filters to use FilteringConfig } // if any of ServerConfig values are zero, then default values from below are used var defaultValues = ServerConfig{ UDPListenAddr: &net.UDPAddr{Port: 53}, FilteringConfig: FilteringConfig{BlockedResponseTTL: 3600}, } func init() { defaultDNS := []string{"8.8.8.8:53", "8.8.4.4:53"} defaultUpstreams := make([]upstream.Upstream, 0) for _, addr := range defaultDNS { u, err := upstream.AddressToUpstream(addr, "", DefaultTimeout) if err == nil { defaultUpstreams = append(defaultUpstreams, u) } } defaultValues.Upstreams = defaultUpstreams } // Start starts the DNS server func (s *Server) Start(config *ServerConfig) error { s.Lock() defer s.Unlock() return s.startInternal(config) } // startInternal starts without locking func (s *Server) startInternal(config *ServerConfig) error { if config != nil { s.ServerConfig = *config } if s.dnsFilter != nil || s.dnsProxy != nil { return errors.New("DNS server is already started") } err := s.initDNSFilter() if err != nil { return err } log.Printf("Loading stats from querylog") err = fillStatsFromQueryLog() if err != nil { return errorx.Decorate(err, "failed to load stats from querylog") } once.Do(func() { go periodicQueryLogRotate() go periodicHourlyTopRotate() go statsRotator() }) // TODO: Add TCPListenAddr proxyConfig := proxy.Config{ UDPListenAddr: s.UDPListenAddr, Ratelimit: s.Ratelimit, RatelimitWhitelist: s.RatelimitWhitelist, RefuseAny: s.RefuseAny, CacheEnabled: true, Upstreams: s.Upstreams, Handler: s.handleDNSRequest, } if proxyConfig.UDPListenAddr == nil { proxyConfig.UDPListenAddr = defaultValues.UDPListenAddr } if len(proxyConfig.Upstreams) == 0 { proxyConfig.Upstreams = defaultValues.Upstreams } // Initialize and start the DNS proxy s.dnsProxy = &proxy.Proxy{Config: proxyConfig} return s.dnsProxy.Start() } // Initializes the DNS filter func (s *Server) initDNSFilter() error { log.Printf("Creating dnsfilter") s.dnsFilter = dnsfilter.New(&s.Config) // add rules only if they are enabled if s.FilteringEnabled { err := s.dnsFilter.AddRules(s.Filters) if err != nil { return errorx.Decorate(err, "could not initialize dnsfilter") } } return nil } // Stop stops the DNS server func (s *Server) Stop() error { s.Lock() defer s.Unlock() return s.stopInternal() } // stopInternal stops without locking func (s *Server) stopInternal() error { if s.dnsProxy != nil { err := s.dnsProxy.Stop() s.dnsProxy = nil if err != nil { return errorx.Decorate(err, "could not stop the DNS server properly") } } if s.dnsFilter != nil { s.dnsFilter.Destroy() s.dnsFilter = nil } // flush remainder to file logBufferLock.Lock() flushBuffer := logBuffer logBuffer = nil logBufferLock.Unlock() err := flushToFile(flushBuffer) if err != nil { log.Printf("Saving querylog to file failed: %s", err) return err } return nil } // IsRunning returns true if the DNS server is running func (s *Server) IsRunning() bool { s.RLock() isRunning := true if s.dnsProxy == nil { isRunning = false } s.RUnlock() return isRunning } // Reconfigure applies the new configuration to the DNS server func (s *Server) Reconfigure(config *ServerConfig) error { s.Lock() defer s.Unlock() log.Print("Start reconfiguring the server") err := s.stopInternal() if err != nil { return errorx.Decorate(err, "could not reconfigure the server") } err = s.startInternal(config) if err != nil { return errorx.Decorate(err, "could not reconfigure the server") } return nil } // handleDNSRequest filters the incoming DNS requests and writes them to the query log func (s *Server) handleDNSRequest(p *proxy.Proxy, d *proxy.DNSContext) error { start := time.Now() // use dnsfilter before cache -- changed settings or filters would require cache invalidation otherwise res, err := s.filterDNSRequest(d) if err != nil { return err } if d.Res == nil { // request was not filtered so let it be processed further err = p.Resolve(d) if err != nil { return err } } shouldLog := true msg := d.Req // don't log ANY request if refuseAny is enabled if len(msg.Question) >= 1 && msg.Question[0].Qtype == dns.TypeANY && s.RefuseAny { shouldLog = false } if s.QueryLogEnabled && shouldLog { elapsed := time.Since(start) upstreamAddr := "" if d.Upstream != nil { upstreamAddr = d.Upstream.Address() } logRequest(msg, d.Res, res, elapsed, d.Addr, upstreamAddr) } return nil } // filterDNSRequest applies the dnsFilter and sets d.Res if the request was filtered func (s *Server) filterDNSRequest(d *proxy.DNSContext) (*dnsfilter.Result, error) { msg := d.Req host := strings.TrimSuffix(msg.Question[0].Name, ".") s.RLock() protectionEnabled := s.ProtectionEnabled dnsFilter := s.dnsFilter s.RUnlock() if !protectionEnabled { return nil, nil } var res dnsfilter.Result var err error res, err = dnsFilter.CheckHost(host) if err != nil { // Return immediately if there's an error return nil, errorx.Decorate(err, "dnsfilter failed to check host '%s'", host) } else if res.IsFiltered { // trace("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule) d.Res = s.genDNSFilterMessage(d, &res) } return &res, err } // 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 { return s.genNXDomain(m) } switch result.Reason { case dnsfilter.FilteredSafeBrowsing: return s.genBlockedHost(m, safeBrowsingBlockHost, d.Upstream) case dnsfilter.FilteredParental: return s.genBlockedHost(m, parentalBlockHost, d.Upstream) default: if result.Ip != nil { return s.genARecord(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 := dns.Msg{} resp.SetReply(request) answer, err := dns.NewRR(fmt.Sprintf("%s %d A %s", request.Question[0].Name, s.BlockedResponseTTL, ip.String())) if err != nil { log.Printf("Couldn't generate A record for replacement host '%s': %s", ip.String(), err) return s.genServerFailure(request) } resp.Answer = append(resp.Answer, answer) return &resp } func (s *Server) genBlockedHost(request *dns.Msg, newAddr string, upstream upstream.Upstream) *dns.Msg { // look up the hostname, TODO: cache replReq := dns.Msg{} replReq.SetQuestion(dns.Fqdn(newAddr), request.Question[0].Qtype) replReq.RecursionDesired = true reply, err := upstream.Exchange(&replReq) if err != nil { log.Printf("Couldn't look up replacement host '%s' on upstream %s: %s", newAddr, upstream.Address(), err) return s.genServerFailure(request) } resp := dns.Msg{} resp.SetReply(request) resp.Authoritative, resp.RecursionAvailable = true, true if reply != nil { for _, answer := range reply.Answer { answer.Header().Name = request.Question[0].Name resp.Answer = append(resp.Answer, answer) } } return &resp } 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.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} } var once sync.Once