// Package dnsforward contains a DNS forwarding server. package dnsforward import ( "errors" "fmt" "net" "net/http" "os" "runtime" "strings" "sync" "time" "github.com/AdguardTeam/AdGuardHome/internal/agherr" "github.com/AdguardTeam/AdGuardHome/internal/aghnet" "github.com/AdguardTeam/AdGuardHome/internal/aghstrings" "github.com/AdguardTeam/AdGuardHome/internal/dhcpd" "github.com/AdguardTeam/AdGuardHome/internal/dnsfilter" "github.com/AdguardTeam/AdGuardHome/internal/querylog" "github.com/AdguardTeam/AdGuardHome/internal/stats" "github.com/AdguardTeam/dnsproxy/proxy" "github.com/AdguardTeam/golibs/log" "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" ) var defaultDNS = []string{ "https://dns10.quad9.net/dns-query", } var defaultBootstrap = []string{"9.9.9.10", "149.112.112.10", "2620:fe::10", "2620:fe::fe:10"} // Often requested by all kinds of DNS probes var defaultBlockedHosts = []string{"version.bind", "id.server", "hostname.bind"} var webRegistered bool // 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 dhcpServer dhcpd.ServerInterface // DHCP server instance (optional) queryLog querylog.QueryLog // Query log instance stats stats.Stats access *accessCtx // autohostSuffix is the suffix used to detect internal hosts. It must // be a valid top-level domain plus dots on each side. autohostSuffix string ipset ipsetCtx subnetDetector *aghnet.SubnetDetector localResolvers aghnet.Exchanger tableHostToIP map[string]net.IP // "hostname -> IP" table for internal addresses (DHCP) tableHostToIPLock sync.Mutex tablePTR map[string]string // "IP -> hostname" table for reverse lookup tablePTRLock sync.Mutex // DNS proxy instance for internal usage // We don't Start() it and so no listen port is required. internalProxy *proxy.Proxy isRunning bool sync.RWMutex conf ServerConfig } // defaultAutohostSuffix is the default suffix used to detect internal hosts // when no suffix is provided. See the documentation for Server.autohostSuffix. const defaultAutohostSuffix = ".lan." // DNSCreateParams are parameters to create a new server. type DNSCreateParams struct { DNSFilter *dnsfilter.DNSFilter Stats stats.Stats QueryLog querylog.QueryLog DHCPServer dhcpd.ServerInterface SubnetDetector *aghnet.SubnetDetector AutohostTLD string } // tldToSuffix converts a top-level domain into an autohost suffix. func tldToSuffix(tld string) (suffix string) { l := len(tld) + 2 b := make([]byte, l) b[0] = '.' copy(b[1:], tld) b[l-1] = '.' return string(b) } // NewServer creates a new instance of the dnsforward.Server // Note: this function must be called only once func NewServer(p DNSCreateParams) (s *Server, err error) { var autohostSuffix string if p.AutohostTLD == "" { autohostSuffix = defaultAutohostSuffix } else { err = aghnet.ValidateDomainNameLabel(p.AutohostTLD) if err != nil { return nil, fmt.Errorf("autohost tld: %w", err) } autohostSuffix = tldToSuffix(p.AutohostTLD) } s = &Server{ dnsFilter: p.DNSFilter, stats: p.Stats, queryLog: p.QueryLog, subnetDetector: p.SubnetDetector, autohostSuffix: autohostSuffix, } if p.DHCPServer != nil { s.dhcpServer = p.DHCPServer s.dhcpServer.SetOnLeaseChanged(s.onDHCPLeaseChanged) s.onDHCPLeaseChanged(dhcpd.LeaseChangedAdded) } if runtime.GOARCH == "mips" || runtime.GOARCH == "mipsle" { // Use plain DNS on MIPS, encryption is too slow defaultDNS = defaultBootstrap } return s, nil } // NewCustomServer creates a new instance of *Server with custom internal proxy. func NewCustomServer(internalProxy *proxy.Proxy) *Server { s := &Server{} if internalProxy != nil { s.internalProxy = internalProxy } return s } // Close - close object func (s *Server) Close() { s.Lock() s.dnsFilter = nil s.stats = nil s.queryLog = nil s.dnsProxy = nil err := s.ipset.Close() if err != nil { log.Error("closing ipset: %s", err) } s.Unlock() } // WriteDiskConfig - write configuration func (s *Server) WriteDiskConfig(c *FilteringConfig) { s.RLock() sc := s.conf.FilteringConfig *c = sc c.RatelimitWhitelist = aghstrings.CloneSlice(sc.RatelimitWhitelist) c.BootstrapDNS = aghstrings.CloneSlice(sc.BootstrapDNS) c.AllowedClients = aghstrings.CloneSlice(sc.AllowedClients) c.DisallowedClients = aghstrings.CloneSlice(sc.DisallowedClients) c.BlockedHosts = aghstrings.CloneSlice(sc.BlockedHosts) c.UpstreamDNS = aghstrings.CloneSlice(sc.UpstreamDNS) s.RUnlock() } // RDNSSettings returns the copy of actual RDNS configuration. func (s *Server) RDNSSettings() (localPTRResolvers []string, resolveClients bool) { s.RLock() defer s.RUnlock() return aghstrings.CloneSlice(s.conf.LocalPTRResolvers), s.conf.ResolveClients } // Resolve - get IP addresses by host name from an upstream server. // No request/response filtering is performed. // Query log and Stats are not updated. // This method may be called before Start(). func (s *Server) Resolve(host string) ([]net.IPAddr, error) { s.RLock() defer s.RUnlock() return s.internalProxy.LookupIPAddr(host) } // RDNSExchanger is a resolver for clients' addresses. type RDNSExchanger interface { // Exchange tries to resolve the ip in a suitable way, e.g. either as // local or as external. Exchange(ip net.IP) (host string, err error) } const ( // rDNSEmptyAnswerErr is returned by Exchange method when the answer // section of respond is empty. rDNSEmptyAnswerErr agherr.Error = "the answer section is empty" // rDNSNotPTRErr is returned by Exchange method when the response is not // of PTR type. rDNSNotPTRErr agherr.Error = "the response is not a ptr" ) // Exchange implements the RDNSExchanger interface for *Server. func (s *Server) Exchange(ip net.IP) (host string, err error) { s.RLock() defer s.RUnlock() if !s.conf.ResolveClients { return "", nil } arpa := dns.Fqdn(aghnet.ReverseAddr(ip)) req := &dns.Msg{ MsgHdr: dns.MsgHdr{ Id: dns.Id(), RecursionDesired: true, }, Compress: true, Question: []dns.Question{{ Name: arpa, Qtype: dns.TypePTR, Qclass: dns.ClassINET, }}, } var resp *dns.Msg if s.subnetDetector.IsLocallyServedNetwork(ip) { resp, err = s.localResolvers.Exchange(req) } else { ctx := &proxy.DNSContext{ Proto: "udp", Req: req, StartTime: time.Now(), } err = s.internalProxy.Resolve(ctx) resp = ctx.Res } if err != nil { return "", err } if len(resp.Answer) == 0 { return "", fmt.Errorf("lookup for %q: %w", arpa, rDNSEmptyAnswerErr) } ptr, ok := resp.Answer[0].(*dns.PTR) if !ok { return "", fmt.Errorf("type checking: %w", rDNSNotPTRErr) } return strings.TrimSuffix(ptr.Ptr, "."), nil } // Start starts the DNS server. func (s *Server) Start() error { s.Lock() defer s.Unlock() return s.startLocked() } // startLocked starts the DNS server without locking. For internal use only. func (s *Server) startLocked() error { err := s.dnsProxy.Start() if err == nil { s.isRunning = true } return err } // defaultLocalTimeout is the default timeout for resolving addresses from // locally-served networks. It is assumed that local resolvers should work much // faster than ordinary upstreams. const defaultLocalTimeout = 1 * time.Second // collectDNSIPAddrs returns the slice of IP addresses without port number which // we are listening on. For internal use only. func (s *Server) collectDNSIPAddrs() (addrs []string, err error) { addrs = make([]string, len(s.conf.TCPListenAddrs)+len(s.conf.UDPListenAddrs)) var i int var ip net.IP for _, addr := range s.conf.TCPListenAddrs { if addr == nil { continue } if ip = addr.IP; ip.IsUnspecified() { return aghnet.CollectAllIfacesAddrs() } addrs[i] = ip.String() i++ } for _, addr := range s.conf.UDPListenAddrs { if addr == nil { continue } if ip = addr.IP; ip.IsUnspecified() { return aghnet.CollectAllIfacesAddrs() } addrs[i] = ip.String() i++ } return addrs[:i], nil } // stringSetSubtract subtracts b from a interpreted as sets. func stringSetSubtract(a, b []string) (c []string) { // unit is an object to be used as value in set. type unit = struct{} cSet := make(map[string]unit) for _, k := range a { cSet[k] = unit{} } for _, k := range b { delete(cSet, k) } c = make([]string, len(cSet)) i := 0 for k := range cSet { c[i] = k i++ } return c } // setupResolvers initializes the resolvers for local addresses. For internal // use only. func (s *Server) setupResolvers(localAddrs []string) (err error) { bootstraps := s.conf.BootstrapDNS if len(localAddrs) == 0 { var sysRes aghnet.SystemResolvers // TODO(e.burkov): Enable the refresher after the actual // implementation passes the public testing. sysRes, err = aghnet.NewSystemResolvers(0, nil) if err != nil { return err } localAddrs = sysRes.Get() bootstraps = nil } log.Debug("upstreams to resolve PTR for local addresses: %v", localAddrs) var ourAddrs []string ourAddrs, err = s.collectDNSIPAddrs() if err != nil { return err } // TODO(e.burkov): The approach of subtracting sets of strings // is not really applicable here since in case of listening on // all network interfaces we should check the whole interface's // network to cut off all the loopback addresses as well. localAddrs = stringSetSubtract(localAddrs, ourAddrs) if s.localResolvers, err = aghnet.NewMultiAddrExchanger( localAddrs, bootstraps, defaultLocalTimeout, ); err != nil { return err } return nil } // Prepare the object func (s *Server) Prepare(config *ServerConfig) error { // Initialize the server configuration // -- if config != nil { s.conf = *config if s.conf.BlockingMode == "custom_ip" { if s.conf.BlockingIPv4 == nil || s.conf.BlockingIPv6 == nil { return fmt.Errorf("dns: invalid custom blocking IP address specified") } } } // Set default values in the case if nothing is configured // -- s.initDefaultSettings() // Initialize IPSET configuration // -- err := s.ipset.init(s.conf.IPSETList) if err != nil { if !errors.Is(err, os.ErrInvalid) && !errors.Is(err, os.ErrPermission) { return fmt.Errorf("cannot initialize ipset: %w", err) } // ipset cannot currently be initialized if the server was // installed from Snap or when the user or the binary doesn't // have the required permissions, or when the kernel doesn't // support netfilter. // // Log and go on. // // TODO(a.garipov): The Snap problem can probably be solved if // we add the netlink-connector interface plug. log.Error("cannot initialize ipset: %s", err) } // Prepare DNS servers settings // -- err = s.prepareUpstreamSettings() if err != nil { return err } // Create DNS proxy configuration // -- var proxyConfig proxy.Config proxyConfig, err = s.createProxyConfig() if err != nil { return err } // Prepare a DNS proxy instance that we use for internal DNS queries // -- s.prepareIntlProxy() // Initialize DNS access module // -- s.access = &accessCtx{} err = s.access.Init(s.conf.AllowedClients, s.conf.DisallowedClients, s.conf.BlockedHosts) if err != nil { return err } // Register web handlers if necessary // -- if !webRegistered && s.conf.HTTPRegister != nil { webRegistered = true s.registerHandlers() } // Create the main DNS proxy instance // -- s.dnsProxy = &proxy.Proxy{Config: proxyConfig} err = s.setupResolvers(s.conf.LocalPTRResolvers) if err != nil { return fmt.Errorf("setting up resolvers: %w", err) } return nil } // Stop stops the DNS server. func (s *Server) Stop() error { s.Lock() defer s.Unlock() return s.stopLocked() } // stopLocked stops the DNS server without locking. For internal use only. func (s *Server) stopLocked() error { if s.dnsProxy != nil { err := s.dnsProxy.Stop() if err != nil { return fmt.Errorf("could not stop the DNS server properly: %w", err) } } s.isRunning = false return nil } // IsRunning returns true if the DNS server is running func (s *Server) IsRunning() bool { s.RLock() defer s.RUnlock() return s.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.stopLocked() if err != nil { return fmt.Errorf("could not reconfigure the server: %w", err) } // It seems that net.Listener.Close() doesn't close file descriptors right away. // We wait for some time and hope that this fd will be closed. time.Sleep(100 * time.Millisecond) err = s.Prepare(config) if err != nil { return fmt.Errorf("could not reconfigure the server: %w", err) } err = s.startLocked() if err != nil { return fmt.Errorf("could not reconfigure the server: %w", err) } return nil } // ServeHTTP is a HTTP handler method we use to provide DNS-over-HTTPS func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) { s.RLock() p := s.dnsProxy s.RUnlock() if p != nil { // an attempt to protect against race in case we're here after Close() was called p.ServeHTTP(w, r) } } // IsBlockedIP - return TRUE if this client should be blocked func (s *Server) IsBlockedIP(ip net.IP) (bool, string) { if ip == nil { return false, "" } return s.access.IsBlockedIP(ip) }