Add dns forwarding server library

2018-11-28 15:40:56 +03:00
parent 39eccc62b1
commit 5a548be16c
8 changed files with 1216 additions and 0 deletions
--- a/dnsforward/dnsforward.go
+++ b/dnsforward/dnsforward.go
@@ -0,0 +1,467 @@
+package dnsforward
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"reflect"
+	"sync"
+
+	"github.com/AdguardTeam/AdGuardHome/dnsfilter"
+	"github.com/joomcode/errorx"
+	"github.com/miekg/dns"
+)
+
+// 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 {
+	udpListen *net.UDPConn
+
+	dnsFilter *dnsfilter.Dnsfilter
+
+	cache cache
+
+	sync.RWMutex
+	ServerConfig
+}
+
+// The zero ServerConfig is empty and ready for use.
+type ServerConfig struct {
+	UDPListenAddr *net.UDPAddr // if nil, then default is is used (port 53 on *)
+	BlockedTTL    uint32       // if 0, then default is used (3600)
+	Upstreams     []Upstream
+	Filters       []Filter
+}
+
+var defaultValues = ServerConfig{
+	UDPListenAddr: &net.UDPAddr{Port: 53},
+	BlockedTTL:    3600,
+	Upstreams: []Upstream{
+		//// dns over HTTPS
+		// &dnsOverHTTPS{Address: "https://1.1.1.1/dns-query"},
+		// &dnsOverHTTPS{Address: "https://dns.google.com/experimental"},
+		// &dnsOverHTTPS{Address: "https://doh.cleanbrowsing.org/doh/security-filter/"},
+		// &dnsOverHTTPS{Address: "https://dns10.quad9.net/dns-query"},
+		// &dnsOverHTTPS{Address: "https://doh.powerdns.org"},
+		// &dnsOverHTTPS{Address: "https://doh.securedns.eu/dns-query"},
+
+		//// dns over TLS
+		// &dnsOverTLS{Address: "tls://8.8.8.8:853"},
+		// &dnsOverTLS{Address: "tls://8.8.4.4:853"},
+		&dnsOverTLS{Address: "tls://1.1.1.1:853"},
+		&dnsOverTLS{Address: "tls://1.0.0.1:853"},
+
+		//// plainDNS
+		// &plainDNS{Address: "8.8.8.8:53"},
+		// &plainDNS{Address: "8.8.4.4:53"},
+		// &plainDNS{Address: "1.1.1.1:53"},
+		// &plainDNS{Address: "1.0.0.1:53"},
+	},
+}
+
+type Filter struct {
+	ID    int64
+	Rules []string
+}
+
+//
+// packet loop
+//
+func (s *Server) packetLoop() {
+	log.Printf("Entering packet handle loop")
+	b := make([]byte, dns.MaxMsgSize)
+	for {
+		s.RLock()
+		conn := s.udpListen
+		s.RUnlock()
+		if conn == nil {
+			log.Printf("udp socket has disappeared, exiting loop")
+			break
+		}
+		n, addr, err := conn.ReadFrom(b)
+		// documentation says to handle the packet even if err occurs, so do that first
+		if n > 0 {
+			// make a copy of all bytes because ReadFrom() will overwrite contents of b on next call
+			// we need the contents to survive the call because we're handling them in goroutine
+			p := make([]byte, n)
+			copy(p, b)
+			go s.handlePacket(p, addr, conn) // ignore errors
+		}
+		if err != nil {
+			if isConnClosed(err) {
+				log.Printf("ReadFrom() returned because we're reading from a closed connection, exiting loop")
+				break
+			}
+			log.Printf("Got error when reading from udp listen: %s", err)
+		}
+	}
+}
+
+//
+// Control functions
+//
+
+func (s *Server) Start(config *ServerConfig) error {
+	s.Lock()
+	defer s.Unlock()
+	if config != nil {
+		s.ServerConfig = *config
+	}
+	// TODO: handle being called Start() second time after Stop()
+	if s.udpListen == nil {
+		log.Printf("Creating UDP socket")
+		var err error
+		addr := s.UDPListenAddr
+		if addr == nil {
+			addr = defaultValues.UDPListenAddr
+		}
+		s.udpListen, err = net.ListenUDP("udp", addr)
+		if err != nil {
+			return errorx.Decorate(err, "Couldn't listen to UDP socket")
+		}
+		log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
+	}
+
+	if s.dnsFilter == nil {
+		log.Printf("Creating dnsfilter")
+		s.dnsFilter = dnsfilter.New()
+	}
+
+	go s.packetLoop()
+
+	return nil
+}
+
+func (s *Server) Stop() error {
+	s.Lock()
+	defer s.Unlock()
+	if s.udpListen != nil {
+		err := s.udpListen.Close()
+		if err != nil {
+			return errorx.Decorate(err, "Couldn't close UDP listening socket")
+		}
+		s.udpListen = nil
+	}
+	return nil
+}
+
+//
+// Server reconfigure
+//
+
+func (s *Server) reconfigureListenAddr(new ServerConfig) error {
+	oldAddr := s.UDPListenAddr
+	if oldAddr == nil {
+		oldAddr = defaultValues.UDPListenAddr
+	}
+	newAddr := new.UDPListenAddr
+	if newAddr == nil {
+		newAddr = defaultValues.UDPListenAddr
+	}
+	if newAddr.Port == 0 {
+		return errorx.IllegalArgument.New("new port cannot be 0")
+	}
+	if reflect.DeepEqual(oldAddr, newAddr) {
+		// do nothing, the addresses are exactly the same
+		log.Printf("Not going to rebind because addresses are same: %v -> %v", oldAddr, newAddr)
+		return nil
+	}
+
+	// rebind, using a strategy:
+	// * if ports are different, bind new first, then close old
+	// * if ports are same, close old first, then bind new
+	var newListen *net.UDPConn
+	var err error
+	if oldAddr.Port != newAddr.Port {
+		log.Printf("Rebinding -- ports are different so bind first then close")
+		newListen, err = net.ListenUDP("udp", newAddr)
+		if err != nil {
+			return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
+		}
+		if s.udpListen != nil {
+			err := s.udpListen.Close()
+			if err != nil {
+				return errorx.Decorate(err, "Couldn't close UDP listening socket")
+			}
+		}
+	} else {
+		log.Printf("Rebinding -- ports are same so close first then bind")
+		if s.udpListen != nil {
+			err := s.udpListen.Close()
+			if err != nil {
+				return errorx.Decorate(err, "Couldn't close UDP listening socket")
+			}
+		}
+		newListen, err = net.ListenUDP("udp", newAddr)
+		if err != nil {
+			return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
+		}
+	}
+	s.Lock()
+	s.udpListen = newListen
+	s.UDPListenAddr = new.UDPListenAddr
+	s.Unlock()
+	log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
+
+	go s.packetLoop() // the old one has quit, use new one
+
+	return nil
+}
+
+func (s *Server) reconfigureBlockedTTL(new ServerConfig) {
+	newVal := new.BlockedTTL
+	if newVal == 0 {
+		newVal = defaultValues.BlockedTTL
+	}
+	oldVal := s.BlockedTTL
+	if oldVal == 0 {
+		oldVal = defaultValues.BlockedTTL
+	}
+	if newVal != oldVal {
+		s.BlockedTTL = new.BlockedTTL
+	}
+}
+
+func (s *Server) reconfigureUpstreams(new ServerConfig) {
+	newVal := new.Upstreams
+	if len(newVal) == 0 {
+		newVal = defaultValues.Upstreams
+	}
+	oldVal := s.Upstreams
+	if len(oldVal) == 0 {
+		oldVal = defaultValues.Upstreams
+	}
+	if reflect.DeepEqual(newVal, oldVal) {
+		// they're exactly the same, do nothing
+		return
+	}
+	s.Upstreams = new.Upstreams
+}
+
+func (s *Server) reconfigureFilters(new ServerConfig) {
+	newFilters := new.Filters
+	if len(newFilters) == 0 {
+		newFilters = defaultValues.Filters
+	}
+	oldFilters := s.Filters
+	if len(oldFilters) == 0 {
+		oldFilters = defaultValues.Filters
+	}
+	if reflect.DeepEqual(newFilters, oldFilters) {
+		// they're exactly the same, do nothing
+		return
+	}
+
+	dnsFilter := dnsfilter.New()
+	for _, f := range newFilters {
+		for _, rule := range f.Rules {
+			err := dnsFilter.AddRule(rule, f.ID)
+			if err == dnsfilter.ErrAlreadyExists || err == dnsfilter.ErrInvalidSyntax {
+				continue
+			}
+			if err != nil {
+				log.Printf("Cannot add rule %s: %s", rule, err)
+				// Just ignore invalid rules
+				continue
+			}
+		}
+	}
+
+	s.Lock()
+	oldDnsFilter := s.dnsFilter
+	s.dnsFilter = dnsFilter
+	s.Unlock()
+
+	oldDnsFilter.Destroy()
+}
+
+func (s *Server) Reconfigure(new ServerConfig) error {
+	s.reconfigureBlockedTTL(new)
+	s.reconfigureUpstreams(new)
+	s.reconfigureFilters(new)
+
+	err := s.reconfigureListenAddr(new)
+	if err != nil {
+		return errorx.Decorate(err, "Couldn't reconfigure to new listening address %+v", new.UDPListenAddr)
+	}
+	return nil
+}
+
+//
+// packet handling functions
+//
+
+func (s *Server) handlePacket(p []byte, addr net.Addr, conn *net.UDPConn) {
+	// log.Printf("Got packet %d bytes from %s: %v", len(p), addr, p)
+	msg := dns.Msg{}
+	err := msg.Unpack(p)
+	if err != nil {
+		log.Printf("failed to unpack DNS packet: %s", err)
+		return
+	}
+
+	//
+	// DNS packet byte format is valid
+	//
+	// any errors below here require a response to client
+	// log.Printf("Unpacked: %v", msg.String())
+	if len(msg.Question) != 1 {
+		log.Printf("Got invalid number of questions: %v", len(msg.Question))
+		err := s.respondWithServerFailure(&msg, addr, conn)
+		if err != nil {
+			log.Printf("Couldn't respond to UDP packet: %s", err)
+			return
+		}
+	}
+
+	{
+		val, ok := s.cache.Get(&msg)
+		if ok && val != nil {
+			err = s.respond(val, addr, conn)
+			if err != nil {
+				if isConnClosed(err) {
+					// ignore this error, the connection was closed and that's ok
+					return
+				}
+				log.Printf("Couldn't respond to UDP packet: %s", err)
+				return
+			}
+			return
+		}
+	}
+	host := msg.Question[0].Name
+	res, err := s.dnsFilter.CheckHost(host)
+	if err != nil {
+		log.Printf("dnsfilter failed to check host '%s': %s", host, err)
+		err := s.respondWithServerFailure(&msg, addr, conn)
+		if err != nil {
+			log.Printf("Couldn't respond to UDP packet: %s", err)
+			return
+		}
+	} else if res.IsFiltered {
+		log.Printf("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule)
+		err := s.respondWithNXDomain(&msg, addr, conn)
+		if err != nil {
+			log.Printf("Couldn't respond to UDP packet: %s", err)
+			return
+		}
+	}
+
+	// TODO: replace with single-socket implementation
+	// TODO: replace 8.8.8.8:53 with configurable upstreams
+	// TODO: support DoH, DoT and TCP
+	upstream := s.chooseUpstream()
+	reply, err := upstream.Exchange(&msg)
+	if err != nil {
+		log.Printf("talking to upstream failed for host '%s': %s", host, err)
+		err := s.respondWithServerFailure(&msg, addr, conn)
+		if err != nil {
+			if isConnClosed(err) {
+				// ignore this error, the connection was closed and that's ok
+				return
+			}
+			log.Printf("Couldn't respond to UDP packet with server failure: %s", err)
+			return
+		}
+		return
+	}
+	if reply == nil {
+		log.Printf("SHOULD NOT HAPPEN upstream returned empty message for host '%s'. Request is %v", host, msg.String())
+		err := s.respondWithServerFailure(&msg, addr, conn)
+		if err != nil {
+			log.Printf("Couldn't respond to UDP packet with should not happen: %s", err)
+			return
+		}
+		return
+	}
+
+	err = s.respond(reply, addr, conn)
+	if err != nil {
+		if isConnClosed(err) {
+			// ignore this error, the connection was closed and that's ok
+			return
+		}
+		log.Printf("Couldn't respond to UDP packet: %s", err)
+		return
+	}
+
+	s.cache.Set(reply)
+}
+
+//
+// packet sending functions
+//
+
+func (s *Server) respond(resp *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
+	// log.Printf("Replying to %s with %s", addr, resp)
+	resp.Compress = true
+	bytes, err := resp.Pack()
+	if err != nil {
+		return errorx.Decorate(err, "Couldn't convert message into wire format")
+	}
+	n, err := conn.WriteTo(bytes, addr)
+	if n == 0 && isConnClosed(err) {
+		return err
+	}
+	if n != len(bytes) {
+		return fmt.Errorf("WriteTo() returned with %d != %d", n, len(bytes))
+	}
+	if err != nil {
+		return errorx.Decorate(err, "WriteTo() returned error")
+	}
+	return nil
+}
+
+func (s *Server) respondWithServerFailure(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
+	resp := dns.Msg{}
+	resp.SetRcode(request, dns.RcodeServerFailure)
+	return s.respond(&resp, addr, conn)
+}
+
+func (s *Server) respondWithNXDomain(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
+	resp := dns.Msg{}
+	resp.SetRcode(request, dns.RcodeNameError)
+	resp.Ns = s.genSOA(request)
+	return s.respond(&resp, addr, conn)
+}
+
+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.BlockedTTL,
+			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.BlockedTTL
+	}
+	if len(zone) > 0 && zone[0] != '.' {
+		soa.Mbox += zone
+	}
+	return []dns.RR{&soa}
+}