495 lines
12 KiB
Go
495 lines
12 KiB
Go
package dnsforward
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import (
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"fmt"
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"log"
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"net"
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"reflect"
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"sync"
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"github.com/AdguardTeam/AdGuardHome/dnsfilter"
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"github.com/joomcode/errorx"
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"github.com/miekg/dns"
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)
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// Server is the main way to start a DNS server
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// Example:
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// s := dnsforward.Server{}
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// err := s.Start(nil) // will start a DNS server listening on default port 53, in a goroutine
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// err := s.Reconfigure(ServerConfig{UDPListenAddr: &net.UDPAddr{Port: 53535}}) // will reconfigure running DNS server to listen on UDP port 53535
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// err := s.Stop() // will stop listening on port 53535 and cancel all goroutines
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// err := s.Start(nil) // will start listening again, on port 53535, in a goroutine
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//
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// The zero Server is empty and ready for use.
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type Server struct {
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udpListen *net.UDPConn
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dnsFilter *dnsfilter.Dnsfilter
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cache cache
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sync.RWMutex
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ServerConfig
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}
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// The zero ServerConfig is empty and ready for use.
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type ServerConfig struct {
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UDPListenAddr *net.UDPAddr // if nil, then default is is used (port 53 on *)
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BlockedTTL uint32 // if 0, then default is used (3600)
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Upstreams []Upstream
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Filters []Filter
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}
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var defaultValues = ServerConfig{
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UDPListenAddr: &net.UDPAddr{Port: 53},
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BlockedTTL: 3600,
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Upstreams: []Upstream{
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//// dns over HTTPS
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// &dnsOverHTTPS{Address: "https://1.1.1.1/dns-query"},
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// &dnsOverHTTPS{Address: "https://dns.google.com/experimental"},
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// &dnsOverHTTPS{Address: "https://doh.cleanbrowsing.org/doh/security-filter/"},
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// &dnsOverHTTPS{Address: "https://dns10.quad9.net/dns-query"},
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// &dnsOverHTTPS{Address: "https://doh.powerdns.org"},
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// &dnsOverHTTPS{Address: "https://doh.securedns.eu/dns-query"},
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//// dns over TLS
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// &dnsOverTLS{Address: "tls://8.8.8.8:853"},
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// &dnsOverTLS{Address: "tls://8.8.4.4:853"},
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// &dnsOverTLS{Address: "tls://1.1.1.1:853"},
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// &dnsOverTLS{Address: "tls://1.0.0.1:853"},
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//// plainDNS
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&plainDNS{Address: "8.8.8.8:53"},
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&plainDNS{Address: "8.8.4.4:53"},
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&plainDNS{Address: "1.1.1.1:53"},
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&plainDNS{Address: "1.0.0.1:53"},
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},
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}
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type Filter struct {
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ID int64
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Rules []string
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}
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//
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// packet loop
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//
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func (s *Server) packetLoop() {
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log.Printf("Entering packet handle loop")
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b := make([]byte, dns.MaxMsgSize)
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for {
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s.RLock()
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conn := s.udpListen
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s.RUnlock()
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if conn == nil {
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log.Printf("udp socket has disappeared, exiting loop")
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break
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}
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n, addr, err := conn.ReadFrom(b)
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// documentation says to handle the packet even if err occurs, so do that first
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if n > 0 {
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// make a copy of all bytes because ReadFrom() will overwrite contents of b on next call
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// we need the contents to survive the call because we're handling them in goroutine
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p := make([]byte, n)
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copy(p, b)
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go s.handlePacket(p, addr, conn) // ignore errors
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}
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if err != nil {
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if isConnClosed(err) {
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log.Printf("ReadFrom() returned because we're reading from a closed connection, exiting loop")
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var err error
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s.Lock()
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if s.udpListen != nil {
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err = s.udpListen.Close()
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s.udpListen = nil
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}
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s.Unlock()
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if err != nil {
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log.Printf("Failed to close udp connection while exiting loop: %s", err)
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}
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break
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}
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log.Printf("Got error when reading from udp listen: %s", err)
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}
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}
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}
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//
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// Control functions
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//
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func (s *Server) Start(config *ServerConfig) error {
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s.Lock()
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defer s.Unlock()
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if config != nil {
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s.ServerConfig = *config
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}
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// TODO: handle being called Start() second time after Stop()
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if s.udpListen == nil {
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log.Printf("Creating UDP socket")
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var err error
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addr := s.UDPListenAddr
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if addr == nil {
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addr = defaultValues.UDPListenAddr
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}
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s.udpListen, err = net.ListenUDP("udp", addr)
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if err != nil {
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s.udpListen = nil
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return errorx.Decorate(err, "Couldn't listen to UDP socket")
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}
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log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
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}
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if s.dnsFilter == nil {
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log.Printf("Creating dnsfilter")
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s.dnsFilter = dnsfilter.New()
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}
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go s.packetLoop()
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return nil
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}
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func (s *Server) Stop() error {
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s.Lock()
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defer s.Unlock()
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if s.udpListen != nil {
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err := s.udpListen.Close()
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s.udpListen = nil
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if err != nil {
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return errorx.Decorate(err, "Couldn't close UDP listening socket")
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}
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}
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return nil
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}
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func (s *Server) IsRunning() bool {
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s.RLock()
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isRunning := true
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if s.udpListen == nil {
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isRunning = false
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}
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s.RUnlock()
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return isRunning
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}
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//
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// Server reconfigure
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//
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func (s *Server) reconfigureListenAddr(new ServerConfig) error {
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oldAddr := s.UDPListenAddr
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if oldAddr == nil {
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oldAddr = defaultValues.UDPListenAddr
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}
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newAddr := new.UDPListenAddr
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if newAddr == nil {
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newAddr = defaultValues.UDPListenAddr
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}
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if newAddr.Port == 0 {
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return errorx.IllegalArgument.New("new port cannot be 0")
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}
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if reflect.DeepEqual(oldAddr, newAddr) {
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// do nothing, the addresses are exactly the same
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log.Printf("Not going to rebind because addresses are same: %v -> %v", oldAddr, newAddr)
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return nil
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}
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// rebind, using a strategy:
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// * if ports are different, bind new first, then close old
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// * if ports are same, close old first, then bind new
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var newListen *net.UDPConn
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var err error
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if oldAddr.Port != newAddr.Port {
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log.Printf("Rebinding -- ports are different so bind first then close")
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newListen, err = net.ListenUDP("udp", newAddr)
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if err != nil {
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return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
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}
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s.Lock()
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if s.udpListen != nil {
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err = s.udpListen.Close()
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s.udpListen = nil
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}
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s.Unlock()
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if err != nil {
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return errorx.Decorate(err, "Couldn't close UDP listening socket")
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}
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} else {
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log.Printf("Rebinding -- ports are same so close first then bind")
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s.Lock()
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if s.udpListen != nil {
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err = s.udpListen.Close()
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s.udpListen = nil
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}
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s.Unlock()
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if err != nil {
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return errorx.Decorate(err, "Couldn't close UDP listening socket")
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}
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newListen, err = net.ListenUDP("udp", newAddr)
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if err != nil {
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return errorx.Decorate(err, "Couldn't bind to %v", newAddr)
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}
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}
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s.Lock()
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s.udpListen = newListen
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s.UDPListenAddr = new.UDPListenAddr
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s.Unlock()
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log.Println(s.udpListen.LocalAddr(), s.UDPListenAddr)
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go s.packetLoop() // the old one has quit, use new one
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return nil
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}
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func (s *Server) reconfigureBlockedTTL(new ServerConfig) {
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newVal := new.BlockedTTL
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if newVal == 0 {
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newVal = defaultValues.BlockedTTL
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}
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oldVal := s.BlockedTTL
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if oldVal == 0 {
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oldVal = defaultValues.BlockedTTL
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}
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if newVal != oldVal {
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s.BlockedTTL = new.BlockedTTL
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}
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}
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func (s *Server) reconfigureUpstreams(new ServerConfig) {
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newVal := new.Upstreams
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if len(newVal) == 0 {
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newVal = defaultValues.Upstreams
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}
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oldVal := s.Upstreams
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if len(oldVal) == 0 {
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oldVal = defaultValues.Upstreams
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}
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if reflect.DeepEqual(newVal, oldVal) {
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// they're exactly the same, do nothing
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return
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}
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s.Upstreams = new.Upstreams
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}
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func (s *Server) reconfigureFilters(new ServerConfig) {
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newFilters := new.Filters
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if len(newFilters) == 0 {
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newFilters = defaultValues.Filters
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}
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oldFilters := s.Filters
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if len(oldFilters) == 0 {
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oldFilters = defaultValues.Filters
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}
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if reflect.DeepEqual(newFilters, oldFilters) {
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// they're exactly the same, do nothing
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return
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}
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dnsFilter := dnsfilter.New()
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for _, f := range newFilters {
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for _, rule := range f.Rules {
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err := dnsFilter.AddRule(rule, f.ID)
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if err == dnsfilter.ErrAlreadyExists || err == dnsfilter.ErrInvalidSyntax {
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continue
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}
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if err != nil {
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log.Printf("Cannot add rule %s: %s", rule, err)
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// Just ignore invalid rules
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continue
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}
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}
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}
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s.Lock()
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oldDnsFilter := s.dnsFilter
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s.dnsFilter = dnsFilter
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s.Unlock()
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oldDnsFilter.Destroy()
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}
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func (s *Server) Reconfigure(new ServerConfig) error {
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s.reconfigureBlockedTTL(new)
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s.reconfigureUpstreams(new)
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s.reconfigureFilters(new)
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err := s.reconfigureListenAddr(new)
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if err != nil {
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return errorx.Decorate(err, "Couldn't reconfigure to new listening address %+v", new.UDPListenAddr)
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}
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return nil
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}
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//
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// packet handling functions
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//
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func (s *Server) handlePacket(p []byte, addr net.Addr, conn *net.UDPConn) {
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// log.Printf("Got packet %d bytes from %s: %v", len(p), addr, p)
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msg := dns.Msg{}
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err := msg.Unpack(p)
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if err != nil {
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log.Printf("failed to unpack DNS packet: %s", err)
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return
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}
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//
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// DNS packet byte format is valid
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//
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// any errors below here require a response to client
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// log.Printf("Unpacked: %v", msg.String())
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if len(msg.Question) != 1 {
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log.Printf("Got invalid number of questions: %v", len(msg.Question))
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err := s.respondWithServerFailure(&msg, addr, conn)
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if err != nil {
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log.Printf("Couldn't respond to UDP packet: %s", err)
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return
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}
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}
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{
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val, ok := s.cache.Get(&msg)
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if ok && val != nil {
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err = s.respond(val, addr, conn)
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if err != nil {
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if isConnClosed(err) {
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// ignore this error, the connection was closed and that's ok
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return
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}
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log.Printf("Couldn't respond to UDP packet: %s", err)
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return
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}
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return
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}
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}
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host := msg.Question[0].Name
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res, err := s.dnsFilter.CheckHost(host)
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if err != nil {
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log.Printf("dnsfilter failed to check host '%s': %s", host, err)
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err := s.respondWithServerFailure(&msg, addr, conn)
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if err != nil {
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log.Printf("Couldn't respond to UDP packet: %s", err)
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return
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}
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} else if res.IsFiltered {
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log.Printf("Host %s is filtered, reason - '%s', matched rule: '%s'", host, res.Reason, res.Rule)
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err := s.respondWithNXDomain(&msg, addr, conn)
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if err != nil {
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log.Printf("Couldn't respond to UDP packet: %s", err)
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return
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}
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}
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// TODO: replace with single-socket implementation
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// TODO: replace 8.8.8.8:53 with configurable upstreams
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// TODO: support DoH, DoT and TCP
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upstream := s.chooseUpstream()
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reply, err := upstream.Exchange(&msg)
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if err != nil {
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log.Printf("talking to upstream failed for host '%s': %s", host, err)
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err := s.respondWithServerFailure(&msg, addr, conn)
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if err != nil {
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if isConnClosed(err) {
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// ignore this error, the connection was closed and that's ok
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return
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}
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log.Printf("Couldn't respond to UDP packet with server failure: %s", err)
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return
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}
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return
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}
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if reply == nil {
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log.Printf("SHOULD NOT HAPPEN upstream returned empty message for host '%s'. Request is %v", host, msg.String())
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err := s.respondWithServerFailure(&msg, addr, conn)
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if err != nil {
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log.Printf("Couldn't respond to UDP packet with should not happen: %s", err)
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return
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}
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return
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}
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err = s.respond(reply, addr, conn)
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if err != nil {
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if isConnClosed(err) {
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// ignore this error, the connection was closed and that's ok
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return
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}
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log.Printf("Couldn't respond to UDP packet: %s", err)
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return
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}
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s.cache.Set(reply)
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}
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//
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// packet sending functions
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//
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func (s *Server) respond(resp *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
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// log.Printf("Replying to %s with %s", addr, resp)
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resp.Compress = true
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bytes, err := resp.Pack()
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if err != nil {
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return errorx.Decorate(err, "Couldn't convert message into wire format")
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}
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n, err := conn.WriteTo(bytes, addr)
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if n == 0 && isConnClosed(err) {
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return err
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}
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if n != len(bytes) {
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return fmt.Errorf("WriteTo() returned with %d != %d", n, len(bytes))
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}
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if err != nil {
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return errorx.Decorate(err, "WriteTo() returned error")
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}
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return nil
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}
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func (s *Server) respondWithServerFailure(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
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resp := dns.Msg{}
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resp.SetRcode(request, dns.RcodeServerFailure)
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return s.respond(&resp, addr, conn)
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}
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func (s *Server) respondWithNXDomain(request *dns.Msg, addr net.Addr, conn *net.UDPConn) error {
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resp := dns.Msg{}
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resp.SetRcode(request, dns.RcodeNameError)
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resp.Ns = s.genSOA(request)
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return s.respond(&resp, addr, conn)
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}
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func (s *Server) genSOA(request *dns.Msg) []dns.RR {
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zone := ""
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if len(request.Question) > 0 {
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zone = request.Question[0].Name
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}
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soa := dns.SOA{
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// values copied from verisign's nonexistent .com domain
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// their exact values are not important in our use case because they are used for domain transfers between primary/secondary DNS servers
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Refresh: 1800,
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Retry: 900,
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Expire: 604800,
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Minttl: 86400,
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// copied from AdGuard DNS
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Ns: "fake-for-negative-caching.adguard.com.",
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Serial: 100500,
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// rest is request-specific
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Hdr: dns.RR_Header{
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Name: zone,
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Rrtype: dns.TypeSOA,
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Ttl: s.BlockedTTL,
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Class: dns.ClassINET,
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},
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Mbox: "hostmaster.", // zone will be appended later if it's not empty or "."
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}
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if soa.Hdr.Ttl == 0 {
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soa.Hdr.Ttl = defaultValues.BlockedTTL
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}
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if len(zone) > 0 && zone[0] != '.' {
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soa.Mbox += zone
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}
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return []dns.RR{&soa}
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}
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