prometheus/vendor/github.com/miekg/dns/server.go

701 lines
19 KiB
Go

// DNS server implementation.
package dns
import (
"bytes"
"io"
"net"
"sync"
"time"
)
// Maximum number of TCP queries before we close the socket.
const maxTCPQueries = 128
// Handler is implemented by any value that implements ServeDNS.
type Handler interface {
ServeDNS(w ResponseWriter, r *Msg)
}
// A ResponseWriter interface is used by an DNS handler to
// construct an DNS response.
type ResponseWriter interface {
// LocalAddr returns the net.Addr of the server
LocalAddr() net.Addr
// RemoteAddr returns the net.Addr of the client that sent the current request.
RemoteAddr() net.Addr
// WriteMsg writes a reply back to the client.
WriteMsg(*Msg) error
// Write writes a raw buffer back to the client.
Write([]byte) (int, error)
// Close closes the connection.
Close() error
// TsigStatus returns the status of the Tsig.
TsigStatus() error
// TsigTimersOnly sets the tsig timers only boolean.
TsigTimersOnly(bool)
// Hijack lets the caller take over the connection.
// After a call to Hijack(), the DNS package will not do anything with the connection.
Hijack()
}
type response struct {
hijacked bool // connection has been hijacked by handler
tsigStatus error
tsigTimersOnly bool
tsigRequestMAC string
tsigSecret map[string]string // the tsig secrets
udp *net.UDPConn // i/o connection if UDP was used
tcp *net.TCPConn // i/o connection if TCP was used
udpSession *SessionUDP // oob data to get egress interface right
remoteAddr net.Addr // address of the client
writer Writer // writer to output the raw DNS bits
}
// ServeMux is an DNS request multiplexer. It matches the
// zone name of each incoming request against a list of
// registered patterns add calls the handler for the pattern
// that most closely matches the zone name. ServeMux is DNSSEC aware, meaning
// that queries for the DS record are redirected to the parent zone (if that
// is also registered), otherwise the child gets the query.
// ServeMux is also safe for concurrent access from multiple goroutines.
type ServeMux struct {
z map[string]Handler
m *sync.RWMutex
}
// NewServeMux allocates and returns a new ServeMux.
func NewServeMux() *ServeMux { return &ServeMux{z: make(map[string]Handler), m: new(sync.RWMutex)} }
// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = NewServeMux()
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as DNS handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler object that calls f.
type HandlerFunc func(ResponseWriter, *Msg)
// ServeDNS calls f(w, r).
func (f HandlerFunc) ServeDNS(w ResponseWriter, r *Msg) {
f(w, r)
}
// HandleFailed returns a HandlerFunc that returns SERVFAIL for every request it gets.
func HandleFailed(w ResponseWriter, r *Msg) {
m := new(Msg)
m.SetRcode(r, RcodeServerFailure)
// does not matter if this write fails
w.WriteMsg(m)
}
func failedHandler() Handler { return HandlerFunc(HandleFailed) }
// ListenAndServe Starts a server on addresss and network speficied. Invoke handler
// for incoming queries.
func ListenAndServe(addr string, network string, handler Handler) error {
server := &Server{Addr: addr, Net: network, Handler: handler}
return server.ListenAndServe()
}
// ActivateAndServe activates a server with a listener from systemd,
// l and p should not both be non-nil.
// If both l and p are not nil only p will be used.
// Invoke handler for incoming queries.
func ActivateAndServe(l net.Listener, p net.PacketConn, handler Handler) error {
server := &Server{Listener: l, PacketConn: p, Handler: handler}
return server.ActivateAndServe()
}
func (mux *ServeMux) match(q string, t uint16) Handler {
mux.m.RLock()
defer mux.m.RUnlock()
var handler Handler
b := make([]byte, len(q)) // worst case, one label of length q
off := 0
end := false
for {
l := len(q[off:])
for i := 0; i < l; i++ {
b[i] = q[off+i]
if b[i] >= 'A' && b[i] <= 'Z' {
b[i] |= ('a' - 'A')
}
}
if h, ok := mux.z[string(b[:l])]; ok { // 'causes garbage, might want to change the map key
if t != TypeDS {
return h
}
// Continue for DS to see if we have a parent too, if so delegeate to the parent
handler = h
}
off, end = NextLabel(q, off)
if end {
break
}
}
// Wildcard match, if we have found nothing try the root zone as a last resort.
if h, ok := mux.z["."]; ok {
return h
}
return handler
}
// Handle adds a handler to the ServeMux for pattern.
func (mux *ServeMux) Handle(pattern string, handler Handler) {
if pattern == "" {
panic("dns: invalid pattern " + pattern)
}
mux.m.Lock()
mux.z[Fqdn(pattern)] = handler
mux.m.Unlock()
}
// HandleFunc adds a handler function to the ServeMux for pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
mux.Handle(pattern, HandlerFunc(handler))
}
// HandleRemove deregistrars the handler specific for pattern from the ServeMux.
func (mux *ServeMux) HandleRemove(pattern string) {
if pattern == "" {
panic("dns: invalid pattern " + pattern)
}
mux.m.Lock()
delete(mux.z, Fqdn(pattern))
mux.m.Unlock()
}
// ServeDNS dispatches the request to the handler whose
// pattern most closely matches the request message. If DefaultServeMux
// is used the correct thing for DS queries is done: a possible parent
// is sought.
// If no handler is found a standard SERVFAIL message is returned
// If the request message does not have exactly one question in the
// question section a SERVFAIL is returned, unlesss Unsafe is true.
func (mux *ServeMux) ServeDNS(w ResponseWriter, request *Msg) {
var h Handler
if len(request.Question) < 1 { // allow more than one question
h = failedHandler()
} else {
if h = mux.match(request.Question[0].Name, request.Question[0].Qtype); h == nil {
h = failedHandler()
}
}
h.ServeDNS(w, request)
}
// Handle registers the handler with the given pattern
// in the DefaultServeMux. The documentation for
// ServeMux explains how patterns are matched.
func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
// HandleRemove deregisters the handle with the given pattern
// in the DefaultServeMux.
func HandleRemove(pattern string) { DefaultServeMux.HandleRemove(pattern) }
// HandleFunc registers the handler function with the given pattern
// in the DefaultServeMux.
func HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
DefaultServeMux.HandleFunc(pattern, handler)
}
// Writer writes raw DNS messages; each call to Write should send an entire message.
type Writer interface {
io.Writer
}
// Reader reads raw DNS messages; each call to ReadTCP or ReadUDP should return an entire message.
type Reader interface {
// ReadTCP reads a raw message from a TCP connection. Implementations may alter
// connection properties, for example the read-deadline.
ReadTCP(conn *net.TCPConn, timeout time.Duration) ([]byte, error)
// ReadUDP reads a raw message from a UDP connection. Implementations may alter
// connection properties, for example the read-deadline.
ReadUDP(conn *net.UDPConn, timeout time.Duration) ([]byte, *SessionUDP, error)
}
// defaultReader is an adapter for the Server struct that implements the Reader interface
// using the readTCP and readUDP func of the embedded Server.
type defaultReader struct {
*Server
}
func (dr *defaultReader) ReadTCP(conn *net.TCPConn, timeout time.Duration) ([]byte, error) {
return dr.readTCP(conn, timeout)
}
func (dr *defaultReader) ReadUDP(conn *net.UDPConn, timeout time.Duration) ([]byte, *SessionUDP, error) {
return dr.readUDP(conn, timeout)
}
// DecorateReader is a decorator hook for extending or supplanting the functionality of a Reader.
// Implementations should never return a nil Reader.
type DecorateReader func(Reader) Reader
// DecorateWriter is a decorator hook for extending or supplanting the functionality of a Writer.
// Implementations should never return a nil Writer.
type DecorateWriter func(Writer) Writer
// A Server defines parameters for running an DNS server.
type Server struct {
// Address to listen on, ":dns" if empty.
Addr string
// if "tcp" it will invoke a TCP listener, otherwise an UDP one.
Net string
// TCP Listener to use, this is to aid in systemd's socket activation.
Listener net.Listener
// UDP "Listener" to use, this is to aid in systemd's socket activation.
PacketConn net.PacketConn
// Handler to invoke, dns.DefaultServeMux if nil.
Handler Handler
// Default buffer size to use to read incoming UDP messages. If not set
// it defaults to MinMsgSize (512 B).
UDPSize int
// The net.Conn.SetReadTimeout value for new connections, defaults to 2 * time.Second.
ReadTimeout time.Duration
// The net.Conn.SetWriteTimeout value for new connections, defaults to 2 * time.Second.
WriteTimeout time.Duration
// TCP idle timeout for multiple queries, if nil, defaults to 8 * time.Second (RFC 5966).
IdleTimeout func() time.Duration
// Secret(s) for Tsig map[<zonename>]<base64 secret>.
TsigSecret map[string]string
// Unsafe instructs the server to disregard any sanity checks and directly hand the message to
// the handler. It will specfically not check if the query has the QR bit not set.
Unsafe bool
// If NotifyStartedFunc is set it is called once the server has started listening.
NotifyStartedFunc func()
// DecorateReader is optional, allows customization of the process that reads raw DNS messages.
DecorateReader DecorateReader
// DecorateWriter is optional, allows customization of the process that writes raw DNS messages.
DecorateWriter DecorateWriter
// For graceful shutdown.
stopUDP chan bool
stopTCP chan bool
wgUDP sync.WaitGroup
wgTCP sync.WaitGroup
// make start/shutdown not racy
lock sync.Mutex
started bool
}
// ListenAndServe starts a nameserver on the configured address in *Server.
func (srv *Server) ListenAndServe() error {
srv.lock.Lock()
if srv.started {
srv.lock.Unlock()
return &Error{err: "server already started"}
}
srv.stopUDP, srv.stopTCP = make(chan bool), make(chan bool)
srv.started = true
addr := srv.Addr
if addr == "" {
addr = ":domain"
}
if srv.UDPSize == 0 {
srv.UDPSize = MinMsgSize
}
switch srv.Net {
case "tcp", "tcp4", "tcp6":
a, e := net.ResolveTCPAddr(srv.Net, addr)
if e != nil {
return e
}
l, e := net.ListenTCP(srv.Net, a)
if e != nil {
return e
}
srv.Listener = l
srv.lock.Unlock()
return srv.serveTCP(l)
case "udp", "udp4", "udp6":
a, e := net.ResolveUDPAddr(srv.Net, addr)
if e != nil {
return e
}
l, e := net.ListenUDP(srv.Net, a)
if e != nil {
return e
}
if e := setUDPSocketOptions(l); e != nil {
return e
}
srv.PacketConn = l
srv.lock.Unlock()
return srv.serveUDP(l)
}
srv.lock.Unlock()
return &Error{err: "bad network"}
}
// ActivateAndServe starts a nameserver with the PacketConn or Listener
// configured in *Server. Its main use is to start a server from systemd.
func (srv *Server) ActivateAndServe() error {
srv.lock.Lock()
if srv.started {
srv.lock.Unlock()
return &Error{err: "server already started"}
}
srv.stopUDP, srv.stopTCP = make(chan bool), make(chan bool)
srv.started = true
pConn := srv.PacketConn
l := srv.Listener
srv.lock.Unlock()
if pConn != nil {
if srv.UDPSize == 0 {
srv.UDPSize = MinMsgSize
}
if t, ok := pConn.(*net.UDPConn); ok {
if e := setUDPSocketOptions(t); e != nil {
return e
}
return srv.serveUDP(t)
}
}
if l != nil {
if t, ok := l.(*net.TCPListener); ok {
return srv.serveTCP(t)
}
}
return &Error{err: "bad listeners"}
}
// Shutdown gracefully shuts down a server. After a call to Shutdown, ListenAndServe and
// ActivateAndServe will return. All in progress queries are completed before the server
// is taken down. If the Shutdown is taking longer than the reading timeout an error
// is returned.
func (srv *Server) Shutdown() error {
srv.lock.Lock()
if !srv.started {
srv.lock.Unlock()
return &Error{err: "server not started"}
}
srv.started = false
net, addr := srv.Net, srv.Addr
switch {
case srv.Listener != nil:
a := srv.Listener.Addr()
net, addr = a.Network(), a.String()
case srv.PacketConn != nil:
a := srv.PacketConn.LocalAddr()
net, addr = a.Network(), a.String()
}
srv.lock.Unlock()
fin := make(chan bool)
switch net {
case "tcp", "tcp4", "tcp6":
go func() {
srv.stopTCP <- true
srv.wgTCP.Wait()
fin <- true
}()
case "udp", "udp4", "udp6":
go func() {
srv.stopUDP <- true
srv.wgUDP.Wait()
fin <- true
}()
}
c := &Client{Net: net}
go c.Exchange(new(Msg), addr) // extra query to help ReadXXX loop to pass
select {
case <-time.After(srv.getReadTimeout()):
return &Error{err: "server shutdown is pending"}
case <-fin:
return nil
}
}
// getReadTimeout is a helper func to use system timeout if server did not intend to change it.
func (srv *Server) getReadTimeout() time.Duration {
rtimeout := dnsTimeout
if srv.ReadTimeout != 0 {
rtimeout = srv.ReadTimeout
}
return rtimeout
}
// serveTCP starts a TCP listener for the server.
// Each request is handled in a separate goroutine.
func (srv *Server) serveTCP(l *net.TCPListener) error {
defer l.Close()
if srv.NotifyStartedFunc != nil {
srv.NotifyStartedFunc()
}
reader := Reader(&defaultReader{srv})
if srv.DecorateReader != nil {
reader = srv.DecorateReader(reader)
}
handler := srv.Handler
if handler == nil {
handler = DefaultServeMux
}
rtimeout := srv.getReadTimeout()
// deadline is not used here
for {
rw, e := l.AcceptTCP()
if e != nil {
continue
}
m, e := reader.ReadTCP(rw, rtimeout)
select {
case <-srv.stopTCP:
return nil
default:
}
if e != nil {
continue
}
srv.wgTCP.Add(1)
go srv.serve(rw.RemoteAddr(), handler, m, nil, nil, rw)
}
}
// serveUDP starts a UDP listener for the server.
// Each request is handled in a separate goroutine.
func (srv *Server) serveUDP(l *net.UDPConn) error {
defer l.Close()
if srv.NotifyStartedFunc != nil {
srv.NotifyStartedFunc()
}
reader := Reader(&defaultReader{srv})
if srv.DecorateReader != nil {
reader = srv.DecorateReader(reader)
}
handler := srv.Handler
if handler == nil {
handler = DefaultServeMux
}
rtimeout := srv.getReadTimeout()
// deadline is not used here
for {
m, s, e := reader.ReadUDP(l, rtimeout)
select {
case <-srv.stopUDP:
return nil
default:
}
if e != nil {
continue
}
srv.wgUDP.Add(1)
go srv.serve(s.RemoteAddr(), handler, m, l, s, nil)
}
}
// Serve a new connection.
func (srv *Server) serve(a net.Addr, h Handler, m []byte, u *net.UDPConn, s *SessionUDP, t *net.TCPConn) {
w := &response{tsigSecret: srv.TsigSecret, udp: u, tcp: t, remoteAddr: a, udpSession: s}
if srv.DecorateWriter != nil {
w.writer = srv.DecorateWriter(w)
} else {
w.writer = w
}
q := 0 // counter for the amount of TCP queries we get
defer func() {
if u != nil {
srv.wgUDP.Done()
}
if t != nil {
srv.wgTCP.Done()
}
}()
reader := Reader(&defaultReader{srv})
if srv.DecorateReader != nil {
reader = srv.DecorateReader(reader)
}
Redo:
req := new(Msg)
err := req.Unpack(m)
if err != nil { // Send a FormatError back
x := new(Msg)
x.SetRcodeFormatError(req)
w.WriteMsg(x)
goto Exit
}
if !srv.Unsafe && req.Response {
goto Exit
}
w.tsigStatus = nil
if w.tsigSecret != nil {
if t := req.IsTsig(); t != nil {
secret := t.Hdr.Name
if _, ok := w.tsigSecret[secret]; !ok {
w.tsigStatus = ErrKeyAlg
}
w.tsigStatus = TsigVerify(m, w.tsigSecret[secret], "", false)
w.tsigTimersOnly = false
w.tsigRequestMAC = req.Extra[len(req.Extra)-1].(*TSIG).MAC
}
}
h.ServeDNS(w, req) // Writes back to the client
Exit:
// TODO(miek): make this number configurable?
if q > maxTCPQueries { // close socket after this many queries
w.Close()
return
}
if w.hijacked {
return // client calls Close()
}
if u != nil { // UDP, "close" and return
w.Close()
return
}
idleTimeout := tcpIdleTimeout
if srv.IdleTimeout != nil {
idleTimeout = srv.IdleTimeout()
}
m, e := reader.ReadTCP(w.tcp, idleTimeout)
if e == nil {
q++
goto Redo
}
w.Close()
return
}
func (srv *Server) readTCP(conn *net.TCPConn, timeout time.Duration) ([]byte, error) {
conn.SetReadDeadline(time.Now().Add(timeout))
l := make([]byte, 2)
n, err := conn.Read(l)
if err != nil || n != 2 {
if err != nil {
return nil, err
}
return nil, ErrShortRead
}
length, _ := unpackUint16(l, 0)
if length == 0 {
return nil, ErrShortRead
}
m := make([]byte, int(length))
n, err = conn.Read(m[:int(length)])
if err != nil || n == 0 {
if err != nil {
return nil, err
}
return nil, ErrShortRead
}
i := n
for i < int(length) {
j, err := conn.Read(m[i:int(length)])
if err != nil {
return nil, err
}
i += j
}
n = i
m = m[:n]
return m, nil
}
func (srv *Server) readUDP(conn *net.UDPConn, timeout time.Duration) ([]byte, *SessionUDP, error) {
conn.SetReadDeadline(time.Now().Add(timeout))
m := make([]byte, srv.UDPSize)
n, s, e := ReadFromSessionUDP(conn, m)
if e != nil || n == 0 {
if e != nil {
return nil, nil, e
}
return nil, nil, ErrShortRead
}
m = m[:n]
return m, s, nil
}
// WriteMsg implements the ResponseWriter.WriteMsg method.
func (w *response) WriteMsg(m *Msg) (err error) {
var data []byte
if w.tsigSecret != nil { // if no secrets, dont check for the tsig (which is a longer check)
if t := m.IsTsig(); t != nil {
data, w.tsigRequestMAC, err = TsigGenerate(m, w.tsigSecret[t.Hdr.Name], w.tsigRequestMAC, w.tsigTimersOnly)
if err != nil {
return err
}
_, err = w.writer.Write(data)
return err
}
}
data, err = m.Pack()
if err != nil {
return err
}
_, err = w.writer.Write(data)
return err
}
// Write implements the ResponseWriter.Write method.
func (w *response) Write(m []byte) (int, error) {
switch {
case w.udp != nil:
n, err := WriteToSessionUDP(w.udp, m, w.udpSession)
return n, err
case w.tcp != nil:
lm := len(m)
if lm < 2 {
return 0, io.ErrShortBuffer
}
if lm > MaxMsgSize {
return 0, &Error{err: "message too large"}
}
l := make([]byte, 2, 2+lm)
l[0], l[1] = packUint16(uint16(lm))
m = append(l, m...)
n, err := io.Copy(w.tcp, bytes.NewReader(m))
return int(n), err
}
panic("not reached")
}
// LocalAddr implements the ResponseWriter.LocalAddr method.
func (w *response) LocalAddr() net.Addr {
if w.tcp != nil {
return w.tcp.LocalAddr()
}
return w.udp.LocalAddr()
}
// RemoteAddr implements the ResponseWriter.RemoteAddr method.
func (w *response) RemoteAddr() net.Addr { return w.remoteAddr }
// TsigStatus implements the ResponseWriter.TsigStatus method.
func (w *response) TsigStatus() error { return w.tsigStatus }
// TsigTimersOnly implements the ResponseWriter.TsigTimersOnly method.
func (w *response) TsigTimersOnly(b bool) { w.tsigTimersOnly = b }
// Hijack implements the ResponseWriter.Hijack method.
func (w *response) Hijack() { w.hijacked = true }
// Close implements the ResponseWriter.Close method
func (w *response) Close() error {
// Can't close the udp conn, as that is actually the listener.
if w.tcp != nil {
e := w.tcp.Close()
w.tcp = nil
return e
}
return nil
}