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net/dns, wgengine: implement DNS over TCP (#4598)
* net/dns, wgengine: implement DNS over TCP Signed-off-by: Tom DNetto <tom@tailscale.com> * wgengine/netstack: intercept only relevant port/protocols to quad-100 Signed-off-by: Tom DNetto <tom@tailscale.com>
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Tom
GitHub
parent
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commit
d1d6ab068e
@ -7,7 +7,9 @@
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import (
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"bufio"
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"context"
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"encoding/binary"
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"errors"
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"io"
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"net"
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"runtime"
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"sync/atomic"
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@ -346,6 +348,123 @@ func (m *Manager) Query(ctx context.Context, bs []byte, from netaddr.IPPort) ([]
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return m.resolver.Query(ctx, bs, from)
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}
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const (
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// RFC 7766 6.2 recommends connection reuse & request pipelining
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// be undertaken, and the connection be closed by the server
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// using an idle timeout on the order of seconds.
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idleTimeoutTCP = 45 * time.Second
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// The RFCs don't specify the max size of a TCP-based DNS query,
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// but we want to keep this reasonable. Given payloads are typically
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// much larger and all known client send a single query, I've arbitrarily
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// chosen 2k.
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maxReqSizeTCP = 2048
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)
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// dnsTCPSession services DNS requests sent over TCP.
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type dnsTCPSession struct {
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m *Manager
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conn net.Conn
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srcAddr netaddr.IPPort
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readClosing chan struct{}
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responses chan []byte // DNS replies pending writing
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ctx context.Context
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closeCtx context.CancelFunc
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}
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func (s *dnsTCPSession) handleWrites() {
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defer s.conn.Close()
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defer close(s.responses)
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defer s.closeCtx()
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for {
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select {
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case <-s.readClosing:
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return // connection closed or timeout, teardown time
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case resp := <-s.responses:
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s.conn.SetWriteDeadline(time.Now().Add(idleTimeoutTCP))
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if err := binary.Write(s.conn, binary.BigEndian, uint16(len(resp))); err != nil {
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s.m.logf("tcp write (len): %v", err)
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return
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}
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if _, err := s.conn.Write(resp); err != nil {
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s.m.logf("tcp write (response): %v", err)
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return
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}
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}
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}
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}
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func (s *dnsTCPSession) handleQuery(q []byte) {
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resp, err := s.m.Query(s.ctx, q, s.srcAddr)
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if err != nil {
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s.m.logf("tcp query: %v", err)
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return
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}
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select {
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case <-s.ctx.Done():
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case s.responses <- resp:
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}
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}
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func (s *dnsTCPSession) handleReads() {
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defer close(s.readClosing)
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for {
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select {
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case <-s.ctx.Done():
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return
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default:
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s.conn.SetReadDeadline(time.Now().Add(idleTimeoutTCP))
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var reqLen uint16
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if err := binary.Read(s.conn, binary.BigEndian, &reqLen); err != nil {
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if err == io.EOF || err == io.ErrClosedPipe {
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return // connection closed nominally, we gucci
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}
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s.m.logf("tcp read (len): %v", err)
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return
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}
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if int(reqLen) > maxReqSizeTCP {
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s.m.logf("tcp request too large (%d > %d)", reqLen, maxReqSizeTCP)
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return
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}
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buf := make([]byte, int(reqLen))
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if _, err := io.ReadFull(s.conn, buf); err != nil {
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s.m.logf("tcp read (payload): %v", err)
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return
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}
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select {
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case <-s.ctx.Done():
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return
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default:
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go s.handleQuery(buf)
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}
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}
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}
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}
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// HandleTCPConn implements magicDNS over TCP, taking a connection and
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// servicing DNS requests sent down it.
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func (m *Manager) HandleTCPConn(conn net.Conn, srcAddr netaddr.IPPort) {
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s := dnsTCPSession{
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m: m,
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conn: conn,
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srcAddr: srcAddr,
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responses: make(chan []byte),
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readClosing: make(chan struct{}),
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}
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s.ctx, s.closeCtx = context.WithCancel(context.Background())
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go s.handleReads()
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s.handleWrites()
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}
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func (m *Manager) Down() error {
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m.ctxCancel()
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if err := m.os.Close(); err != nil {
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136
net/dns/manager_tcp_test.go
Normal file
136
net/dns/manager_tcp_test.go
Normal file
@ -0,0 +1,136 @@
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// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package dns
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import (
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"encoding/binary"
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"io"
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"net"
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"testing"
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"github.com/google/go-cmp/cmp"
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dns "golang.org/x/net/dns/dnsmessage"
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"inet.af/netaddr"
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"tailscale.com/net/tsdial"
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"tailscale.com/util/dnsname"
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)
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func mkDNSRequest(domain dnsname.FQDN, tp dns.Type) []byte {
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var dnsHeader dns.Header
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question := dns.Question{
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Name: dns.MustNewName(domain.WithTrailingDot()),
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Type: tp,
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Class: dns.ClassINET,
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}
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builder := dns.NewBuilder(nil, dnsHeader)
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if err := builder.StartQuestions(); err != nil {
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panic(err)
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}
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if err := builder.Question(question); err != nil {
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panic(err)
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}
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if err := builder.StartAdditionals(); err != nil {
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panic(err)
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}
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ednsHeader := dns.ResourceHeader{
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Name: dns.MustNewName("."),
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Type: dns.TypeOPT,
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Class: dns.Class(4095),
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}
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if err := builder.OPTResource(ednsHeader, dns.OPTResource{}); err != nil {
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panic(err)
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}
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payload, _ := builder.Finish()
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return payload
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}
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func TestDNSOverTCP(t *testing.T) {
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f := fakeOSConfigurator{
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SplitDNS: true,
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BaseConfig: OSConfig{
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Nameservers: mustIPs("8.8.8.8"),
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SearchDomains: fqdns("coffee.shop"),
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},
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}
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m := NewManager(t.Logf, &f, nil, new(tsdial.Dialer), nil)
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m.resolver.TestOnlySetHook(f.SetResolver)
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m.Set(Config{
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Hosts: hosts(
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"dave.ts.com.", "1.2.3.4",
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"bradfitz.ts.com.", "2.3.4.5"),
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Routes: upstreams("ts.com", ""),
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SearchDomains: fqdns("tailscale.com", "universe.tf"),
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})
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defer m.Down()
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c, s := net.Pipe()
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defer s.Close()
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go m.HandleTCPConn(s, netaddr.IPPort{})
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defer c.Close()
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wantResults := map[dnsname.FQDN]string{
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"dave.ts.com.": "1.2.3.4",
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"bradfitz.ts.com.": "2.3.4.5",
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}
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for domain, _ := range wantResults {
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b := mkDNSRequest(domain, dns.TypeA)
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binary.Write(c, binary.BigEndian, uint16(len(b)))
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c.Write(b)
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}
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results := map[dnsname.FQDN]string{}
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for i := 0; i < len(wantResults); i++ {
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var respLength uint16
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if err := binary.Read(c, binary.BigEndian, &respLength); err != nil {
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t.Fatalf("reading len: %v", err)
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}
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resp := make([]byte, int(respLength))
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if _, err := io.ReadFull(c, resp); err != nil {
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t.Fatalf("reading data: %v", err)
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}
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var parser dns.Parser
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if _, err := parser.Start(resp); err != nil {
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t.Errorf("parser.Start() failed: %v", err)
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continue
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}
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q, err := parser.Question()
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if err != nil {
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t.Errorf("parser.Question(): %v", err)
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continue
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}
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if err := parser.SkipAllQuestions(); err != nil {
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t.Errorf("parser.SkipAllQuestions(): %v", err)
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continue
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}
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ah, err := parser.AnswerHeader()
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if err != nil {
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t.Errorf("parser.AnswerHeader(): %v", err)
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continue
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}
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if ah.Type != dns.TypeA {
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t.Errorf("unexpected answer type: got %v, want %v", ah.Type, dns.TypeA)
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continue
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}
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res, err := parser.AResource()
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if err != nil {
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t.Errorf("parser.AResource(): %v", err)
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continue
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}
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results[dnsname.FQDN(q.Name.String())] = net.IP(res.A[:]).String()
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}
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c.Close()
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if diff := cmp.Diff(wantResults, results); diff != "" {
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t.Errorf("wrong results (-got+want)\n%s", diff)
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}
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}
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@ -373,6 +373,19 @@ func (ns *Impl) handleLocalPackets(p *packet.Parsed, t *tstun.Wrapper) filter.Re
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if dst := p.Dst.IP(); dst != magicDNSIP && dst != magicDNSIPv6 {
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return filter.Accept
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}
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// Of traffic to the service IP, we only care about UDP 53, and TCP
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// on port 80 & 53.
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switch p.IPProto {
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case ipproto.TCP:
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if port := p.Dst.Port(); port != 53 && port != 80 {
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return filter.Accept
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}
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case ipproto.UDP:
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if port := p.Dst.Port(); port != 53 {
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return filter.Accept
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}
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}
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var pn tcpip.NetworkProtocolNumber
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switch p.IPVersion {
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@ -758,6 +771,11 @@ func (ns *Impl) acceptTCP(r *tcp.ForwarderRequest) {
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// block until the TCP handshake is complete.
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c := gonet.NewTCPConn(&wq, ep)
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if reqDetails.LocalPort == 53 && (dialIP == magicDNSIP || dialIP == magicDNSIPv6) {
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go ns.dns.HandleTCPConn(c, netaddr.IPPortFrom(clientRemoteIP, reqDetails.RemotePort))
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return
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}
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if ns.lb != nil {
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if reqDetails.LocalPort == 22 && ns.processSSH() && ns.isLocalIP(dialIP) {
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if err := ns.lb.HandleSSHConn(c); err != nil {
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