mirror of
https://github.com/tailscale/tailscale.git
synced 2024-12-05 16:05:36 +00:00
4dfde7bffc
We already disable dynamic updates by setting DisableDynamicUpdate to 1 for the Tailscale interface. However, this does not prevent non-dynamic DNS registration from happening when `ipconfig /registerdns` runs and in similar scenarios. Notably, dns/windowsManager.SetDNS runs `ipconfig /registerdns`, triggering DNS registration for all interfaces that do not explicitly disable it. In this PR, we update dns/windowsManager.disableDynamicUpdates to also set RegistrationEnabled to 0. Fixes #13411 Signed-off-by: Nick Khyl <nickk@tailscale.com>
618 lines
18 KiB
Go
618 lines
18 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package dns
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import (
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"bufio"
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"bytes"
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"errors"
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"fmt"
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"net/netip"
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"os"
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"os/exec"
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"path/filepath"
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"sort"
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"strings"
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"sync"
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"syscall"
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"time"
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"golang.org/x/sys/windows"
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"golang.org/x/sys/windows/registry"
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"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
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"tailscale.com/atomicfile"
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"tailscale.com/control/controlknobs"
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"tailscale.com/envknob"
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"tailscale.com/health"
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"tailscale.com/types/logger"
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"tailscale.com/util/dnsname"
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"tailscale.com/util/winutil"
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)
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const (
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versionKey = `SOFTWARE\Microsoft\Windows NT\CurrentVersion`
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)
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var configureWSL = envknob.RegisterBool("TS_DEBUG_CONFIGURE_WSL")
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type windowsManager struct {
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logf logger.Logf
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guid string
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knobs *controlknobs.Knobs // or nil
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nrptDB *nrptRuleDatabase
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wslManager *wslManager
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mu sync.Mutex
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closing bool
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}
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// NewOSConfigurator created a new OS configurator.
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//
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// The health tracker and the knobs may be nil.
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func NewOSConfigurator(logf logger.Logf, health *health.Tracker, knobs *controlknobs.Knobs, interfaceName string) (OSConfigurator, error) {
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ret := &windowsManager{
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logf: logf,
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guid: interfaceName,
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knobs: knobs,
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wslManager: newWSLManager(logf, health),
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}
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if isWindows10OrBetter() {
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ret.nrptDB = newNRPTRuleDatabase(logf)
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}
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go func() {
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// Log WSL status once at startup.
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if distros, err := wslDistros(); err != nil {
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logf("WSL: could not list distributions: %v", err)
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} else {
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logf("WSL: found %d distributions", len(distros))
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}
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}()
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return ret, nil
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}
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func (m *windowsManager) openInterfaceKey(pfx winutil.RegistryPathPrefix) (registry.Key, error) {
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var key registry.Key
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var err error
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path := pfx.WithSuffix(m.guid)
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m.mu.Lock()
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closing := m.closing
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m.mu.Unlock()
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if closing {
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// Do not wait for the interface key to appear if the manager is being closed.
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// If it's being closed due to the removal of the wintun adapter,
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// the key would already be gone by now and will not reappear until tailscaled is restarted.
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key, err = registry.OpenKey(registry.LOCAL_MACHINE, string(path), registry.SET_VALUE)
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} else {
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key, err = winutil.OpenKeyWait(registry.LOCAL_MACHINE, path, registry.SET_VALUE)
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}
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if err != nil {
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return 0, fmt.Errorf("opening %s: %w", path, err)
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}
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return key, nil
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}
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func (m *windowsManager) muteKeyNotFoundIfClosing(err error) error {
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m.mu.Lock()
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defer m.mu.Unlock()
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if !m.closing || (!errors.Is(err, windows.ERROR_FILE_NOT_FOUND) && !errors.Is(err, windows.ERROR_PATH_NOT_FOUND)) {
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return err
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}
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return nil
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}
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func delValue(key registry.Key, name string) error {
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if err := key.DeleteValue(name); err != nil && err != registry.ErrNotExist {
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return err
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}
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return nil
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}
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// setSplitDNS configures one or more NRPT (Name Resolution Policy Table) rules
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// to resolve queries for domains using resolvers, rather than the
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// system's "primary" resolver.
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//
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// If no resolvers are provided, the Tailscale NRPT rules are deleted.
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func (m *windowsManager) setSplitDNS(resolvers []netip.Addr, domains []dnsname.FQDN) error {
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if m.nrptDB == nil {
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if resolvers == nil {
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// Just a no-op in this case.
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return nil
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}
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return fmt.Errorf("Split DNS unsupported on this Windows version")
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}
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defer m.nrptDB.Refresh()
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if len(resolvers) == 0 {
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return m.nrptDB.DelAllRuleKeys()
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}
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servers := make([]string, 0, len(resolvers))
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for _, resolver := range resolvers {
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servers = append(servers, resolver.String())
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}
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return m.nrptDB.WriteSplitDNSConfig(servers, domains)
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}
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func setTailscaleHosts(prevHostsFile []byte, hosts []*HostEntry) ([]byte, error) {
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b := bytes.ReplaceAll(prevHostsFile, []byte("\r\n"), []byte("\n"))
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sc := bufio.NewScanner(bytes.NewReader(b))
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const (
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header = "# TailscaleHostsSectionStart"
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footer = "# TailscaleHostsSectionEnd"
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)
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var comments = []string{
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"# This section contains MagicDNS entries for Tailscale.",
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"# Do not edit this section manually.",
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}
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var out bytes.Buffer
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var inSection bool
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for sc.Scan() {
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line := strings.TrimSpace(sc.Text())
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if line == header {
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inSection = true
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continue
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}
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if line == footer {
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inSection = false
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continue
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}
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if inSection {
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continue
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}
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fmt.Fprintln(&out, line)
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}
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if err := sc.Err(); err != nil {
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return nil, err
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}
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if len(hosts) > 0 {
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fmt.Fprintln(&out, header)
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for _, c := range comments {
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fmt.Fprintln(&out, c)
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}
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fmt.Fprintln(&out)
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for _, he := range hosts {
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fmt.Fprintf(&out, "%s %s\n", he.Addr, strings.Join(he.Hosts, " "))
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}
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fmt.Fprintln(&out)
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fmt.Fprintln(&out, footer)
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}
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return bytes.ReplaceAll(out.Bytes(), []byte("\n"), []byte("\r\n")), nil
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}
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// setHosts sets the hosts file to contain the given host entries.
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func (m *windowsManager) setHosts(hosts []*HostEntry) error {
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systemDir, err := windows.GetSystemDirectory()
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if err != nil {
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return err
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}
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hostsFile := filepath.Join(systemDir, "drivers", "etc", "hosts")
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b, err := os.ReadFile(hostsFile)
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if err != nil {
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return err
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}
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outB, err := setTailscaleHosts(b, hosts)
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if err != nil {
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return err
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}
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const fileMode = 0 // ignored on windows.
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// This can fail spuriously with an access denied error, so retry it a
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// few times.
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for range 5 {
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if err = atomicfile.WriteFile(hostsFile, outB, fileMode); err == nil {
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return nil
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}
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time.Sleep(10 * time.Millisecond)
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}
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return err
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}
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// setPrimaryDNS sets the given resolvers and domains as the Tailscale
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// interface's DNS configuration.
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// If resolvers is non-empty, those resolvers become the system's
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// "primary" resolvers.
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// domains can be set without resolvers, which just contributes new
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// paths to the global DNS search list.
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func (m *windowsManager) setPrimaryDNS(resolvers []netip.Addr, domains []dnsname.FQDN) error {
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var ipsv4 []string
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var ipsv6 []string
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for _, ip := range resolvers {
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if ip.Is4() {
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ipsv4 = append(ipsv4, ip.String())
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} else {
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ipsv6 = append(ipsv6, ip.String())
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}
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}
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domStrs := make([]string, 0, len(domains))
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for _, dom := range domains {
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domStrs = append(domStrs, dom.WithoutTrailingDot())
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}
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key4, err := m.openInterfaceKey(winutil.IPv4TCPIPInterfacePrefix)
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if err != nil {
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return m.muteKeyNotFoundIfClosing(err)
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}
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defer key4.Close()
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if len(ipsv4) == 0 {
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if err := delValue(key4, "NameServer"); err != nil {
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return err
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}
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} else if err := key4.SetStringValue("NameServer", strings.Join(ipsv4, ",")); err != nil {
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return err
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}
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if len(domains) == 0 {
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if err := delValue(key4, "SearchList"); err != nil {
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return err
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}
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} else if err := key4.SetStringValue("SearchList", strings.Join(domStrs, ",")); err != nil {
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return err
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}
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key6, err := m.openInterfaceKey(winutil.IPv6TCPIPInterfacePrefix)
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if err != nil {
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return m.muteKeyNotFoundIfClosing(err)
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}
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defer key6.Close()
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if len(ipsv6) == 0 {
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if err := delValue(key6, "NameServer"); err != nil {
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return err
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}
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} else if err := key6.SetStringValue("NameServer", strings.Join(ipsv6, ",")); err != nil {
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return err
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}
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if len(domains) == 0 {
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if err := delValue(key6, "SearchList"); err != nil {
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return err
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}
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} else if err := key6.SetStringValue("SearchList", strings.Join(domStrs, ",")); err != nil {
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return err
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}
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// Disable LLMNR on the Tailscale interface. We don't do multicast, and we
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// certainly don't do LLMNR, so it's pointless to make Windows try it. It is
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// being deprecated.
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if err := key4.SetDWordValue("EnableMulticast", 0); err != nil {
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return err
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}
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if err := key6.SetDWordValue("EnableMulticast", 0); err != nil {
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return err
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}
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return nil
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}
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func (m *windowsManager) disableLocalDNSOverrideViaNRPT() bool {
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return m.knobs != nil && m.knobs.DisableLocalDNSOverrideViaNRPT.Load()
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}
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func (m *windowsManager) SetDNS(cfg OSConfig) error {
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// We can configure Windows DNS in one of two ways:
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//
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// - In primary DNS mode, we set the NameServer and SearchList
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// registry keys on our interface. Because our interface metric
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// is very low, this turns us into the one and only "primary"
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// resolver for the OS, i.e. all queries flow to the
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// resolver(s) we specify.
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// - In split DNS mode, we set the Domain registry key on our
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// interface (which adds that domain to the global search list,
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// but does not contribute other DNS configuration from the
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// interface), and configure an NRPT (Name Resolution Policy
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// Table) rule to route queries for our suffixes to the
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// provided resolver.
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//
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// When switching modes, we delete all the configuration related
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// to the other mode, so these two are an XOR.
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//
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// Windows actually supports much more advanced configurations as
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// well, with arbitrary routing of hosts and suffixes to arbitrary
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// resolvers. However, we use it in a "simple" split domain
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// configuration only, routing one set of things to the "split"
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// resolver and the rest to the primary.
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// Unconditionally disable dynamic DNS updates and NetBIOS on our
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// interfaces.
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if err := m.disableDynamicUpdates(); err != nil {
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m.logf("disableDynamicUpdates error: %v\n", err)
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}
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if err := m.disableNetBIOS(); err != nil {
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m.logf("disableNetBIOS error: %v\n", err)
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}
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if len(cfg.MatchDomains) == 0 {
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var resolvers []netip.Addr
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var domains []dnsname.FQDN
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if !m.disableLocalDNSOverrideViaNRPT() {
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// Create a default catch-all rule to make ourselves the actual primary resolver.
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// Without this rule, Windows 8.1 and newer devices issue parallel DNS requests to DNS servers
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// associated with all network adapters, even when "Override local DNS" is enabled and/or
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// a Mullvad exit node is being used, resulting in DNS leaks.
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resolvers = cfg.Nameservers
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domains = []dnsname.FQDN{"."}
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}
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if err := m.setSplitDNS(resolvers, domains); err != nil {
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return err
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}
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if err := m.setHosts(nil); err != nil {
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return err
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}
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if err := m.setPrimaryDNS(cfg.Nameservers, cfg.SearchDomains); err != nil {
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return err
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}
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} else {
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if err := m.setSplitDNS(cfg.Nameservers, cfg.MatchDomains); err != nil {
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return err
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}
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// Unset the resolver on the interface to ensure that we do not become
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// the primary resolver. Although this is what we want, at the moment
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// (2022-08-13) it causes single label resolutions from the OS resolver
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// to wait for a MDNS response from the Tailscale interface.
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// See #1659 and #5366 for more details.
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//
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// Still set search domains on the interface, since NRPT only handles
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// query routing and not search domain expansion.
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if err := m.setPrimaryDNS(nil, cfg.SearchDomains); err != nil {
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return err
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}
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// As we are not the primary resolver in this setup, we need to
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// explicitly set some single name hosts to ensure that we can resolve
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// them quickly and get around the 2.3s delay that otherwise occurs due
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// to multicast timeouts.
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if err := m.setHosts(cfg.Hosts); err != nil {
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return err
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}
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}
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// Force DNS re-registration in Active Directory. What we actually
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// care about is that this command invokes the undocumented hidden
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// function that forces Windows to notice that adapter settings
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// have changed, which makes the DNS settings actually take
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// effect.
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//
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// This command can take a few seconds to run, so run it async, best effort.
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//
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// After re-registering DNS, also flush the DNS cache to clear out
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// any cached split-horizon queries that are no longer the correct
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// answer.
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go func() {
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t0 := time.Now()
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m.logf("running ipconfig /registerdns ...")
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cmd := exec.Command("ipconfig", "/registerdns")
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cmd.SysProcAttr = &syscall.SysProcAttr{
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CreationFlags: windows.DETACHED_PROCESS,
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}
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err := cmd.Run()
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d := time.Since(t0).Round(time.Millisecond)
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if err != nil {
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m.logf("error running ipconfig /registerdns after %v: %v", d, err)
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} else {
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m.logf("ran ipconfig /registerdns in %v", d)
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}
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t0 = time.Now()
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m.logf("running ipconfig /flushdns ...")
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cmd = exec.Command("ipconfig", "/flushdns")
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cmd.SysProcAttr = &syscall.SysProcAttr{
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CreationFlags: windows.DETACHED_PROCESS,
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}
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err = cmd.Run()
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d = time.Since(t0).Round(time.Millisecond)
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if err != nil {
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m.logf("error running ipconfig /flushdns after %v: %v", d, err)
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} else {
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m.logf("ran ipconfig /flushdns in %v", d)
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}
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}()
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// On initial setup of WSL, the restart caused by --shutdown is slow,
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// so we do it out-of-line.
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if configureWSL() {
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go func() {
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if err := m.wslManager.SetDNS(cfg); err != nil {
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m.logf("WSL SetDNS: %v", err) // continue
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} else {
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m.logf("WSL SetDNS: success")
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}
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}()
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}
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return nil
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}
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func (m *windowsManager) SupportsSplitDNS() bool {
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return m.nrptDB != nil
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}
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func (m *windowsManager) Close() error {
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m.mu.Lock()
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if m.closing {
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m.mu.Unlock()
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return nil
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}
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m.closing = true
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m.mu.Unlock()
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err := m.SetDNS(OSConfig{})
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if m.nrptDB != nil {
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m.nrptDB.Close()
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m.nrptDB = nil
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}
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return err
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}
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// disableDynamicUpdates sets the appropriate registry values to prevent the
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// Windows DHCP client from sending dynamic DNS updates for our interface to
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// AD domain controllers.
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func (m *windowsManager) disableDynamicUpdates() error {
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prefixen := []winutil.RegistryPathPrefix{
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winutil.IPv4TCPIPInterfacePrefix,
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winutil.IPv6TCPIPInterfacePrefix,
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}
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for _, prefix := range prefixen {
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k, err := m.openInterfaceKey(prefix)
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if err != nil {
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return m.muteKeyNotFoundIfClosing(err)
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}
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defer k.Close()
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if err := k.SetDWordValue("RegistrationEnabled", 0); err != nil {
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return err
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}
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if err := k.SetDWordValue("DisableDynamicUpdate", 1); err != nil {
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return err
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}
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if err := k.SetDWordValue("MaxNumberOfAddressesToRegister", 0); err != nil {
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return err
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}
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}
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return nil
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}
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// setSingleDWORD opens the Registry Key in HKLM for the interface associated
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// with the windowsManager and sets the "keyPrefix\value" to data.
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func (m *windowsManager) setSingleDWORD(prefix winutil.RegistryPathPrefix, value string, data uint32) error {
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k, err := m.openInterfaceKey(prefix)
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if err != nil {
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return m.muteKeyNotFoundIfClosing(err)
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}
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defer k.Close()
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return k.SetDWordValue(value, data)
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}
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// disableNetBIOS sets the appropriate registry values to prevent Windows from
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// sending NetBIOS name resolution requests for our interface which we do not
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// handle nor want to. By leaving it enabled and not handling it we introduce
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// short-name resolution delays in certain conditions as Windows waits for
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// NetBIOS responses from our interface (#1659).
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//
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// Further, LLMNR and NetBIOS are being deprecated anyway in favor of MDNS.
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// https://techcommunity.microsoft.com/t5/networking-blog/aligning-on-mdns-ramping-down-netbios-name-resolution-and-llmnr/ba-p/3290816
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func (m *windowsManager) disableNetBIOS() error {
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return m.setSingleDWORD(winutil.NetBTInterfacePrefix, "NetbiosOptions", 2)
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}
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func (m *windowsManager) GetBaseConfig() (OSConfig, error) {
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resolvers, err := m.getBasePrimaryResolver()
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if err != nil {
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return OSConfig{}, err
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}
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return OSConfig{
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Nameservers: resolvers,
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// Don't return any search domains here, because even Windows
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// 7 correctly handles blending search domains from multiple
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// sources, and any search domains we add here will get tacked
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// onto the Tailscale config unnecessarily.
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}, nil
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}
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// getBasePrimaryResolver returns a guess of the non-Tailscale primary
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// resolver on the system.
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// It's used on Windows 7 to emulate split DNS by trying to figure out
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// what the "previous" primary resolver was. It might be wrong, or
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// incomplete.
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func (m *windowsManager) getBasePrimaryResolver() (resolvers []netip.Addr, err error) {
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tsGUID, err := windows.GUIDFromString(m.guid)
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if err != nil {
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return nil, err
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}
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tsLUID, err := winipcfg.LUIDFromGUID(&tsGUID)
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if err != nil {
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return nil, err
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}
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ifrows, err := winipcfg.GetIPInterfaceTable(windows.AF_INET)
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if err == windows.ERROR_NOT_FOUND {
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// IPv4 seems disabled, try to get interface metrics from IPv6 instead.
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ifrows, err = winipcfg.GetIPInterfaceTable(windows.AF_INET6)
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}
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if err != nil {
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return nil, err
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}
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type candidate struct {
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id winipcfg.LUID
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metric uint32
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}
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var candidates []candidate
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for _, row := range ifrows {
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if !row.Connected {
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continue
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}
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if row.InterfaceLUID == tsLUID {
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continue
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}
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candidates = append(candidates, candidate{row.InterfaceLUID, row.Metric})
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}
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if len(candidates) == 0 {
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// No resolvers set outside of Tailscale.
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return nil, nil
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}
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sort.Slice(candidates, func(i, j int) bool { return candidates[i].metric < candidates[j].metric })
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for _, candidate := range candidates {
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ips, err := candidate.id.DNS()
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if err != nil {
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return nil, err
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}
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ipLoop:
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for _, ip := range ips {
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ip = ip.Unmap()
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// Skip IPv6 site-local resolvers. These are an ancient
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// and obsolete IPv6 RFC, which Windows still faithfully
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// implements. The net result is that some low-metric
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// interfaces can "have" DNS resolvers, but they're just
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// site-local resolver IPs that don't go anywhere. So, we
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// skip the site-local resolvers in order to find the
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// first interface that has real DNS servers configured.
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for _, sl := range siteLocalResolvers {
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if ip.WithZone("") == sl {
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continue ipLoop
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}
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}
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resolvers = append(resolvers, ip)
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}
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if len(resolvers) > 0 {
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// Found some resolvers, we're done.
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break
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}
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}
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return resolvers, nil
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}
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var siteLocalResolvers = []netip.Addr{
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netip.MustParseAddr("fec0:0:0:ffff::1"),
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netip.MustParseAddr("fec0:0:0:ffff::2"),
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netip.MustParseAddr("fec0:0:0:ffff::3"),
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}
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func isWindows10OrBetter() bool {
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key, err := registry.OpenKey(registry.LOCAL_MACHINE, versionKey, registry.READ)
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if err != nil {
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// Fail safe, assume old Windows.
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return false
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}
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// This key above only exists in Windows 10 and above. Its mere
|
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// presence is good enough.
|
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if _, _, err := key.GetIntegerValue("CurrentMajorVersionNumber"); err != nil {
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return false
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}
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return true
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}
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