mirror of https://github.com/tailscale/tailscale/
wgengine/router: dns: unify on *BSD, multimode on Linux, Magic DNS (#536)
Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>reviewable/pr553/r1
Dmytro Shynkevych
4 years ago
committed by
GitHub
parent
6e8f0860af
commit
30bbbe9467
@ -0,0 +1,83 @@
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// Copyright (c) 2020 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 router
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import (
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"time"
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"inet.af/netaddr"
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)
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// DNSConfig is the subset of Config that contains DNS parameters.
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type DNSConfig struct {
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// Nameservers are the IP addresses of the nameservers to use.
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Nameservers []netaddr.IP
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// Domains are the search domains to use.
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Domains []string
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}
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// EquivalentTo determines whether its argument and receiver
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// represent equivalent DNS configurations (then DNS reconfig is a no-op).
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func (lhs DNSConfig) EquivalentTo(rhs DNSConfig) bool {
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if len(lhs.Nameservers) != len(rhs.Nameservers) {
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return false
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}
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if len(lhs.Domains) != len(rhs.Domains) {
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return false
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}
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// With how we perform resolution order shouldn't matter,
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// but it is unlikely that we will encounter different orders.
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for i, server := range lhs.Nameservers {
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if rhs.Nameservers[i] != server {
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return false
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}
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}
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for i, domain := range lhs.Domains {
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if rhs.Domains[i] != domain {
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return false
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}
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}
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return true
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}
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// dnsReconfigTimeout is the timeout for DNS reconfiguration.
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//
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// This is useful because certain conditions can cause indefinite hangs
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// (such as improper dbus auth followed by contextless dbus.Object.Call).
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// Such operations should be wrapped in a timeout context.
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const dnsReconfigTimeout = time.Second
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// dnsMode determines how DNS settings are managed.
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type dnsMode uint8
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const (
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// dnsDirect indicates that /etc/resolv.conf is edited directly.
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dnsDirect dnsMode = iota
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// dnsResolvconf indicates that a resolvconf binary is used.
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dnsResolvconf
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// dnsNetworkManager indicates that the NetworkManaer DBus API is used.
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dnsNetworkManager
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// dnsResolved indicates that the systemd-resolved DBus API is used.
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dnsResolved
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)
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func (m dnsMode) String() string {
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switch m {
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case dnsDirect:
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return "direct"
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case dnsResolvconf:
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return "resolvconf"
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case dnsNetworkManager:
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return "networkmanager"
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case dnsResolved:
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return "resolved"
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default:
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return "???"
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}
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}
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@ -0,0 +1,151 @@
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// Copyright (c) 2020 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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// +build linux freebsd openbsd
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package router
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"io/ioutil"
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"os"
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"strings"
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"inet.af/netaddr"
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"tailscale.com/atomicfile"
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)
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const (
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tsConf = "/etc/resolv.tailscale.conf"
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backupConf = "/etc/resolv.pre-tailscale-backup.conf"
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resolvConf = "/etc/resolv.conf"
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)
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// dnsWriteConfig writes DNS configuration in resolv.conf format to the given writer.
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func dnsWriteConfig(w io.Writer, servers []netaddr.IP, domains []string) {
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io.WriteString(w, "# resolv.conf(5) file generated by tailscale\n")
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io.WriteString(w, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
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for _, ns := range servers {
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io.WriteString(w, "nameserver ")
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io.WriteString(w, ns.String())
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io.WriteString(w, "\n")
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}
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if len(domains) > 0 {
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io.WriteString(w, "search")
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for _, domain := range domains {
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io.WriteString(w, " ")
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io.WriteString(w, domain)
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}
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io.WriteString(w, "\n")
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}
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}
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// dnsReadConfig reads DNS configuration from /etc/resolv.conf.
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func dnsReadConfig() (DNSConfig, error) {
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var config DNSConfig
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f, err := os.Open("/etc/resolv.conf")
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if err != nil {
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return config, err
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}
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scanner := bufio.NewScanner(f)
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for scanner.Scan() {
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line := strings.TrimSpace(scanner.Text())
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if strings.HasPrefix(line, "nameserver") {
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nameserver := strings.TrimPrefix(line, "nameserver")
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nameserver = strings.TrimSpace(nameserver)
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ip, err := netaddr.ParseIP(nameserver)
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if err != nil {
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return config, err
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}
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config.Nameservers = append(config.Nameservers, ip)
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continue
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}
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if strings.HasPrefix(line, "search") {
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domain := strings.TrimPrefix(line, "search")
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domain = strings.TrimSpace(domain)
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config.Domains = append(config.Domains, domain)
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continue
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}
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}
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return config, nil
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}
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// dnsDirectUp replaces /etc/resolv.conf with a file generated
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// from the given configuration, creating a backup of its old state.
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//
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// This way of configuring DNS is precarious, since it does not react
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// to the disappearance of the Tailscale interface.
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// The caller must call dnsDirectDown before program shutdown
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// and ensure that router.Cleanup is run if the program terminates unexpectedly.
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func dnsDirectUp(config DNSConfig) error {
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// Write the tsConf file.
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buf := new(bytes.Buffer)
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dnsWriteConfig(buf, config.Nameservers, config.Domains)
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if err := atomicfile.WriteFile(tsConf, buf.Bytes(), 0644); err != nil {
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return err
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}
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if linkPath, err := os.Readlink(resolvConf); err != nil {
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// Remove any old backup that may exist.
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os.Remove(backupConf)
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// Backup the existing /etc/resolv.conf file.
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contents, err := ioutil.ReadFile(resolvConf)
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// If the original did not exist, still back up an empty file.
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// The presence of a backup file is the way we know that Up ran.
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if err != nil && !os.IsNotExist(err) {
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return err
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}
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if err := atomicfile.WriteFile(backupConf, contents, 0644); err != nil {
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return err
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}
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} else if linkPath != tsConf {
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// Backup the existing symlink.
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os.Remove(backupConf)
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if err := os.Symlink(linkPath, backupConf); err != nil {
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return err
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}
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} else {
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// Nothing to do, resolvConf already points to tsConf.
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return nil
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}
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os.Remove(resolvConf)
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if err := os.Symlink(tsConf, resolvConf); 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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// dnsDirectDown restores /etc/resolv.conf to its state before dnsDirectUp.
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// It is idempotent and behaves correctly even if dnsDirectUp has never been run.
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func dnsDirectDown() error {
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if _, err := os.Stat(backupConf); err != nil {
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// If the backup file does not exist, then Up never ran successfully.
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if os.IsNotExist(err) {
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return nil
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}
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return err
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}
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if ln, err := os.Readlink(resolvConf); err != nil {
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return err
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} else if ln != tsConf {
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return fmt.Errorf("resolv.conf is not a symlink to %s", tsConf)
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}
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if err := os.Rename(backupConf, resolvConf); err != nil {
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return err
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}
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os.Remove(tsConf)
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return nil
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}
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@ -0,0 +1,209 @@
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// Copyright (c) 2020 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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// +build linux
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package router
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import (
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"bufio"
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"bytes"
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"context"
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"encoding/binary"
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"fmt"
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"os"
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"os/exec"
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"github.com/godbus/dbus/v5"
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)
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type nmSettings map[string]map[string]dbus.Variant
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// nmIsActive determines if NetworkManager is currently managing system DNS settings.
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func nmIsActive() bool {
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// This is somewhat tricky because NetworkManager supports a number
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// of DNS configuration modes. In all cases, we expect it to be installed
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// and /etc/resolv.conf to contain a mention of NetworkManager in the comments.
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_, err := exec.LookPath("NetworkManager")
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if err != nil {
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return false
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}
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f, err := os.Open("/etc/resolv.conf")
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if err != nil {
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return false
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}
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defer f.Close()
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scanner := bufio.NewScanner(f)
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for scanner.Scan() {
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line := scanner.Bytes()
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// Look for the word "NetworkManager" until comments end.
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if len(line) > 0 && line[0] != '#' {
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return false
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}
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if bytes.Contains(line, []byte("NetworkManager")) {
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return true
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}
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}
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return false
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}
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// dnsNetworkManagerUp updates the DNS config for the Tailscale interface
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// through the NetworkManager DBus API.
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func dnsNetworkManagerUp(config DNSConfig, interfaceName string) error {
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ctx, cancel := context.WithTimeout(context.Background(), dnsReconfigTimeout)
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defer cancel()
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conn, err := dbus.SystemBus()
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if err != nil {
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return fmt.Errorf("connecting to system bus: %w", err)
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}
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defer conn.Close()
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// This is how we get at the DNS settings:
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// org.freedesktop.NetworkManager
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// ⇩
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// org.freedesktop.NetworkManager.Device
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// (describes a network interface)
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// ⇩
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// org.freedesktop.NetworkManager.Connection.Active
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// (active instance of a connection initialized from settings)
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// ⇩
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// org.freedesktop.NetworkManager.Connection
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// (connection settings)
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// contains {dns, dns-priority, dns-search}
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//
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// Ref: https://developer.gnome.org/NetworkManager/stable/settings-ipv4.html.
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nm := conn.Object(
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"org.freedesktop.NetworkManager",
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dbus.ObjectPath("/org/freedesktop/NetworkManager"),
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)
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var devicePath dbus.ObjectPath
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err = nm.CallWithContext(
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ctx, "org.freedesktop.NetworkManager.GetDeviceByIpIface", 0,
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interfaceName,
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).Store(&devicePath)
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if err != nil {
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return fmt.Errorf("GetDeviceByIpIface: %w", err)
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}
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device := conn.Object("org.freedesktop.NetworkManager", devicePath)
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var activeConnPath dbus.ObjectPath
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err = device.CallWithContext(
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ctx, "org.freedesktop.DBus.Properties.Get", 0,
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"org.freedesktop.NetworkManager.Device", "ActiveConnection",
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).Store(&activeConnPath)
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if err != nil {
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return fmt.Errorf("getting ActiveConnection: %w", err)
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}
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activeConn := conn.Object("org.freedesktop.NetworkManager", activeConnPath)
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var connPath dbus.ObjectPath
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err = activeConn.CallWithContext(
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ctx, "org.freedesktop.DBus.Properties.Get", 0,
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"org.freedesktop.NetworkManager.Connection.Active", "Connection",
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).Store(&connPath)
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if err != nil {
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return fmt.Errorf("getting Connection: %w", err)
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}
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connection := conn.Object("org.freedesktop.NetworkManager", connPath)
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// Note: strictly speaking, the following is not safe.
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//
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// It appears that the way to update connection settings
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// in NetworkManager is to get an entire connection settings object,
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// modify the fields we are interested in, then submit the modified object.
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//
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// This is unfortunate: if the network state changes in the meantime
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// (most relevantly to us, if routes change), we will overwrite those changes.
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//
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// That said, fortunately, this should have no real effect, as Tailscale routes
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// do not seem to show up in NetworkManager at all,
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// so they are presumably immune from being tampered with.
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var settings nmSettings
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err = connection.CallWithContext(
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ctx, "org.freedesktop.NetworkManager.Settings.Connection.GetSettings", 0,
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).Store(&settings)
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if err != nil {
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return fmt.Errorf("getting Settings: %w", err)
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}
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// Frustratingly, NetworkManager represents IPv4 addresses as uint32s,
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// although IPv6 addresses are represented as byte arrays.
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// Perform the conversion here.
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var (
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dnsv4 []uint32
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dnsv6 [][]byte
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)
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for _, ip := range config.Nameservers {
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b := ip.As16()
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if ip.Is4() {
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dnsv4 = append(dnsv4, binary.BigEndian.Uint32(b[12:]))
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} else {
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dnsv6 = append(dnsv6, b[:])
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}
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}
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ipv4Map := settings["ipv4"]
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ipv4Map["dns"] = dbus.MakeVariant(dnsv4)
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ipv4Map["dns-search"] = dbus.MakeVariant(config.Domains)
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// dns-priority = -1 ensures that we have priority
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// over other interfaces, except those exploiting this same trick.
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// Ref: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1211110/comments/92.
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ipv4Map["dns-priority"] = dbus.MakeVariant(-1)
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// In principle, we should not need set this to true,
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// as our interface does not configure any automatic DNS settings (presumably via DHCP).
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// All the same, better to be safe.
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ipv4Map["ignore-auto-dns"] = dbus.MakeVariant(true)
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ipv6Map := settings["ipv6"]
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// This is a hack.
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// Methods "disabled", "ignore", "link-local" (IPv6 default) prevent us from setting DNS.
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// It seems that our only recourse is "manual" or "auto".
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// "manual" requires addresses, so we use "auto", which will assign us a random IPv6 /64.
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ipv6Map["method"] = dbus.MakeVariant("auto")
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// Our IPv6 config is a fake, so it should never become the default route.
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ipv6Map["never-default"] = dbus.MakeVariant(true)
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// Moreover, we should ignore all autoconfigured routes (hopefully none), as they are bogus.
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ipv6Map["ignore-auto-routes"] = dbus.MakeVariant(true)
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// Finally, set the actual DNS config.
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ipv6Map["dns"] = dbus.MakeVariant(dnsv6)
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ipv6Map["dns-search"] = dbus.MakeVariant(config.Domains)
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ipv6Map["dns-priority"] = dbus.MakeVariant(-1)
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ipv6Map["ignore-auto-dns"] = dbus.MakeVariant(true)
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// deprecatedProperties are the properties in interface settings
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// that are deprecated by NetworkManager.
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//
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// In practice, this means that they are returned for reading,
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// but submitting a settings object with them present fails
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// with hard-to-diagnose errors. They must be removed.
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deprecatedProperties := []string{
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"addresses", "routes",
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}
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for _, property := range deprecatedProperties {
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delete(ipv4Map, property)
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delete(ipv6Map, property)
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}
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err = connection.CallWithContext(
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ctx, "org.freedesktop.NetworkManager.Settings.Connection.UpdateUnsaved", 0, settings,
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).Store()
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if err != nil {
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return fmt.Errorf("setting Settings: %w", err)
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}
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return nil
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}
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// dnsNetworkManagerDown undoes the changes made by dnsNetworkManagerUp.
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func dnsNetworkManagerDown(interfaceName string) error {
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return dnsNetworkManagerUp(DNSConfig{Nameservers: nil, Domains: nil}, interfaceName)
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}
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@ -0,0 +1,84 @@
|
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
|
||||
// Use of this source code is governed by a BSD-style
|
||||
// license that can be found in the LICENSE file.
|
||||
|
||||
// +build linux freebsd
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|
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package router
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|
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import (
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"bufio"
|
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"bytes"
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"fmt"
|
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"os"
|
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"os/exec"
|
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)
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// resolvconfIsActive indicates whether the system appears to be using resolvconf.
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// If this is true, then dnsManualUp should be avoided:
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// resolvconf has exclusive ownership of /etc/resolv.conf.
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func resolvconfIsActive() bool {
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// Sanity-check first: if there is no resolvconf binary, then this is fruitless.
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//
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// However, this binary may be a shim like the one systemd-resolved provides.
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// Such a shim may not behave as expected: in particular, systemd-resolved
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// does not seem to respect the exclusive mode -x, saying:
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// -x Send DNS traffic preferably over this interface
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// whereas e.g. openresolv sends DNS traffix _exclusively_ over that interface,
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// or not at all (in case of another exclusive-mode request later in time).
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//
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// Moreover, resolvconf may be installed but unused, in which case we should
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// not use it either, lest we clobber existing configuration.
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//
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// To handle all the above correctly, we scan the comments in /etc/resolv.conf
|
||||
// to ensure that it was generated by a resolvconf implementation.
|
||||
_, err := exec.LookPath("resolvconf")
|
||||
if err != nil {
|
||||
return false
|
||||
}
|
||||
|
||||
f, err := os.Open("/etc/resolv.conf")
|
||||
if err != nil {
|
||||
return false
|
||||
}
|
||||
defer f.Close()
|
||||
|
||||
scanner := bufio.NewScanner(f)
|
||||
for scanner.Scan() {
|
||||
line := scanner.Bytes()
|
||||
// Look for the word "resolvconf" until comments end.
|
||||
if len(line) > 0 && line[0] != '#' {
|
||||
return false
|
||||
}
|
||||
if bytes.Contains(line, []byte("resolvconf")) {
|
||||
return true
|
||||
}
|
||||
}
|
||||
return false
|
||||
}
|
||||
|
||||
// dnsResolvconfUp invokes the resolvconf binary to associate
|
||||
// the given DNS configuration the Tailscale interface.
|
||||
func dnsResolvconfUp(config DNSConfig, interfaceName string) error {
|
||||
stdin := new(bytes.Buffer)
|
||||
dnsWriteConfig(stdin, config.Nameservers, config.Domains) // dns_direct.go
|
||||
|
||||
cmd := exec.Command("resolvconf", "-m", "0", "-x", "-a", interfaceName+".inet")
|
||||
cmd.Stdin = stdin
|
||||
out, err := cmd.CombinedOutput()
|
||||
if err != nil {
|
||||
return fmt.Errorf("running %s: %s", cmd, out)
|
||||
}
|
||||
|
||||
return nil
|
||||
}
|
||||
|
||||
// dnsResolvconfDown undoes the action of dnsResolvconfUp.
|
||||
func dnsResolvconfDown(interfaceName string) error {
|
||||
cmd := exec.Command("resolvconf", "-f", "-d", interfaceName+".inet")
|
||||
out, err := cmd.CombinedOutput()
|
||||
if err != nil {
|
||||
return fmt.Errorf("running %s: %s", cmd, out)
|
||||
}
|
||||
return nil
|
||||
}
|
||||
@ -0,0 +1,177 @@
|
||||
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
|
||||
// Use of this source code is governed by a BSD-style
|
||||
// license that can be found in the LICENSE file.
|
||||
|
||||
// +build linux
|
||||
|
||||
package router
|
||||
|
||||
import (
|
||||
"context"
|
||||
"errors"
|
||||
"fmt"
|
||||
"os/exec"
|
||||
|
||||
"github.com/godbus/dbus/v5"
|
||||
"golang.org/x/sys/unix"
|
||||
"inet.af/netaddr"
|
||||
"tailscale.com/net/interfaces"
|
||||
)
|
||||
|
||||
// resolvedListenAddr is the listen address of the resolved stub resolver.
|
||||
//
|
||||
// We only consider resolved to be the system resolver if the stub resolver is;
|
||||
// that is, if this address is the sole nameserver in /etc/resolved.conf.
|
||||
// In other cases, resolved may still be managing the system DNS configuration directly.
|
||||
// Then the nameserver list will be a concatenation of those for all
|
||||
// the interfaces that register their interest in being a default resolver with
|
||||
// SetLinkDomains([]{{"~.", true}, ...})
|
||||
// which includes at least the interface with the default route, i.e. not us.
|
||||
// This does not work for us: there is a possibility of getting NXDOMAIN
|
||||
// from the other nameservers before we are asked or get a chance to respond.
|
||||
// We consider this case as lacking resolved support and fall through to dnsDirect.
|
||||
//
|
||||
// While it may seem that we need to read a config option to get at this,
|
||||
// this address is, in fact, hard-coded into resolved.
|
||||
var resolvedListenAddr = netaddr.IPv4(127, 0, 0, 53)
|
||||
|
||||
var errNotReady = errors.New("interface not ready")
|
||||
|
||||
type resolvedLinkNameserver struct {
|
||||
Family int32
|
||||
Address []byte
|
||||
}
|
||||
|
||||
type resolvedLinkDomain struct {
|
||||
Domain string
|
||||
RoutingOnly bool
|
||||
}
|
||||
|
||||
// resolvedIsActive determines if resolved is currently managing system DNS settings.
|
||||
func resolvedIsActive() bool {
|
||||
// systemd-resolved is never installed without systemd.
|
||||
_, err := exec.LookPath("systemctl")
|
||||
if err != nil {
|
||||
return false
|
||||
}
|
||||
|
||||
// is-active exits with code 3 if the service is not active.
|
||||
err = exec.Command("systemctl", "is-active", "systemd-resolved").Run()
|
||||
if err != nil {
|
||||
return false
|
||||
}
|
||||
|
||||
config, err := dnsReadConfig()
|
||||
if err != nil {
|
||||
return false
|
||||
}
|
||||
|
||||
// The sole nameserver must be the systemd-resolved stub.
|
||||
if len(config.Nameservers) == 1 && config.Nameservers[0] == resolvedListenAddr {
|
||||
return true
|
||||
}
|
||||
|
||||
return false
|
||||
}
|
||||
|
||||
// dnsResolvedUp sets the DNS parameters for the Tailscale interface
|
||||
// to given nameservers and search domains using the resolved DBus API.
|
||||
func dnsResolvedUp(config DNSConfig) error {
|
||||
ctx, cancel := context.WithTimeout(context.Background(), dnsReconfigTimeout)
|
||||
defer cancel()
|
||||
|
||||
conn, err := dbus.SystemBus()
|
||||
if err != nil {
|
||||
return fmt.Errorf("connecting to system bus: %w", err)
|
||||
}
|
||||
defer conn.Close()
|
||||
|
||||
resolved := conn.Object(
|
||||
"org.freedesktop.resolve1",
|
||||
dbus.ObjectPath("/org/freedesktop/resolve1"),
|
||||
)
|
||||
|
||||
_, iface, err := interfaces.Tailscale()
|
||||
if err != nil {
|
||||
return fmt.Errorf("getting interface index: %w", err)
|
||||
}
|
||||
if iface == nil {
|
||||
return errNotReady
|
||||
}
|
||||
|
||||
var linkNameservers = make([]resolvedLinkNameserver, len(config.Nameservers))
|
||||
for i, server := range config.Nameservers {
|
||||
ip := server.As16()
|
||||
if server.Is4() {
|
||||
linkNameservers[i] = resolvedLinkNameserver{
|
||||
Family: unix.AF_INET,
|
||||
Address: ip[12:],
|
||||
}
|
||||
} else {
|
||||
linkNameservers[i] = resolvedLinkNameserver{
|
||||
Family: unix.AF_INET6,
|
||||
Address: ip[:],
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
err = resolved.CallWithContext(
|
||||
ctx, "org.freedesktop.resolve1.Manager.SetLinkDNS", 0,
|
||||
iface.Index, linkNameservers,
|
||||
).Store()
|
||||
if err != nil {
|
||||
return fmt.Errorf("SetLinkDNS: %w", err)
|
||||
}
|
||||
|
||||
var linkDomains = make([]resolvedLinkDomain, len(config.Domains))
|
||||
for i, domain := range config.Domains {
|
||||
linkDomains[i] = resolvedLinkDomain{
|
||||
Domain: domain,
|
||||
RoutingOnly: false,
|
||||
}
|
||||
}
|
||||
|
||||
err = resolved.CallWithContext(
|
||||
ctx, "org.freedesktop.resolve1.Manager.SetLinkDomains", 0,
|
||||
iface.Index, linkDomains,
|
||||
).Store()
|
||||
if err != nil {
|
||||
return fmt.Errorf("SetLinkDomains: %w", err)
|
||||
}
|
||||
|
||||
return nil
|
||||
}
|
||||
|
||||
// dnsResolvedDown undoes the changes made by dnsResolvedUp.
|
||||
func dnsResolvedDown() error {
|
||||
ctx, cancel := context.WithTimeout(context.Background(), dnsReconfigTimeout)
|
||||
defer cancel()
|
||||
|
||||
conn, err := dbus.SystemBus()
|
||||
if err != nil {
|
||||
return fmt.Errorf("connecting to system bus: %w", err)
|
||||
}
|
||||
|
||||
resolved := conn.Object(
|
||||
"org.freedesktop.resolve1",
|
||||
dbus.ObjectPath("/org/freedesktop/resolve1"),
|
||||
)
|
||||
|
||||
_, iface, err := interfaces.Tailscale()
|
||||
if err != nil {
|
||||
return fmt.Errorf("getting interface index: %w", err)
|
||||
}
|
||||
if iface == nil {
|
||||
return errNotReady
|
||||
}
|
||||
|
||||
err = resolved.CallWithContext(
|
||||
ctx, "org.freedesktop.resolve1.Manager.RevertLink", 0,
|
||||
iface.Index,
|
||||
).Store()
|
||||
if err != nil {
|
||||
return fmt.Errorf("RevertLink: %w", err)
|
||||
}
|
||||
|
||||
return nil
|
||||
}
|
||||
Loading…
Reference in New Issue