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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.
package dns
import (
"bytes"
"context"
"errors"
"fmt"
"io/ioutil"
"os"
"os/exec"
"time"
"github.com/godbus/dbus/v5"
"tailscale.com/types/logger"
"tailscale.com/util/cmpver"
)
type kv struct {
k, v string
}
func (kv kv) String() string {
return fmt.Sprintf("%s=%s", kv.k, kv.v)
}
func NewOSConfigurator(logf logger.Logf, interfaceName string) (ret OSConfigurator, err error) {
var debug []kv
dbg := func(k, v string) {
debug = append(debug, kv{k, v})
}
defer func() {
if ret != nil {
dbg("ret", fmt.Sprintf("%T", ret))
}
logf("dns: %v", debug)
}()
bs, err := ioutil.ReadFile("/etc/resolv.conf")
if os.IsNotExist(err) {
dbg("rc", "missing")
return newDirectManager()
}
if err != nil {
return nil, fmt.Errorf("reading /etc/resolv.conf: %w", err)
}
switch resolvOwner(bs) {
case "systemd-resolved":
dbg("rc", "resolved")
if err := dbusPing("org.freedesktop.resolve1", "/org/freedesktop/resolve1"); err != nil {
dbg("resolved", "no")
return newDirectManager()
}
if err := dbusPing("org.freedesktop.NetworkManager", "/org/freedesktop/NetworkManager/DnsManager"); err != nil {
dbg("nm", "no")
return newResolvedManager(logf, interfaceName)
}
dbg("nm", "yes")
if err := nmIsUsingResolved(); err != nil {
dbg("nm-resolved", "no")
return newResolvedManager(logf, interfaceName)
}
dbg("nm-resolved", "yes")
// Version of NetworkManager before 1.26.6 programmed resolved
// incorrectly, such that NM's settings would always take
// precedence over other settings set by other resolved
// clients.
//
// If we're dealing with such a version, we have to set our
// DNS settings through NM to have them take.
//
// However, versions 1.26.6 later both fixed the resolved
// programming issue _and_ started ignoring DNS settings for
// "unmanaged" interfaces - meaning NM 1.26.6 and later
// actively ignore DNS configuration we give it. So, for those
// NM versions, we can and must use resolved directly.
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
// Failed to figure out NM's version, can't make a correct
// decision.
return nil, fmt.Errorf("checking NetworkManager version: %v", err)
}
if old {
dbg("nm-old", "yes")
return newNMManager(interfaceName)
}
dbg("nm-old", "no")
return newResolvedManager(logf, interfaceName)
case "resolvconf":
dbg("rc", "resolvconf")
if err := resolvconfSourceIsNM(bs); err == nil {
dbg("src-is-nm", "yes")
if err := dbusPing("org.freedesktop.NetworkManager", "/org/freedesktop/NetworkManager/DnsManager"); err == nil {
dbg("nm", "yes")
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
return nil, fmt.Errorf("checking NetworkManager version: %v", err)
}
if old {
dbg("nm-old", "yes")
return newNMManager(interfaceName)
} else {
dbg("nm-old", "no")
}
} else {
dbg("nm", "no")
}
} else {
dbg("src-is-nm", "no")
}
if _, err := exec.LookPath("resolvconf"); err != nil {
dbg("resolvconf", "no")
return newDirectManager()
}
dbg("resolvconf", "yes")
return newResolvconfManager(logf)
case "NetworkManager":
dbg("rc", "nm")
if err := dbusPing("org.freedesktop.NetworkManager", "/org/freedesktop/NetworkManager/DnsManager"); err != nil {
dbg("nm", "no")
return newDirectManager()
}
dbg("nm", "yes")
old, err := nmVersionOlderThan("1.26.6")
if err != nil {
return nil, fmt.Errorf("checking NetworkManager version: %v", err)
}
if old {
dbg("nm-old", "yes")
return newNMManager(interfaceName)
}
dbg("nm-old", "no")
return newDirectManager()
default:
dbg("rc", "unknown")
return newDirectManager()
}
}
func resolvconfSourceIsNM(resolvDotConf []byte) error {
b := bytes.NewBuffer(resolvDotConf)
cfg, err := readResolv(b)
if err != nil {
return fmt.Errorf("parsing /etc/resolv.conf: %w", err)
}
var (
paths = []string{
"/etc/resolvconf/run/interface/NetworkManager",
"/run/resolvconf/interface/NetworkManager",
"/var/run/resolvconf/interface/NetworkManager",
"/run/resolvconf/interfaces/NetworkManager",
"/var/run/resolvconf/interfaces/NetworkManager",
}
nmCfg OSConfig
found bool
)
for _, path := range paths {
nmCfg, err = readResolvFile(path)
if os.IsNotExist(err) {
continue
} else if err != nil {
return err
}
found = true
break
}
if !found {
return errors.New("NetworkManager resolvconf snippet not found")
}
if !nmCfg.Equal(cfg) {
return errors.New("NetworkManager config not applied by resolvconf")
}
return nil
}
func nmVersionOlderThan(want string) (bool, error) {
conn, err := dbus.SystemBus()
if err != nil {
// DBus probably not running.
return false, err
}
nm := conn.Object("org.freedesktop.NetworkManager", dbus.ObjectPath("/org/freedesktop/NetworkManager"))
v, err := nm.GetProperty("org.freedesktop.NetworkManager.Version")
if err != nil {
return false, err
}
version, ok := v.Value().(string)
if !ok {
return false, fmt.Errorf("unexpected type %T for NM version", v.Value())
}
return cmpver.Compare(version, want) < 0, nil
}
func nmIsUsingResolved() error {
conn, err := dbus.SystemBus()
if err != nil {
// DBus probably not running.
return err
}
nm := conn.Object("org.freedesktop.NetworkManager", dbus.ObjectPath("/org/freedesktop/NetworkManager/DnsManager"))
v, err := nm.GetProperty("org.freedesktop.NetworkManager.DnsManager.Mode")
if err != nil {
return fmt.Errorf("getting NM mode: %w", err)
}
mode, ok := v.Value().(string)
if !ok {
return fmt.Errorf("unexpected type %T for NM DNS mode", v.Value())
}
if mode != "systemd-resolved" {
return errors.New("NetworkManager is not using systemd-resolved for DNS")
}
return nil
}
func dbusPing(name, objectPath string) error {
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
defer cancel()
conn, err := dbus.SystemBus()
if err != nil {
// DBus probably not running.
return err
}
obj := conn.Object(name, dbus.ObjectPath(objectPath))
call := obj.CallWithContext(ctx, "org.freedesktop.DBus.Peer.Ping", 0)
return call.Err
}
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