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tailscale/net/dns/nm.go

238 lines
7.0 KiB
Go

// 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
//lint:file-ignore U1000 refactoring, temporarily unused code.
package dns
import (
"bufio"
"bytes"
"context"
"fmt"
"os"
"time"
"github.com/godbus/dbus/v5"
"tailscale.com/util/endian"
)
// isNMActive determines if NetworkManager is currently managing system DNS settings.
func isNMActive() bool {
ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
defer cancel()
conn, err := dbus.SystemBus()
if err != nil {
// Probably no DBus on this system. Either way, we can't
// control NM without DBus.
return false
}
// Try to ping NetworkManager's DnsManager object. If it responds,
// NM is running and we're allowed to touch it.
nm := conn.Object("org.freedesktop.NetworkManager", dbus.ObjectPath("/org/freedesktop/NetworkManager/DnsManager"))
call := nm.CallWithContext(ctx, "org.freedesktop.DBus.Peer.Ping", 0)
if call.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 "NetworkManager" until comments end.
if len(line) > 0 && line[0] != '#' {
return false
}
if bytes.Contains(line, []byte("NetworkManager")) {
return true
}
}
return false
}
// nmManager uses the NetworkManager DBus API.
type nmManager struct {
interfaceName string
}
func newNMManager(interfaceName string) nmManager {
return nmManager{
interfaceName: interfaceName,
}
}
type nmConnectionSettings map[string]map[string]dbus.Variant
func (m nmManager) SetDNS(config OSConfig) error {
ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
defer cancel()
// NetworkManager only lets you set DNS settings on "active"
// connections, which requires an assigned IP address. This got
// configured before the DNS manager was invoked, but it might
// take a little time for the netlink notifications to propagate
// up. So, keep retrying for the duration of the reconfigTimeout.
var err error
for ctx.Err() == nil {
err = m.trySet(ctx, config)
if err == nil {
break
}
time.Sleep(10 * time.Millisecond)
}
return err
}
func (m nmManager) trySet(ctx context.Context, config OSConfig) error {
conn, err := dbus.SystemBus()
if err != nil {
return fmt.Errorf("connecting to system bus: %w", err)
}
// This is how we get at the DNS settings:
//
// org.freedesktop.NetworkManager
// |
// [GetDeviceByIpIface]
// |
// v
// org.freedesktop.NetworkManager.Device <--------\
// (describes a network interface) |
// | |
// [GetAppliedConnection] [Reapply]
// | |
// v |
// org.freedesktop.NetworkManager.Connection |
// (connection settings) ------/
// contains {dns, dns-priority, dns-search}
//
// Ref: https://developer.gnome.org/NetworkManager/stable/settings-ipv4.html.
nm := conn.Object(
"org.freedesktop.NetworkManager",
dbus.ObjectPath("/org/freedesktop/NetworkManager"),
)
var devicePath dbus.ObjectPath
err = nm.CallWithContext(
ctx, "org.freedesktop.NetworkManager.GetDeviceByIpIface", 0,
m.interfaceName,
).Store(&devicePath)
if err != nil {
return fmt.Errorf("getDeviceByIpIface: %w", err)
}
device := conn.Object("org.freedesktop.NetworkManager", devicePath)
var (
settings nmConnectionSettings
version uint64
)
err = device.CallWithContext(
ctx, "org.freedesktop.NetworkManager.Device.GetAppliedConnection", 0,
uint32(0),
).Store(&settings, &version)
if err != nil {
return fmt.Errorf("getAppliedConnection: %w", err)
}
// Frustratingly, NetworkManager represents IPv4 addresses as uint32s,
// although IPv6 addresses are represented as byte arrays.
// Perform the conversion here.
var (
dnsv4 []uint32
dnsv6 [][]byte
)
for _, ip := range config.Nameservers {
b := ip.As16()
if ip.Is4() {
dnsv4 = append(dnsv4, endian.Native.Uint32(b[12:]))
} else {
dnsv6 = append(dnsv6, b[:])
}
}
ipv4Map := settings["ipv4"]
ipv4Map["dns"] = dbus.MakeVariant(dnsv4)
ipv4Map["dns-search"] = dbus.MakeVariant(config.SearchDomains)
// We should only request priority if we have nameservers to set.
if len(dnsv4) == 0 {
ipv4Map["dns-priority"] = dbus.MakeVariant(100)
} else {
// dns-priority = -1 ensures that we have priority
// over other interfaces, except those exploiting this same trick.
// Ref: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1211110/comments/92.
ipv4Map["dns-priority"] = dbus.MakeVariant(-1)
}
// In principle, we should not need set this to true,
// as our interface does not configure any automatic DNS settings (presumably via DHCP).
// All the same, better to be safe.
ipv4Map["ignore-auto-dns"] = dbus.MakeVariant(true)
ipv6Map := settings["ipv6"]
// This is a hack.
// Methods "disabled", "ignore", "link-local" (IPv6 default) prevent us from setting DNS.
// It seems that our only recourse is "manual" or "auto".
// "manual" requires addresses, so we use "auto", which will assign us a random IPv6 /64.
ipv6Map["method"] = dbus.MakeVariant("auto")
// Our IPv6 config is a fake, so it should never become the default route.
ipv6Map["never-default"] = dbus.MakeVariant(true)
// Moreover, we should ignore all autoconfigured routes (hopefully none), as they are bogus.
ipv6Map["ignore-auto-routes"] = dbus.MakeVariant(true)
// Finally, set the actual DNS config.
ipv6Map["dns"] = dbus.MakeVariant(dnsv6)
ipv6Map["dns-search"] = dbus.MakeVariant(config.SearchDomains)
if len(dnsv6) == 0 {
ipv6Map["dns-priority"] = dbus.MakeVariant(100)
} else {
ipv6Map["dns-priority"] = dbus.MakeVariant(-1)
}
ipv6Map["ignore-auto-dns"] = dbus.MakeVariant(true)
// deprecatedProperties are the properties in interface settings
// that are deprecated by NetworkManager.
//
// In practice, this means that they are returned for reading,
// but submitting a settings object with them present fails
// with hard-to-diagnose errors. They must be removed.
deprecatedProperties := []string{
"addresses", "routes",
}
for _, property := range deprecatedProperties {
delete(ipv4Map, property)
delete(ipv6Map, property)
}
err = device.CallWithContext(
ctx, "org.freedesktop.NetworkManager.Device.Reapply", 0,
settings, version, uint32(0),
).Store()
if err != nil {
return fmt.Errorf("reapply: %w", err)
}
return nil
}
func (m nmManager) SupportsSplitDNS() bool { return false }
func (m nmManager) GetBaseConfig() (OSConfig, error) {
return OSConfig{}, ErrGetBaseConfigNotSupported
}
func (m nmManager) Close() error {
return m.SetDNS(OSConfig{})
}