wgengine/router/dns: move to net/dns.
Preparation for merging the APIs and whatnot. Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson
committed by
Dave Anderson
Dave Anderson
parent
8432999835
commit
9f7f2af008
205
net/dns/nm.go
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205
net/dns/nm.go
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@ -0,0 +1,205 @@
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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 dns
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import (
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"bufio"
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"bytes"
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"context"
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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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"tailscale.com/util/endian"
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)
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// isNMActive determines if NetworkManager is currently managing system DNS settings.
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func isNMActive() 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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// nmManager uses the NetworkManager DBus API.
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type nmManager struct {
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interfaceName string
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}
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func newNMManager(mconfig ManagerConfig) managerImpl {
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return nmManager{
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interfaceName: mconfig.InterfaceName,
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}
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}
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type nmConnectionSettings map[string]map[string]dbus.Variant
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// Up implements managerImpl.
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func (m nmManager) Up(config Config) error {
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ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
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defer cancel()
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// conn is a shared connection whose lifecycle is managed by the dbus package.
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// We should not interfere with that by closing it.
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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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// This is how we get at the DNS settings:
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//
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// org.freedesktop.NetworkManager
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// |
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// [GetDeviceByIpIface]
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// |
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// v
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// org.freedesktop.NetworkManager.Device <--------\
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// (describes a network interface) |
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// | |
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// [GetAppliedConnection] [Reapply]
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// | |
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// v |
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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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m.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 (
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settings nmConnectionSettings
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version uint64
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)
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err = device.CallWithContext(
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ctx, "org.freedesktop.NetworkManager.Device.GetAppliedConnection", 0,
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uint32(0),
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).Store(&settings, &version)
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if err != nil {
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return fmt.Errorf("getAppliedConnection: %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, endian.Native.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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// We should only request priority if we have nameservers to set.
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if len(dnsv4) == 0 {
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ipv4Map["dns-priority"] = dbus.MakeVariant(100)
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} else {
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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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}
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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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if len(dnsv6) == 0 {
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ipv6Map["dns-priority"] = dbus.MakeVariant(100)
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} else {
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ipv6Map["dns-priority"] = dbus.MakeVariant(-1)
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}
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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 = device.CallWithContext(
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ctx, "org.freedesktop.NetworkManager.Device.Reapply", 0,
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settings, version, uint32(0),
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).Store()
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if err != nil {
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return fmt.Errorf("reapply: %w", err)
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}
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return nil
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}
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// Down implements managerImpl.
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func (m nmManager) Down() error {
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return m.Up(Config{Nameservers: nil, Domains: nil})
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}
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