tailscale/wgengine/router_linux.go

294 lines
7.1 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.
package wgengine
import (
"bytes"
"fmt"
"io/ioutil"
"log"
"os"
"os/exec"
"path/filepath"
"strings"
"github.com/coreos/go-iptables/iptables"
"github.com/tailscale/wireguard-go/device"
"github.com/tailscale/wireguard-go/tun"
"github.com/tailscale/wireguard-go/wgcfg"
"tailscale.com/atomicfile"
"tailscale.com/types/logger"
)
const DefaultTunName = "tailscale0"
type linuxRouter struct {
logf func(fmt string, args ...interface{})
tunname string
local wgcfg.CIDR
routes map[wgcfg.CIDR]struct{}
ipt4 *iptables.IPTables
}
func newUserspaceRouter(logf logger.Logf, _ *device.Device, tunDev tun.Device) (Router, error) {
tunname, err := tunDev.Name()
if err != nil {
return nil, err
}
ipt4, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
if err != nil {
return nil, err
}
return &linuxRouter{
logf: logf,
tunname: tunname,
ipt4: ipt4,
}, nil
}
func cmd(args ...string) *exec.Cmd {
if len(args) == 0 {
log.Fatalf("exec.Cmd(%#v) invalid; need argv[0]\n", args)
}
return exec.Command(args[0], args[1:]...)
}
func (r *linuxRouter) Up() error {
out, err := cmd("ip", "link", "set", r.tunname, "up").CombinedOutput()
if err != nil {
// TODO: this should return an error; why is it calling log.Fatalf?
// Audit callers to make sure they're handling errors.
log.Fatalf("running ip link failed: %v\n%s", err, out)
}
err = r.ipt4.AppendUnique("filter", "FORWARD", r.forwardRule()...)
if err != nil {
r.logf("iptables forward failed: %v", err)
}
err = r.ipt4.AppendUnique("nat", "POSTROUTING", r.natRule()...)
if err != nil {
r.logf("iptables nat failed: %v", err)
}
return nil
}
func (r *linuxRouter) SetRoutes(rs RouteSettings) error {
var errq error
if rs.LocalAddr != r.local {
if r.local != (wgcfg.CIDR{}) {
addrdel := []string{"ip", "addr",
"del", r.local.String(),
"dev", r.tunname}
out, err := cmd(addrdel...).CombinedOutput()
if err != nil {
r.logf("addr del failed: %v: %v\n%s", addrdel, err, out)
if errq == nil {
errq = err
}
}
}
addradd := []string{"ip", "addr",
"add", rs.LocalAddr.String(),
"dev", r.tunname}
out, err := cmd(addradd...).CombinedOutput()
if err != nil {
r.logf("addr add failed: %v: %v\n%s", addradd, err, out)
if errq == nil {
errq = err
}
}
}
newRoutes := make(map[wgcfg.CIDR]struct{})
for _, peer := range rs.Cfg.Peers {
for _, route := range peer.AllowedIPs {
newRoutes[route] = struct{}{}
}
}
for route := range r.routes {
if _, keep := newRoutes[route]; !keep {
net := route.IPNet()
nip := net.IP.Mask(net.Mask)
nstr := fmt.Sprintf("%v/%d", nip, route.Mask)
addrdel := []string{"ip", "route",
"del", nstr,
"via", r.local.IP.String(),
"dev", r.tunname}
out, err := cmd(addrdel...).CombinedOutput()
if err != nil {
r.logf("addr del failed: %v: %v\n%s", addrdel, err, out)
if errq == nil {
errq = err
}
}
}
}
for route := range newRoutes {
if _, exists := r.routes[route]; !exists {
net := route.IPNet()
nip := net.IP.Mask(net.Mask)
nstr := fmt.Sprintf("%v/%d", nip, route.Mask)
addradd := []string{"ip", "route",
"add", nstr,
"via", rs.LocalAddr.IP.String(),
"dev", r.tunname}
out, err := cmd(addradd...).CombinedOutput()
if err != nil {
r.logf("addr add failed: %v: %v\n%s", addradd, err, out)
if errq == nil {
errq = err
}
}
}
}
r.local = rs.LocalAddr
r.routes = newRoutes
// TODO: this:
if false {
if err := r.replaceResolvConf(rs.DNS, rs.DNSDomains); err != nil {
errq = fmt.Errorf("replacing resolv.conf failed: %v", err)
}
}
return errq
}
func (r *linuxRouter) forwardRule() []string {
return []string{
"-m", "comment", "--comment", "tailscale",
"-i", r.tunname,
"-j", "ACCEPT",
}
}
func (r *linuxRouter) natRule() []string {
// TODO(apenwarr): hardcoded eth0 interface is obviously not right.
return []string{
"-m", "comment", "--comment", "tailscale",
"-o", "eth0",
"-j", "MASQUERADE",
}
}
func (r *linuxRouter) Close() error {
var ret error
set := func(err error) {
if ret == nil && err != nil {
ret = err
}
}
if err := r.restoreResolvConf(); err != nil {
r.logf("failed to restore system resolv.conf: %v", err)
set(err)
}
set(r.ipt4.Delete("filter", "FORWARD", r.forwardRule()...))
set(r.ipt4.Delete("nat", "POSTROUTING", r.natRule()...))
// TODO(apenwarr): clean up routes etc.
return ret
}
const (
tsConf = "/etc/resolv.tailscale.conf"
backupConf = "/etc/resolv.pre-tailscale-backup.conf"
resolvConf = "/etc/resolv.conf"
)
func (r *linuxRouter) replaceResolvConf(servers []wgcfg.IP, domains []string) error {
if len(servers) == 0 {
return r.restoreResolvConf()
}
// First write the tsConf file.
buf := new(bytes.Buffer)
fmt.Fprintf(buf, "# resolv.conf(5) file generated by tailscale\n")
fmt.Fprintf(buf, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
for _, ns := range servers {
fmt.Fprintf(buf, "nameserver %s\n", ns)
}
if len(domains) > 0 {
fmt.Fprintf(buf, "search "+strings.Join(domains, " ")+"\n")
}
f, err := ioutil.TempFile(filepath.Dir(tsConf), filepath.Base(tsConf)+".*")
if err != nil {
return err
}
f.Close()
if err := atomicfile.WriteFile(f.Name(), buf.Bytes(), 0644); err != nil {
return err
}
os.Chmod(f.Name(), 0644) // ioutil.TempFile creates the file with 0600
if err := os.Rename(f.Name(), tsConf); err != nil {
return err
}
if linkPath, err := os.Readlink(resolvConf); err != nil {
// Remove any old backup that may exist.
os.Remove(backupConf)
// Backup the existing /etc/resolv.conf file.
contents, err := ioutil.ReadFile(resolvConf)
if os.IsNotExist(err) {
// No existing /etc/resolv.conf file to backup.
// Nothing to do.
return nil
} else if err != nil {
return err
}
if err := atomicfile.WriteFile(backupConf, contents, 0644); err != nil {
return err
}
} else if linkPath != tsConf {
// Backup the existing symlink.
os.Remove(backupConf)
if err := os.Symlink(linkPath, backupConf); err != nil {
return err
}
} else {
// Nothing to do, resolvConf already points to tsConf.
return nil
}
os.Remove(resolvConf)
if err := os.Symlink(tsConf, resolvConf); err != nil {
return nil
}
out, _ := exec.Command("service", "systemd-resolved", "restart").CombinedOutput()
if len(out) > 0 {
r.logf("service systemd-resolved restart: %s", out)
}
return nil
}
func (r *linuxRouter) restoreResolvConf() error {
if _, err := os.Stat(backupConf); err != nil {
if os.IsNotExist(err) {
return nil // no backup resolv.conf to restore
}
return err
}
if ln, err := os.Readlink(resolvConf); err != nil {
return err
} else if ln != tsConf {
return fmt.Errorf("resolv.conf is not a symlink to %s", tsConf)
}
if err := os.Rename(backupConf, resolvConf); err != nil {
return err
}
os.Remove(tsConf) // best effort removal of tsConf file
out, _ := exec.Command("service", "systemd-resolved", "restart").CombinedOutput()
if len(out) > 0 {
r.logf("service systemd-resolved restart: %s", out)
}
return nil
}