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tailscale/wgengine/router/router_linux.go

1301 lines
36 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package router
import (
"errors"
"fmt"
"net"
"net/netip"
"os"
"os/exec"
"strconv"
"strings"
"sync/atomic"
"syscall"
"time"
"github.com/tailscale/netlink"
"github.com/tailscale/wireguard-go/tun"
"go4.org/netipx"
"golang.org/x/sys/unix"
"golang.org/x/time/rate"
"tailscale.com/envknob"
"tailscale.com/net/netmon"
"tailscale.com/types/logger"
"tailscale.com/types/preftype"
"tailscale.com/util/linuxfw"
"tailscale.com/util/multierr"
"tailscale.com/version/distro"
)
const (
netfilterOff = preftype.NetfilterOff
netfilterNoDivert = preftype.NetfilterNoDivert
netfilterOn = preftype.NetfilterOn
)
type linuxRouter struct {
closed atomic.Bool
logf func(fmt string, args ...any)
tunname string
netMon *netmon.Monitor
unregNetMon func()
addrs map[netip.Prefix]bool
routes map[netip.Prefix]bool
localRoutes map[netip.Prefix]bool
snatSubnetRoutes bool
netfilterMode preftype.NetfilterMode
// ruleRestorePending is whether a timer has been started to
// restore deleted ip rules.
ruleRestorePending atomic.Bool
ipRuleFixLimiter *rate.Limiter
// Various feature checks for the network stack.
ipRuleAvailable bool // whether kernel was built with IP_MULTIPLE_TABLES
fwmaskWorks bool // whether we can use 'ip rule...fwmark <mark>/<mask>'
// ipPolicyPrefBase is the base priority at which ip rules are installed.
ipPolicyPrefBase int
nfr linuxfw.NetfilterRunner
cmd commandRunner
}
func newUserspaceRouter(logf logger.Logf, tunDev tun.Device, netMon *netmon.Monitor) (Router, error) {
tunname, err := tunDev.Name()
if err != nil {
return nil, err
}
nfr, err := linuxfw.New(logf)
if err != nil {
return nil, err
}
cmd := osCommandRunner{
ambientCapNetAdmin: useAmbientCaps(),
}
return newUserspaceRouterAdvanced(logf, tunname, netMon, nfr, cmd)
}
func newUserspaceRouterAdvanced(logf logger.Logf, tunname string, netMon *netmon.Monitor, nfr linuxfw.NetfilterRunner, cmd commandRunner) (Router, error) {
r := &linuxRouter{
logf: logf,
tunname: tunname,
netfilterMode: netfilterOff,
netMon: netMon,
nfr: nfr,
cmd: cmd,
ipRuleFixLimiter: rate.NewLimiter(rate.Every(5*time.Second), 10),
ipPolicyPrefBase: 5200,
}
if r.useIPCommand() {
r.ipRuleAvailable = (cmd.run("ip", "rule") == nil)
} else {
if rules, err := netlink.RuleList(netlink.FAMILY_V4); err != nil {
r.logf("error querying IP rules (does kernel have IP_MULTIPLE_TABLES?): %v", err)
r.logf("warning: running without policy routing")
} else {
r.logf("[v1] policy routing available; found %d rules", len(rules))
r.ipRuleAvailable = true
}
}
// To be a good denizen of the 4-byte 'fwmark' bitspace on every packet, we try to
// only use the third byte. However, support for masking to part of the fwmark bitspace
// was only added to busybox in 1.33.0. As such, we want to detect older versions and
// not issue such a stanza.
var err error
if r.fwmaskWorks, err = ipCmdSupportsFwmask(); err != nil {
r.logf("failed to determine ip command fwmask support: %v", err)
}
if r.fwmaskWorks {
r.logf("[v1] ip command supports fwmark masks")
} else {
r.logf("[v1] ip command does NOT support fwmark masks")
}
// A common installation of OpenWRT involves use of the 'mwan3' package.
// This package installs ip-tables rules like:
// -A mwan3_fallback_policy -m mark --mark 0x0/0x3f00 -j MARK --set-xmark 0x100/0x3f00
//
// which coupled with an ip rule:
// 2001: from all fwmark 0x100/0x3f00 lookup 1
//
// has the effect of gobbling tailscale packets, because tailscale by default installs
// its policy routing rules at priority 52xx.
//
// As such, if we are running on openWRT, detect a mwan3 config, AND detect a rule
// with a preference 2001 (corresponding to the first interface wman3 manages), we
// shift the priority of our policies to 13xx. This effectively puts us between mwan3's
// permit-by-src-ip rules and mwan3 lookup of its own routing table which would drop
// the packet.
isMWAN3, err := checkOpenWRTUsingMWAN3()
if err != nil {
r.logf("error checking mwan3 installation: %v", err)
} else if isMWAN3 {
r.ipPolicyPrefBase = 1300
r.logf("mwan3 on openWRT detected, switching policy base priority to 1300")
}
r.fixupWSLMTU()
return r, nil
}
// ipCmdSupportsFwmask returns true if the system 'ip' binary supports using a
// fwmark stanza with a mask specified. To our knowledge, everything except busybox
// pre-1.33 supports this.
func ipCmdSupportsFwmask() (bool, error) {
ipPath, err := exec.LookPath("ip")
if err != nil {
return false, fmt.Errorf("lookpath: %v", err)
}
stat, err := os.Lstat(ipPath)
if err != nil {
return false, fmt.Errorf("lstat: %v", err)
}
if stat.Mode()&os.ModeSymlink == 0 {
// Not a symlink, so can't be busybox. Must be regular ip utility.
return true, nil
}
linkDest, err := os.Readlink(ipPath)
if err != nil {
return false, err
}
if !strings.Contains(strings.ToLower(linkDest), "busybox") {
// Not busybox, presumably supports fwmark masks.
return true, nil
}
// If we got this far, the ip utility is a busybox version with an
// unknown version.
// We run `ip --version` and look for the busybox banner (which
// is a stable 'BusyBox vX.Y.Z (<builddate>)' string) to determine
// the version.
out, err := exec.Command("ip", "--version").CombinedOutput()
if err != nil {
return false, err
}
major, minor, _, err := busyboxParseVersion(string(out))
if err != nil {
return false, nil
}
// Support for masks added in 1.33.0.
switch {
case major > 1:
return true, nil
case major == 1 && minor >= 33:
return true, nil
default:
return false, nil
}
}
func busyboxParseVersion(output string) (major, minor, patch int, err error) {
bannerStart := strings.Index(output, "BusyBox v")
if bannerStart < 0 {
return 0, 0, 0, errors.New("missing BusyBox banner")
}
bannerEnd := bannerStart + len("BusyBox v")
end := strings.Index(output[bannerEnd:], " ")
if end < 0 {
return 0, 0, 0, errors.New("missing end delimiter")
}
elements := strings.Split(output[bannerEnd:bannerEnd+end], ".")
if len(elements) < 3 {
return 0, 0, 0, fmt.Errorf("expected 3 version elements, got %d", len(elements))
}
if major, err = strconv.Atoi(elements[0]); err != nil {
return 0, 0, 0, fmt.Errorf("parsing major: %v", err)
}
if minor, err = strconv.Atoi(elements[1]); err != nil {
return 0, 0, 0, fmt.Errorf("parsing minor: %v", err)
}
if patch, err = strconv.Atoi(elements[2]); err != nil {
return 0, 0, 0, fmt.Errorf("parsing patch: %v", err)
}
return major, minor, patch, nil
}
func useAmbientCaps() bool {
if distro.Get() != distro.Synology {
return false
}
return distro.DSMVersion() >= 7
}
var forceIPCommand = envknob.RegisterBool("TS_DEBUG_USE_IP_COMMAND")
// useIPCommand reports whether r should use the "ip" command (or its
// fake commandRunner for tests) instead of netlink.
func (r *linuxRouter) useIPCommand() bool {
if r.cmd == nil {
panic("invalid init")
}
if forceIPCommand() {
return true
}
// In the future we might need to fall back to using the "ip"
// command if, say, netlink is blocked somewhere but the ip
// command is allowed to use netlink. For now we only use the ip
// command runner in tests.
_, ok := r.cmd.(osCommandRunner)
return !ok
}
// onIPRuleDeleted is the callback from the network monitor for when an IP
// policy rule is deleted. See Issue 1591.
//
// If an ip rule is deleted (with pref number 52xx, as Tailscale sets), then
// set a timer to restore our rules, in case they were deleted. The timer lets
// us do one fixup in response to a batch of rule deletes. It also lets us
// delay arbitrarily to prevent a high-speed fight over the rule between
// competing processes. (Although empirically, systemd doesn't fight us
// like that... yet.)
//
// Note that we don't care about the table number. We don't strictly even care
// about the priority number. We could just do this in response to any netlink
// change. Filtering by known priority ranges cuts back on some logspam.
func (r *linuxRouter) onIPRuleDeleted(table uint8, priority uint32) {
if int(priority) < r.ipPolicyPrefBase || int(priority) >= (r.ipPolicyPrefBase+100) {
// Not our rule.
return
}
if !r.ruleRestorePending.Swap(true) {
// Another timer is already pending.
return
}
rr := r.ipRuleFixLimiter.Reserve()
if !rr.OK() {
r.ruleRestorePending.Swap(false)
return
}
time.AfterFunc(rr.Delay()+250*time.Millisecond, func() {
if r.ruleRestorePending.Swap(false) && !r.closed.Load() {
r.logf("somebody (likely systemd-networkd) deleted ip rules; restoring Tailscale's")
r.justAddIPRules()
}
})
}
func (r *linuxRouter) Up() error {
if r.unregNetMon == nil && r.netMon != nil {
r.unregNetMon = r.netMon.RegisterRuleDeleteCallback(r.onIPRuleDeleted)
}
if err := r.addIPRules(); err != nil {
return fmt.Errorf("adding IP rules: %w", err)
}
if err := r.setNetfilterMode(netfilterOff); err != nil {
return fmt.Errorf("setting netfilter mode: %w", err)
}
if err := r.upInterface(); err != nil {
return fmt.Errorf("bringing interface up: %w", err)
}
return nil
}
func (r *linuxRouter) Close() error {
r.closed.Store(true)
if r.unregNetMon != nil {
r.unregNetMon()
}
if err := r.downInterface(); err != nil {
return err
}
if err := r.delIPRules(); err != nil {
return err
}
if err := r.setNetfilterMode(netfilterOff); err != nil {
return err
}
if err := r.delRoutes(); err != nil {
return err
}
r.addrs = nil
r.routes = nil
r.localRoutes = nil
return nil
}
// Set implements the Router interface.
func (r *linuxRouter) Set(cfg *Config) error {
var errs []error
if cfg == nil {
cfg = &shutdownConfig
}
if err := r.setNetfilterMode(cfg.NetfilterMode); err != nil {
errs = append(errs, err)
}
newLocalRoutes, err := cidrDiff("localRoute", r.localRoutes, cfg.LocalRoutes, r.addThrowRoute, r.delThrowRoute, r.logf)
if err != nil {
errs = append(errs, err)
}
r.localRoutes = newLocalRoutes
newRoutes, err := cidrDiff("route", r.routes, cfg.Routes, r.addRoute, r.delRoute, r.logf)
if err != nil {
errs = append(errs, err)
}
r.routes = newRoutes
newAddrs, err := cidrDiff("addr", r.addrs, cfg.LocalAddrs, r.addAddress, r.delAddress, r.logf)
if err != nil {
errs = append(errs, err)
}
r.addrs = newAddrs
switch {
case cfg.SNATSubnetRoutes == r.snatSubnetRoutes:
// state already correct, nothing to do.
case cfg.SNATSubnetRoutes:
if err := r.addSNATRule(); err != nil {
errs = append(errs, err)
}
default:
if err := r.delSNATRule(); err != nil {
errs = append(errs, err)
}
}
r.snatSubnetRoutes = cfg.SNATSubnetRoutes
return multierr.New(errs...)
}
// setNetfilterMode switches the router to the given netfilter
// mode. Netfilter state is created or deleted appropriately to
// reflect the new mode, and r.snatSubnetRoutes is updated to reflect
// the current state of subnet SNATing.
func (r *linuxRouter) setNetfilterMode(mode preftype.NetfilterMode) error {
if distro.Get() == distro.Synology {
mode = netfilterOff
}
if r.netfilterMode == mode {
return nil
}
// Depending on the netfilter mode we switch from and to, we may
// have created the Tailscale netfilter chains. If so, we have to
// go back through existing router state, and add the netfilter
// rules for that state.
//
// This bool keeps track of whether the current state transition
// is one that requires adding rules of existing state.
reprocess := false
switch mode {
case netfilterOff:
switch r.netfilterMode {
case netfilterNoDivert:
if err := r.nfr.DelBase(); err != nil {
return err
}
if err := r.nfr.DelChains(); err != nil {
r.logf("note: %v", err)
// harmless, continue.
// This can happen if someone left a ref to
// this table somewhere else.
}
case netfilterOn:
if err := r.nfr.DelHooks(r.logf); err != nil {
return err
}
if err := r.nfr.DelBase(); err != nil {
return err
}
if err := r.nfr.DelChains(); err != nil {
r.logf("note: %v", err)
// harmless, continue.
// This can happen if someone left a ref to
// this table somewhere else.
}
}
r.snatSubnetRoutes = false
case netfilterNoDivert:
switch r.netfilterMode {
case netfilterOff:
reprocess = true
if err := r.nfr.AddChains(); err != nil {
return err
}
if err := r.nfr.AddBase(r.tunname); err != nil {
return err
}
r.snatSubnetRoutes = false
case netfilterOn:
if err := r.nfr.DelHooks(r.logf); err != nil {
return err
}
}
case netfilterOn:
// Because of bugs in old version of iptables-compat,
// we can't add a "-j ts-forward" rule to FORWARD
// while ts-forward contains an "-m mark" rule. But
// we can add the row *before* populating ts-forward.
// So we have to delBase, then add the hooks,
// then re-addBase, just in case.
switch r.netfilterMode {
case netfilterOff:
reprocess = true
if err := r.nfr.AddChains(); err != nil {
return err
}
if err := r.nfr.DelBase(); err != nil {
return err
}
// AddHooks adds the ts loopback rule.
if err := r.nfr.AddHooks(); err != nil {
return err
}
// AddBase adds base ts rules
if err := r.nfr.AddBase(r.tunname); err != nil {
return err
}
r.snatSubnetRoutes = false
case netfilterNoDivert:
reprocess = true
if err := r.nfr.DelBase(); err != nil {
return err
}
if err := r.nfr.AddHooks(); err != nil {
return err
}
if err := r.nfr.AddBase(r.tunname); err != nil {
return err
}
r.snatSubnetRoutes = false
}
default:
panic("unhandled netfilter mode")
}
r.netfilterMode = mode
if !reprocess {
return nil
}
for cidr := range r.addrs {
if err := r.addLoopbackRule(cidr.Addr()); err != nil {
return err
}
}
return nil
}
func (r *linuxRouter) getV6Available() bool {
return r.nfr.HasIPV6()
}
func (r *linuxRouter) getV6NATAvailable() bool {
return r.nfr.HasIPV6NAT()
}
// addAddress adds an IP/mask to the tunnel interface. Fails if the
// address is already assigned to the interface, or if the addition
// fails.
func (r *linuxRouter) addAddress(addr netip.Prefix) error {
if !r.getV6Available() && addr.Addr().Is6() {
return nil
}
if r.useIPCommand() {
if err := r.cmd.run("ip", "addr", "add", addr.String(), "dev", r.tunname); err != nil {
return fmt.Errorf("adding address %q to tunnel interface: %w", addr, err)
}
} else {
link, err := r.link()
if err != nil {
return fmt.Errorf("adding address %v, %w", addr, err)
}
if err := netlink.AddrReplace(link, nlAddrOfPrefix(addr)); err != nil {
return fmt.Errorf("adding address %v from tunnel interface: %w", addr, err)
}
}
if err := r.addLoopbackRule(addr.Addr()); err != nil {
return err
}
return nil
}
// delAddress removes an IP/mask from the tunnel interface. Fails if
// the address is not assigned to the interface, or if the removal
// fails.
func (r *linuxRouter) delAddress(addr netip.Prefix) error {
if !r.getV6Available() && addr.Addr().Is6() {
return nil
}
if err := r.delLoopbackRule(addr.Addr()); err != nil {
return err
}
if r.useIPCommand() {
if err := r.cmd.run("ip", "addr", "del", addr.String(), "dev", r.tunname); err != nil {
return fmt.Errorf("deleting address %q from tunnel interface: %w", addr, err)
}
} else {
link, err := r.link()
if err != nil {
return fmt.Errorf("deleting address %v, %w", addr, err)
}
if err := netlink.AddrDel(link, nlAddrOfPrefix(addr)); err != nil {
return fmt.Errorf("deleting address %v from tunnel interface: %w", addr, err)
}
}
return nil
}
// addLoopbackRule adds a firewall rule to permit loopback traffic to
// a local Tailscale IP.
func (r *linuxRouter) addLoopbackRule(addr netip.Addr) error {
if r.netfilterMode == netfilterOff {
return nil
}
if err := r.nfr.AddLoopbackRule(addr); err != nil {
return err
}
return nil
}
// delLoopbackRule removes the firewall rule permitting loopback
// traffic to a Tailscale IP.
func (r *linuxRouter) delLoopbackRule(addr netip.Addr) error {
if r.netfilterMode == netfilterOff {
return nil
}
if err := r.nfr.DelLoopbackRule(addr); err != nil {
return err
}
return nil
}
// addRoute adds a route for cidr, pointing to the tunnel
// interface. Fails if the route already exists, or if adding the
// route fails.
func (r *linuxRouter) addRoute(cidr netip.Prefix) error {
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
if r.useIPCommand() {
return r.addRouteDef([]string{normalizeCIDR(cidr), "dev", r.tunname}, cidr)
}
linkIndex, err := r.linkIndex()
if err != nil {
return err
}
return netlink.RouteReplace(&netlink.Route{
LinkIndex: linkIndex,
Dst: netipx.PrefixIPNet(cidr.Masked()),
Table: r.routeTable(),
})
}
// addThrowRoute adds a throw route for the provided cidr.
// This has the effect that lookup in the routing table is terminated
// pretending that no route was found. Fails if the route already exists,
// or if adding the route fails.
func (r *linuxRouter) addThrowRoute(cidr netip.Prefix) error {
if !r.ipRuleAvailable {
return nil
}
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
if r.useIPCommand() {
return r.addRouteDef([]string{"throw", normalizeCIDR(cidr)}, cidr)
}
err := netlink.RouteReplace(&netlink.Route{
Dst: netipx.PrefixIPNet(cidr.Masked()),
Table: tailscaleRouteTable.Num,
Type: unix.RTN_THROW,
})
if err != nil {
r.logf("THROW ERROR adding %v: %#v", cidr, err)
}
return err
}
func (r *linuxRouter) addRouteDef(routeDef []string, cidr netip.Prefix) error {
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
args := append([]string{"ip", "route", "add"}, routeDef...)
if r.ipRuleAvailable {
args = append(args, "table", tailscaleRouteTable.ipCmdArg())
}
err := r.cmd.run(args...)
if err == nil {
return nil
}
// This is an ugly hack to detect failure to add a route that
// already exists (as happens in when we're racing to add
// kernel-maintained routes when enabling exit nodes w/o Local
// LAN access, Issue 3060). Fortunately in the common case we
// use netlink directly instead and don't exercise this code.
if errCode(err) == 2 && strings.Contains(err.Error(), "RTNETLINK answers: File exists") {
r.logf("ignoring route add of %v; already exists", cidr)
return nil
}
return err
}
var (
errESRCH error = syscall.ESRCH
errENOENT error = syscall.ENOENT
errEEXIST error = syscall.EEXIST
)
// delRoute removes the route for cidr pointing to the tunnel
// interface. Fails if the route doesn't exist, or if removing the
// route fails.
func (r *linuxRouter) delRoute(cidr netip.Prefix) error {
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
if r.useIPCommand() {
return r.delRouteDef([]string{normalizeCIDR(cidr), "dev", r.tunname}, cidr)
}
linkIndex, err := r.linkIndex()
if err != nil {
return err
}
err = netlink.RouteDel(&netlink.Route{
LinkIndex: linkIndex,
Dst: netipx.PrefixIPNet(cidr.Masked()),
Table: r.routeTable(),
})
if errors.Is(err, errESRCH) {
// Didn't exist to begin with.
return nil
}
return err
}
// delThrowRoute removes the throw route for the cidr. Fails if the route
// doesn't exist, or if removing the route fails.
func (r *linuxRouter) delThrowRoute(cidr netip.Prefix) error {
if !r.ipRuleAvailable {
return nil
}
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
if r.useIPCommand() {
return r.delRouteDef([]string{"throw", normalizeCIDR(cidr)}, cidr)
}
err := netlink.RouteDel(&netlink.Route{
Dst: netipx.PrefixIPNet(cidr.Masked()),
Table: r.routeTable(),
Type: unix.RTN_THROW,
})
if errors.Is(err, errESRCH) {
// Didn't exist to begin with.
return nil
}
return err
}
func (r *linuxRouter) delRouteDef(routeDef []string, cidr netip.Prefix) error {
if !r.getV6Available() && cidr.Addr().Is6() {
return nil
}
args := append([]string{"ip", "route", "del"}, routeDef...)
if r.ipRuleAvailable {
args = append(args, "table", tailscaleRouteTable.ipCmdArg())
}
err := r.cmd.run(args...)
if err != nil {
ok, err := r.hasRoute(routeDef, cidr)
if err != nil {
r.logf("warning: error checking whether %v even exists after error deleting it: %v", err)
} else {
if !ok {
r.logf("warning: tried to delete route %v but it was already gone; ignoring error", cidr)
return nil
}
}
}
return err
}
func dashFam(ip netip.Addr) string {
if ip.Is6() {
return "-6"
}
return "-4"
}
func (r *linuxRouter) hasRoute(routeDef []string, cidr netip.Prefix) (bool, error) {
args := append([]string{"ip", dashFam(cidr.Addr()), "route", "show"}, routeDef...)
if r.ipRuleAvailable {
args = append(args, "table", tailscaleRouteTable.ipCmdArg())
}
out, err := r.cmd.output(args...)
if err != nil {
return false, err
}
return len(out) > 0, nil
}
func (r *linuxRouter) link() (netlink.Link, error) {
link, err := netlink.LinkByName(r.tunname)
if err != nil {
return nil, fmt.Errorf("failed to look up link %q: %w", r.tunname, err)
}
return link, nil
}
func (r *linuxRouter) linkIndex() (int, error) {
// TODO(bradfitz): cache this? It doesn't change often, and on start-up
// hundreds of addRoute calls to add /32s can happen quickly.
link, err := r.link()
if err != nil {
return 0, err
}
return link.Attrs().Index, nil
}
// routeTable returns the route table to use.
func (r *linuxRouter) routeTable() int {
if r.ipRuleAvailable {
return tailscaleRouteTable.Num
}
return 0
}
// upInterface brings up the tunnel interface.
func (r *linuxRouter) upInterface() error {
if r.useIPCommand() {
return r.cmd.run("ip", "link", "set", "dev", r.tunname, "up")
}
link, err := r.link()
if err != nil {
return fmt.Errorf("bringing interface up, %w", err)
}
return netlink.LinkSetUp(link)
}
// downInterface sets the tunnel interface administratively down.
func (r *linuxRouter) downInterface() error {
if r.useIPCommand() {
return r.cmd.run("ip", "link", "set", "dev", r.tunname, "down")
}
link, err := r.link()
if err != nil {
return fmt.Errorf("bringing interface down, %w", err)
}
return netlink.LinkSetDown(link)
}
// fixupWSLMTU sets the MTU on the eth0 interface to 1360 bytes if running under
// WSL, eth0 is the default route, and has the MTU 1280 bytes.
func (r *linuxRouter) fixupWSLMTU() {
if !distro.IsWSL() {
return
}
if r.useIPCommand() {
r.logf("fixupWSLMTU: not implemented by ip command")
return
}
link, err := netlink.LinkByName("eth0")
if err != nil {
r.logf("warning: fixupWSLMTU: could not open eth0: %v", err)
return
}
routes, err := netlink.RouteGet(net.IPv4(8, 8, 8, 8))
if err != nil || len(routes) == 0 {
if err == nil {
err = fmt.Errorf("none found")
}
r.logf("fixupWSLMTU: could not get default route: %v", err)
return
}
if routes[0].LinkIndex != link.Attrs().Index {
r.logf("fixupWSLMTU: default route is not via eth0")
return
}
if link.Attrs().MTU == 1280 {
if err := netlink.LinkSetMTU(link, 1360); err != nil {
r.logf("warning: fixupWSLMTU: could not raise eth0 MTU: %v", err)
}
}
}
// addrFamily is an address family: IPv4 or IPv6.
type addrFamily byte
const (
v4 = addrFamily(4)
v6 = addrFamily(6)
)
func (f addrFamily) dashArg() string {
switch f {
case 4:
return "-4"
case 6:
return "-6"
}
panic("illegal")
}
func (f addrFamily) netlinkInt() int {
switch f {
case 4:
return netlink.FAMILY_V4
case 6:
return netlink.FAMILY_V6
}
panic("illegal")
}
func (r *linuxRouter) addrFamilies() []addrFamily {
if r.getV6Available() {
return []addrFamily{v4, v6}
}
return []addrFamily{v4}
}
// addIPRules adds the policy routing rule that avoids tailscaled
// routing loops. If the rule exists and appears to be a
// tailscale-managed rule, it is gracefully replaced.
func (r *linuxRouter) addIPRules() error {
if !r.ipRuleAvailable {
return nil
}
// Clear out old rules. After that, any error adding a rule is fatal,
// because there should be no reason we add a duplicate.
if err := r.delIPRules(); err != nil {
return err
}
return r.justAddIPRules()
}
// RouteTable is a Linux routing table: both its name and number.
// See /etc/iproute2/rt_tables.
type RouteTable struct {
Name string
Num int
}
var routeTableByNumber = map[int]RouteTable{}
// IpCmdArg returns the string form of the table to pass to the "ip" command.
func (rt RouteTable) ipCmdArg() string {
if rt.Num >= 253 {
return rt.Name
}
return strconv.Itoa(rt.Num)
}
func newRouteTable(name string, num int) RouteTable {
rt := RouteTable{name, num}
routeTableByNumber[num] = rt
return rt
}
// MustRouteTable returns the RouteTable with the given number key.
// It panics if the number is unknown because this result is a part
// of IP rule argument and we don't want to continue with an invalid
// argument with table no exist.
func mustRouteTable(num int) RouteTable {
rt, ok := routeTableByNumber[num]
if !ok {
panic(fmt.Sprintf("unknown route table %v", num))
}
return rt
}
var (
mainRouteTable = newRouteTable("main", 254)
defaultRouteTable = newRouteTable("default", 253)
// tailscaleRouteTable is the routing table number for Tailscale
// network routes. See addIPRules for the detailed policy routing
// logic that ends up doing lookups within that table.
//
// NOTE(danderson): We chose 52 because those are the digits above the
// letters "TS" on a qwerty keyboard, and 52 is sufficiently unlikely
// to be picked by other software.
//
// NOTE(danderson): You might wonder why we didn't pick some
// high table number like 5252, to further avoid the potential
// for collisions with other software. Unfortunately,
// Busybox's `ip` implementation believes that table numbers
// are 8-bit integers, so for maximum compatibility we had to
// stay in the 0-255 range even though linux itself supports
// larger numbers. (but nowadays we use netlink directly and
// aren't affected by the busybox binary's limitations)
tailscaleRouteTable = newRouteTable("tailscale", 52)
)
// ipRules are the policy routing rules that Tailscale uses.
// The priority is the value represented here added to r.ipPolicyPrefBase,
// which is usually 5200.
//
// NOTE(apenwarr): We leave spaces between each pref number.
// This is so the sysadmin can override by inserting rules in
// between if they want.
//
// NOTE(apenwarr): This sequence seems complicated, right?
// If we could simply have a rule that said "match packets that
// *don't* have this fwmark", then we would only need to add one
// link to table 52 and we'd be done. Unfortunately, older kernels
// and 'ip rule' implementations (including busybox), don't support
// checking for the lack of a fwmark, only the presence. The technique
// below works even on very old kernels.
var ipRules = []netlink.Rule{
// Packets from us, tagged with our fwmark, first try the kernel's
// main routing table.
{
Priority: 10,
Mark: linuxfw.TailscaleBypassMarkNum,
Table: mainRouteTable.Num,
},
// ...and then we try the 'default' table, for correctness,
// even though it's been empty on every Linux system I've ever seen.
{
Priority: 30,
Mark: linuxfw.TailscaleBypassMarkNum,
Table: defaultRouteTable.Num,
},
// If neither of those matched (no default route on this system?)
// then packets from us should be aborted rather than falling through
// to the tailscale routes, because that would create routing loops.
{
Priority: 50,
Mark: linuxfw.TailscaleBypassMarkNum,
Type: unix.RTN_UNREACHABLE,
},
// If we get to this point, capture all packets and send them
// through to the tailscale route table. For apps other than us
// (ie. with no fwmark set), this is the first routing table, so
// it takes precedence over all the others, ie. VPN routes always
// beat non-VPN routes.
{
Priority: 70,
Table: tailscaleRouteTable.Num,
},
// If that didn't match, then non-fwmark packets fall through to the
// usual rules (pref 32766 and 32767, ie. main and default).
}
// justAddIPRules adds policy routing rule without deleting any first.
func (r *linuxRouter) justAddIPRules() error {
if !r.ipRuleAvailable {
return nil
}
if r.useIPCommand() {
return r.addIPRulesWithIPCommand()
}
var errAcc error
for _, family := range r.addrFamilies() {
for _, ru := range ipRules {
// Note: r is a value type here; safe to mutate it.
ru.Family = family.netlinkInt()
if ru.Mark != 0 {
ru.Mask = linuxfw.TailscaleFwmarkMaskNum
}
ru.Goto = -1
ru.SuppressIfgroup = -1
ru.SuppressPrefixlen = -1
ru.Flow = -1
ru.Priority += r.ipPolicyPrefBase
err := netlink.RuleAdd(&ru)
if errors.Is(err, errEEXIST) {
// Ignore dups.
continue
}
if err != nil && errAcc == nil {
errAcc = err
}
}
}
return errAcc
}
func (r *linuxRouter) addIPRulesWithIPCommand() error {
rg := newRunGroup(nil, r.cmd)
for _, family := range r.addrFamilies() {
for _, rule := range ipRules {
args := []string{
"ip", family.dashArg(),
"rule", "add",
"pref", strconv.Itoa(rule.Priority + r.ipPolicyPrefBase),
}
if rule.Mark != 0 {
if r.fwmaskWorks {
args = append(args, "fwmark", fmt.Sprintf("0x%x/%s", rule.Mark, linuxfw.TailscaleFwmarkMask))
} else {
args = append(args, "fwmark", fmt.Sprintf("0x%x", rule.Mark))
}
}
if rule.Table != 0 {
args = append(args, "table", mustRouteTable(rule.Table).ipCmdArg())
}
if rule.Type == unix.RTN_UNREACHABLE {
args = append(args, "type", "unreachable")
}
rg.Run(args...)
}
}
return rg.ErrAcc
}
// delRoutes removes any local routes that we added that would not be
// cleaned up on interface down.
func (r *linuxRouter) delRoutes() error {
for rt := range r.localRoutes {
if err := r.delThrowRoute(rt); err != nil {
r.logf("failed to delete throw route(%q): %v", rt, err)
}
}
return nil
}
// delIPRules removes the policy routing rules that avoid
// tailscaled routing loops, if it exists.
func (r *linuxRouter) delIPRules() error {
if !r.ipRuleAvailable {
return nil
}
if r.useIPCommand() {
return r.delIPRulesWithIPCommand()
}
var errAcc error
for _, family := range r.addrFamilies() {
for _, ru := range ipRules {
// Note: r is a value type here; safe to mutate it.
// When deleting rules, we want to be a bit specific (mention which
// table we were routing to) but not *too* specific (fwmarks, etc).
// That leaves us some flexibility to change these values in later
// versions without having ongoing hacks for every possible
// combination.
ru.Family = family.netlinkInt()
ru.Mark = -1
ru.Mask = -1
ru.Goto = -1
ru.SuppressIfgroup = -1
ru.SuppressPrefixlen = -1
ru.Priority += r.ipPolicyPrefBase
err := netlink.RuleDel(&ru)
if errors.Is(err, errENOENT) {
// Didn't exist to begin with.
continue
}
if err != nil && errAcc == nil {
errAcc = err
}
}
}
return errAcc
}
func (r *linuxRouter) delIPRulesWithIPCommand() error {
// Error codes: 'ip rule' returns error code 2 if the rule is a
// duplicate (add) or not found (del). It returns a different code
// for syntax errors. This is also true of busybox.
//
// Some older versions of iproute2 also return error code 254 for
// unknown rules during deletion.
rg := newRunGroup([]int{2, 254}, r.cmd)
for _, family := range r.addrFamilies() {
// When deleting rules, we want to be a bit specific (mention which
// table we were routing to) but not *too* specific (fwmarks, etc).
// That leaves us some flexibility to change these values in later
// versions without having ongoing hacks for every possible
// combination.
for _, rule := range ipRules {
args := []string{
"ip", family.dashArg(),
"rule", "del",
"pref", strconv.Itoa(rule.Priority + r.ipPolicyPrefBase),
}
if rule.Table != 0 {
args = append(args, "table", mustRouteTable(rule.Table).ipCmdArg())
} else {
args = append(args, "type", "unreachable")
}
rg.Run(args...)
}
}
return rg.ErrAcc
}
// addSNATRule adds a netfilter rule to SNAT traffic destined for
// local subnets.
func (r *linuxRouter) addSNATRule() error {
if r.netfilterMode == netfilterOff {
return nil
}
if err := r.nfr.AddSNATRule(); err != nil {
return err
}
return nil
}
// delSNATRule removes the netfilter rule to SNAT traffic destined for
// local subnets. Fails if the rule does not exist.
func (r *linuxRouter) delSNATRule() error {
if r.netfilterMode == netfilterOff {
return nil
}
if err := r.nfr.DelSNATRule(); err != nil {
return err
}
return nil
}
// cidrDiff calls add and del as needed to make the set of prefixes in
// old and new match. Returns a map reflecting the actual new state
// (which may be somewhere in between old and new if some commands
// failed), and any error encountered while reconfiguring.
func cidrDiff(kind string, old map[netip.Prefix]bool, new []netip.Prefix, add, del func(netip.Prefix) error, logf logger.Logf) (map[netip.Prefix]bool, error) {
newMap := make(map[netip.Prefix]bool, len(new))
for _, cidr := range new {
newMap[cidr] = true
}
// ret starts out as a copy of old, and updates as we
// add/delete. That way we can always return it and have it be the
// true state of what we've done so far.
ret := make(map[netip.Prefix]bool, len(old))
for cidr := range old {
ret[cidr] = true
}
// We want to add before we delete, so that if there is no overlap, we don't
// end up in a state where we have no addresses on an interface as that
// results in other kernel entities (like routes) pointing to that interface
// to also be deleted.
var addFail []error
for cidr := range newMap {
if old[cidr] {
continue
}
if err := add(cidr); err != nil {
logf("%s add failed: %v", kind, err)
addFail = append(addFail, err)
} else {
ret[cidr] = true
}
}
if len(addFail) == 1 {
return ret, addFail[0]
}
if len(addFail) > 0 {
return ret, fmt.Errorf("%d add %s failures; first was: %w", len(addFail), kind, addFail[0])
}
var delFail []error
for cidr := range old {
if newMap[cidr] {
continue
}
if err := del(cidr); err != nil {
logf("%s del failed: %v", kind, err)
delFail = append(delFail, err)
} else {
delete(ret, cidr)
}
}
if len(delFail) == 1 {
return ret, delFail[0]
}
if len(delFail) > 0 {
return ret, fmt.Errorf("%d delete %s failures; first was: %w", len(delFail), kind, delFail[0])
}
return ret, nil
}
// normalizeCIDR returns cidr as an ip/mask string, with the host bits
// of the IP address zeroed out.
func normalizeCIDR(cidr netip.Prefix) string {
return cidr.Masked().String()
}
// cleanup removes all the rules and routes that were added by the linux router.
// The function calls cleanup for both iptables and nftables since which ever
// netfilter runner is used, the cleanup function for the other one doesn't do anything.
func cleanup(logf logger.Logf, interfaceName string) {
if interfaceName != "userspace-networking" {
linuxfw.IPTablesCleanup(logf)
linuxfw.NfTablesCleanUp(logf)
}
}
// Checks if the running openWRT system is using mwan3, based on the heuristic
// of the config file being present as well as a policy rule with a specific
// priority (2000 + 1 - first interface mwan3 manages) and non-zero mark.
func checkOpenWRTUsingMWAN3() (bool, error) {
if distro.Get() != distro.OpenWrt {
return false, nil
}
if _, err := os.Stat("/etc/config/mwan3"); err != nil {
if os.IsNotExist(err) {
return false, nil
}
return false, err
}
rules, err := netlink.RuleList(netlink.FAMILY_V4)
if err != nil {
return false, err
}
for _, r := range rules {
// We want to match on a rule like this:
// 2001: from all fwmark 0x100/0x3f00 lookup 1
//
// We dont match on the mask because it can vary, or the
// table because I'm not sure if it can vary.
if r.Priority >= 2001 && r.Priority <= 2004 && r.Mark != 0 {
return true, nil
}
}
return false, nil
}
func nlAddrOfPrefix(p netip.Prefix) *netlink.Addr {
return &netlink.Addr{
IPNet: netipx.PrefixIPNet(p),
}
}