/
router_linux.go
1549 lines (1395 loc) · 43.3 KB
/
router_linux.go
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// 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/health"
"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
health *health.Tracker
unregNetMon func()
addrs map[netip.Prefix]bool
routes map[netip.Prefix]bool
localRoutes map[netip.Prefix]bool
snatSubnetRoutes bool
statefulFiltering bool
netfilterMode preftype.NetfilterMode
netfilterKind string
// 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
v6Available bool // whether the kernel supports IPv6
fwmaskWorks bool // whether we can use 'ip rule...fwmark <mark>/<mask>'
// ipPolicyPrefBase is the base priority at which ip rules are installed.
ipPolicyPrefBase int
cmd commandRunner
nfr linuxfw.NetfilterRunner
magicsockPortV4 uint16
magicsockPortV6 uint16
}
func newUserspaceRouter(logf logger.Logf, tunDev tun.Device, netMon *netmon.Monitor, health *health.Tracker) (Router, error) {
tunname, err := tunDev.Name()
if err != nil {
return nil, err
}
cmd := osCommandRunner{
ambientCapNetAdmin: useAmbientCaps(),
}
return newUserspaceRouterAdvanced(logf, tunname, netMon, cmd, health)
}
func newUserspaceRouterAdvanced(logf logger.Logf, tunname string, netMon *netmon.Monitor, cmd commandRunner, health *health.Tracker) (Router, error) {
r := &linuxRouter{
logf: logf,
tunname: tunname,
netfilterMode: netfilterOff,
netMon: netMon,
health: health,
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.v6Available = linuxfw.CheckIPv6(r.logf) == nil
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.setNetfilterMode(netfilterOff); err != nil {
return fmt.Errorf("setting netfilter mode: %w", err)
}
if err := r.addIPRules(); err != nil {
return fmt.Errorf("adding IP rules: %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
}
// setupNetfilter initializes the NetfilterRunner in r.nfr. It expects r.nfr
// to be nil, or the current netfilter to be set to netfilterOff.
// kind should be either a linuxfw.FirewallMode, or the empty string for auto.
func (r *linuxRouter) setupNetfilter(kind string) error {
r.netfilterKind = kind
var err error
r.nfr, err = linuxfw.New(r.logf, r.netfilterKind)
if err != nil {
return fmt.Errorf("could not create new netfilter: %w", err)
}
return nil
}
// Set implements the Router interface.
func (r *linuxRouter) Set(cfg *Config) error {
var errs []error
if cfg == nil {
cfg = &shutdownConfig
}
if cfg.NetfilterKind != r.netfilterKind {
if err := r.setNetfilterMode(netfilterOff); err != nil {
err = fmt.Errorf("could not disable existing netfilter: %w", err)
errs = append(errs, err)
} else {
r.nfr = nil
if err := r.setupNetfilter(cfg.NetfilterKind); err != nil {
errs = append(errs, err)
}
}
}
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
// Ensure that the SNAT rule is added or removed as needed.
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
// As above, for stateful filtering
switch {
case cfg.StatefulFiltering == r.statefulFiltering:
// state already correct, nothing to do.
case cfg.StatefulFiltering:
if err := r.addStatefulRule(); err != nil {
errs = append(errs, err)
}
default:
if err := r.delStatefulRule(); err != nil {
errs = append(errs, err)
}
}
r.statefulFiltering = cfg.StatefulFiltering
r.updateStatefulFilteringWithDockerWarning(cfg)
// Issue 11405: enable IP forwarding on gokrazy.
advertisingRoutes := len(cfg.SubnetRoutes) > 0
if distro.Get() == distro.Gokrazy && advertisingRoutes {
r.enableIPForwarding()
}
return multierr.New(errs...)
}
var warnStatefulFilteringWithDocker = health.NewWarnable()
func (r *linuxRouter) updateStatefulFilteringWithDockerWarning(cfg *Config) {
// If stateful filtering is disabled, clear the warning.
if !r.statefulFiltering {
r.health.SetWarnable(warnStatefulFilteringWithDocker, nil)
return
}
advertisingRoutes := len(cfg.SubnetRoutes) > 0
// TODO(andrew-d,maisem): we might want to check if we're running in a
// container, since, if so, stateful filtering might prevent other
// containers from connecting through the Tailscale in this container.
//
// For now, just check for the case where we're running Tailscale on
// the host and Docker is also running.
// If this node isn't a subnet router or exit node, then we would never
// have allowed traffic from a Docker container in to Tailscale, since
// there wouldn't be an AllowedIP for the container's source IP. So we
// don't need to warn in this case.
//
// cfg.SubnetRoutes contains all subnet routes for the node, including
// the default route (0.0.0.0/0 or ::/0) if this node is an exit node.
if advertisingRoutes {
// Check for the presence of a Docker interface and warn if it's found
// on the system.
//
// TODO(andrew-d): do a better job at detecting Docker, e.g. by looking
// for it in the $PATH or by checking for the presence of the Docker
// socket/daemon/etc.
ifstate := r.netMon.InterfaceState()
if _, found := ifstate.Interface["docker0"]; found {
r.health.SetWarnable(warnStatefulFilteringWithDocker, fmt.Errorf(""+
"Stateful filtering is enabled and Docker was detected; this may prevent Docker containers "+
"on this host from connecting to Tailscale nodes. "+
"See https://tailscale.com/s/stateful-docker",
))
return
}
}
// If we get here, then we have no warnings; clear anything existing.
r.health.SetWarnable(warnStatefulFilteringWithDocker, nil)
}
// UpdateMagicsockPort implements the Router interface.
func (r *linuxRouter) UpdateMagicsockPort(port uint16, network string) error {
if r.nfr == nil {
if err := r.setupNetfilter(r.netfilterKind); err != nil {
return fmt.Errorf("could not setup netfilter: %w", err)
}
}
var magicsockPort *uint16
switch network {
case "udp4":
magicsockPort = &r.magicsockPortV4
case "udp6":
// Skip setting up MagicSock port if the host does not support
// IPv6. MagicSock IPv6 port needs a filter rule to function. In
// some cases (hosts with partial iptables support) filter
// tables are not supported, so skip setting up the port for
// those hosts too.
if !r.getV6FilteringAvailable() {
return nil
}
magicsockPort = &r.magicsockPortV6
default:
return fmt.Errorf("unsupported network %s", network)
}
// set the port, we'll make the firewall rule when netfilter turns back on
if r.netfilterMode == netfilterOff {
*magicsockPort = port
return nil
}
if *magicsockPort == port {
return nil
}
if *magicsockPort != 0 {
if err := r.nfr.DelMagicsockPortRule(*magicsockPort, network); err != nil {
return fmt.Errorf("del magicsock port rule: %w", err)
}
}
if port != 0 {
if err := r.nfr.AddMagicsockPortRule(*magicsockPort, network); err != nil {
return fmt.Errorf("add magicsock port rule: %w", err)
}
}
*magicsockPort = port
return nil
}
// 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 !platformCanNetfilter() {
mode = netfilterOff
}
if r.nfr == nil {
var err error
r.nfr, err = linuxfw.New(r.logf, r.netfilterKind)
if err != nil {
return err
}
}
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
}
if r.magicsockPortV4 != 0 {
if err := r.nfr.AddMagicsockPortRule(r.magicsockPortV4, "udp4"); err != nil {
return fmt.Errorf("could not add magicsock port rule v4: %w", err)
}
}
if r.magicsockPortV6 != 0 && r.getV6FilteringAvailable() {
if err := r.nfr.AddMagicsockPortRule(r.magicsockPortV6, "udp6"); err != nil {
return fmt.Errorf("could not add magicsock port rule v6: %w", 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
}
if r.magicsockPortV4 != 0 {
if err := r.nfr.AddMagicsockPortRule(r.magicsockPortV4, "udp4"); err != nil {
return fmt.Errorf("could not add magicsock port rule v4: %w", err)
}
}
if r.magicsockPortV6 != 0 && r.getV6FilteringAvailable() {
if err := r.nfr.AddMagicsockPortRule(r.magicsockPortV6, "udp6"); err != nil {
return fmt.Errorf("could not add magicsock port rule v6: %w", 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 fmt.Errorf("error adding loopback rule: %w", err)
}
}
return nil
}
// getV6FilteringAvailable returns true if the router is able to setup the
// required tailscale filter rules for IPv6.
func (r *linuxRouter) getV6FilteringAvailable() bool {
return r.nfr.HasIPV6() && r.nfr.HasIPV6Filter()
}
// getV6Available returns true if the host supports IPv6.
func (r *linuxRouter) getV6Available() bool {
return r.nfr.HasIPV6()
}
// 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 addr.Is6() && !r.nfr.HasIPV6Filter() {
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 addr.Is6() && !r.nfr.HasIPV6Filter() {
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)
}
func (r *linuxRouter) enableIPForwarding() {
sysctls := map[string]string{
"net.ipv4.ip_forward": "1",
"net.ipv6.conf.all.forwarding": "1",
}
for k, v := range sysctls {
if err := writeSysctl(k, v); err != nil {
r.logf("warning: %v", k, v, err)
continue
}
r.logf("sysctl(%v=%v): ok", k, v)
}
}