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wgengine/router: support various degrees of broken IPv6.

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Gracefully skips touching the v6 NAT table on systems that don't have
it, and doesn't configure IPv6 at all if IPv6 is globally disabled.

Signed-off-by: David Anderson <danderson@tailscale.com>
This commit is contained in:
David Anderson 2020-09-22 21:55:28 +00:00 committed by Dave Anderson
parent 0d80904fc2
commit fddbcb0c7b
1 changed files with 138 additions and 29 deletions
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167
wgengine/router/router_linux.go
View File

@ -5,7 +5,12 @@
package router
import (
"bytes"
"fmt"
"io/ioutil"
"os"
"os/exec"
"strconv"
"strings"
"github.com/coreos/go-iptables/iptables"
@ -79,13 +84,17 @@ type netfilterRunner interface {
type linuxRouter struct {
logf func(fmt string, args ...interface{})
ipRuleAvailable bool
tunname string
addrs map[netaddr.IPPrefix]bool
routes map[netaddr.IPPrefix]bool
snatSubnetRoutes bool
netfilterMode NetfilterMode
// Various feature checks for the network stack.
ipRuleAvailable bool
v6Available bool
v6NATAvailable bool
dns *dns.Manager
ipt4 netfilterRunner
@ -104,9 +113,14 @@ func newUserspaceRouter(logf logger.Logf, _ *device.Device, tunDev tun.Device) (
return nil, err
}
ipt6, err := iptables.NewWithProtocol(iptables.ProtocolIPv6)
if err != nil {
return nil, err
var ipt6 netfilterRunner
if supportsV6() {
// The iptables package probes for `ip6tables` and errors out
// if unavailable. We want that to be a non-fatal error.
ipt6, err = iptables.NewWithProtocol(iptables.ProtocolIPv6)
if err != nil {
return nil, err
}
}
return newUserspaceRouterAdvanced(logf, tunname, ipt4, ipt6, osCommandRunner{})
@ -120,15 +134,21 @@ func newUserspaceRouterAdvanced(logf logger.Logf, tunname string, netfilter4, ne
InterfaceName: tunname,
}
supportsV6 := supportsV6()
return &linuxRouter{
logf: logf,
logf: logf,
tunname: tunname,
netfilterMode: NetfilterOff,
ipRuleAvailable: ipRuleAvailable,
tunname: tunname,
netfilterMode: NetfilterOff,
ipt4: netfilter4,
ipt6: netfilter6,
cmd: cmd,
dns: dns.NewManager(mconfig),
v6Available: supportsV6,
v6NATAvailable: supportsV6 && supportsV6NAT(),
ipt4: netfilter4,
ipt6: netfilter6,
cmd: cmd,
dns: dns.NewManager(mconfig),
}, nil
}
@ -423,6 +443,13 @@ func (r *linuxRouter) downInterface() error {
return r.cmd.run("ip", "link", "set", "dev", r.tunname, "down")
}
func (r *linuxRouter) iprouteFamilies() []string {
if r.v6Available {
return []string{"-4", "-6"}
}
return []string{"-4"}
}
// 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.
@ -439,7 +466,7 @@ func (r *linuxRouter) addIPRules() error {
rg := newRunGroup(nil, r.cmd)
for _, family := range []string{"-4", "-6"} {
for _, family := range r.iprouteFamilies() {
// NOTE(apenwarr): We leave spaces between each pref number.
// This is so the sysadmin can override by inserting rules in
// between if they want.
@ -512,7 +539,7 @@ func (r *linuxRouter) delIPRules() error {
// unknown rules during deletion.
rg := newRunGroup([]int{2, 254}, r.cmd)
for _, family := range []string{"-4", "-6"} {
for _, family := range r.iprouteFamilies() {
// 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
@ -554,6 +581,13 @@ func (r *linuxRouter) delIPRules() error {
return rg.ErrAcc
}
func (r *linuxRouter) netfilterFamilies() []netfilterRunner {
if r.v6Available {
return []netfilterRunner{r.ipt4, r.ipt6}
}
return []netfilterRunner{r.ipt4}
}
// addNetfilterChains creates custom Tailscale chains in netfilter.
func (r *linuxRouter) addNetfilterChains() error {
create := func(ipt netfilterRunner, table, chain string) error {
@ -568,14 +602,19 @@ func (r *linuxRouter) addNetfilterChains() error {
return nil
}
for _, ipt := range []netfilterRunner{r.ipt4, r.ipt6} {
for _, ipt := range r.netfilterFamilies() {
if err := create(ipt, "filter", "ts-input"); err != nil {
return err
}
if err := create(ipt, "filter", "ts-forward"); err != nil {
return err
}
if err := create(ipt, "nat", "ts-postrouting"); err != nil {
}
if err := create(r.ipt4, "nat", "ts-postrouting"); err != nil {
return err
}
if r.v6NATAvailable {
if err := create(r.ipt6, "nat", "ts-postrouting"); err != nil {
return err
}
}
@ -588,8 +627,10 @@ func (r *linuxRouter) addNetfilterBase() error {
if err := r.addNetfilterBase4(); err != nil {
return err
}
if err := r.addNetfilterBase6(); err != nil {
return err
if r.v6Available {
if err := r.addNetfilterBase6(); err != nil {
return err
}
}
return nil
}
@ -686,14 +727,19 @@ func (r *linuxRouter) delNetfilterChains() error {
return nil
}
for _, ipt := range []netfilterRunner{r.ipt4, r.ipt6} {
for _, ipt := range r.netfilterFamilies() {
if err := del(ipt, "filter", "ts-input"); err != nil {
return err
}
if err := del(ipt, "filter", "ts-forward"); err != nil {
return err
}
if err := del(ipt, "nat", "ts-postrouting"); err != nil {
}
if err := del(r.ipt4, "nat", "ts-postrouting"); err != nil {
return err
}
if r.v6NATAvailable {
if err := del(r.ipt6, "nat", "ts-postrouting"); err != nil {
return err
}
}
@ -716,14 +762,19 @@ func (r *linuxRouter) delNetfilterBase() error {
return nil
}
for _, ipt := range []netfilterRunner{r.ipt4, r.ipt6} {
for _, ipt := range r.netfilterFamilies() {
if err := del(ipt, "filter", "ts-input"); err != nil {
return err
}
if err := del(ipt, "filter", "ts-forward"); err != nil {
return err
}
if err := del(ipt, "nat", "ts-postrouting"); err != nil {
}
if err := del(r.ipt4, "nat", "ts-postrouting"); err != nil {
return err
}
if r.v6NATAvailable {
if err := del(r.ipt6, "nat", "ts-postrouting"); err != nil {
return err
}
}
@ -752,14 +803,19 @@ func (r *linuxRouter) addNetfilterHooks() error {
return nil
}
for _, ipt := range []netfilterRunner{r.ipt4, r.ipt6} {
for _, ipt := range r.netfilterFamilies() {
if err := divert(ipt, "filter", "INPUT"); err != nil {
return err
}
if err := divert(ipt, "filter", "FORWARD"); err != nil {
return err
}
if err := divert(ipt, "nat", "POSTROUTING"); err != nil {
}
if err := divert(r.ipt4, "nat", "POSTROUTING"); err != nil {
return err
}
if r.v6NATAvailable {
if err := divert(r.ipt6, "nat", "POSTROUTING"); err != nil {
return err
}
}
@ -784,14 +840,19 @@ func (r *linuxRouter) delNetfilterHooks() error {
return nil
}
for _, ipt := range []netfilterRunner{r.ipt4, r.ipt6} {
for _, ipt := range r.netfilterFamilies() {
if err := del(ipt, "filter", "INPUT"); err != nil {
return err
}
if err := del(ipt, "filter", "FORWARD"); err != nil {
return err
}
if err := del(ipt, "nat", "POSTROUTING"); err != nil {
}
if err := del(r.ipt4, "nat", "POSTROUTING"); err != nil {
return err
}
if r.v6NATAvailable {
if err := del(r.ipt6, "nat", "POSTROUTING"); err != nil {
return err
}
}
@ -809,8 +870,10 @@ func (r *linuxRouter) addSNATRule() error {
if err := r.ipt4.Append("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("adding %v in v4/nat/ts-postrouting: %w", args, err)
}
if err := r.ipt6.Append("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("adding %v in v6/nat/ts-postrouting: %w", args, err)
if r.v6NATAvailable {
if err := r.ipt6.Append("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("adding %v in v6/nat/ts-postrouting: %w", args, err)
}
}
return nil
}
@ -826,8 +889,10 @@ func (r *linuxRouter) delSNATRule() error {
if err := r.ipt4.Delete("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("deleting %v in v4/nat/ts-postrouting: %w", args, err)
}
if err := r.ipt6.Delete("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("deleting %v in v6/nat/ts-postrouting: %w", args, err)
if r.v6NATAvailable {
if err := r.ipt6.Delete("nat", "ts-postrouting", args...); err != nil {
return fmt.Errorf("deleting %v in v6/nat/ts-postrouting: %w", args, err)
}
}
return nil
}
@ -915,3 +980,47 @@ func normalizeCIDR(cidr netaddr.IPPrefix) string {
func cleanup(logf logger.Logf, interfaceName string) {
// TODO(dmytro): clean up iptables.
}
// supportsV6 returns whether the system appears to have a working
// IPv6 network stack.
func supportsV6() bool {
_, err := os.Stat("/proc/sys/net/ipv6")
if os.IsNotExist(err) {
return false
}
bs, err := ioutil.ReadFile("/proc/sys/net/ipv6/conf/all/disable_ipv6")
if err != nil {
// Be conservative if we can't find the ipv6 configuration knob.
return false
}
disabled, err := strconv.ParseBool(strings.TrimSpace(string(bs)))
if err != nil {
return false
}
if disabled {
return false
}
// Some distros ship ip6tables separately from iptables.
if _, err := exec.LookPath("ip6tables"); err != nil {
return false
}
return true
}
// supportsV6NAT returns whether the system has a "nat" table in the
// IPv6 netfilter stack.
//
// The nat table was added after the initial release of ipv6
// netfilter, so some older distros ship a kernel that can't NAT IPv6
// traffic.
func supportsV6NAT() bool {
bs, err := ioutil.ReadFile("/proc/net/ip6_tables_names")
if err != nil {
// Can't read the file. Assume SNAT works.
return true
}
return bytes.Contains(bs, []byte("nat\n"))
}