mirror of https://github.com/tailscale/tailscale/
net/netutil: add CheckIPForwardingLinux (#4301)
Combine the code between `LocalBackend.CheckIPForwarding` and `controlclient.ipForwardingBroken`. Fixes #4300 Signed-off-by: Maisem Ali <maisem@tailscale.com>pull/4319/head
Maisem Ali
3 years ago
committed by
GitHub
parent
7c7f37342f
commit
309ddef852
@ -0,0 +1,221 @@
|
||||
// Copyright (c) 2022 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 netutil contains misc shared networking code & types.
|
||||
package netutil
|
||||
|
||||
import (
|
||||
"bytes"
|
||||
"fmt"
|
||||
"os"
|
||||
"os/exec"
|
||||
"path/filepath"
|
||||
"runtime"
|
||||
"strconv"
|
||||
"strings"
|
||||
|
||||
"inet.af/netaddr"
|
||||
"tailscale.com/net/interfaces"
|
||||
)
|
||||
|
||||
// protocolsRequiredForForwarding reports whether IPv4 and/or IPv6 protocols are
|
||||
// required to forward the specified routes.
|
||||
// The state param must be specified.
|
||||
func protocolsRequiredForForwarding(routes []netaddr.IPPrefix, state *interfaces.State) (v4, v6 bool) {
|
||||
if len(routes) == 0 {
|
||||
// Nothing to route, so no need to warn.
|
||||
return false, false
|
||||
}
|
||||
|
||||
localIPs := make(map[netaddr.IP]bool)
|
||||
for _, addrs := range state.InterfaceIPs {
|
||||
for _, pfx := range addrs {
|
||||
localIPs[pfx.IP()] = true
|
||||
}
|
||||
}
|
||||
|
||||
for _, r := range routes {
|
||||
// It's possible to advertise a route to one of the local
|
||||
// machine's local IPs. IP forwarding isn't required for this
|
||||
// to work, so we shouldn't warn for such exports.
|
||||
if r.IsSingleIP() && localIPs[r.IP()] {
|
||||
continue
|
||||
}
|
||||
if r.IP().Is4() {
|
||||
v4 = true
|
||||
} else {
|
||||
v6 = true
|
||||
}
|
||||
}
|
||||
return v4, v6
|
||||
}
|
||||
|
||||
// CheckIPForwarding reports whether IP forwarding is enabled correctly
|
||||
// for subnet routing and exit node functionality on any interface.
|
||||
// The state param can be nil, in which case interfaces.GetState is used.
|
||||
// The routes should only be advertised routes, and should not contain the
|
||||
// nodes Tailscale IPs.
|
||||
// It returns an error if it is unable to determine if IP forwarding is enabled.
|
||||
// It returns a warning describing configuration issues if IP forwarding is
|
||||
// non-functional or partly functional.
|
||||
func CheckIPForwarding(routes []netaddr.IPPrefix, state *interfaces.State) (warn, err error) {
|
||||
if runtime.GOOS != "linux" {
|
||||
switch runtime.GOOS {
|
||||
case "dragonfly", "freebsd", "netbsd", "openbsd":
|
||||
return fmt.Errorf("Subnet routing and exit nodes only work with additional manual configuration on %v, and is not currently officially supported.", runtime.GOOS), nil
|
||||
}
|
||||
return nil, nil
|
||||
}
|
||||
const kbLink = "\nSee https://tailscale.com/kb/1104/enable-ip-forwarding/"
|
||||
if state == nil {
|
||||
var err error
|
||||
state, err = interfaces.GetState()
|
||||
if err != nil {
|
||||
return nil, err
|
||||
}
|
||||
}
|
||||
wantV4, wantV6 := protocolsRequiredForForwarding(routes, state)
|
||||
if !wantV4 && !wantV6 {
|
||||
return nil, nil
|
||||
}
|
||||
|
||||
v4e, err := ipForwardingEnabledLinux(ipv4, "")
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("Couldn't check system's IP forwarding configuration, subnet routing/exit nodes may not work: %w%s", err, kbLink)
|
||||
}
|
||||
v6e, err := ipForwardingEnabledLinux(ipv6, "")
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("Couldn't check system's IP forwarding configuration, subnet routing/exit nodes may not work: %w%s", err, kbLink)
|
||||
}
|
||||
|
||||
if v4e && v6e {
|
||||
// IP forwarding is enabled systemwide, all is well.
|
||||
return nil, nil
|
||||
}
|
||||
|
||||
if !wantV4 {
|
||||
if !v6e {
|
||||
return nil, fmt.Errorf("IPv6 forwarding is disabled, subnet routing/exit nodes may not work.%s", kbLink)
|
||||
}
|
||||
return nil, nil
|
||||
}
|
||||
// IP forwarding isn't enabled globally, but it might be enabled
|
||||
// on a per-interface basis. Check if it's on for all interfaces,
|
||||
// and warn appropriately if it's not.
|
||||
// Note: you might be wondering why we check only the state of
|
||||
// ipv6.conf.all.forwarding, rather than per-interface forwarding
|
||||
// configuration. According to kernel documentation, it seems
|
||||
// that to actually forward packets, you need to enable
|
||||
// forwarding globally, and the per-interface forwarding
|
||||
// setting only alters other things such as how router
|
||||
// advertisements are handled. The kernel itself warns that
|
||||
// enabling forwarding per-interface and not globally will
|
||||
// probably not work, so I feel okay calling those configs
|
||||
// broken until we have proof otherwise.
|
||||
var (
|
||||
anyEnabled bool
|
||||
warnings []string
|
||||
)
|
||||
if wantV6 && !v6e {
|
||||
warnings = append(warnings, "IPv6 forwarding is disabled.")
|
||||
}
|
||||
for _, iface := range state.Interface {
|
||||
if iface.Name == "lo" {
|
||||
continue
|
||||
}
|
||||
v4e, err := ipForwardingEnabledLinux(ipv4, iface.Name)
|
||||
if err != nil {
|
||||
return nil, fmt.Errorf("Couldn't check system's IP forwarding configuration, subnet routing/exit nodes may not work: %w%s", err, kbLink)
|
||||
} else if !v4e {
|
||||
warnings = append(warnings, fmt.Sprintf("Traffic received on %s won't be forwarded (%s disabled)", iface.Name, ipForwardSysctlKey(dotFormat, ipv4, iface.Name)))
|
||||
} else {
|
||||
anyEnabled = true
|
||||
}
|
||||
}
|
||||
if !anyEnabled {
|
||||
// IP forwarding is completely disabled, just say that rather
|
||||
// than enumerate all the interfaces on the system.
|
||||
return fmt.Errorf("IP forwarding is disabled, subnet routing/exit nodes will not work.%s", kbLink), nil
|
||||
}
|
||||
if len(warnings) > 0 {
|
||||
// If partially enabled, enumerate the bits that won't work.
|
||||
return fmt.Errorf("%s\nSubnet routes and exit nodes may not work correctly.%s", strings.Join(warnings, "\n"), kbLink), nil
|
||||
}
|
||||
|
||||
return nil, nil
|
||||
}
|
||||
|
||||
// ipForwardSysctlKey returns the sysctl key for the given protocol and iface.
|
||||
// When the dotFormat parameter is true the output is formatted as `net.ipv4.ip_forward`,
|
||||
// else it is `net/ipv4/ip_forward`
|
||||
func ipForwardSysctlKey(format sysctlFormat, p protocol, iface string) string {
|
||||
if iface == "" {
|
||||
if format == dotFormat {
|
||||
if p == ipv4 {
|
||||
return "net.ipv4.ip_forward"
|
||||
}
|
||||
return "net.ipv6.conf.all.forwarding"
|
||||
}
|
||||
if p == ipv4 {
|
||||
return "net/ipv4/ip_forward"
|
||||
}
|
||||
return "net/ipv6/conf/all/forwarding"
|
||||
}
|
||||
|
||||
var k string
|
||||
if p == ipv4 {
|
||||
k = "net/ipv4/conf/%s/forwarding"
|
||||
} else {
|
||||
k = "net/ipv6/conf/%s/forwarding"
|
||||
}
|
||||
if format == dotFormat {
|
||||
// Swap the delimiters.
|
||||
iface = strings.ReplaceAll(iface, ".", "/")
|
||||
k = strings.ReplaceAll(k, "/", ".")
|
||||
}
|
||||
return fmt.Sprintf(k, iface)
|
||||
}
|
||||
|
||||
type sysctlFormat int
|
||||
|
||||
const (
|
||||
dotFormat sysctlFormat = iota
|
||||
slashFormat
|
||||
)
|
||||
|
||||
type protocol int
|
||||
|
||||
const (
|
||||
ipv4 protocol = iota
|
||||
ipv6
|
||||
)
|
||||
|
||||
// ipForwardingEnabledLinux reports whether the IP Forwarding is enabled for the
|
||||
// given interface.
|
||||
// The iface param determines which interface to check against, "" means to check
|
||||
// global config.
|
||||
// It tries to lookup the value directly from `/proc/sys`, and fallsback to
|
||||
// using `sysctl` on failure.
|
||||
func ipForwardingEnabledLinux(p protocol, iface string) (bool, error) {
|
||||
k := ipForwardSysctlKey(slashFormat, p, iface)
|
||||
bs, err := os.ReadFile(filepath.Join("/proc/sys", k))
|
||||
if err != nil {
|
||||
// Fallback to using sysctl.
|
||||
// Sysctl accepts `/` as separator.
|
||||
bs, err = exec.Command("sysctl", "-n", k).Output()
|
||||
if err != nil {
|
||||
// But in case it doesn't.
|
||||
k := ipForwardSysctlKey(dotFormat, p, iface)
|
||||
bs, err = exec.Command("sysctl", "-n", k).Output()
|
||||
if err != nil {
|
||||
return false, fmt.Errorf("couldn't check %s (%v)", k, err)
|
||||
}
|
||||
}
|
||||
}
|
||||
on, err := strconv.ParseBool(string(bytes.TrimSpace(bs)))
|
||||
if err != nil {
|
||||
return false, fmt.Errorf("couldn't parse %s (%v)", k, err)
|
||||
}
|
||||
return on, nil
|
||||
}
|
||||
Loading…
Reference in New Issue