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