mirror of
https://github.com/tailscale/tailscale.git
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162488a775
This is a continuation of the earlier 2a67beaacf but more aggressive;
this now remembers that we failed to find the "home" router IP so we
don't try again later on the next call.
Updates #7621
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
326 lines
9.5 KiB
Go
326 lines
9.5 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package interfaces
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import (
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"bufio"
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"bytes"
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"errors"
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"fmt"
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"io"
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"log"
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"net"
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"net/netip"
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"os"
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"os/exec"
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"runtime"
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"strings"
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"sync/atomic"
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"github.com/jsimonetti/rtnetlink"
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"github.com/mdlayher/netlink"
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"go4.org/mem"
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"golang.org/x/sys/unix"
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"tailscale.com/net/netaddr"
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"tailscale.com/util/lineread"
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)
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func init() {
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likelyHomeRouterIP = likelyHomeRouterIPLinux
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}
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var procNetRouteErr atomic.Bool
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// errStopReading is a sentinel error value used internally by
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// lineread.File callers to stop reading. It doesn't escape to
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// callers/users.
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var errStopReading = errors.New("stop reading")
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/*
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Parse 10.0.0.1 out of:
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$ cat /proc/net/route
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Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
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ens18 00000000 0100000A 0003 0 0 0 00000000 0 0 0
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ens18 0000000A 00000000 0001 0 0 0 0000FFFF 0 0 0
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*/
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func likelyHomeRouterIPLinux() (ret netip.Addr, ok bool) {
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if procNetRouteErr.Load() {
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// If we failed to read /proc/net/route previously, don't keep trying.
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// But if we're on Android, go into the Android path.
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if runtime.GOOS == "android" {
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return likelyHomeRouterIPAndroid()
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}
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return ret, false
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}
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lineNum := 0
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var f []mem.RO
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err := lineread.File(procNetRoutePath, func(line []byte) error {
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lineNum++
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if lineNum == 1 {
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// Skip header line.
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return nil
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}
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if lineNum > maxProcNetRouteRead {
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return errStopReading
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}
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f = mem.AppendFields(f[:0], mem.B(line))
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if len(f) < 4 {
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return nil
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}
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gwHex, flagsHex := f[2], f[3]
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flags, err := mem.ParseUint(flagsHex, 16, 16)
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if err != nil {
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return nil // ignore error, skip line and keep going
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}
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if flags&(unix.RTF_UP|unix.RTF_GATEWAY) != unix.RTF_UP|unix.RTF_GATEWAY {
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return nil
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}
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ipu32, err := mem.ParseUint(gwHex, 16, 32)
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if err != nil {
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return nil // ignore error, skip line and keep going
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}
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ip := netaddr.IPv4(byte(ipu32), byte(ipu32>>8), byte(ipu32>>16), byte(ipu32>>24))
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if ip.IsPrivate() {
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ret = ip
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return errStopReading
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}
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return nil
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})
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if errors.Is(err, errStopReading) {
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err = nil
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}
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if err != nil {
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procNetRouteErr.Store(true)
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if runtime.GOOS == "android" {
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return likelyHomeRouterIPAndroid()
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}
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log.Printf("interfaces: failed to read /proc/net/route: %v", err)
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}
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if ret.IsValid() {
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return ret, true
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}
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if lineNum >= maxProcNetRouteRead {
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// If we went over our line limit without finding an answer, assume
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// we're a big fancy Linux router (or at least not a home system)
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// and set the error bit so we stop trying this in the future (and wasting CPU).
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// See https://github.com/tailscale/tailscale/issues/7621.
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//
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// Remember that "likelyHomeRouterIP" exists purely to find the port
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// mapping service (UPnP, PMP, PCP) often present on a home router. If we hit
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// the route (line) limit without finding an answer, we're unlikely to ever
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// find one in the future.
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procNetRouteErr.Store(true)
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}
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return netip.Addr{}, false
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}
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// Android apps don't have permission to read /proc/net/route, at
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// least on Google devices and the Android emulator.
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func likelyHomeRouterIPAndroid() (ret netip.Addr, ok bool) {
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cmd := exec.Command("/system/bin/ip", "route", "show", "table", "0")
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out, err := cmd.StdoutPipe()
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if err != nil {
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return
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}
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if err := cmd.Start(); err != nil {
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log.Printf("interfaces: running /system/bin/ip: %v", err)
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return
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}
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// Search for line like "default via 10.0.2.2 dev radio0 table 1016 proto static mtu 1500 "
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lineread.Reader(out, func(line []byte) error {
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const pfx = "default via "
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if !mem.HasPrefix(mem.B(line), mem.S(pfx)) {
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return nil
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}
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line = line[len(pfx):]
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sp := bytes.IndexByte(line, ' ')
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if sp == -1 {
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return nil
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}
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ipb := line[:sp]
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if ip, err := netip.ParseAddr(string(ipb)); err == nil && ip.Is4() {
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ret = ip
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log.Printf("interfaces: found Android default route %v", ip)
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}
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return nil
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})
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cmd.Process.Kill()
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cmd.Wait()
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return ret, ret.IsValid()
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}
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func defaultRoute() (d DefaultRouteDetails, err error) {
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v, err := defaultRouteInterfaceProcNet()
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if err == nil {
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d.InterfaceName = v
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return d, nil
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}
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if runtime.GOOS == "android" {
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v, err = defaultRouteInterfaceAndroidIPRoute()
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d.InterfaceName = v
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return d, err
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}
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// Issue 4038: the default route (such as on Unifi UDM Pro)
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// might be in a non-default table, so it won't show up in
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// /proc/net/route. Use netlink to find the default route.
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//
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// TODO(bradfitz): this allocates a fair bit. We should track
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// this in wgengine/monitor instead and have
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// interfaces.GetState take a link monitor or similar so the
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// routing table can be cached and the monitor's existing
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// subscription to route changes can update the cached state,
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// rather than querying the whole thing every time like
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// defaultRouteFromNetlink does.
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//
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// Then we should just always try to use the cached route
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// table from netlink every time, and only use /proc/net/route
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// as a fallback for weird environments where netlink might be
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// banned but /proc/net/route is emulated (e.g. stuff like
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// Cloud Run?).
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return defaultRouteFromNetlink()
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}
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func defaultRouteFromNetlink() (d DefaultRouteDetails, err error) {
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c, err := rtnetlink.Dial(&netlink.Config{Strict: true})
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if err != nil {
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return d, fmt.Errorf("defaultRouteFromNetlink: Dial: %w", err)
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}
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defer c.Close()
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rms, err := c.Route.List()
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if err != nil {
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return d, fmt.Errorf("defaultRouteFromNetlink: List: %w", err)
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}
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for _, rm := range rms {
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if rm.Attributes.Gateway == nil {
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// A default route has a gateway. If it doesn't, skip it.
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continue
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}
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if rm.Attributes.Dst != nil {
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// A default route has a nil destination to mean anything
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// so ignore any route for a specific destination.
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// TODO(bradfitz): better heuristic?
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// empirically this seems like enough.
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continue
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}
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// TODO(bradfitz): care about address family, if
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// callers ever start caring about v4-vs-v6 default
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// route differences.
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idx := int(rm.Attributes.OutIface)
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if idx == 0 {
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continue
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}
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if iface, err := net.InterfaceByIndex(idx); err == nil {
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d.InterfaceName = iface.Name
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d.InterfaceIndex = idx
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return d, nil
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}
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}
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return d, errNoDefaultRoute
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}
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var zeroRouteBytes = []byte("00000000")
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var procNetRoutePath = "/proc/net/route"
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// maxProcNetRouteRead is the max number of lines to read from
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// /proc/net/route looking for a default route.
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const maxProcNetRouteRead = 1000
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var errNoDefaultRoute = errors.New("no default route found")
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func defaultRouteInterfaceProcNetInternal(bufsize int) (string, error) {
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f, err := os.Open(procNetRoutePath)
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if err != nil {
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return "", err
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}
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defer f.Close()
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br := bufio.NewReaderSize(f, bufsize)
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lineNum := 0
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for {
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lineNum++
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line, err := br.ReadSlice('\n')
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if err == io.EOF || lineNum > maxProcNetRouteRead {
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return "", errNoDefaultRoute
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}
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if err != nil {
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return "", err
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}
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if !bytes.Contains(line, zeroRouteBytes) {
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continue
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}
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fields := strings.Fields(string(line))
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ifc := fields[0]
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ip := fields[1]
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netmask := fields[7]
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if strings.HasPrefix(ifc, "tailscale") ||
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strings.HasPrefix(ifc, "wg") {
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continue
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}
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if ip == "00000000" && netmask == "00000000" {
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// default route
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return ifc, nil // interface name
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}
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}
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}
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// returns string interface name and an error.
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// io.EOF: full route table processed, no default route found.
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// other io error: something went wrong reading the route file.
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func defaultRouteInterfaceProcNet() (string, error) {
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rc, err := defaultRouteInterfaceProcNetInternal(128)
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if rc == "" && (errors.Is(err, io.EOF) || err == nil) {
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// https://github.com/google/gvisor/issues/5732
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// On a regular Linux kernel you can read the first 128 bytes of /proc/net/route,
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// then come back later to read the next 128 bytes and so on.
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//
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// In Google Cloud Run, where /proc/net/route comes from gVisor, you have to
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// read it all at once. If you read only the first few bytes then the second
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// read returns 0 bytes no matter how much originally appeared to be in the file.
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//
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// At the time of this writing (Mar 2021) Google Cloud Run has eth0 and eth1
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// with a 384 byte /proc/net/route. We allocate a large buffer to ensure we'll
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// read it all in one call.
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return defaultRouteInterfaceProcNetInternal(4096)
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}
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return rc, err
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}
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// defaultRouteInterfaceAndroidIPRoute tries to find the machine's default route interface name
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// by parsing the "ip route" command output. We use this on Android where /proc/net/route
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// can be missing entries or have locked-down permissions.
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// See also comments in https://github.com/tailscale/tailscale/pull/666.
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func defaultRouteInterfaceAndroidIPRoute() (ifname string, err error) {
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cmd := exec.Command("/system/bin/ip", "route", "show", "table", "0")
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out, err := cmd.StdoutPipe()
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if err != nil {
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return "", err
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}
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if err := cmd.Start(); err != nil {
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log.Printf("interfaces: running /system/bin/ip: %v", err)
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return "", err
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}
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// Search for line like "default via 10.0.2.2 dev radio0 table 1016 proto static mtu 1500 "
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lineread.Reader(out, func(line []byte) error {
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const pfx = "default via "
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if !mem.HasPrefix(mem.B(line), mem.S(pfx)) {
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return nil
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}
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ff := strings.Fields(string(line))
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for i, v := range ff {
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if i > 0 && ff[i-1] == "dev" && ifname == "" {
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ifname = v
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}
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}
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return nil
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})
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cmd.Process.Kill()
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cmd.Wait()
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if ifname == "" {
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return "", errors.New("no default routes found")
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}
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return ifname, nil
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}
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