mirror of
https://github.com/tailscale/tailscale.git
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118 lines
3.1 KiB
Go
118 lines
3.1 KiB
Go
// Copyright (c) 2020 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 interfaces
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import (
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"bytes"
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"log"
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"os/exec"
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"runtime"
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"go4.org/mem"
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"inet.af/netaddr"
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"tailscale.com/syncs"
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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 syncs.AtomicBool
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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 netaddr.IP, ok bool) {
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if procNetRouteErr.Get() {
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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("/proc/net/route", 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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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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const RTF_UP = 0x0001
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const RTF_GATEWAY = 0x0002
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if flags&(RTF_UP|RTF_GATEWAY) != RTF_UP|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 isPrivateIP(ip) {
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ret = ip
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}
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return nil
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})
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if err != nil {
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procNetRouteErr.Set(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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return ret, !ret.IsZero()
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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 netaddr.IP, 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 := netaddr.ParseIP(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.IsZero()
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}
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