mirror of https://github.com/tailscale/tailscale/
interfaces: create android impl (#11784)
-Move Android impl into interfaces_android.go -Instead of using ip route to get the interface name, use the one passed in by Android (ip route is restricted in Android 13+ per termux/termux-app#2993) Follow-up will be to do the same for router Fixes tailscale/corp#19215 Fixes tailscale/corp#19124 Signed-off-by: kari-ts <kari@tailscale.com>pull/11812/head
kari-ts
7 months ago
committed by
GitHub
parent
7132b782d4
commit
048cb61dd0
@ -0,0 +1,183 @@
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// 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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"bytes"
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"errors"
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"log"
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"net/netip"
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"os/exec"
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"sync/atomic"
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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/syncs"
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"tailscale.com/util/lineread"
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)
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var (
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lastKnownDefaultRouteIfName syncs.AtomicValue[string]
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)
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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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func init() {
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likelyHomeRouterIP = likelyHomeRouterIPAndroid
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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 likelyHomeRouterIPAndroid() (ret netip.Addr, myIP 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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return likelyHomeRouterIPHelper()
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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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return likelyHomeRouterIP()
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}
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if ret.IsValid() {
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// Try to get the local IP of the interface associated with
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// this route to short-circuit finding the IP associated with
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// this gateway. This isn't fatal if it fails.
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if len(f) > 0 && !disableLikelyHomeRouterIPSelf() {
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ForeachInterface(func(ni Interface, pfxs []netip.Prefix) {
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// Ensure this is the same interface
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if !f[0].EqualString(ni.Name) {
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return
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}
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// Find the first IPv4 address and use it.
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for _, pfx := range pfxs {
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if addr := pfx.Addr(); addr.Is4() {
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myIP = addr
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break
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}
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}
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})
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}
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return ret, myIP, 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{}, 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 likelyHomeRouterIPHelper() (ret netip.Addr, _ 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, netip.Addr{}, ret.IsValid()
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}
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// UpdateLastKnownDefaultRouteInterface is called by libtailscale in the Android app when
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// the connectivity manager detects a network path transition. If ifName is "", network has been lost.
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// After updating the interface, Android calls Monitor.InjectEvent(), triggering a link change.
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func UpdateLastKnownDefaultRouteInterface(ifName string) {
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if old := lastKnownDefaultRouteIfName.Swap(ifName); old != ifName {
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log.Printf("defaultroute: update from Android, ifName = %s (was %s)", ifName, old)
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}
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}
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func defaultRoute() (d DefaultRouteDetails, err error) {
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if ifName := lastKnownDefaultRouteIfName.Load(); ifName != "" {
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d.InterfaceName = ifName
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}
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return d, nil
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}
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