// Copyright (c) 2020 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 interfaces import ( "errors" "os/exec" "go4.org/mem" "inet.af/netaddr" "tailscale.com/util/lineread" "tailscale.com/version" ) /* Parse out 10.0.0.1 from: $ netstat -r -n -f inet Routing tables Internet: Destination Gateway Flags Netif Expire default 10.0.0.1 UGSc en0 default link#14 UCSI utun2 10/16 link#4 UCS en0 ! 10.0.0.1/32 link#4 UCS en0 ! ... */ func likelyHomeRouterIPDarwinExec() (ret netaddr.IP, ok bool) { if version.IsMobile() { // Don't try to do subprocesses on iOS. Ends up with log spam like: // kernel: "Sandbox: IPNExtension(86580) deny(1) process-fork" // This is why we have likelyHomeRouterIPDarwinSyscall. return ret, false } cmd := exec.Command("/usr/sbin/netstat", "-r", "-n", "-f", "inet") stdout, err := cmd.StdoutPipe() if err != nil { return } if err := cmd.Start(); err != nil { return } defer cmd.Wait() var f []mem.RO lineread.Reader(stdout, func(lineb []byte) error { line := mem.B(lineb) if !mem.Contains(line, mem.S("default")) { return nil } f = mem.AppendFields(f[:0], line) if len(f) < 3 || !f[0].EqualString("default") { return nil } ipm, flagsm := f[1], f[2] if !mem.Contains(flagsm, mem.S("G")) { return nil } ip, err := netaddr.ParseIP(string(mem.Append(nil, ipm))) if err == nil && isPrivateIP(ip) { ret = ip // We've found what we're looking for. return errStopReadingNetstatTable } return nil }) return ret, !ret.IsZero() } var errStopReadingNetstatTable = errors.New("found private gateway")