From bbb4631e04c99726f9ca1eacfc54ffd9f7e1618f Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Mon, 15 Feb 2021 08:40:52 -0800
Subject: [PATCH] safesocket, wgengine: add some darwin failure diagnostic
 hints

---
 safesocket/unixsocket.go | 14 ++++++++++++++
 wgengine/userspace.go    | 27 +++++++++++++++++++--------
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/safesocket/unixsocket.go b/safesocket/unixsocket.go
index fd2a58852..8128bef57 100644
--- a/safesocket/unixsocket.go
+++ b/safesocket/unixsocket.go
@@ -13,6 +13,7 @@ import (
 	"log"
 	"net"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -54,6 +55,9 @@ func listen(path string, port uint16) (ln net.Listener, _ uint16, err error) {
 	c, err := net.Dial("unix", path)
 	if err == nil {
 		c.Close()
+		if tailscaledRunningUnderLaunchd() {
+			return nil, 0, fmt.Errorf("%v: address already in use; tailscaled already running under launchd (to stop, run: $ sudo launchctl stop com.tailscale.tailscaled)", path)
+		}
 		return nil, 0, fmt.Errorf("%v: address already in use", path)
 	}
 	_ = os.Remove(path)
@@ -86,6 +90,16 @@ func listen(path string, port uint16) (ln net.Listener, _ uint16, err error) {
 	return pipe, 0, err
 }
 
+func tailscaledRunningUnderLaunchd() bool {
+	if runtime.GOOS != "darwin" {
+		return false
+	}
+	plist, err := exec.Command("launchctl", "list", "com.tailscale.tailscaled").Output()
+	_ = plist // parse it? https://github.com/DHowett/go-plist if we need something.
+	running := err == nil
+	return running
+}
+
 // socketPermissionsForOS returns the permissions to use for the
 // tailscaled.sock.
 func socketPermissionsForOS() os.FileMode {
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index 5793232b4..f3ce131c9 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -171,16 +171,16 @@ func NewFakeUserspaceEngine(logf logger.Logf, listenPort uint16, impl FakeImplFu
 
 // NewUserspaceEngine creates the named tun device and returns a
 // Tailscale Engine running on it.
-func NewUserspaceEngine(logf logger.Logf, tunname string, listenPort uint16) (Engine, error) {
-	if tunname == "" {
+func NewUserspaceEngine(logf logger.Logf, tunName string, listenPort uint16) (Engine, error) {
+	if tunName == "" {
 		return nil, fmt.Errorf("--tun name must not be blank")
 	}
 
-	logf("Starting userspace wireguard engine with tun device %q", tunname)
+	logf("Starting userspace wireguard engine with tun device %q", tunName)
 
-	tun, err := tun.CreateTUN(tunname, minimalMTU)
+	tun, err := tun.CreateTUN(tunName, minimalMTU)
 	if err != nil {
-		diagnoseTUNFailure(logf)
+		diagnoseTUNFailure(tunName, logf)
 		logf("CreateTUN: %v", err)
 		return nil, err
 	}
@@ -1363,16 +1363,27 @@ func (e *userspaceEngine) Ping(ip netaddr.IP, cb func(*ipnstate.PingResult)) {
 // the system and log some diagnostic info that might help debug why
 // TUN failed. Because TUN's already failed and things the program's
 // about to end, we might as well log a lot.
-func diagnoseTUNFailure(logf logger.Logf) {
+func diagnoseTUNFailure(tunName string, logf logger.Logf) {
 	switch runtime.GOOS {
 	case "linux":
-		diagnoseLinuxTUNFailure(logf)
+		diagnoseLinuxTUNFailure(tunName, logf)
+	case "darwin":
+		diagnoseDarwinTUNFailure(tunName, logf)
 	default:
 		logf("no TUN failure diagnostics for OS %q", runtime.GOOS)
 	}
 }
 
-func diagnoseLinuxTUNFailure(logf logger.Logf) {
+func diagnoseDarwinTUNFailure(tunName string, logf logger.Logf) {
+	if os.Getuid() != 0 {
+		logf("failed to create TUN device as non-root user; use 'sudo tailscaled', or run under launchd with 'sudo tailscaled install-system-daemon'")
+	}
+	if tunName != "utun" {
+		logf("failed to create TUN device %q; try using tun device \"utun\" instead for automatic selection", tunName)
+	}
+}
+
+func diagnoseLinuxTUNFailure(tunName string, logf logger.Logf) {
 	kernel, err := exec.Command("uname", "-r").Output()
 	kernel = bytes.TrimSpace(kernel)
 	if err != nil {