ssh/tailssh: various typo fixes, clarifications.

Signed-off-by: David Anderson <danderson@tailscale.com>

ssh/tailssh/incubator.go

@@ -2,10 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file contains the code for the incubator process.
-// Taiscaled launches the incubator as the same user as it was launched as.
-// The incbuator then registers a new session with the OS, sets its own UID to
-// the specified `--uid`` and then lauches the requested `--cmd`.
+// This file contains the code for the incubator process.  Taiscaled
+// launches the incubator as the same user as it was launched as.  The
+// incubator then registers a new session with the OS, sets its UID
+// and groups to the specified `--uid`, `--gid` and `--groups`, and
+// then lauches the requested `--cmd`.
 
 //go:build linux || (darwin && !ios)
 // +build linux darwin,!ios
@@ -137,9 +138,10 @@ func (stdRWC) Close() error {
 // This is sometimes necessary for mounting home directories and decrypting file
 // systems.
 //
-// Taiscaled launches the incubator as the same user as it was launched as.
-// The incbuator then registers a new session with the OS, sets its own UID to
-// the specified `--uid`` and then lauches the requested `--cmd`.
+// Tailscaled launches the incubator as the same user as it was
+// launched as.  The incubator then registers a new session with the
+// OS, sets its UID and groups to the specified `--uid`, `--gid` and
+// `--groups` and then launches the requested `--cmd`.
 func beIncubator(args []string) error {
 	var (
 		flags      = flag.NewFlagSet("", flag.ExitOnError)
@@ -171,7 +173,7 @@ func beIncubator(args []string) error {
 	// Inform the system that we are about to log someone in.
 	// We can only do this if we are running as root.
 	// This is best effort to still allow running on machines where
-	// we don't support starting session, e.g. darwin.
+	// we don't support starting sessions, e.g. darwin.
 	sessionCloser, err := maybeStartLoginSession(logf, uint32(*uid), *localUser, *remoteUser, *remoteIP, *ttyName)
 	if err == nil && sessionCloser != nil {
 		defer sessionCloser()
@@ -285,7 +287,7 @@ func resizeWindow(f *os.File, winCh <-chan ssh.Window) {
 }
 
 // opcodeShortName is a mapping of SSH opcode
-// to mnemonic names expected by the termios packaage.
+// to mnemonic names expected by the termios package.
 // These are meant to be platform independent.
 var opcodeShortName = map[uint8]string{
 	gossh.VINTR:         "intr",
@@ -498,7 +500,7 @@ func loginShell(uid string) string {
 	if e := os.Getenv("SHELL"); e != "" {
 		return e
 	}
-	return "/bin/bash"
+	return "/bin/sh"
 }
 
 func envForUser(u *user.User) []string {

ssh/tailssh/tailssh.go

@@ -367,10 +367,8 @@ func (c *conn) setInfo(cm gossh.ConnMetadata) error {
 	return nil
 }
 
-// evaluatePolicy returns the SSHAction, sshConnInfo and localUser after
-// evaluating the sshUser and remoteAddr against the SSHPolicy. The remoteAddr
-// and localAddr params must be Tailscale IPs. The pubKey may be nil for "none"
-// auth.
+// evaluatePolicy returns the SSHAction and localUser after evaluating
+// the SSHPolicy for this conn. The pubKey may be nil for "none" auth.
 func (c *conn) evaluatePolicy(pubKey gossh.PublicKey) (_ *tailcfg.SSHAction, localUser string, _ error) {
 	pol, ok := c.sshPolicy()
 	if !ok {
@@ -692,7 +690,7 @@ func (c *conn) fetchSSHAction(ctx context.Context, url string) (*tailcfg.SSHActi
 // unless the process has already exited.
 func (ss *sshSession) killProcessOnContextDone() {
 	<-ss.ctx.Done()
-	// Either the process has already existed, in which case this does nothing.
+	// Either the process has already exited, in which case this does nothing.
 	// Or, the process is still running in which case this will kill it.
 	ss.exitOnce.Do(func() {
 		err := ss.ctx.Err()
@@ -703,6 +701,8 @@ func (ss *sshSession) killProcessOnContextDone() {
 			}
 		}
 		ss.logf("terminating SSH session from %v: %v", ss.conn.info.src.IP(), err)
+		// We don't need to Process.Wait here, sshSession.run() does
+		// the waiting regardless of termination reason.
 		ss.cmd.Process.Kill()
 	})
 }
@@ -746,7 +746,7 @@ func (srv *server) endSession(ss *sshSession) {
 var errSessionDone = errors.New("session is done")
 
 // handleSSHAgentForwarding starts a Unix socket listener and in the background
-// forwards agent connections between the listenr and the ssh.Session.
+// forwards agent connections between the listener and the ssh.Session.
 // On success, it assigns ss.agentListener.
 func (ss *sshSession) handleSSHAgentForwarding(s ssh.Session, lu *user.User) error {
 	if !ssh.AgentRequested(ss) || !ss.action.AllowAgentForwarding {
@@ -896,7 +896,6 @@ func (ss *sshSession) run() {
 	ss.exitOnce.Do(func() {})
 
 	if err == nil {
-		ss.logf("Wait: ok")
 		ss.Exit(0)
 		return
 	}
@@ -1214,7 +1213,7 @@ func (w loggingWriter) Write(p []byte) (n int, err error) {
 	}
 	j = append(j, '\n')
 	if err := w.writeCastLine(j); err != nil {
-		return 0, nil
+		return 0, err
 	}
 	return w.w.Write(p)
 }