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chore: add unit test for X11 eviction#18565
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8 changes: 5 additions & 3 deletionsagent/agentssh/x11.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -83,16 +83,17 @@ func (*Server) x11Callback(_ ssh.Context, _ ssh.X11) bool { | ||
| // x11Handler is called when a session has requested X11 forwarding. | ||
| // It listens for X11 connections and forwards them to the client. | ||
| func (x *x11Forwarder) x11Handler(sshCtx ssh.Context, sshSession ssh.Session) (displayNumber int, handled bool) { | ||
| x11, hasX11 := sshSession.X11() | ||
| if !hasX11 { | ||
| return -1, false | ||
| } | ||
| serverConn, valid :=sshCtx.Value(ssh.ContextKeyConn).(*gossh.ServerConn) | ||
| if !valid { | ||
| x.logger.Warn(sshCtx, "failed to get server connection") | ||
| return -1, false | ||
| } | ||
| ctx := slog.With(sshCtx, slog.F("session_id", fmt.Sprintf("%x", serverConn.SessionID()))) | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. This is an under-appreciated feature of slog, nice to see it in action! | ||
| hostname, err := os.Hostname() | ||
| if err != nil { | ||
| @@ -127,6 +128,7 @@ func (x *x11Forwarder) x11Handler(ctx ssh.Context, sshSession ssh.Session) (disp | ||
| }() | ||
| go x.listenForConnections(ctx, x11session, serverConn, x11) | ||
| x.logger.Debug(ctx, "X11 forwarding started", slog.F("display", x11session.display)) | ||
| return x11session.display, true | ||
| } | ||
160 changes: 160 additions & 0 deletionsagent/agentssh/x11_test.go
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -5,6 +5,7 @@ import ( | ||
| "bytes" | ||
| "encoding/hex" | ||
| "fmt" | ||
| "io" | ||
| "net" | ||
| "os" | ||
| "path/filepath" | ||
| @@ -127,3 +128,162 @@ func TestServer_X11(t *testing.T) { | ||
| _, err = fs.Stat(filepath.Join(home, ".Xauthority")) | ||
| require.NoError(t, err) | ||
| } | ||
| func TestServer_X11_EvictionLRU(t *testing.T) { | ||
| t.Parallel() | ||
| if runtime.GOOS != "linux" { | ||
| t.Skip("X11 forwarding is only supported on Linux") | ||
| } | ||
| ctx := testutil.Context(t, testutil.WaitLong) | ||
| logger := testutil.Logger(t) | ||
| fs := afero.NewMemMapFs() | ||
| // Use in-process networking for X11 forwarding. | ||
| inproc := testutil.NewInProcNet() | ||
| cfg := &agentssh.Config{ | ||
| X11Net: inproc, | ||
| } | ||
| s, err := agentssh.NewServer(ctx, logger, prometheus.NewRegistry(), fs, agentexec.DefaultExecer, cfg) | ||
| require.NoError(t, err) | ||
| defer s.Close() | ||
| err = s.UpdateHostSigner(42) | ||
| require.NoError(t, err) | ||
| ln, err := net.Listen("tcp", "127.0.0.1:0") | ||
| require.NoError(t, err) | ||
| done := testutil.Go(t, func() { | ||
| err := s.Serve(ln) | ||
| assert.Error(t, err) | ||
| }) | ||
| c := sshClient(t, ln.Addr().String()) | ||
| // Calculate how many simultaneous X11 sessions we can create given the | ||
| // configured port range. | ||
| startPort := agentssh.X11StartPort + agentssh.X11DefaultDisplayOffset | ||
| maxSessions := agentssh.X11MaxPort - startPort + 1 | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. Suggestion: If we made | ||
| require.Greater(t, maxSessions, 0, "expected a positive maxSessions value") | ||
| // shellSession holds references to the session and its standard streams so | ||
| // that the test can keep them open (and optionally interact with them) for | ||
| // the lifetime of the test. If we don't start the Shell with pipes in place, | ||
| // the session will be torn down asynchronously during the test. | ||
| type shellSession struct { | ||
| sess *gossh.Session | ||
| stdin io.WriteCloser | ||
| stdout io.Reader | ||
| stderr io.Reader | ||
| // scanner is used to read the output of the session, line by line. | ||
| scanner *bufio.Scanner | ||
| } | ||
| sessions := make([]shellSession, 0, maxSessions) | ||
| for i := 0; i < maxSessions; i++ { | ||
| sess, err := c.NewSession() | ||
| require.NoError(t, err) | ||
| _, err = sess.SendRequest("x11-req", true, gossh.Marshal(ssh.X11{ | ||
| AuthProtocol: "MIT-MAGIC-COOKIE-1", | ||
| AuthCookie: hex.EncodeToString([]byte(fmt.Sprintf("cookie%d", i))), | ||
| ScreenNumber: uint32(0), | ||
| })) | ||
| require.NoError(t, err) | ||
| stdin, err := sess.StdinPipe() | ||
| require.NoError(t, err) | ||
| stdout, err := sess.StdoutPipe() | ||
| require.NoError(t, err) | ||
| stderr, err := sess.StderrPipe() | ||
| require.NoError(t, err) | ||
| require.NoError(t, sess.Shell()) | ||
| // The SSH server lazily starts the session. We need to write a command | ||
| // and read back to ensure the X11 forwarding is started. | ||
| scanner := bufio.NewScanner(stdout) | ||
| msg := fmt.Sprintf("ready-%d", i) | ||
| _, err = stdin.Write([]byte("echo " + msg + "\n")) | ||
| require.NoError(t, err) | ||
| // Read until we get the message (first token may be empty due to shell prompt) | ||
| for scanner.Scan() { | ||
| line := strings.TrimSpace(scanner.Text()) | ||
| if strings.Contains(line, msg) { | ||
| break | ||
| } | ||
| } | ||
| require.NoError(t, scanner.Err()) | ||
| sessions = append(sessions, shellSession{ | ||
| sess: sess, | ||
| stdin: stdin, | ||
| stdout: stdout, | ||
| stderr: stderr, | ||
| scanner: scanner, | ||
| }) | ||
| } | ||
| // Create one more session which should evict the first (LRU) session and | ||
| // therefore reuse the very first display/port. | ||
| extraSess, err := c.NewSession() | ||
| require.NoError(t, err) | ||
| _, err = extraSess.SendRequest("x11-req", true, gossh.Marshal(ssh.X11{ | ||
| AuthProtocol: "MIT-MAGIC-COOKIE-1", | ||
| AuthCookie: hex.EncodeToString([]byte("extra")), | ||
| ScreenNumber: uint32(0), | ||
| })) | ||
| require.NoError(t, err) | ||
| // Ask the remote side for the DISPLAY value so we can extract the display | ||
| // number that was assigned to this session. | ||
| out, err := extraSess.Output("echo DISPLAY=$DISPLAY") | ||
| require.NoError(t, err) | ||
| // Example output line: "DISPLAY=localhost:10.0". | ||
| var newDisplayNumber int | ||
| { | ||
| sc := bufio.NewScanner(bytes.NewReader(out)) | ||
| for sc.Scan() { | ||
| line := strings.TrimSpace(sc.Text()) | ||
| if strings.HasPrefix(line, "DISPLAY=") { | ||
| parts := strings.SplitN(line, ":", 2) | ||
| require.Len(t, parts, 2) | ||
| displayPart := parts[1] | ||
| if strings.Contains(displayPart, ".") { | ||
| displayPart = strings.SplitN(displayPart, ".", 2)[0] | ||
| } | ||
| var convErr error | ||
| newDisplayNumber, convErr = strconv.Atoi(displayPart) | ||
| require.NoError(t, convErr) | ||
| break | ||
| } | ||
| } | ||
| require.NoError(t, sc.Err()) | ||
| } | ||
| // The display number should have wrapped around to the starting value. | ||
| assert.Equal(t, agentssh.X11DefaultDisplayOffset, newDisplayNumber, "expected display number to be reused after eviction") | ||
| // validate that the first session was torn down. | ||
| _, err = sessions[0].stdin.Write([]byte("echo DISPLAY=$DISPLAY\n")) | ||
| require.ErrorIs(t, err, io.EOF) | ||
| err = sessions[0].sess.Wait() | ||
| require.Error(t, err) | ||
| // Cleanup. | ||
| for _, sh := range sessions[1:] { | ||
| err = sh.stdin.Close() | ||
| require.NoError(t, err) | ||
| err = sh.sess.Wait() | ||
| require.NoError(t, err) | ||
| } | ||
| err = extraSess.Close() | ||
| require.ErrorIs(t, err, io.EOF) | ||
| err = s.Close() | ||
| require.NoError(t, err) | ||
| _ = testutil.TryReceive(ctx, t, done) | ||
| } | ||
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