Added concurrent application launch prevention

securedrop_client/app.py

@@ -21,9 +21,10 @@
 import os
 import signal
 import sys
+import socket
 from argparse import ArgumentParser
 from sqlalchemy.orm import sessionmaker
-from PyQt5.QtWidgets import QApplication
+from PyQt5.QtWidgets import QApplication, QMessageBox
 from PyQt5.QtCore import Qt, QTimer
 from logging.handlers import TimedRotatingFileHandler
 from securedrop_client import __version__
@@ -106,6 +107,24 @@ def arg_parser() -> ArgumentParser:
     return parser
 
 
+def prevent_second_instance(app: QApplication, unique_name: str) -> None:
+    # Null byte triggers abstract namespace
+    IDENTIFIER = '\0' + app.applicationName() + unique_name
+    ALREADY_BOUND_ERRNO = 98
+
+    app.instance_binding = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
+    try:
+        app.instance_binding.bind(IDENTIFIER)
+    except OSError as e:
+        if e.errno == ALREADY_BOUND_ERRNO:
+            err_dialog = QMessageBox()
+            err_dialog.setText(app.applicationName() + ' is already running.')
+            err_dialog.exec()
+            sys.exit()
+        else:
+            raise
+
+
 def start_app(args, qt_args) -> None:
     """
     Create all the top-level assets for the application, set things up and
@@ -129,6 +148,8 @@ def start_app(args, qt_args) -> None:
     app.setApplicationVersion(__version__)
     app.setAttribute(Qt.AA_UseHighDpiPixmaps)
 
+    prevent_second_instance(app, args.sdc_home)
+
     gui = Window()
     app.setWindowIcon(load_icon(gui.icon))
     app.setStyleSheet(load_css('sdclient.css'))

tests/test_app.py

@@ -7,8 +7,8 @@
 from PyQt5.QtWidgets import QApplication
 from unittest import mock
 from securedrop_client.app import ENCODING, excepthook, configure_logging, \
-    start_app, arg_parser, DEFAULT_SDC_HOME, run, configure_signal_handlers
-
+    start_app, arg_parser, DEFAULT_SDC_HOME, run, configure_signal_handlers, \
+    prevent_second_instance
 
 app = QApplication([])
 
@@ -46,6 +46,54 @@ def test_configure_logging(safe_tmpdir):
         assert sys.excepthook == excepthook
 
 
+@mock.patch('securedrop_client.app.sys.exit')
+@mock.patch('securedrop_client.app.QMessageBox')
+class TestSecondInstancePrevention(object):
+    @classmethod
+    def setup_class(cls):
+        cls.mock_app = mock.MagicMock()
+        cls.mock_app.applicationName = mock.MagicMock(return_value='sd')
+
+    @staticmethod
+    def socket_mock_generator(already_bound_errno=98):
+        namespace = set()
+
+        def kernel_bind(addr):
+            if addr in namespace:
+                error = OSError()
+                error.errno = already_bound_errno
+                raise error
+            else:
+                namespace.add(addr)
+
+        socket_mock = mock.MagicMock()
+        socket_mock.socket().bind = mock.MagicMock(side_effect=kernel_bind)
+        return socket_mock
+
+    def test_diff_name(self, mock_msgbox, mock_exit):
+        mock_socket = self.socket_mock_generator()
+        with mock.patch('securedrop_client.app.socket', new=mock_socket):
+            prevent_second_instance(self.mock_app, 'name1')
+            prevent_second_instance(self.mock_app, 'name2')
+
+            mock_exit.assert_not_called()
+
+    def test_same_name(self, mock_msgbox, mock_exit):
+        mock_socket = self.socket_mock_generator()
+        with mock.patch('securedrop_client.app.socket', new=mock_socket):
+            prevent_second_instance(self.mock_app, 'name1')
+            prevent_second_instance(self.mock_app, 'name1')
+
+            mock_exit.assert_any_call()
+
+    def test_unknown_kernel_error(self, mock_msgbox, mock_exit):
+        mock_socket = self.socket_mock_generator(131)  # crazy unexpected error
+        with mock.patch('securedrop_client.app.socket', new=mock_socket):
+            with pytest.raises(OSError):
+                prevent_second_instance(self.mock_app, 'name1')
+                prevent_second_instance(self.mock_app, 'name1')
+
+
 def test_start_app(safe_tmpdir):
     """
     Ensure the expected things are configured and the application is started.
@@ -60,6 +108,7 @@ def test_start_app(safe_tmpdir):
             mock.patch('securedrop_client.app.QApplication') as mock_app, \
             mock.patch('securedrop_client.app.Window') as mock_win, \
             mock.patch('securedrop_client.app.Client') as mock_client, \
+            mock.patch('securedrop_client.app.prevent_second_instance'), \
             mock.patch('securedrop_client.app.sys') as mock_sys, \
             mock.patch('securedrop_client.app.sessionmaker',
                        return_value=mock_session_class):
@@ -128,6 +177,7 @@ def test_create_app_dir_permissions(tmpdir):
                 mock.patch('securedrop_client.app.Window') as mock_win, \
                 mock.patch('securedrop_client.app.Client') as mock_client, \
                 mock.patch('securedrop_client.app.sys') as mock_sys, \
+                mock.patch('securedrop_client.app.prevent_second_instance'), \
                 mock.patch('securedrop_client.app.sessionmaker',
                            return_value=mock_session_class):
 
@@ -180,6 +230,7 @@ def fake_known_args():
 def test_signal_interception():
     # check that initializing an app calls configure_signal_handlers
     with mock.patch('securedrop_client.app.QApplication'), \
+            mock.patch('securedrop_client.app.prevent_second_instance'), \
             mock.patch('sys.exit'), \
             mock.patch('securedrop_client.models.make_engine'), \
             mock.patch('securedrop_client.app.init'), \