shell-screenshot: Only allow one screenshot request at a time per sender

We currently allow infinite number of screenshot requests to be active at
the same time, which can "dos" the system and cause OOM.

So fail subsequent requests for the same sender when a screenshot operation
is already running.

https://bugzilla.gnome.org/show_bug.cgi?id=737456

js/ui/screenshot.js

@@ -65,9 +65,41 @@ const ScreenshotService = new Lang.Class({
         this._dbusImpl = Gio.DBusExportedObject.wrapJSObject(ScreenshotIface, this);
         this._dbusImpl.export(Gio.DBus.session, '/org/gnome/Shell/Screenshot');
 
+        this._screenShooter = new Map();
+
         Gio.DBus.session.own_name('org.gnome.Shell.Screenshot', Gio.BusNameOwnerFlags.REPLACE, null, null);
     },
 
+    _createScreenshot: function(invocation) {
+        let sender = invocation.get_sender();
+        if (this._screenShooter.has(sender)) {
+            invocation.return_value(GLib.Variant.new('(bs)', [false, '']));
+            return null;
+        }
+
+        let shooter = new Shell.Screenshot();
+        shooter._watchNameId =
+                        Gio.bus_watch_name(Gio.BusType.SESSION, sender, 0, null,
+                                           Lang.bind(this, this._onNameVanished));
+
+        this._screenShooter.set(sender, shooter);
+
+        return shooter;
+    },
+
+    _onNameVanished: function(connection, name) {
+        this._removeShooterForSender(name);
+    },
+
+    _removeShooterForSender: function(sender) {
+        let shooter = this._screenShooter.get(sender);
+        if (!shooter)
+            return;
+
+        Gio.bus_unwatch_name(shooter._watchNameId);
+        this._screenShooter.delete(sender);
+    },
+
     _checkArea: function(x, y, width, height) {
         return x >= 0 && y >= 0 &&
                width > 0 && height > 0 &&
@@ -76,9 +108,15 @@ const ScreenshotService = new Lang.Class({
     },
 
     _onScreenshotComplete: function(obj, result, area, filenameUsed, flash, invocation) {
-        if (flash && result) {
+        if (result) {
+            if (flash) {
                 let flashspot = new Flashspot(area);
-            flashspot.fire();
+                flashspot.fire(Lang.bind(this, function() {
+                    this._removeShooterForSender(invocation.get_sender());
+                }));
+            }
+            else
+                this._removeShooterForSender(invocation.get_sender());
         }
 
         let retval = GLib.Variant.new('(bs)', [result, filenameUsed]);
@@ -112,7 +150,9 @@ const ScreenshotService = new Lang.Class({
                                             "Invalid params");
             return;
         }
-        let screenshot = new Shell.Screenshot();
+        let screenshot = this._createScreenshot(invocation);
+        if (!screenshot)
+            return;
         screenshot.screenshot_area (x, y, width, height, filename,
                                 Lang.bind(this, this._onScreenshotComplete,
                                           flash, invocation));
@@ -120,7 +160,9 @@ const ScreenshotService = new Lang.Class({
 
     ScreenshotWindowAsync : function (params, invocation) {
         let [include_frame, include_cursor, flash, filename] = params;
-        let screenshot = new Shell.Screenshot();
+        let screenshot = this._createScreenshot(invocation);
+        if (!screenshot)
+            return;
         screenshot.screenshot_window (include_frame, include_cursor, filename,
                                   Lang.bind(this, this._onScreenshotComplete,
                                             flash, invocation));
@@ -128,7 +170,9 @@ const ScreenshotService = new Lang.Class({
 
     ScreenshotAsync : function (params, invocation) {
         let [include_cursor, flash, filename] = params;
-        let screenshot = new Shell.Screenshot();
+        let screenshot = this._createScreenshot(invocation);
+        if (!screenshot)
+            return;
         screenshot.screenshot(include_cursor, filename,
                           Lang.bind(this, this._onScreenshotComplete,
                                     flash, invocation));
@@ -302,7 +346,7 @@ const Flashspot = new Lang.Class({
         this.actor.set_position(area.x, area.y);
     },
 
-    fire: function() {
+    fire: function(doneCallback) {
         this.actor.show();
         this.actor.opacity = 255;
         Tweener.addTween(this.actor,
@@ -310,6 +354,8 @@ const Flashspot = new Lang.Class({
                            time: FLASHSPOT_ANIMATION_OUT_TIME,
                            transition: 'easeOutQuad',
                            onComplete: Lang.bind(this, function() {
+                               if (doneCallback)
+                                   doneCallback();
                                this.destroy();
                            })
                          });

src/shell-screenshot.c

@@ -23,12 +23,12 @@ struct _ShellScreenshot
 {
   GObject parent_instance;
 
-  ShellGlobal *global;
+  ShellScreenshotPrivate *priv;
 };
 
-/* Used for async screenshot grabbing */
+struct _ShellScreenshotPrivate
-typedef struct _screenshot_data {
+{
-  ShellScreenshot  *screenshot;
+  ShellGlobal *global;
 
   char *filename;
   char *filename_used;
@@ -39,9 +39,9 @@ typedef struct _screenshot_data {
   gboolean include_cursor;
 
   ShellScreenshotCallback callback;
-} _screenshot_data;
+};
 
-G_DEFINE_TYPE(ShellScreenshot, shell_screenshot, G_TYPE_OBJECT);
+G_DEFINE_TYPE_WITH_PRIVATE (ShellScreenshot, shell_screenshot, G_TYPE_OBJECT);
 
 static void
 shell_screenshot_class_init (ShellScreenshotClass *screenshot_class)
@@ -52,7 +52,8 @@ shell_screenshot_class_init (ShellScreenshotClass *screenshot_class)
 static void
 shell_screenshot_init (ShellScreenshot *screenshot)
 {
-  screenshot->global = shell_global_get ();
+  screenshot->priv = shell_screenshot_get_instance_private (screenshot);
+  screenshot->priv->global = shell_global_get ();
 }
 
 static void
@@ -60,18 +61,18 @@ on_screenshot_written (GObject *source,
                        GAsyncResult *result,
                        gpointer user_data)
 {
-  _screenshot_data *screenshot_data = (_screenshot_data*) user_data;
+  ShellScreenshot *screenshot = SHELL_SCREENSHOT (source);
-  if (screenshot_data->callback)
+  ShellScreenshotPrivate *priv = screenshot->priv;
-    screenshot_data->callback (screenshot_data->screenshot,
-                               g_simple_async_result_get_op_res_gboolean (G_SIMPLE_ASYNC_RESULT (result)),
-                               &screenshot_data->screenshot_area,
-                               screenshot_data->filename_used);
 
-  cairo_surface_destroy (screenshot_data->image);
+  if (priv->callback)
-  g_object_unref (screenshot_data->screenshot);
+    priv->callback (screenshot,
-  g_free (screenshot_data->filename);
+                    g_simple_async_result_get_op_res_gboolean (G_SIMPLE_ASYNC_RESULT (result)),
-  g_free (screenshot_data->filename_used);
+                    &priv->screenshot_area,
-  g_free (screenshot_data);
+                    priv->filename_used);
+
+  g_clear_pointer (&priv->image, cairo_surface_destroy);
+  g_clear_pointer (&priv->filename, g_free);
+  g_clear_pointer (&priv->filename_used, g_free);
 }
 
 /* called in an I/O thread */
@@ -170,12 +171,15 @@ write_screenshot_thread (GSimpleAsyncResult *result,
 {
   cairo_status_t status;
   GOutputStream *stream;
-  _screenshot_data *screenshot_data = g_async_result_get_user_data (G_ASYNC_RESULT (result));
+  ShellScreenshot *screenshot = SHELL_SCREENSHOT (object);
+  ShellScreenshotPrivate *priv;
 
-  g_assert (screenshot_data != NULL);
+  g_assert (screenshot != NULL);
 
-  stream = prepare_write_stream (screenshot_data->filename,
+  priv = screenshot->priv;
-                                 &screenshot_data->filename_used);
+
+  stream = prepare_write_stream (priv->filename,
+                                 &priv->filename_used);
 
   if (stream == NULL)
     status = CAIRO_STATUS_FILE_NOT_FOUND;
@@ -183,10 +187,10 @@ write_screenshot_thread (GSimpleAsyncResult *result,
     {
       GdkPixbuf *pixbuf;
 
-      pixbuf = gdk_pixbuf_get_from_surface (screenshot_data->image,
+      pixbuf = gdk_pixbuf_get_from_surface (priv->image,
                                             0, 0,
-                                            cairo_image_surface_get_width (screenshot_data->image),
+                                            cairo_image_surface_get_width (priv->image),
-                                            cairo_image_surface_get_height (screenshot_data->image));
+                                            cairo_image_surface_get_height (priv->image));
 
       if (gdk_pixbuf_save_to_stream (pixbuf, stream, "png", NULL, NULL,
                                     "tEXt::Software", "gnome-screenshot", NULL))
@@ -204,7 +208,7 @@ write_screenshot_thread (GSimpleAsyncResult *result,
 }
 
 static void
-do_grab_screenshot (_screenshot_data *screenshot_data,
+do_grab_screenshot (ShellScreenshot *screenshot,
                     int               x,
                     int               y,
                     int               width,
@@ -215,16 +219,17 @@ do_grab_screenshot (_screenshot_data *screenshot_data,
   CoglContext *context;
   int stride;
   guchar *data;
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
   backend = clutter_get_default_backend ();
   context = clutter_backend_get_cogl_context (backend);
 
-  screenshot_data->image = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+  priv->image = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
                                             width, height);
 
 
-  data = cairo_image_surface_get_data (screenshot_data->image);
+  data = cairo_image_surface_get_data (priv->image);
-  stride = cairo_image_surface_get_stride (screenshot_data->image);
+  stride = cairo_image_surface_get_stride (priv->image);
 
   bitmap = cogl_bitmap_new_for_data (context,
                                      width,
@@ -237,7 +242,7 @@ do_grab_screenshot (_screenshot_data *screenshot_data,
                                             COGL_READ_PIXELS_COLOR_BUFFER,
                                             bitmap);
 
-  cairo_surface_mark_dirty (screenshot_data->image);
+  cairo_surface_mark_dirty (priv->image);
   cogl_object_unref (bitmap);
 }
 
@@ -310,17 +315,19 @@ _draw_cursor_image (MetaCursorTracker     *tracker,
 
 static void
 grab_screenshot (ClutterActor *stage,
-                 _screenshot_data *screenshot_data)
+                 ShellScreenshot *screenshot)
 {
-  MetaScreen *screen = shell_global_get_screen (screenshot_data->screenshot->global);
+  MetaScreen *screen;
   MetaCursorTracker *tracker;
   int width, height;
   GSimpleAsyncResult *result;
   GSettings *settings;
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
+  screen = shell_global_get_screen (priv->global);
   meta_screen_get_size (screen, &width, &height);
 
-  do_grab_screenshot (screenshot_data, 0, 0, width, height);
+  do_grab_screenshot (screenshot, 0, 0, width, height);
 
   if (meta_screen_get_n_monitors (screen) > 1)
     {
@@ -346,7 +353,7 @@ grab_screenshot (ClutterActor *stage,
       cairo_region_xor (stage_region, screen_region);
       cairo_region_destroy (screen_region);
 
-      cr = cairo_create (screenshot_data->image);
+      cr = cairo_create (priv->image);
 
       for (i = 0; i < cairo_region_num_rectangles (stage_region); i++)
         {
@@ -360,41 +367,42 @@ grab_screenshot (ClutterActor *stage,
       cairo_region_destroy (stage_region);
     }
 
-  screenshot_data->screenshot_area.x = 0;
+  priv->screenshot_area.x = 0;
-  screenshot_data->screenshot_area.y = 0;
+  priv->screenshot_area.y = 0;
-  screenshot_data->screenshot_area.width = width;
+  priv->screenshot_area.width = width;
-  screenshot_data->screenshot_area.height = height;
+  priv->screenshot_area.height = height;
 
   settings = g_settings_new (A11Y_APPS_SCHEMA);
-  if (screenshot_data->include_cursor &&
+  if (priv->include_cursor &&
       !g_settings_get_boolean (settings, MAGNIFIER_ACTIVE_KEY))
     {
       tracker = meta_cursor_tracker_get_for_screen (screen);
-      _draw_cursor_image (tracker, screenshot_data->image, screenshot_data->screenshot_area);
+      _draw_cursor_image (tracker, priv->image, priv->screenshot_area);
     }
   g_object_unref (settings);
 
-  g_signal_handlers_disconnect_by_func (stage, (void *)grab_screenshot, (gpointer)screenshot_data);
+  g_signal_handlers_disconnect_by_func (stage, (void *)grab_screenshot, (gpointer)screenshot);
 
-  result = g_simple_async_result_new (NULL, on_screenshot_written, (gpointer)screenshot_data, grab_screenshot);
+  result = g_simple_async_result_new (G_OBJECT (screenshot), on_screenshot_written, NULL, grab_screenshot);
   g_simple_async_result_run_in_thread (result, write_screenshot_thread, G_PRIORITY_DEFAULT, NULL);
   g_object_unref (result);
 }
 
 static void
 grab_area_screenshot (ClutterActor *stage,
-                      _screenshot_data *screenshot_data)
+                      ShellScreenshot *screenshot)
 {
   GSimpleAsyncResult *result;
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
-  do_grab_screenshot (screenshot_data,
+  do_grab_screenshot (screenshot,
-                      screenshot_data->screenshot_area.x,
+                      priv->screenshot_area.x,
-                      screenshot_data->screenshot_area.y,
+                      priv->screenshot_area.y,
-                      screenshot_data->screenshot_area.width,
+                      priv->screenshot_area.width,
-                      screenshot_data->screenshot_area.height);
+                      priv->screenshot_area.height);
 
-  g_signal_handlers_disconnect_by_func (stage, (void *)grab_area_screenshot, (gpointer)screenshot_data);
+  g_signal_handlers_disconnect_by_func (stage, (void *)grab_area_screenshot, (gpointer)screenshot);
-  result = g_simple_async_result_new (NULL, on_screenshot_written, (gpointer)screenshot_data, grab_area_screenshot);
+  result = g_simple_async_result_new (G_OBJECT (screenshot), on_screenshot_written, NULL, grab_area_screenshot);
   g_simple_async_result_run_in_thread (result, write_screenshot_thread, G_PRIORITY_DEFAULT, NULL);
   g_object_unref (result);
 }
@@ -418,16 +426,21 @@ shell_screenshot_screenshot (ShellScreenshot *screenshot,
                              ShellScreenshotCallback callback)
 {
   ClutterActor *stage;
-  _screenshot_data *data = g_new0 (_screenshot_data, 1);
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
-  data->screenshot = g_object_ref (screenshot);
+  if (priv->filename != NULL) {
-  data->filename = g_strdup (filename);
+    if (callback)
-  data->callback = callback;
+      callback (screenshot, FALSE, NULL, "");
-  data->include_cursor = include_cursor;
+    return;
+  }
 
-  stage = CLUTTER_ACTOR (shell_global_get_stage (screenshot->global));
+  priv->filename = g_strdup (filename);
+  priv->callback = callback;
+  priv->include_cursor = include_cursor;
 
-  g_signal_connect_after (stage, "paint", G_CALLBACK (grab_screenshot), (gpointer)data);
+  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));
+
+  g_signal_connect_after (stage, "paint", G_CALLBACK (grab_screenshot), (gpointer)screenshot);
 
   clutter_actor_queue_redraw (stage);
 }
@@ -457,19 +470,24 @@ shell_screenshot_screenshot_area (ShellScreenshot *screenshot,
                                   ShellScreenshotCallback callback)
 {
   ClutterActor *stage;
-  _screenshot_data *data = g_new0 (_screenshot_data, 1);
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
-  data->screenshot = g_object_ref (screenshot);
+  if (priv->filename != NULL) {
-  data->filename = g_strdup (filename);
+    if (callback)
-  data->screenshot_area.x = x;
+      callback (screenshot, FALSE, NULL, "");
-  data->screenshot_area.y = y;
+    return;
-  data->screenshot_area.width = width;
+  }
-  data->screenshot_area.height = height;
-  data->callback = callback;
 
-  stage = CLUTTER_ACTOR (shell_global_get_stage (screenshot->global));
+  priv->filename = g_strdup (filename);
+  priv->screenshot_area.x = x;
+  priv->screenshot_area.y = y;
+  priv->screenshot_area.width = width;
+  priv->screenshot_area.height = height;
+  priv->callback = callback;
 
-  g_signal_connect_after (stage, "paint", G_CALLBACK (grab_area_screenshot), (gpointer)data);
+  stage = CLUTTER_ACTOR (shell_global_get_stage (priv->global));
+
+  g_signal_connect_after (stage, "paint", G_CALLBACK (grab_area_screenshot), (gpointer)screenshot);
 
   clutter_actor_queue_redraw (stage);
 }
@@ -496,10 +514,9 @@ shell_screenshot_screenshot_window (ShellScreenshot *screenshot,
 {
   GSimpleAsyncResult *result;
   GSettings *settings;
+  ShellScreenshotPrivate *priv = screenshot->priv;
 
-  _screenshot_data *screenshot_data = g_new0 (_screenshot_data, 1);
+  MetaScreen *screen = shell_global_get_screen (priv->global);
-
-  MetaScreen *screen = shell_global_get_screen (screenshot->global);
   MetaCursorTracker *tracker;
   MetaDisplay *display = meta_screen_get_display (screen);
   MetaWindow *window = meta_display_get_focus_window (display);
@@ -509,21 +526,15 @@ shell_screenshot_screenshot_window (ShellScreenshot *screenshot,
   MetaRectangle rect;
   cairo_rectangle_int_t clip;
 
-  screenshot_data->screenshot = g_object_ref (screenshot);
+  if (priv->filename != NULL || !window) {
-  screenshot_data->filename = g_strdup (filename);
+    if (callback)
-  screenshot_data->callback = callback;
+      callback (screenshot, FALSE, NULL, "");
-
-  if (!window)
-    {
-      screenshot_data->filename_used = g_strdup ("");
-      result = g_simple_async_result_new (NULL, on_screenshot_written, (gpointer)screenshot_data, shell_screenshot_screenshot_window);
-      g_simple_async_result_set_op_res_gboolean (result, FALSE);
-      g_simple_async_result_complete (result);
-      g_object_unref (result);
-
     return;
   }
 
+  priv->filename = g_strdup (filename);
+  priv->callback = callback;
+
   window_actor = CLUTTER_ACTOR (meta_window_get_compositor_private (window));
   clutter_actor_get_position (window_actor, &actor_x, &actor_y);
 
@@ -532,26 +543,26 @@ shell_screenshot_screenshot_window (ShellScreenshot *screenshot,
   if (!include_frame)
     meta_window_frame_rect_to_client_rect (window, &rect, &rect);
 
-  screenshot_data->screenshot_area.x = rect.x;
+  priv->screenshot_area.x = rect.x;
-  screenshot_data->screenshot_area.y = rect.y;
+  priv->screenshot_area.y = rect.y;
   clip.x = rect.x - (gint) actor_x;
   clip.y = rect.y - (gint) actor_y;
 
-  clip.width = screenshot_data->screenshot_area.width = rect.width;
+  clip.width = priv->screenshot_area.width = rect.width;
-  clip.height = screenshot_data->screenshot_area.height = rect.height;
+  clip.height = priv->screenshot_area.height = rect.height;
 
   stex = META_SHAPED_TEXTURE (meta_window_actor_get_texture (META_WINDOW_ACTOR (window_actor)));
-  screenshot_data->image = meta_shaped_texture_get_image (stex, &clip);
+  priv->image = meta_shaped_texture_get_image (stex, &clip);
 
   settings = g_settings_new (A11Y_APPS_SCHEMA);
   if (include_cursor && !g_settings_get_boolean (settings, MAGNIFIER_ACTIVE_KEY))
     {
       tracker = meta_cursor_tracker_get_for_screen (screen);
-      _draw_cursor_image (tracker, screenshot_data->image, screenshot_data->screenshot_area);
+      _draw_cursor_image (tracker, priv->image, priv->screenshot_area);
     }
   g_object_unref (settings);
 
-  result = g_simple_async_result_new (NULL, on_screenshot_written, (gpointer)screenshot_data, shell_screenshot_screenshot_window);
+  result = g_simple_async_result_new (G_OBJECT (screenshot), on_screenshot_written, NULL, shell_screenshot_screenshot_window);
   g_simple_async_result_run_in_thread (result, write_screenshot_thread, G_PRIORITY_DEFAULT, NULL);
   g_object_unref (result);
 }

src/shell-screenshot.h

@@ -12,6 +12,7 @@
  */
 
 typedef struct _ShellScreenshot         ShellScreenshot;
+typedef struct _ShellScreenshotPrivate  ShellScreenshotPrivate;
 typedef struct _ShellScreenshotClass    ShellScreenshotClass;
 
 #define SHELL_TYPE_SCREENSHOT              (shell_screenshot_get_type ())