Bug 42835: Create an actor to filter file data transfers

toolkit/actors/FilesFilterChild.sys.mjs

+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const lazy = {};
+
+ChromeUtils.defineLazyGetter(lazy, "console", () => {
+  return console.createInstance({
+    prefix: "FilesFilter",
+  });
+});
+
+export class FilesFilterChild extends JSWindowActorChild {
+  handleEvent(event) {
+    if (!Services.prefs.getBoolPref("browser.filesfilter.enabled", true)) {
+      return;
+    }
+    // drop or paste
+    const { composedTarget } = event;
+    const dt = event.clipboardData || event.dataTransfer;
+
+    if ([...dt.files].some(f => f.mozFullPath)) {
+      if (
+        ["HTMLInputElement", "HTMLTextAreaElement"].includes(
+          ChromeUtils.getClassName(composedTarget)
+        )
+      ) {
+        event.preventDefault();
+        lazy.console.log(
+          `Preventing path leak on ${event.type} for ${[...dt.files]
+            .map(f => `${f.name} (${f.mozFullPath})`)
+            .join(", ")}.`
+        );
+      }
+      return;
+    }
+
+    // "Paste Without Formatting" (ctrl+shift+V) in HTML editors coerces files into paths
+    if (!(event.clipboardData && /[\/\\]/.test(dt.getData("text")))) {
+      return;
+    }
+
+    // check wether the clipboard contains a file
+    const { clipboard } = Services;
+    if (
+      [clipboard.kSelectionClipboard, clipboard.kGlobalClipboard].some(
+        clipboardType =>
+          clipboard.isClipboardTypeSupported(clipboardType) &&
+          clipboard.hasDataMatchingFlavors(
+            ["application/x-moz-file"],
+            clipboardType
+          )
+      )
+    ) {
+      event.preventDefault();
+      event.stopPropagation();
+      lazy.console.log(
+        `Preventing path leak on "Paste Without Formatting" for ${dt.getData(
+          "text"
+        )}.`
+      );
+    }
+  }
+}

toolkit/actors/FilesFilterParent.sys.mjs

+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+export class FilesFilterParent extends JSWindowActorParent {
+  // just a stub for now
+}

toolkit/actors/moz.build

@@ -55,6 +55,8 @@ FINAL_TARGET_FILES.actors += [
     "DateTimePickerChild.sys.mjs",
     "DateTimePickerParent.sys.mjs",
     "ExtFindChild.sys.mjs",
+    "FilesFilterChild.sys.mjs",
+    "FilesFilterParent.sys.mjs",
     "FindBarChild.sys.mjs",
     "FindBarParent.sys.mjs",
     "FinderChild.sys.mjs",

toolkit/modules/ActorManagerParent.sys.mjs

@@ -244,6 +244,22 @@ let JSWINDOWACTORS = {
     allFrames: true,
   },
 
+  FilesFilter: {
+    parent: {
+      esModuleURI: "resource://gre/actors/FilesFilterParent.sys.mjs",
+    },
+
+    child: {
+      esModuleURI: "resource://gre/actors/FilesFilterChild.sys.mjs",
+      events: {
+        drop: {},
+        paste: { capture: true },
+      },
+    },
+
+    allFrames: true,
+  },
+
   FindBar: {
     parent: {
       esModuleURI: "resource://gre/actors/FindBarParent.sys.mjs",