tor-browser

commit e1d22ea27f3632f31e15b603fa1b6a3029d30221
parent 4002601fa705d444acbe2c659c681f16678dada3
Author: Vincent Hilla <vhilla@mozilla.com>
Date:   Wed,  3 Dec 2025 19:06:46 +0000

Bug 2003255 - Force sync about:blank despite busy DocLoader. r=dom-core,smaug

Differential Revision: https://phabricator.services.mozilla.com/D274763

Diffstat:
M
docshell/test/browser/browser.toml
 | 
2
++
A
docshell/test/browser/browser_initialDocument_noLoadBlocking.js
 | 
71
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
M
dom/base/Document.h
 | 
2
++
M
uriloader/base/nsDocLoader.cpp
 | 
20
+++++++++++++++++---

4 files changed, 92 insertions(+), 3 deletions(-)
diff --git a/docshell/test/browser/browser.toml b/docshell/test/browser/browser.toml
@@ -316,6 +316,8 @@ skip-if = [
 ["browser_history_triggeringprincipal_viewsource.js"]
 https_first_disabled = true
 
+["browser_initialDocument_noLoadBlocking.js"]
+
 ["browser_initial_entry_without_interaction.js"]
 
 ["browser_isInitialDocument.js"]
diff --git a/docshell/test/browser/browser_initialDocument_noLoadBlocking.js b/docshell/test/browser/browser_initialDocument_noLoadBlocking.js
@@ -0,0 +1,71 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// See bug 2003255
+add_task(async function test_extension_cannot_block_initial_load() {
+  let extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      manifest_version: 2,
+      name: "insert script to about:blank",
+      version: "1.0",
+      content_scripts: [
+        {
+          matches: ["<all_urls>"],
+          js: ["content.js"],
+          run_at: "document_start",
+          all_frames: true,
+          match_about_blank: true,
+        },
+      ],
+    },
+
+    files: {
+      "content.js": function () {
+        if (window.location.href != "about:blank#unique-hash") {
+          return;
+        }
+
+        const script = document.createElement("script");
+        script.src =
+          "data:,(window.parent.postMessage(`script ${window.location.href}`))()";
+        (document.documentElement || document).appendChild(script);
+      },
+    },
+  });
+
+  await extension.startup();
+
+  const url = "https://example.com/";
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, url);
+
+  await ContentTask.spawn(tab.linkedBrowser, [url], async function (url) {
+    Assert.equal(content.location.href, url, "Correct content document");
+
+    const scriptEvaluated = new Promise(
+      res =>
+        (content.onmessage = ({ data }) => {
+          if (data == "script about:blank#unique-hash") {
+            res();
+          }
+        })
+    );
+
+    let loaded = false;
+    const iframe = content.document.createElement("iframe");
+    iframe.onload = () => (loaded = true);
+    // Let's set a unique hash in case there are other about:blank
+    iframe.src = "about:blank#unique-hash";
+    content.document.body.append(iframe);
+    Assert.ok(loaded, "Load occurred synchronously");
+
+    const extScript = iframe.contentDocument.querySelector("script");
+    Assert.ok(!!extScript, "Extension inserted script synchronously");
+
+    await scriptEvaluated;
+  });
+
+  BrowserTestUtils.removeTab(tab);
+  await extension.unload();
+});
diff --git a/dom/base/Document.h b/dom/base/Document.h
@@ -4197,6 +4197,8 @@ class Document : public nsINode,
 
   bool DOMNotificationsSuspended() const { return mSuspendDOMNotifications; }
 
+  bool IsExpectingEndLoad() { return mDidCallBeginLoad; }
+
  protected:
   RefPtr<DocumentL10n> mDocumentL10n;
 
diff --git a/uriloader/base/nsDocLoader.cpp b/uriloader/base/nsDocLoader.cpp
@@ -756,8 +756,19 @@ void nsDocLoader::DocLoaderIsEmpty(bool aFlushLayout,
        alive long enough to survive this function call. */
     nsCOMPtr<nsIDocumentLoader> kungFuDeathGrip(this);
 
+    nsCOMPtr<Document> doc = do_GetInterface(GetAsSupports(this));
+    // Force load if
+    // - we are currently in the synchronous load path of the docshell, i.e. we
+    // are completing the initial about:blank load
+    // - and Document::EndLoad was already called (we're likely called from
+    // there right now).
+    const bool forceInitialSyncLoad = doc &&
+                                      doc->InitialAboutBlankLoadCompleting() &&
+                                      !doc->IsExpectingEndLoad();
+    MOZ_ASSERT_IF(forceInitialSyncLoad, !mIsFlushingLayout);
+
     // Don't flush layout if we're still busy.
-    if (IsBusy()) {
+    if (IsBusy() && !forceInitialSyncLoad) {
       return;
     }
 
@@ -792,8 +803,11 @@ void nsDocLoader::DocLoaderIsEmpty(bool aFlushLayout,
     //
     // Note, mDocumentRequest can be null while mDocumentOpenedButNotLoaded is
     // false if the flushing above re-entered this method.
-    if (IsBusy() || (!mDocumentRequest && !mDocumentOpenedButNotLoaded &&
-                     !mIsLoadingJavascriptURI)) {
+    const bool hasActiveLoad = mDocumentRequest ||
+                               mDocumentOpenedButNotLoaded ||
+                               mIsLoadingJavascriptURI;
+    MOZ_ASSERT_IF(forceInitialSyncLoad, hasActiveLoad);
+    if ((IsBusy() && !forceInitialSyncLoad) || !hasActiveLoad) {
       return;
     }