Bug 1503681 - rel=noopener implicit for target=_blank in anchor and area elements when no rel attribute is set, r=nika

In case anchor and area elements have target=_blank and no rel=opener/noopener,
this patch makes so that rel=noopener is implied. This feature is behind pref
'dom_targetBlankNoOpener_enabled'.

See: whatwg/html#4078

Author: bakulf

docshell/base/nsDocShell.cpp

@@ -13281,18 +13281,43 @@ nsDocShell::OnLinkClickSync(nsIContent* aContent,
     nsAutoString referrer;
     aContent->AsElement()->GetAttr(kNameSpaceID_None, nsGkAtoms::rel, referrer);
     nsWhitespaceTokenizerTemplate<nsContentUtils::IsHTMLWhitespace> tok(referrer);
+
+    bool targetBlank = aTargetSpec.LowerCaseEqualsLiteral("_blank");
+    bool explicitOpenerSet = false;
+
+    // The opener behaviour follows a hierarchy, such that if a higher priority
+    // behaviour is specified, it always takes priority. That priority is
+    // currently: norefrerer > noopener > opener > default
+
     while (tok.hasMoreTokens()) {
       const nsAString& token = tok.nextToken();
       if (token.LowerCaseEqualsLiteral("noreferrer")) {
         flags |= INTERNAL_LOAD_FLAGS_DONT_SEND_REFERRER |
                  INTERNAL_LOAD_FLAGS_NO_OPENER;
-        // We now have all the flags we could possibly have, so just stop.
+        // noreferrer cannot be overwritten by a 'rel=opener'.
+        explicitOpenerSet = true;
         break;
       }
+
       if (token.LowerCaseEqualsLiteral("noopener")) {
         flags |= INTERNAL_LOAD_FLAGS_NO_OPENER;
+        explicitOpenerSet = true;
+      }
+
+      if (targetBlank &&
+          StaticPrefs::dom_targetBlankNoOpener_enabled() &&
+          token.LowerCaseEqualsLiteral("opener") &&
+          !explicitOpenerSet) {
+        explicitOpenerSet = true;
       }
     }
+
+    if (targetBlank &&
+        StaticPrefs::dom_targetBlankNoOpener_enabled() &&
+        !explicitOpenerSet) {
+      flags |= INTERNAL_LOAD_FLAGS_NO_OPENER;
+    }
+
     if (aNoOpenerImplied) {
       flags |= INTERNAL_LOAD_FLAGS_NO_OPENER;
     }

dom/html/test/browser.ini

@@ -37,3 +37,7 @@ skip-if = os == 'mac' # bug 1494843
 [browser_refresh_wyciwyg_url.js]
 support-files =
   file_refresh_wyciwyg_url.html
+[browser_targetBlankNoOpener.js]
+support-files =
+  empty.html
+  image_yellow.png

dom/html/test/browser_targetBlankNoOpener.js

@@ -0,0 +1,83 @@
+const TEST_URL = "http://mochi.test:8888/browser/dom/html/test/empty.html";
+
+async function checkOpener(browser, elm, name, rel) {
+  let p = BrowserTestUtils.waitForNewTab(gBrowser, null, true, true);
+
+  await ContentTask.spawn(browser, {url: TEST_URL, name, rel, elm }, async obj => {
+    let element;
+
+    if (obj.elm == "anchor") {
+      element = content.document.createElement("a");
+      content.document.body.appendChild(element);
+      element.appendChild(content.document.createTextNode(obj.name));
+    } else {
+      let img = content.document.createElement('img');
+      img.src = "image_yellow.png";
+      content.document.body.appendChild(img);
+
+      element = content.document.createElement("area");
+      img.appendChild(element);
+
+      element.setAttribute("shape", "rect");
+      element.setAttribute("coords", "0,0,100,100");
+    }
+
+    element.setAttribute("target", "_blank");
+    element.setAttribute("href", obj.url);
+
+    if (obj.rel) {
+      element.setAttribute("rel", obj.rel);
+    }
+
+    element.click();
+  });
+
+  let newTab = await p;
+  let newBrowser = gBrowser.getBrowserForTab(newTab);
+
+  let hasOpener = await ContentTask.spawn(newTab.linkedBrowser, null, _ => !!content.window.opener);
+
+  BrowserTestUtils.removeTab(newTab);
+  return hasOpener;
+}
+
+async function runTests(browser, elm) {
+  info("Creating an " + elm + " with target=_blank rel=opener");
+  ok(!!(await checkOpener(browser, elm, "rel=opener", "opener")), "We want the opener with rel=opener");
+
+  info("Creating an " + elm + " with target=_blank rel=noopener");
+  ok(!(await checkOpener(browser, elm, "rel=noopener", "noopener")), "We don't want the opener with rel=noopener");
+
+  info("Creating an " + elm + " with target=_blank");
+  ok(!(await checkOpener(browser, elm, "no rel", null)), "We don't want the opener with no rel is passed");
+
+  info("Creating an " + elm + " with target=_blank rel='noopener opener'");
+  ok(!(await checkOpener(browser, elm, "rel=noopener+opener", "noopener opener")), "noopener wins with rel=noopener+opener");
+
+  info("Creating an " + elm + " with target=_blank rel='noreferrer opener'");
+  ok(!(await checkOpener(browser, elm, "noreferrer wins", "noreferrer opener")), "We don't want the opener with rel=noreferrer+opener");
+
+  info("Creating an " + elm + " with target=_blank rel='opener noreferrer'");
+  ok(!(await checkOpener(browser, elm, "noreferrer wins again", "noreferrer opener")), "We don't want the opener with rel=opener+noreferrer");
+}
+
+add_task(async _ => {
+  await SpecialPowers.flushPrefEnv();
+  await SpecialPowers.pushPrefEnv({"set": [
+    ["dom.block_multiple_popups", false],
+    ["dom.disable_open_during_load", true],
+    ["dom.targetBlankNoOpener.enabled", true],
+  ]});
+
+  let tab = BrowserTestUtils.addTab(gBrowser, TEST_URL);
+  gBrowser.selectedTab = tab;
+
+  let browser = gBrowser.getBrowserForTab(tab);
+  await BrowserTestUtils.browserLoaded(browser);
+
+  await runTests(browser, 'anchor');
+  await runTests(browser, 'area');
+
+  info("Removing the tab");
+  BrowserTestUtils.removeTab(tab);
+});

dom/html/test/empty.html

@@ -0,0 +1 @@
+<html><body></body></html>

dom/html/test/image_yellow.png

@@ -460,6 +460,20 @@ VARCACHE_PREF(
   bool, true
 )
 
+// For area and anchor elements with target=_blank and no rel set to
+// opener/noopener, this pref sets noopener by default.
+#ifdef EARLY_BETA_OR_EARLIER
+#define PREF_VALUE true
+#else
+#define PREF_VALUE false
+#endif
+VARCACHE_PREF(
+  "dom.targetBlankNoOpener.enabled",
+   dom_targetBlankNoOpener_enabled,
+  bool, PREF_VALUE
+)
+#undef PREF_VALUE
+
 //---------------------------------------------------------------------------
 // Clear-Site-Data prefs
 //---------------------------------------------------------------------------