[tbb-commits] [tor-browser/tor-browser-52.3.0esr-7.5-2] bug 23104 - Add a default line height compensation

Fri Sep 22 07:00:22 UTC 2017

commit 323d2525fcd2de963a2e291eab91d5ca9ea7ac9b
Author: igt0 <igt0-tor at gmail.com>
Date:   Sat Sep 16 16:50:17 2017 -0300

    bug 23104 - Add a default line height compensation
    
    Many fonts have issues with their vertical metrics. they
    are used to influence the height of ascenders and depth
    of descenders. Gecko uses it to calculate the line height
    (font height + ascender + descender), however because of
    that idiosyncratic behavior across multiple operating
    systems, it can be used to identify the user's OS.
    
    The solution proposed in the patch uses a default factor
    to be multiplied with the font size, simulating the concept
    of ascender and descender. This way all operating
    systems will have the same line height.
---
 layout/generic/ReflowInput.cpp   |  6 +++++
 tbb-tests/mochitest.ini          |  1 +
 tbb-tests/test_tor_bug23104.html | 52 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)

diff --git a/layout/generic/ReflowInput.cpp b/layout/generic/ReflowInput.cpp
index 42f4a24b5314..e219ae032cc6 100644
--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -30,6 +30,7 @@
 #include "CounterStyleManager.h"
 #include <algorithm>
 #include "mozilla/dom/HTMLInputElement.h"
+#include "nsContentUtils.h"
 
 #ifdef DEBUG
 #undef NOISY_VERTICAL_ALIGN
@@ -2768,6 +2769,11 @@ GetNormalLineHeight(nsFontMetrics* aFontMetrics)
   nscoord externalLeading = aFontMetrics->ExternalLeading();
   nscoord internalLeading = aFontMetrics->InternalLeading();
   nscoord emHeight = aFontMetrics->EmHeight();
+
+  if (nsContentUtils::ShouldResistFingerprinting()) {
+    return NSToCoordRound(emHeight * NORMAL_LINE_HEIGHT_FACTOR);
+  }
+
   switch (GetNormalLineHeightCalcControl()) {
   case eIncludeExternalLeading:
     normalLineHeight = emHeight+ internalLeading + externalLeading;
diff --git a/tbb-tests/mochitest.ini b/tbb-tests/mochitest.ini
index 3d2e7c9db803..fca972a51211 100644
--- a/tbb-tests/mochitest.ini
+++ b/tbb-tests/mochitest.ini
@@ -10,3 +10,4 @@ support-files =
 [test_tor_bug2875.html]
 [test_tor_bug4755.html]
 [test_tor_bug5856.html]
+[test_tor_bug23104.html]
diff --git a/tbb-tests/test_tor_bug23104.html b/tbb-tests/test_tor_bug23104.html
new file mode 100644
index 000000000000..c2e4a51f1f75
--- /dev/null
+++ b/tbb-tests/test_tor_bug23104.html
@@ -0,0 +1,52 @@
+<!DOCTYPE HTML>
+<meta charset="UTF-8">
+<html>
+<head>
+  <title>Test for Tor Bug #23104: CSS line-height reveals the platform Tor browser is running</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="application/javascript" src="/tests/SimpleTest/SpawnTask.js"></script>
+  <style type="text/css">
+    span {
+      background-color: #000;
+      color: #fff;
+      font-size: 16.5px;
+    }
+  </style>
+</head>
+<body>
+<span id="test1">Test1</span>
+<span id="test2">كلمة</span>
+<span id="test3">ação</span>
+<script type="application/javascript;version=1.7">
+
+let setPref = function* (key, value) {
+  return new Promise(function(resolve, reject) {
+    SpecialPowers.pushPrefEnv({"set": [[key, value]]}, resolve);
+  });
+}
+
+function getStyle(el, styleprop) {
+  el = document.getElementById(el);
+  return document.defaultView.getComputedStyle(el, null).getPropertyValue(styleprop);
+}
+
+function validateElement(elementName, isFingerprintResistent) {
+  var fontSize = getStyle(elementName, 'font-size');
+  var lineHeight = getStyle(elementName, 'line-height');
+  var validationCb = isFingerprintResistent ? is : isnot;
+  validationCb(parseFloat(lineHeight), Math.ceil(parseFloat(fontSize)) * 1.2, 'Line Height validation');
+}
+
+add_task(function* () {
+  for (let resistFingerprintingValue of [true, false]) {
+  yield setPref("privacy.resistFingerprinting", resistFingerprintingValue);
+    for (let elementId of ['test1', 'test2', 'test3']) {
+      validateElement(elementId, resistFingerprintingValue);
+    }
+  }
+});
+
+</script>
+</body>
+</html>
+



