[tbb-commits] [tor-browser] 13/81: Bug 41116: Normalize system fonts.

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pierov pushed a commit to branch tor-browser-102.4.0esr-12.0-1
in repository tor-browser.

commit a01b29d93482e6a0c57edef419eccfffb2f316e0
Author: Pier Angelo Vendrame <pierov at torproject.org>
AuthorDate: Mon Sep 19 12:57:40 2022 +0200

    Bug 41116: Normalize system fonts.
    
    System fonts are an enormous fingerprinting vector.
    Even with font allow lists and with our custom configuration on Linux,
    which counter metrics measurements, getComputedStyle leaks several
    details.
    This patch counters both these kinds of attacks.
---
 widget/nsXPLookAndFeel.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/widget/nsXPLookAndFeel.cpp b/widget/nsXPLookAndFeel.cpp
index 3cc2c561dbc5..8791038a2a3f 100644
--- a/widget/nsXPLookAndFeel.cpp
+++ b/widget/nsXPLookAndFeel.cpp
@@ -1000,6 +1000,17 @@ widget::LookAndFeelFont nsXPLookAndFeel::StyleToLookAndFeelFont(
 
 bool nsXPLookAndFeel::GetFontValue(FontID aID, nsString& aName,
                                    gfxFontStyle& aStyle) {
+  if (nsContentUtils::ShouldResistFingerprinting()) {
+#ifdef XP_MACOSX
+    aName = u"-apple-system"_ns;
+#else
+    aName = u"sans-serif"_ns;
+#endif
+    aStyle = gfxFontStyle();
+    aStyle.size = 12;
+    return true;
+  }
+
   if (const LookAndFeelFont* cached = sFontCache.Get(aID)) {
     return LookAndFeelFontToStyle(*cached, aName, aStyle);
   }

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