[tbb-bugs] #16739 [Tor Browser]: Whitelist fonts by filename rather than font name

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#16739: Whitelist fonts by filename rather than font name
---------------------------------+--------------------------------------
     Reporter:  arthuredelstein  |      Owner:  tbb-team
         Type:  enhancement      |     Status:  new
     Priority:  normal           |  Milestone:
    Component:  Tor Browser      |    Version:
   Resolution:                   |   Keywords:  tbb-fingerprinting-fonts
Actual Points:                   |  Parent ID:
       Points:                   |
---------------------------------+--------------------------------------

Comment (by dcf):

 So I tried a simple and dumb thing to disable system fonts with
 Fontconfig, and it mostly works! All I did was comment out `FcSetSystem`
 leaving only `FcSetApplication`. I tested this patch on top of
 [https://gitweb.torproject.org/builders/tor-browser-
 bundle.git/log/?id=tbb-5.0a4-build2 tbb-5.0a4-build2]; i.e., with the Noto
 fonts installed but without the font whitelisting patch of #13313.
 {{{
 #!diff
 --- a/gfx/thebes/gfxFontconfigUtils.cpp
 +++ b/gfx/thebes/gfxFontconfigUtils.cpp
 @@ -589,9 +589,9 @@ gfxFontconfigUtils::UpdateFontListInternal(bool
 aForce)

      // These FcFontSets are owned by fontconfig
      FcFontSet *fontSets[] = {
 -        FcConfigGetFonts(currentConfig, FcSetSystem)
 +        // FcConfigGetFonts(currentConfig, FcSetSystem),
  #ifdef MOZ_BUNDLED_FONTS
 -        , FcConfigGetFonts(currentConfig, FcSetApplication)
 +        FcConfigGetFonts(currentConfig, FcSetApplication),
  #endif
      };

 @@ -809,9 +809,9 @@ gfxFontconfigUtils::AddFullnameEntries()
  {
      // These FcFontSets are owned by fontconfig
      FcFontSet *fontSets[] = {
 -        FcConfigGetFonts(nullptr, FcSetSystem)
 +        // FcConfigGetFonts(nullptr, FcSetSystem),
  #ifdef MOZ_BUNDLED_FONTS
 -        , FcConfigGetFonts(nullptr, FcSetApplication)
 +        FcConfigGetFonts(nullptr, FcSetApplication),
  #endif
      };

 @@ -979,9 +979,9 @@ gfxFontconfigUtils::GetLangSupportEntry(const FcChar8
 *aLang, bool aWithFonts)

      // These FcFontSets are owned by fontconfig
      FcFontSet *fontSets[] = {
 -        FcConfigGetFonts(nullptr, FcSetSystem)
 +        // FcConfigGetFonts(nullptr, FcSetSystem),
  #ifdef MOZ_BUNDLED_FONTS
 -        , FcConfigGetFonts(nullptr, FcSetApplication)
 +        FcConfigGetFonts(nullptr, FcSetApplication),
  #endif
      };

 }}}
 It seems like the only negative side effect of the patch is an extension
 of the monospace font thing in comment:6:ticket:16672. Not only is it
 monospace in the tab titles and URL bar, but also Latin text in web pages
 is rendered using the monospace Cousine font. This might just be because
 the branch I built did not have the font prefs that came along with the
 whitelisting patch.

 (BTW we [[comment:1:ticket:13313|already know]] that you can whitelist a
 directory in Fontconfig using fonts.conf; this is another way.)

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16739#comment:1>
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