Bug 31254 – [GTK] FontCache::getFontDataForCharacters() crashes when a page uses custom fonts

• Component: WebKitGTK
• Status: RESOLVED FIXED

[Jarda Gresula]

http://jacobian.org/writing/python-is-unix/ crashes GtkLauncher
with the following backtrace:

#0  0x00007f70b895e800 in ?? () from /usr/lib/libfontconfig.so.1
#1  0x00007f70b895e8a0 in ?? () from /usr/lib/libfontconfig.so.1
#2  0x00007f70b895c577 in FcFontSetSort () from /usr/lib/libfontconfig.so.1
#3  0x00007f70b895cb39 in FcFontSort () from /usr/lib/libfontconfig.so.1
#4  0x00007f70bd4a9440 in WebCore::FontCache::getFontDataForCharacters (...) at WebCore/platform/graphics/gtk/FontCacheGtk.cpp:43
#5  0x00007f70bd1a47ed in WebCore::Font::glyphDataForCharacter (...) at WebCore/platform/graphics/FontFastPath.cpp:151
#6  0x00007f70bd1be6e9 in WebCore::WidthIterator::advance (...) at WebCore/platform/graphics/WidthIterator.cpp:116
#7  0x00007f70bd1a3a23 in WebCore::Font::floatWidthForSimpleText (...) at WebCore/platform/graphics/FontFastPath.cpp:327
[..]

The reason is that WebCore::FontCache::getFontDataForCharacters() assumes that
prim->m_pattern is always non-NULL which is not the case for a custom font.

The following fix works for me:

--- a/WebCore/platform/graphics/gtk/FontCacheGtk.cpp
+++ b/WebCore/platform/graphics/gtk/FontCacheGtk.cpp
@@ -39,6 +39,10 @@ const SimpleFontData* FontCache::getFontDataForCharacters(const Font& font, cons
     FcResult fresult;
     FontPlatformData* prim = const_cast<FontPlatformData*>(&font.primaryFont()->platformData());

+    // prim->m_pattern can be null if it is a custom font
+    if (!prim->m_pattern)
+        return 0;
+
     if (!prim->m_fallbacks)
         prim->m_fallbacks = FcFontSort(NULL, prim->m_pattern, FcTrue, NULL, &fresult);

[Martin Robinson]

This check seems to exist in the code now. Thanks for reporting!