Make OffscreenCanvas WebGL(2) context consider taintedness of image source

third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 213 matching lines @@
   bool has_url = (source_url.IsValid() && !source_url.IsAboutBlankURL());
 
   if (has_url) {
     if (source_url.ProtocolIsData() ||
         clean_ur_ls_.Contains(source_url.GetString()))
       return false;
     if (dirty_ur_ls_.Contains(source_url.GetString()))
       return true;
   }
 
-  DCHECK_EQ(!canvas(),
-            !!destination_security_origin);  // Must have one or the other
-  bool taint_origin = image_source->WouldTaintOrigin(
-      destination_security_origin ? destination_security_origin
-                                  : canvas()->GetSecurityOrigin());
-
+  bool taint_origin =
+      image_source->WouldTaintOrigin(destination_security_origin);

[Justin Novosad, 2017/04/12 14:53:40]

Just checking: I assume OCRC2D was already calling this correctly and with a
non-null destination_security_origin, and we already have tests for that?

[xlai (Olivia), 2017/04/12 19:37:28]

Yes, OCRC2D is already doing this correct. It calls WouldTaintOrigin in two
functions and each has its own security test:
drawImage:
LayoutTests/http/tests/security/offscreencanvas-read-blocked-no-crossorigin.html
createPattern:
LayoutTests/http/tests/security/cross-origin-OffscreenCanvas2D-createPattern.html

   if (has_url) {
     if (taint_origin)
       dirty_ur_ls_.insert(source_url.GetString());
     else
       clean_ur_ls_.insert(source_url.GetString());
   }
   return taint_origin;
 }
 
 DEFINE_TRACE(CanvasRenderingContext) {
   visitor->Trace(canvas_);
   visitor->Trace(offscreen_canvas_);
 }
 
 }  // namespace blink