Enable SRI only for same origin and CORS content.

Source/core/dom/ScriptLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 333 matching lines @@
         if (resource && !resource->mimeTypeAllowedByNosniff()) {
             contextDocument->addConsoleMessage(ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel, "Refused to execute script from '" + resource->url().elidedString() + "' because its MIME type ('" + resource->mimeType() + "') is not executable, and strict MIME type checking is enabled."));
             return;
         }
 
         if (resource && resource->mimeType().lower().startsWith("image/")) {
             contextDocument->addConsoleMessage(ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel, "Refused to execute script from '" + resource->url().elidedString() + "' because its MIME type ('" + resource->mimeType() + "') is not executable."));
             UseCounter::count(frame, UseCounter::BlockedSniffingImageToScript);
             return;
         }
-
-        if (!SubresourceIntegrity::CheckSubresourceIntegrity(*m_element, sourceCode.source(), sourceCode.resource()->url(), sourceCode.resource()->mimeType()))
-            return;
     }
 
     // FIXME: Can this be moved earlier in the function?
     // Why are we ever attempting to execute scripts without a frame?
     if (!frame)
         return;
 
     const bool isImportedScript = contextDocument != elementDocument;
     // http://www.whatwg.org/specs/web-apps/current-work/#execute-the-script-block step 2.3
     // with additional support for HTML imports.
     IgnoreDestructiveWriteCountIncrementer ignoreDestructiveWriteCountIncrementer(m_isExternalScript || isImportedScript ? contextDocument.get() : 0);
 
     if (isHTMLScriptLoader(m_element))
         contextDocument->pushCurrentScript(toHTMLScriptElement(m_element));
 
     AccessControlStatus corsCheck = NotSharableCrossOrigin;
     if (!m_isExternalScript || (sourceCode.resource() && sourceCode.resource()->passesAccessControlCheck(&m_element->document(), m_element->document().securityOrigin())))
         corsCheck = SharableCrossOrigin;
 
+    if (m_isExternalScript) {
+        bool canRequest = m_element->document().securityOrigin()->canRequest(sourceCode.resource()->resourceRequest().url());
+        if (!canRequest && corsCheck == NotSharableCrossOrigin && m_element->fastHasAttribute(HTMLNames::integrityAttr)) {
+            contextDocument->addConsoleMessage(ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel, "Cannot enforce integrity on non-CORS enabled resource."));

[Mike West, 2015/02/26 08:44:52]

So we continue loading the resource if the CORS check fails? This isn't what we
do for other CORS-related checks, like `<script crossorigin>`... was this an
intentional decision? I'm willing to defer to the folks actually editing the
spec, but I'd like to know it was a conscious decision.

[jww, 2015/03/06 02:16:42]

You're right, I misread the algorithm (as you point out in a more detailed
comment later). I'm changing this to kill the resource.

+        } else if ((canRequest || corsCheck == SharableCrossOrigin) && !SubresourceIntegrity::CheckSubresourceIntegrity(*m_element, sourceCode.source(), sourceCode.resource()->url(), sourceCode.resource()->mimeType())) {
+            return;
+        }
+    }
+
     // Create a script from the script element node, using the script
     // block's source and the script block's type.
     // Note: This is where the script is compiled and actually executed.
     frame->script().executeScriptInMainWorld(sourceCode, corsCheck, compilationFinishTime);
 
     if (isHTMLScriptLoader(m_element)) {
         ASSERT(contextDocument->currentScript() == m_element);
         contextDocument->popCurrentScript();
     }
 }
@@ skipping 88 matching lines @@
     if (isHTMLScriptLoader(element))
         return toHTMLScriptElement(element)->loader();
 
     if (isSVGScriptLoader(element))
         return toSVGScriptElement(element)->loader();
 
     return 0;
 }
 
 } // namespace blink