CSP: 'frame-ancestors' should override 'x-frame-options'.

Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google 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.
@@ skipping 451 matching lines @@
     ASSERT(frame());
 
     m_applicationCacheHost->didReceiveResponseForMainResource(response);
 
     // The memory cache doesn't understand the application cache or its caching rules. So if a main resource is served
     // from the application cache, ensure we don't save the result for future use. All responses loaded
     // from appcache will have a non-zero appCacheID().
     if (response.appCacheID())
         memoryCache()->remove(m_mainResource.get());
 
-    DEFINE_STATIC_LOCAL(AtomicString, xFrameOptionHeader, ("x-frame-options", AtomicString::ConstructFromLiteral));
-    HTTPHeaderMap::const_iterator it = response.httpHeaderFields().find(xFrameOptionHeader);
-    if (it != response.httpHeaderFields().end()) {
-        String content = it->value;
-        if (frameLoader()->shouldInterruptLoadForXFrameOptions(content, response.url(), mainResourceIdentifier())) {
-            String message = "Refused to display '" + response.url().elidedString() + "' in a frame because it set 'X-Frame-Options' to '" + content + "'.";
-            RefPtrWillBeRawPtr<ConsoleMessage> consoleMessage = ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel, message);
-            consoleMessage->setRequestIdentifier(mainResourceIdentifier());
-            frame()->document()->addConsoleMessage(consoleMessage.release());
-
-            cancelLoadAfterXFrameOptionsOrCSPDenied(response);
-            return;
-        }
-    }
-
     m_contentSecurityPolicy = ContentSecurityPolicy::create();
     m_contentSecurityPolicy->setOverrideURLForSelf(response.url());
     m_contentSecurityPolicy->didReceiveHeaders(ContentSecurityPolicyResponseHeaders(response));
     if (!m_contentSecurityPolicy->allowAncestors(m_frame, response.url())) {
         cancelLoadAfterXFrameOptionsOrCSPDenied(response);
         return;
     }
 
+    DEFINE_STATIC_LOCAL(AtomicString, xFrameOptionHeader, ("x-frame-options", AtomicString::ConstructFromLiteral));
+
+    // 'frame-ancestors' obviates 'x-frame-options': https://w3c.github.io/webappsec/specs/content-security-policy/#frame-ancestors-and-frame-options
+    if (!m_contentSecurityPolicy->isFrameAncestorsEnforced()) {
+        HTTPHeaderMap::const_iterator it = response.httpHeaderFields().find(xFrameOptionHeader);
+        if (it != response.httpHeaderFields().end()) {
+            String content = it->value;
+            if (frameLoader()->shouldInterruptLoadForXFrameOptions(content, response.url(), mainResourceIdentifier())) {
+                String message = "Refused to display '" + response.url().elidedString() + "' in a frame because it set 'X-Frame-Options' to '" + content + "'.";
+                RefPtrWillBeRawPtr<ConsoleMessage> consoleMessage = ConsoleMessage::create(SecurityMessageSource, ErrorMessageLevel, message);
+                consoleMessage->setRequestIdentifier(mainResourceIdentifier());
+                frame()->document()->addConsoleMessage(consoleMessage.release());
+
+                cancelLoadAfterXFrameOptionsOrCSPDenied(response);
+                return;
+            }
+        }
+    }
+
     ASSERT(!mainResourceLoader() || !mainResourceLoader()->defersLoading());
 
     m_response = response;
 
     if (isArchiveMIMEType(m_response.mimeType()) && m_mainResource->dataBufferingPolicy() != BufferData)
         m_mainResource->setDataBufferingPolicy(BufferData);
 
     if (!shouldContinueForResponse()) {
         InspectorInstrumentation::continueWithPolicyIgnore(m_frame, this, m_mainResource->identifier(), m_response);
         cancelMainResourceLoad(ResourceError::cancelledError(m_request.url()));
@@ skipping 360 matching lines @@
 {
     m_writer = createWriterFor(ownerDocument, init, mimeType(), m_writer ? m_writer->encoding() : emptyAtom, true, ForceSynchronousParsing);
     if (!source.isNull())
         m_writer->appendReplacingData(source);
     endWriting(m_writer.get());
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 } // namespace blink