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// Copyright 2021 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "third_party/blink/renderer/core/loader/subresource_redirect_util.h"
#include "base/metrics/histogram_functions.h"
#include "third_party/blink/public/common/features.h"
#include "third_party/blink/renderer/core/frame/csp/content_security_policy.h"
#include "third_party/blink/renderer/core/html/cross_origin_attribute.h"
#include "third_party/blink/renderer/platform/network/network_state_notifier.h"
#include "third_party/blink/renderer/platform/weborigin/security_origin.h"
namespace blink {
namespace {
// Records the ineligibility metrics.
void RecordSubresourceRedirectIneligibility(
BlinkSubresourceRedirectIneligibility reason) {
base::UmaHistogramEnumeration("SubresourceRedirect.Blink.Ineligibility",
reason);
}
// Returns whether the URL scheme is http or https.
bool IsSchemeHttpOrHttps(const KURL& url) {
return url.Protocol() == url::kHttpsScheme ||
url.Protocol() == url::kHttpScheme;
}
} // namespace
bool ShouldEnableSubresourceRedirect(HTMLImageElement* image_element,
const KURL& url) {
if (!image_element)
return false;
// Allow redirection only when DataSaver is enabled and subresource redirect
// feature is enabled which allows redirecting to better optimized versions.
if (!base::FeatureList::IsEnabled(blink::features::kSubresourceRedirect) ||
!GetNetworkStateNotifier().SaveDataEnabled()) {
return false;
}
// Allow redirection only for http(s) subresources on http(s) documents.
if (!IsSchemeHttpOrHttps(url) ||
!IsSchemeHttpOrHttps(image_element->GetDocument().Url())) {
return false;
}
// Enable subresource redirect only for <img> elements created by parser.
// Images created from javascript, fetched via XHR/Fetch API should not be
// subresource redirected due to the additional CORB/CORS handling needed for
// them.
if (!image_element->ElementCreatedByParser()) {
RecordSubresourceRedirectIneligibility(
SecurityOrigin::AreSameOrigin(url, image_element->GetDocument().Url())
? BlinkSubresourceRedirectIneligibility::
kJavascriptCreatedSameOrigin
: BlinkSubresourceRedirectIneligibility::
kJavascriptCreatedCrossOrigin);
return false;
}
// Create a cross origin URL by appending a string to the original host. This
// is used to find whether CSP is restricting image fetches from other
// origins.
KURL cross_origin_url = url;
cross_origin_url.SetHost(url.Host() + "crossorigin.com");
auto* content_security_policy =
image_element->GetExecutionContext()->GetContentSecurityPolicy();
if (content_security_policy &&
!content_security_policy->AllowImageFromSource(
cross_origin_url, cross_origin_url, RedirectStatus::kNoRedirect,
ReportingDisposition::kSuppressReporting)) {
// Check if an object is allowed by CSP as a proxy to determine whether the
// image resource was disallowed by default-src or img-src directives. When
// an object is allowed it means default-src did not disallow the image.
RecordSubresourceRedirectIneligibility(
content_security_policy->AllowRequest(
mojom::blink::RequestContextType::OBJECT,
network::mojom::RequestDestination::kObject, cross_origin_url,
String() /* nonce */, IntegrityMetadataSet(),
ParserDisposition::kParserInserted, cross_origin_url,
RedirectStatus::kNoRedirect,
ReportingDisposition::kSuppressReporting,
ContentSecurityPolicy::CheckHeaderType::kCheckEnforce)
? BlinkSubresourceRedirectIneligibility::
kContentSecurityPolicyImgSrcRestricted
: BlinkSubresourceRedirectIneligibility::
kContentSecurityPolicyDefaultSrcRestricted);
return false;
}
// Allow subresource redirect only when cross-origin attribute is not set,
// which indicates CORS validation is not triggered for the image.
if (GetCrossOriginAttributeValue(image_element->FastGetAttribute(
html_names::kCrossoriginAttr)) != kCrossOriginAttributeNotSet) {
RecordSubresourceRedirectIneligibility(
BlinkSubresourceRedirectIneligibility::kCrossOriginAttributeSet);
return false;
}
return true;
}
} // namespace blink
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