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// Copyright 2015 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 "content/child/site_isolation_stats_gatherer.h"
#include <stddef.h>
#include <stdint.h>
#include "base/macros.h"
#include "base/metrics/histogram_macros.h"
#include "base/strings/string_piece.h"
#include "base/strings/string_util.h"
#include "content/public/common/resource_response_info.h"
#include "net/http/http_response_headers.h"
namespace content {
namespace {
// The gathering of UMA stats for site isolation is deactivated by default, and
// only activated in renderer processes.
static bool g_stats_gathering_enabled = false;
bool IsRenderableStatusCode(int status_code) {
// Chrome only uses the content of a response with one of these status codes
// for CSS/JavaScript. For images, Chrome just ignores status code.
const int renderable_status_code[] = {
200, 201, 202, 203, 206, 300, 301, 302, 303, 305, 306, 307};
for (size_t i = 0; i < arraysize(renderable_status_code); ++i) {
if (renderable_status_code[i] == status_code)
return true;
return false;
void IncrementHistogramCount(const std::string& name) {
// The default value of min, max, bucket_count are copied from histogram.h.
base::HistogramBase* histogram_pointer = base::Histogram::FactoryGet(
name, 1, 100000, 50, base::HistogramBase::kUmaTargetedHistogramFlag);
void IncrementHistogramEnum(const std::string& name,
uint32_t sample,
uint32_t boundary_value) {
// The default value of min, max, bucket_count are copied from histogram.h.
base::HistogramBase* histogram_pointer = base::LinearHistogram::FactoryGet(
name, 1, boundary_value, boundary_value + 1,
void HistogramCountBlockedResponse(
const std::string& bucket_prefix,
const std::unique_ptr<SiteIsolationResponseMetaData>& resp_data,
bool nosniff_block) {
std::string block_label(nosniff_block ? ".NoSniffBlocked" : ".Blocked");
IncrementHistogramCount(bucket_prefix + block_label);
// The content is blocked if it is sniffed as HTML/JSON/XML. When
// the blocked response is with an error status code, it is not
// disruptive for the following reasons : 1) the blocked content is
// not a binary object (such as an image) since it is sniffed as
// text; 2) then, this blocking only breaks the renderer behavior
// only if it is either JavaScript or CSS. However, the renderer
// doesn't use the contents of JS/CSS with unaffected status code
// (e.g, 404). 3) the renderer is expected not to use the cross-site
// document content for purposes other than JS/CSS (e.g, XHR).
bool renderable_status_code =
if (renderable_status_code) {
bucket_prefix + block_label + ".RenderableStatusCode2",
resp_data->resource_type, RESOURCE_TYPE_LAST_TYPE);
} else {
IncrementHistogramCount(bucket_prefix + block_label +
void HistogramCountNotBlockedResponse(const std::string& bucket_prefix,
bool sniffed_as_js) {
IncrementHistogramCount(bucket_prefix + ".NotBlocked");
if (sniffed_as_js)
IncrementHistogramCount(bucket_prefix + ".NotBlocked.MaybeJS");
} // namespace
SiteIsolationResponseMetaData::SiteIsolationResponseMetaData() {
void SiteIsolationStatsGatherer::SetEnabled(bool enabled) {
g_stats_gathering_enabled = enabled;
const url::Origin& frame_origin,
const GURL& response_url,
ResourceType resource_type,
int origin_pid,
const ResourceResponseInfo& info) {
if (!g_stats_gathering_enabled)
return nullptr;
// if |origin_pid| is non-zero, it means that this response is for a plugin
// spawned from this renderer process. We exclude responses for plugins for
// now, but eventually, we're going to make plugin processes directly talk to
// the browser process so that we don't apply cross-site document blocking to
// them.
if (origin_pid)
return nullptr;
UMA_HISTOGRAM_COUNTS("SiteIsolation.AllResponses", 1);
// See if this is for navigation. If it is, don't block it, under the
// assumption that we will put it in an appropriate process.
if (IsResourceTypeFrame(resource_type))
return nullptr;
if (!CrossSiteDocumentClassifier::IsBlockableScheme(response_url))
return nullptr;
// TODO(csharrison): Add a path for IsSameSite/IsValidCorsHeaderSet to take an
// Origin.
if (CrossSiteDocumentClassifier::IsSameSite(frame_origin, response_url))
return nullptr;
CrossSiteDocumentMimeType canonical_mime_type =
if (canonical_mime_type == CROSS_SITE_DOCUMENT_MIME_TYPE_OTHERS)
return nullptr;
// Every CORS request should have the Access-Control-Allow-Origin header even
// if it is preceded by a pre-flight request. Therefore, if this is a CORS
// request, it has this header. response.httpHeaderField() internally uses
// case-insensitive matching for the header name.
std::string access_control_origin;
// We can use a case-insensitive header name for EnumerateHeader().
info.headers->EnumerateHeader(NULL, "access-control-allow-origin",
if (CrossSiteDocumentClassifier::IsValidCorsHeaderSet(
frame_origin, response_url, access_control_origin)) {
return nullptr;
// Real XSD data collection starts from here.
std::string no_sniff;
info.headers->EnumerateHeader(NULL, "x-content-type-options", &no_sniff);
std::unique_ptr<SiteIsolationResponseMetaData> resp_data(
new SiteIsolationResponseMetaData);
resp_data->response_url = response_url;
resp_data->resource_type = resource_type;
resp_data->canonical_mime_type = canonical_mime_type;
resp_data->http_status_code = info.headers->response_code();
resp_data->no_sniff = base::LowerCaseEqualsASCII(no_sniff, "nosniff");
return resp_data;
bool SiteIsolationStatsGatherer::OnReceivedFirstChunk(
const std::unique_ptr<SiteIsolationResponseMetaData>& resp_data,
const char* raw_data,
int raw_length) {
if (!g_stats_gathering_enabled)
return false;
base::StringPiece data(raw_data, raw_length);
// Record the length of the first received chunk of data to see if it's enough
// for sniffing.
UMA_HISTOGRAM_COUNTS("SiteIsolation.XSD.DataLength", raw_length);
// Record the number of cross-site document responses with a specific mime
// type (text/html, text/xml, etc).
// Store the result of cross-site document blocking analysis.
bool would_block = false;
bool sniffed_as_js = SniffForJS(data);
// Record the number of responses whose content is sniffed for what its mime
// type claims it to be. For example, we apply a HTML sniffer for a document
// tagged with text/html here. Whenever this check becomes true, we'll block
// the response.
if (resp_data->canonical_mime_type != CROSS_SITE_DOCUMENT_MIME_TYPE_PLAIN) {
std::string bucket_prefix;
bool sniffed_as_target_document = false;
if (resp_data->canonical_mime_type == CROSS_SITE_DOCUMENT_MIME_TYPE_HTML) {
bucket_prefix = "SiteIsolation.XSD.HTML";
sniffed_as_target_document =
} else if (resp_data->canonical_mime_type ==
bucket_prefix = "SiteIsolation.XSD.XML";
sniffed_as_target_document =
} else if (resp_data->canonical_mime_type ==
bucket_prefix = "SiteIsolation.XSD.JSON";
sniffed_as_target_document =
} else {
NOTREACHED() << "Not a blockable mime type: "
<< resp_data->canonical_mime_type;
if (sniffed_as_target_document) {
would_block = true;
HistogramCountBlockedResponse(bucket_prefix, resp_data, false);
} else {
if (resp_data->no_sniff) {
would_block = true;
HistogramCountBlockedResponse(bucket_prefix, resp_data, true);
} else {
HistogramCountNotBlockedResponse(bucket_prefix, sniffed_as_js);
} else {
// This block is for plain text documents. We apply our HTML, XML,
// and JSON sniffer to a text document in the order, and block it
// if any of them succeeds in sniffing.
std::string bucket_prefix;
if (CrossSiteDocumentClassifier::SniffForHTML(data))
bucket_prefix = "SiteIsolation.XSD.Plain.HTML";
else if (CrossSiteDocumentClassifier::SniffForXML(data))
bucket_prefix = "SiteIsolation.XSD.Plain.XML";
else if (CrossSiteDocumentClassifier::SniffForJSON(data))
bucket_prefix = "SiteIsolation.XSD.Plain.JSON";
if (bucket_prefix.size() > 0) {
would_block = true;
HistogramCountBlockedResponse(bucket_prefix, resp_data, false);
} else if (resp_data->no_sniff) {
would_block = true;
HistogramCountBlockedResponse("SiteIsolation.XSD.Plain", resp_data, true);
} else {
return would_block;
bool SiteIsolationStatsGatherer::SniffForJS(base::StringPiece data) {
// The purpose of this function is to try to see if there's any possibility
// that this data can be JavaScript (superset of JS). Search for "var " for JS
// detection. This is a real hack and should only be used for stats gathering.
return data.find("var ") != base::StringPiece::npos;
} // namespace content