UMA data collector for cross-site documents(XSD)

content/child/site_isolation_policy.cc

Index: content/child/site_isolation_policy.cc
diff --git a/content/child/site_isolation_policy.cc b/content/child/site_isolation_policy.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7832c0187d353d168a63cb959c37db3d4be4e6f0
--- /dev/null
+++ b/content/child/site_isolation_policy.cc
@@ -0,0 +1,561 @@
+// Copyright (c) 2013 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_policy.h"
+
+#include "base/basictypes.h"
+#include "base/command_line.h"
+#include "base/logging.h"
+#include "base/metrics/histogram.h"
+#include "base/strings/string_util.h"
+#include "content/public/common/content_switches.h"
+#include "net/base/registry_controlled_domains/registry_controlled_domain.h"
+#include "net/http/http_response_headers.h"
+#include "third_party/WebKit/public/platform/WebHTTPHeaderVisitor.h"
+#include "third_party/WebKit/public/platform/WebString.h"
+#include "third_party/WebKit/public/platform/WebURL.h"
+#include "third_party/WebKit/public/platform/WebURLRequest.h"
+#include "third_party/WebKit/public/platform/WebURLResponse.h"
+#include "third_party/WebKit/public/web/WebDocument.h"
+#include "third_party/WebKit/public/web/WebFrame.h"
+#include "third_party/WebKit/public/web/WebFrameClient.h"
+#include "third_party/WebKit/public/web/WebSecurityOrigin.h"
+
+using WebKit::WebDocument;
+using WebKit::WebString;
+using WebKit::WebURL;
+using WebKit::WebURLResponse;
+using WebKit::WebURLRequest;
+
+namespace content {
+
+namespace {
+
+// MIME types
+const char kTextHtml[] = "text/html";
+const char kTextXml[] = "text/xml";
+const char xAppRssXml[] = "application/rss+xml";
+const char kAppXml[] = "application/xml";
+const char kAppJson[] = "application/json";
+const char kTextJson[] = "text/json";
+const char kTextXjson[] = "text/x-json";
+const char kTextPlain[] = "text/plain";
+
+}  // anonymous namespace

[awong, 2013/08/26 20:31:41]

nit:

}  // namespace

+
+SiteIsolationPolicy::ResponseMetaData::ResponseMetaData() {}
+
+void SiteIsolationPolicy::OnReceivedResponse(
+    int request_id,
+    GURL& frame_origin,

[awong, 2013/08/26 20:31:41]

non-const refs are not allowed in function signatures by style guide. Please
remove all uses of non-const references.

+    GURL& response_url,
+    ResourceType::Type resource_type,
+    const webkit_glue::ResourceResponseInfo& info) {
+  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 (ResourceType::IsFrame(resource_type))
+    return;
+
+  if (!IsBlockableScheme(response_url))
+    return;
+
+  if (IsSameSite(frame_origin, response_url))
+    return;
+
+  SiteIsolationPolicy::ResponseMetaData::CanonicalMimeType canonical_mime_type =
+      GetCanonicalMimeType(info.mime_type);
+
+  if (canonical_mime_type == SiteIsolationPolicy::ResponseMetaData::Others)
+    return;
+
+  // 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", &access_control_origin);
+  if (IsValidCorsHeaderSet(frame_origin, response_url, access_control_origin))
+    return;
+
+  // Real XSD data collection starts from here.
+  std::string no_sniff;
+  info.headers->EnumerateHeader(NULL, "x-content-type-options", &no_sniff);
+
+  ResponseMetaData resp_data;
+  resp_data.frame_origin = frame_origin.spec();
+  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 = LowerCaseEqualsASCII(no_sniff, "nosniff");
+
+  RequestIdToMetaDataMap* metadata_map = GetRequestIdToMetaDataMap();
+  (*metadata_map)[request_id] = resp_data;
+}
+
+// These macros are defined here so that we prevent code size bloat-up due to
+// the UMA_HISTOGRAM_* macros. Similar logic is used for recording UMA stats for
+// different MIME types, but we cannot create a helper function for this since
+// UMA_HISTOGRAM_* macros do not accept variables as their bucket names. As a
+// solution, macros are used instead to capture the repeated pattern for
+// recording UMA stats.  TODO(dsjang): this is only needed for collecting UMA
+// stat. Will be deleted when this class is used for actual blocking.
+
+#define SITE_ISOLATION_POLICY_COUNT_BLOCK(BUCKET_PREFIX) \
+    UMA_HISTOGRAM_COUNTS( BUCKET_PREFIX ".Blocked", 1); \
+    result = true;                                      \
+    if (renderable_status_code) { \
+      UMA_HISTOGRAM_ENUMERATION( \
+          BUCKET_PREFIX ".Blocked.RenderableStatusCode", \
+        resp_data.resource_type, \
+        WebURLRequest::TargetIsUnspecified + 1); \
+    } else { \
+      UMA_HISTOGRAM_COUNTS(BUCKET_PREFIX ".Blocked.NonRenderableStatusCode",1);\
+    }
+
+#define SITE_ISOLATION_POLICY_COUNT_NO_SNIFF_BLOCK(BUCKET_PREFIX) \
+    UMA_HISTOGRAM_COUNTS( BUCKET_PREFIX ".NoSniffBlocked", 1); \
+    result = true;  \
+    if (renderable_status_code) { \
+      UMA_HISTOGRAM_ENUMERATION( \
+          BUCKET_PREFIX ".NoSniffBlocked.RenderableStatusCode", \
+        resp_data.resource_type, \
+        WebURLRequest::TargetIsUnspecified + 1); \
+    } else { \
+      UMA_HISTOGRAM_ENUMERATION( \
+          BUCKET_PREFIX ".NoSniffBlocked.NonRenderableStatusCode", \
+        resp_data.resource_type, \
+        WebURLRequest::TargetIsUnspecified + 1); \
+    }
+
+#define SITE_ISOLATION_POLICY_COUNT_NOTBLOCK(BUCKET_PREFIX) \
+    UMA_HISTOGRAM_COUNTS(BUCKET_PREFIX ".NotBlocked", 1); \
+    if (is_sniffed_for_js) \
+      UMA_HISTOGRAM_COUNTS(BUCKET_PREFIX ".NotBlocked.MaybeJS", 1); \
+
+#define SITE_ISOLATION_POLICY_SNIFF_AND_COUNT(SNIFF_EXPR,BUCKET_PREFIX) \
+  if (SNIFF_EXPR) { \
+    SITE_ISOLATION_POLICY_COUNT_BLOCK(BUCKET_PREFIX) \
+  } else { \
+    if (resp_data.no_sniff) { \
+      SITE_ISOLATION_POLICY_COUNT_NO_SNIFF_BLOCK(BUCKET_PREFIX) \
+    } else { \
+      SITE_ISOLATION_POLICY_COUNT_NOTBLOCK(BUCKET_PREFIX) \
+    } \
+  }
+
+bool SiteIsolationPolicy::ShouldBlockResponse(
+    int request_id,
+    const char* data,
+    int length,
+    std::string* alternative_data) {
+  RequestIdToMetaDataMap* metadata_map = GetRequestIdToMetaDataMap();
+  RequestIdToResultMap* result_map = GetRequestIdToResultMap();
+
+  // If there's an entry for |request_id| in blocked_map, this request's first
+  // data packet has already been examined. We can return the result here.
+  if (result_map->count(request_id) != 0) {
+    if ((*result_map)[request_id]) {
+      // Here, the blocking result has been set for the previous run of
+      // ShouldBlockResponse(), so we set alternative data to an empty string so
+      // that ResourceDispatcher doesn't call its peer's onReceivedData() with
+      // the alternative data.
+      alternative_data->erase();
+      return true;
+    }
+    return false;
+  }
+
+  // If result_map doesn't have an entry for |request_id|, we're receiving the
+  // first data packet for request_id. If request_id is not registered, this
+  // request is identified as a non-target of our policy. So we return true.
+  if (metadata_map->count(request_id) == 0) {
+    // We set request_id to true so that we always return true for this request.
+    (*result_map)[request_id] = false;
+    return false;
+  }
+
+  // We now look at the first data packet received for request_id.
+  ResponseMetaData resp_data = (*metadata_map)[request_id];
+  metadata_map->erase(request_id);
+
+  // Record the length of the first received network packet to see if it's
+  // enough for sniffing.
+  UMA_HISTOGRAM_COUNTS("SiteIsolation.XSD.DataLength", length);
+
+  // Record the number of cross-site document responses with a specific mime
+  // type (text/html, text/xml, etc).
+  UMA_HISTOGRAM_ENUMERATION(
+      "SiteIsolation.XSD.MimeType",
+      resp_data.canonical_mime_type,
+      SiteIsolationPolicy::ResponseMetaData::MaxCanonicalMimeType);
+
+  // Store the result of cross-site document blocking analysis. True means we
+  // can return this document to the renderer, false means that we have to block
+  // the response data.
+  bool result = false;
+
+  // The content is blocked if it is sniffed for HTML/JSON/XML. When the blocked
+  // response is with an error status code, it is not disruptive by the
+  // following reasons : 1) the blocked content is not a binary object (such as
+  // an image) since it is sniffed for 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 = IsRenderableStatusCodeForDocument(
+      resp_data.http_status_code);
+
+  // This is only used for false-negative analysis for non-blocked resources.
+  bool is_sniffed_for_js = SniffForJS(data, length);
+
+  // 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.
+  switch (resp_data.canonical_mime_type) {
+    case SiteIsolationPolicy::ResponseMetaData::HTML:
+      SITE_ISOLATION_POLICY_SNIFF_AND_COUNT(SniffForHTML(data, length),
+                                            "SiteIsolation.XSD.HTML");
+      break;
+    case SiteIsolationPolicy::ResponseMetaData::XML:
+      SITE_ISOLATION_POLICY_SNIFF_AND_COUNT(SniffForXML(data, length),
+                                            "SiteIsolation.XSD.XML");
+      break;
+    case SiteIsolationPolicy::ResponseMetaData::JSON:
+      SITE_ISOLATION_POLICY_SNIFF_AND_COUNT(SniffForJSON(data, length),
+                                            "SiteIsolation.XSD.JSON");
+      break;
+    case SiteIsolationPolicy::ResponseMetaData::Plain:
+      if (SniffForHTML(data, length)) {
+        SITE_ISOLATION_POLICY_COUNT_BLOCK(
+            "SiteIsolation.XSD.Plain.HTML");
+      } else if (SniffForXML(data, length)) {
+        SITE_ISOLATION_POLICY_COUNT_BLOCK(
+            "SiteIsolation.XSD.Plain.XML");
+      } else if (SniffForJSON(data, length)) {
+        SITE_ISOLATION_POLICY_COUNT_BLOCK(
+            "SiteIsolation.XSD.Plain.JSON");
+      } else if (is_sniffed_for_js) {
+        if (resp_data.no_sniff) {
+          SITE_ISOLATION_POLICY_COUNT_NO_SNIFF_BLOCK(
+              "SiteIsolation.XSD.Plain");
+        } else {
+          SITE_ISOLATION_POLICY_COUNT_NOTBLOCK(
+              "SiteIsolation.XSD.Plain");
+        }
+      }
+      break;
+    default :
+      NOTREACHED() <<
+          "Not a blockable mime type. This mime type shouldn't reach here.";

[awong, 2013/08/26 20:31:41]

Also output the mime_type.
NOTREACHED() << "Not a blockable mime type: " << resp_data.canonical_mime_type;

You don't need the "shouldn't reach here" because the assert itself already says
thsi.

+      break;
+  }
+
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();

[awong, 2013/08/26 20:31:41]

Might as well keep this a pointer so it doesn't look like a local.

+  if (!command_line.HasSwitch(switches::kBlockCrossSiteDocuments))
+    result = false;
+  (*result_map)[request_id] = result;
+
+  if (result) {
+    alternative_data->erase();
+    alternative_data->insert(0, " ");
+    LOG(ERROR) << resp_data.response_url
+               << " is blocked as an illegal cross-site document from "
+               << resp_data.frame_origin;
+
+  }
+  return result;
+}
+
+#undef SITE_ISOLATION_POLICY_COUNT_NOTBLOCK

[awong, 2013/08/26 20:31:41]

How bad does this look if you expand out the macros?

Using macros often has long term consequences.  Aside from being hard to read,
it breaks code analysis tools, refactoring tools, and often makes debugging/
crash parts harder because it messes with the line numbers.

+#undef SITE_ISOLATION_POLICY_SNIFF_AND_COUNT
+#undef SITE_ISOLATION_POLICY_COUNT_BLOCK
+
+void SiteIsolationPolicy::OnRequestComplete(int request_id) {
+  RequestIdToMetaDataMap* metadata_map = GetRequestIdToMetaDataMap();
+  RequestIdToResultMap* result_map = GetRequestIdToResultMap();
+  metadata_map->erase(request_id);
+  result_map->erase(request_id);
+}
+
+SiteIsolationPolicy::ResponseMetaData::CanonicalMimeType
+SiteIsolationPolicy::GetCanonicalMimeType(const std::string& mime_type) {
+  if (LowerCaseEqualsASCII(mime_type, kTextHtml)) {
+    return SiteIsolationPolicy::ResponseMetaData::HTML;
+  }
+
+  if (LowerCaseEqualsASCII(mime_type, kTextPlain)) {
+    return SiteIsolationPolicy::ResponseMetaData::Plain;
+  }
+
+  if (LowerCaseEqualsASCII(mime_type, kAppJson) ||
+      LowerCaseEqualsASCII(mime_type, kTextJson) ||
+      LowerCaseEqualsASCII(mime_type, kTextXjson)) {
+    return SiteIsolationPolicy::ResponseMetaData::JSON;
+  }
+
+  if (LowerCaseEqualsASCII(mime_type, kTextXml) ||
+      LowerCaseEqualsASCII(mime_type, xAppRssXml) ||
+      LowerCaseEqualsASCII(mime_type, kAppXml)) {
+    return SiteIsolationPolicy::ResponseMetaData::XML;
+  }
+
+ return SiteIsolationPolicy::ResponseMetaData::Others;
+
+}
+
+bool SiteIsolationPolicy::IsBlockableScheme(const GURL& url) {
+  // We exclude ftp:// from here. FTP doesn't provide a Content-Type
+  // header which our policy depends on, so we cannot protect any
+  // document from FTP servers.
+  return url.SchemeIs("http") || url.SchemeIs("https");
+}
+
+bool SiteIsolationPolicy::IsSameSite(const GURL& frame_origin,
+                                     const GURL& response_url) {
+
+  if (!frame_origin.is_valid() || !response_url.is_valid())
+    return false;
+
+  if (frame_origin.scheme() != response_url.scheme())
+    return false;
+
+  // SameDomainOrHost() extracts the effective domains (public suffix plus one)
+  // from the two URLs and compare them.
+  // TODO(dsjang): use INCLUDE_PRIVATE_REGISTRIES when http://crbug.com/7988 is
+  // fixed.
+  return net::registry_controlled_domains::SameDomainOrHost(
+      frame_origin,
+      response_url,
+      net::registry_controlled_domains::EXCLUDE_PRIVATE_REGISTRIES);
+}
+
+bool SiteIsolationPolicy::IsFrameNavigating(WebKit::WebFrame* frame) {
+  // When a navigation starts, frame->provisionalDataSource() is set
+  // to a not-null value which stands for the request made for the
+  // navigation. As soon as the network request is committed to the
+  // frame, frame->provisionalDataSource() is converted to null, and
+  // the committed data source is moved to frame->dataSource(). This
+  // is the most reliable way to detect whether the frame is in
+  // navigation or not.
+  return frame->provisionalDataSource() != NULL;
+}
+
+// We don't use Webkit's existing CORS policy implementation since
+// their policy works in terms of origins, not sites. For example,
+// when frame is sub.a.com and it is not allowed to access a document
+// with sub1.a.com. But under Site Isolation, it's allowed.
+bool SiteIsolationPolicy::IsValidCorsHeaderSet(
+    GURL& frame_origin,
+    GURL& website_origin,
+    std::string access_control_origin) {

[awong, 2013/08/26 20:31:41]

Should this be const std::string&?

+  // Many websites are sending back "\"*\"" instead of "*". This is
+  // non-standard practice, and not supported by Chrome. Refer to
+  // CrossOriginAccessControl::passesAccessControlCheck().
+
+  // TODO(dsjang): * is not allowed for the response from a request
+  // with cookies. This allows for more than what the renderer will
+  // eventually be able to receive, so we won't see illegal cross-site
+  // documents allowed by this. We have to find a way to see if this
+  // response is from a cookie-tagged request or not in the future.
+  if (access_control_origin == "*")
+    return true;
+
+  // TODO(dsjang): The CORS spec only treats a fully specified URL, except for
+  // "*", but many websites are using just a domain for access_control_origin,
+  // and this is blocked by Webkit's CORS logic here :
+  // CrossOriginAccessControl::passesAccessControlCheck(). GURL is set
+  // is_valid() to false when it is created from a URL containing * in the
+  // domain part.
+
+  GURL cors_origin(access_control_origin);
+  return IsSameSite(frame_origin, cors_origin);
+}
+
+// This function is a slight modification of |net::SniffForHTML|.
+bool SiteIsolationPolicy::SniffForHTML(const char* data, size_t length) {

[awong, 2013/08/26 20:31:41]

Converting all these functions to taking a StringPiece seems like a safer
api...though we should double check that the copy behavior of StringPiece.

+  // The content sniffer used by Chrome and Firefox are using "<!--"
+  // as one of the HTML signatures, but it also appears in valid
+  // JavaScript, considered as well-formed JS by the browser.  Since
+  // we do not want to block any JS, we exclude it from our HTML
+  // signatures. This can weaken our document block policy, but we can
+  // break less websites.
+  // TODO(dsjang): parameterize |net::SniffForHTML| with an option
+  // that decides whether to include <!-- or not, so that we can
+  // remove this function.
+  const char* html_signatures[] = {"<!DOCTYPE html",  // HTML5 spec

[awong, 2013/08/26 20:31:41]

General locally scoped constants should be declared static.

As is, this directs the compiler to, per function invocation, perform one memcpy
copy of the array onto the stack.

Also, constants should be named kHtmlSignatures as per style guide.

Please fix here and elsewhere.

Also, I think this is better formatted as

const char* kHtmlSignatures {
    "<!DOCTYPE html",  // HTML5 spec
    ...
};

The alignment is easier to read.

+                                   "<script",         // HTML5 spec, Mozilla
+                                   "<html",           // HTML5 spec, Mozilla
+                                   "<head",           // HTML5 spec, Mozilla
+                                   "<iframe",         // Mozilla
+                                   "<h1",             // Mozilla
+                                   "<div",            // Mozilla
+                                   "<font",           // Mozilla
+                                   "<table",          // Mozilla
+                                   "<a",              // Mozilla
+                                   "<style",          // Mozilla
+                                   "<title",          // Mozilla
+                                   "<b",              // Mozilla
+                                   "<body",           // Mozilla
+                                   "<br", "<p",       // Mozilla
+                                   "<?xml"            // Mozilla
+  };
+
+  if (MatchesSignature(
+          data, length, html_signatures, arraysize(html_signatures)))
+    return true;

[awong, 2013/08/26 20:31:41]

with a linebreak in the conditional, use braces.

+
+  // "<!--" is specially treated since web JS can use "<!--" "-->" pair for
+  // comments.
+  const char* comment_begins[] = {"<!--" };
+
+  if (MatchesSignature(
+          data, length, comment_begins, arraysize(comment_begins))) {
+    // Search for --> and do SniffForHTML after that. If we can find the
+    // comment's end, we start HTML sniffing from there again.
+    const char end_comment[] = "-->";
+    const size_t end_comment_size = strlen(end_comment);
+
+    for (size_t i = 0; i <= length - end_comment_size; ++i) {
+      if (!strncmp(data + i, end_comment, end_comment_size)) {
+        size_t skipped = i + end_comment_size;
+        return SniffForHTML(data + skipped, length - skipped);

[awong, 2013/08/26 20:31:41]

This recursion is based on data from the user (the network in this case).  How
are you bounding the recursion depth?

+      }
+    }
+  }
+
+  return false;
+}
+
+bool SiteIsolationPolicy::SniffForXML(const char* data, size_t length) {
+  // TODO(dsjang): Chrome's mime_sniffer is using strncasecmp() for
+  // this signature. However, XML is case-sensitive. Don't we have to
+  // be more lenient only to block documents starting with the exact
+  // string <?xml rather than <?XML ?
+  const char* xml_signatures[] = {"<?xml"  // Mozilla
+  };
+  return MatchesSignature(
+      data, length, xml_signatures, arraysize(xml_signatures));
+}
+
+bool SiteIsolationPolicy::SniffForJSON(const char* data, size_t length) {
+  // TODO(dsjang): We have to come up with a better way to sniff
+  // JSON. However, even RE cannot help us that much due to the fact
+  // that we don't do full parsing.  This DFA starts with state 0, and
+  // finds {, "/' and : in that order. We're avoiding adding a
+  // dependency on a regular expression library.
+  const int kInitState = 0;
+  const int kLeftBraceState = 1;
+  const int kLeftQuoteState = 2;
+  const int kColonState = 3;
+  const int kDeadState = 4;
+
+  int state = kInitState;
+  for (size_t i = 0; i < length && state < kColonState; ++i) {
+    const char c = data[i];
+    if (c == ' ' || c == '\t' || c == '\r' || c == '\n')
+      continue;
+
+    switch (state) {
+      case kInitState:
+        if (c == '{')
+          state = kLeftBraceState;
+        else
+          state = kDeadState;
+        break;
+      case kLeftBraceState:
+        if (c == '\"' || c == '\'')
+          state = kLeftQuoteState;
+        else
+          state = kDeadState;
+        break;
+      case kLeftQuoteState:
+        if (c == ':')
+          state = kColonState;
+        break;
+      default:
+        NOTREACHED();
+        break;
+    }
+  }
+  return state == kColonState;
+}
+
+bool SiteIsolationPolicy::MatchesSignature(const char* raw_data,
+                                           size_t raw_length,
+                                           const char* signatures[],
+                                           size_t arr_size) {
+  size_t start = 0;
+  // Skip white characters at the beginning of the document.
+  for (start = 0; start < raw_length; ++start) {
+    char c = raw_data[start];
+    if (!(c == ' ' || c == '\t' || c == '\r' || c == '\n'))
+      break;
+  }
+
+  // There is no not-whitespace character in this document.
+  if (!(start < raw_length))
+    return false;
+
+  const char* data = raw_data + start;
+  size_t length = raw_length - start;
+
+  for (size_t sig_index = 0; sig_index < arr_size; ++sig_index) {
+    const char* signature = signatures[sig_index];
+    size_t signature_length = strlen(signature);
+
+    if (length < signature_length)
+      continue;
+
+    if (!base::strncasecmp(signature, data, signature_length))
+      return true;
+  }
+  return false;
+}
+
+bool SiteIsolationPolicy::IsRenderableStatusCodeForDocument(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;
+}
+
+bool SiteIsolationPolicy::SniffForJS(const char* data, size_t length) {
+  // TODO(dsjang): This is a real hack. The only purpose of this function is to
+  // try to see if there's any possibility that this data can be JavaScript
+  // (superset of JS). This function will be removed once UMA stats are
+  // gathered.
+
+  // Search for "var " for JS detection.
+  for (size_t i = 0; i < length - 3; ++i) {
+    if (strncmp(data + i, "var ", 4) == 0)

[awong, 2013/08/26 20:31:41]

For safe use of strncmp, your "n" should always be based on the minmal size of
the two buffers.

In particular, if one of your buffers is known to be null-terminated and is
constant, then setting "n" to that size doesn't increase safety at all.

Here, length - i, is the conceptually correct "n" for safety (though that still
needs to be paired with a length > sizeof(kVar) check otherwise data with value
"va" would match).

+      return true;
+  }
+  return false;
+}
+
+SiteIsolationPolicy::RequestIdToMetaDataMap*
+SiteIsolationPolicy::GetRequestIdToMetaDataMap() {
+  CR_DEFINE_STATIC_LOCAL(RequestIdToMetaDataMap, metadata_map_, ());

[awong, 2013/08/26 20:31:41]

This variable is declared like a static local, but really you're using it as a
global.  Would a LazyInstance declared at the top of this file be more
appropriate?

+  return &metadata_map_;
+}
+
+SiteIsolationPolicy::RequestIdToResultMap*
+SiteIsolationPolicy::GetRequestIdToResultMap() {
+  CR_DEFINE_STATIC_LOCAL(RequestIdToResultMap, result_map_, ());
+  return &result_map_;
+}
+
+}  // namespace content