Chrome Participated Tamper Detect

components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detect.cc

+// Copyright 2014 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 "components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detect.h"
+
+#include <algorithm>
+#include <cstring>
+
+#include "base/base64.h"
+#include "base/md5.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/sparse_histogram.h"
+#include "base/strings/string_number_conversions.h"
+#include "components/data_reduction_proxy/common/data_reduction_proxy_headers.h"
+#include "net/android/network_library.h"
+#include "net/http/http_response_headers.h"
+#include "net/http/http_util.h"
+
+// Macro for UMA reporting. First reporting to either |https_histogram| or
+// |http_histogram| depending on |scheme_is_https|, with |carrier_id| as bucket
+// which counts for each carrier, how many responses have been tampered with.
+// Then reporting to |http(s)_histogram|_Total, which counts the total number of
+// detected tampering (sum of tampering detected for all carriers).
+#define UMA_REPORT(scheme_is_https, http_histogram, https_histogram, carrier_id) \
+  do { \
+    if (scheme_is_https) { \
+      UMA_HISTOGRAM_SPARSE_SLOWLY(https_histogram, carrier_id); \
+      UMA_HISTOGRAM_COUNTS(https_histogram "_Total", 1); \
+    } else { \
+      UMA_HISTOGRAM_SPARSE_SLOWLY(http_histogram, carrier_id); \
+      UMA_HISTOGRAM_COUNTS(http_histogram "_Total", 1); \
+    }\
+  } while (0)
+
+namespace {
+// Four fingerprints will be added to Chrome-Proxy header. One starts with
+// |kTamperDetectFingerprintChromeProxy|, which is the fingerprint for the
+// Chrome-Proxy header. The other three have been put together into a string
+// starts with key tag |kTamperDetectFingerprint|.
+const char kTamperDetectFingerprints[] = "fp";

[bengr, 2014/07/16 21:24:48]

To avoid name conflicts, all chrome-proxy actions should be defined in
data_reduction_proxy_headers.{cc|h}

[xingx, 2014/07/18 17:25:01]

Done.

+const char kTamperDetectFingerprintChromeProxy[] = "cp";
+
+// Fingerprint |kTamperDetectFingerprint| contains three fingerprints, each
+// starts with a key tag followed by "=" and its fingerprint value. Three
+// fingerprints and their respective tags are defined below.
+const char kTamperDetectFingerprintVia[] = "via";
+const char kTamperDetectFingerprintOther[] = "oh";
+const char kTamperDetectFingerprintContengLength[] = "cl";
+} // namespace

[bengr, 2014/07/16 21:24:48]

Add a space before //

[xingx, 2014/07/18 17:25:01]

Done.

+
+namespace data_reduction_proxy {
+
+// static
+void DataReductionProxyTamperDetection::CheckResponseFingerprint(
+    const net::HttpResponseHeaders* headers,

[bengr, 2014/07/16 21:24:47]

check that headers is non-NULL.

[xingx, 2014/07/18 17:25:01]

Done.

+    const bool is_secure_scheme)

[bengr, 2014/07/16 21:24:48]

can this function be const?

[xingx, 2014/07/18 17:25:01]

Right now the function is static, so can't be const, any suggestion?

+{

[bengr, 2014/07/16 21:24:48]

Move the curly up a line.

[xingx, 2014/07/18 17:25:01]

Done.

+  // If Chrome-Proxy header fingerprint absents, quits tamper detection ASAP.

[bengr, 2014/07/16 21:24:48]

If the Chrome-Proxy header fingerprint is absent, abort tamper detection.

[xingx, 2014/07/18 17:25:01]

Done.

+  if (!GetDataReductionProxyActionValue(
+      headers, kTamperDetectFingerprintChromeProxy, NULL))
+    return;
+
+  // Found tamper detection request field. Saves Chrome-Proxy header values to
+  // get fingerprints.
+  std::vector<std::string> values = GetHeaderValues(headers, "Chrome-Proxy");

[bengr, 2014/07/16 21:24:47]

I still don't understand why you need this.

[bengr, 2014/07/16 21:24:47]

values -> chrome_proxy_header_values

[xingx, 2014/07/18 17:25:01]

Acknowledged.

[xingx, 2014/07/18 17:25:02]

Acknowledged.

+
+  // |chrome_proxy_fingerprint| holds the value of fingerprint of Chrome-Proxy
+  // header. |other_fingerprints| holds the value of other fingerprints.
+  // |values| saves all the values of Chrome-Proxy header but with fingerprint
+  // for Chrome-Proxy header removed.
+  std::string chrome_proxy_fingerprint, other_fingerprints;
+  if (!GetTamperDetectionFingerprints(&values,
+                                      &chrome_proxy_fingerprint,
+                                      &other_fingerprints))
+    return;

[bengr, 2014/07/16 21:24:48]

I would add curly braces around this.

[xingx, 2014/07/18 17:25:01]

Done.

+
+  // Get carrier ID.
+  unsigned carrier_id = 0;
+#if defined(OS_ANDROID)

[bengr, 2014/07/16 21:24:47]

Is this busted on other platforms?

[xingx, 2014/07/18 17:25:01]

Discussed with Bolian, right now for other platforms the carrier_id is 0 (WiFi
is 0 as well).

+  base::StringToUint(net::android::GetTelephonyNetworkOperator(), &carrier_id);
+#endif
+
+  DataReductionProxyTamperDetection tamper_detection(headers,
+                                                     is_secure_scheme,
+                                                     carrier_id,
+                                                     &values);
+
+  // Check if Chrome-Proxy header has been tampered with.
+  if (tamper_detection.IsChromeProxyHeaderTampered(chrome_proxy_fingerprint)) {
+    tamper_detection.ReportChromeProxyHeaderTamperedUMA();
+    return;
+  } else {
+    UMA_REPORT(is_secure_scheme,
+               "DataReductionProxy.HTTPSHeaderTamperDetection",
+               "DataReductionProxy.HTTPHeaderTamperDetection",
+               carrier_id);
+  }
+
+  // Separate fingerprints from |other_fingerprints|, with delimiter "|".
+  net::HttpUtil::ValuesIterator it(
+      other_fingerprints.begin(), other_fingerprints.end(), '|');

[bengr, 2014/07/16 21:24:48]

Are fingerprints guaranteed not to contain '|'. Say so in the comment.

[xingx, 2014/07/18 17:25:02]

Modified the design.

+
+  // For each fingerprint, get its name |key| and the fingerprint |value|

[bengr, 2014/07/16 21:24:48]

|value|.

[xingx, 2014/07/18 17:25:02]

Done.

+  size_t delimiter_pos = std::string::npos;
+  while (it.GetNext()) {
+    delimiter_pos = it.value().find("=");
+    if (delimiter_pos == std::string::npos)
+      continue;
+    std::string key = it.value().substr(0, delimiter_pos);
+    std::string value = it.value().substr(delimiter_pos + 1);

[bengr, 2014/07/16 21:24:48]

Make each fingerprint a Chrome-Proxy action starting with 'f' and declared in
data_reduction_proxy_header.h

[xingx, 2014/07/18 17:25:01]

Done.

+
+    FingerprintCode fingerprint_code = tamper_detection.GetFingerprintCode(key);
+    switch (fingerprint_code) {
+    case VIA:
+      if (tamper_detection.IsViaHeaderTampered(value))
+        tamper_detection.ReportViaHeaderTamperedUMA();
+      break;
+    case OTHERHEADERS:
+      if (tamper_detection.AreOtherHeadersTampered(value))
+        tamper_detection.ReportOtherHeadersTamperedUMA();
+      break;
+    case CONTENTLENGTH:
+      if (tamper_detection.IsContentLengthHeaderTampered(value))
+        tamper_detection.ReportContentLengthHeaderTamperedUMA();
+      break;
+    default:
+      NOTREACHED();
+      break;
+    }
+  }
+  return;
+}
+
+// Constructor initializes fingerprint code map.
+DataReductionProxyTamperDetection::DataReductionProxyTamperDetection(
+    const net::HttpResponseHeaders* headers,

[bengr, 2014/07/16 21:24:48]

DCHECK that headers is non-NULL

[xingx, 2014/07/18 17:25:01]

Done.

+    const bool is_secure,
+    const unsigned carrier_id,
+    std::vector<std::string>* values)
+    : response_headers_(headers),
+      is_secure_scheme_(is_secure),
+      carrier_id_(carrier_id),
+      clean_chrome_proxy_header_values_(values) {
+  fingperprint_tag_code_map_ = std::map<std::string, FingerprintCode>();
+  fingperprint_tag_code_map_[kTamperDetectFingerprintVia] = VIA;
+  fingperprint_tag_code_map_[kTamperDetectFingerprintOther] = OTHERHEADERS;
+  fingperprint_tag_code_map_[kTamperDetectFingerprintContengLength] =
+      CONTENTLENGTH;
+};
+
+DataReductionProxyTamperDetection::~DataReductionProxyTamperDetection() {};
+
+// Checks whether the Chrome-Proxy header has been tampered with. |fingerprint|
+// is the fingerprint received from data reduction proxy, which is Base64
+// encoded. Decodes it first. Calculates the hash value of Chrome-Proxy header.
+// Note that |clean_chrome_proxy_header_values_| holds the values of
+// Chrome-Proxy header with its own fingerprint removed, so it's the correct
+// values to be used to calculate fingerprint. Compares calculated fingerprint
+// to the fingerprint from data reduction proxy (the removed value) and see
+// there is tamper detected or not.
+bool DataReductionProxyTamperDetection::IsChromeProxyHeaderTampered(
+    const std::string& fingerprint) const {
+  std::string received_fingerprint;
+  if (!base::Base64Decode(fingerprint, &received_fingerprint))
+    return true;
+  // Calculate the MD5 hash value of Chrome-Proxy.
+  std::string actual_fingerprint = GetMD5(
+      ValuesToSortedString(clean_chrome_proxy_header_values_));
+
+  return received_fingerprint != actual_fingerprint;
+}
+
+// Reports Chrome-Proxy header tamper detected.
+void DataReductionProxyTamperDetection::ReportChromeProxyHeaderTamperedUMA()
+    const {
+  UMA_REPORT(is_secure_scheme_,

[bengr, 2014/07/16 21:24:47]

I'd rename the macro to be less general sounding. E.g.,
REPORT_TAMPER_DETECTION_UMA

[xingx, 2014/07/18 17:25:01]

Done.

+             "DataReductionProxy.HTTPSHeaderTampered_ChromeProxy",
+             "DataReductionProxy.HTTPHeaderTampered_ChromeProxy",
+             carrier_id_);
+}
+
+// Checks whether there are other proxies/middleboxes' name after the data
+// reduction proxy's name in Via header.
+bool DataReductionProxyTamperDetection::IsViaHeaderTampered(
+    const std::string& fingerprint) const {
+  bool has, is_the_last;
+  has = HasDataReductionProxyViaHeader(response_headers_, &is_the_last);
+
+  // Via header of the data reductoin proxy is missing.

[bengr, 2014/07/16 21:24:47]

spelling

[xingx, 2014/07/18 17:25:01]

Done.

+  if (!has) {
+    UMA_REPORT(is_secure_scheme_,
+               "DataReductionProxy.HTTPSHeaderTampered_Via_Missing",
+               "DataReductionProxy.HTTPHeaderTampered_Via_Missing",
+               carrier_id_);
+    return false;
+  }
+
+  return !is_the_last;
+}
+
+// Reports Via header tamper detected.
+void DataReductionProxyTamperDetection::ReportViaHeaderTamperedUMA() const {
+  UMA_REPORT(is_secure_scheme_,
+             "DataReductionProxy.HTTPSHeaderTampered_Via",
+             "DataReductionProxy.HTTPHeaderTampered_Via",
+             carrier_id_);
+}
+
+// Checks whether values of a predefined list of headers have been tampered.
+// The format for |fingerprint| is:
+//     [base64encoded_fingerprint]:header_name1:header_namer2:...
+// Firstly extract the header names in the |fingerprint|. For each header, get
+// all the values of such header, sort the values and concatenate them to a
+// string. Concatenate the string for all the headers (with delimiter ";") and
+// calculate the MD5 hash value on it. Compare such hash value to the
+// fingerprint received from data reduction proxy.
+bool DataReductionProxyTamperDetection::AreOtherHeadersTampered(
+    const std::string& fingerprint) const {
+  std::string received_fingerprint;
+
+  // Fingerprint should never be empty.
+  DCHECK(fingerprint.size());
+
+  net::HttpUtil::ValuesIterator it(fingerprint.begin(),
+                                   fingerprint.end(), ':');
+
+  // The first value from fingerprint is the actual fingerprint; the following
+  // values are the header names will be included for fingerprint calculation.
+  // Make sure there is [base64fingerprint] and it can be decoded.
+  if (!(it.GetNext() &&
+        base::Base64Decode(it.value(), &received_fingerprint))) {
+    NOTREACHED();
+    return true;
+  }
+
+  std::string header_values;
+  // Enumerate the list of headers.
+  while (it.GetNext()) {
+    // Get values of one header.
+    std::vector<std::string> values =

[bengr, 2014/07/16 21:24:48]

rename as response_header_values

[xingx, 2014/07/18 17:25:01]

Done.

+        GetHeaderValues(response_headers_, it.value());
+    // Sort the values and concatenate them.
+    header_values += ValuesToSortedString(&values)  + ";";

[bengr, 2014/07/16 21:24:47]

are the values guaranteed not to contain ';'? Add a comment explaining.

[xingx, 2014/07/18 17:25:02]

Done.

+  }
+
+  // Calculate MD5 hash value on the concatenated string.
+  std::string actual_fingerprint = GetMD5(header_values);
+
+  return received_fingerprint != actual_fingerprint;
+}
+
+// Reports other headers tamper detected.
+void DataReductionProxyTamperDetection::ReportOtherHeadersTamperedUMA() const {
+  UMA_REPORT(is_secure_scheme_,
+             "DataReductionProxy.HTTPSHeaderTampered_OtherHeaders",
+             "DataReductionProxy.HTTPHeaderTampered_OtherHeaders",
+             carrier_id_);
+}
+
+// Checks whether the Content-Length value is different from what data reduction
+// proxy sees. Reports it as modified only if Content-Length can be decoded as
+// an interger at both end and such two numbers are not equal.
+bool DataReductionProxyTamperDetection::IsContentLengthHeaderTampered(
+    const std::string& fingerprint) const {
+  int received_content_length, actual_content_length;
+  // If Content-Length value from data reduction proxy is not available or
+  // it cannot be converted to an integer, pass.
+  if (base::StringToInt(fingerprint, &received_content_length)) {
+    std::string actual_content_length_;
+    // If there is no Content-Length header received, pass.
+    if (response_headers_->GetNormalizedHeader("Content-Length",
+                                     &actual_content_length_)) {

[bengr, 2014/07/16 21:24:47]

indentation.

[xingx, 2014/07/18 17:25:02]

Done.

+      // If the Content-Length value cannot be converted to integer,
+      // i.e., not valid, pass.
+      if (!base::StringToInt(actual_content_length_, &actual_content_length))
+        return false;
+      return received_content_length != actual_content_length;
+    }
+  }
+  return false;
+}
+
+// Reports Content-Length tamper detected.
+// Gets MIME type of the response and report to different UMA histogram.
+// Right now MIME types contain JavaScript, CSS, Images, and others.
+void DataReductionProxyTamperDetection::ReportContentLengthHeaderTamperedUMA()
+    const {
+  UMA_REPORT(is_secure_scheme_,
+             "DataReductionProxy.HTTPSHeaderTampered_ContentLength",
+             "DataReductionProxy.HTTPHeaderTampered_ContentLength",
+             carrier_id_);
+
+  // Get MIME type.
+  std::string mime_type;
+  response_headers_->GetMimeType(&mime_type);
+
+  // Reports tampered JavaScript.
+  if (mime_type.compare("text/javascript") == 0 ||
+      mime_type.compare("application/x-javascript") == 0 ||
+      mime_type.compare("application/javascript") == 0)
+    UMA_REPORT(is_secure_scheme_,
+               "DataReductionProxy.HTTPSHeaderTampered_ContentLength_JS",
+               "DataReductionProxy.HTTPHeaderTampered_ContentLength_JS",
+               carrier_id_);
+  // Reports tampered CSSs.
+  else if (mime_type.compare("text/css") == 0)
+    UMA_REPORT(is_secure_scheme_,
+               "DataReductionProxy.HTTPSHeaderTampered_ContentLength_CSS",
+               "DataReductionProxy.HTTPHeaderTampered_ContentLength_CSS",
+               carrier_id_);
+  // Reports tampered images.
+  else if (mime_type.find("image") == 0)
+    UMA_REPORT(is_secure_scheme_,
+               "DataReductionProxy.HTTPSHeaderTampered_ContentLength_Image",
+               "DataReductionProxy.HTTPHeaderTampered_ContentLength_Image",
+               carrier_id_);
+  // Reports tampered other MIME types.
+  else
+    UMA_REPORT(is_secure_scheme_,
+               "DataReductionProxy.HTTPSHeaderTampered_ContentLength_Other",
+               "DataReductionProxy.HTTPHeaderTampered_ContentLength_Other",
+               carrier_id_);
+}
+
+DataReductionProxyTamperDetection::FingerprintCode
+    DataReductionProxyTamperDetection::GetFingerprintCode(
+    const std::string& tag) {
+  std::map<std::string, DataReductionProxyTamperDetection::FingerprintCode>
+      ::iterator it = fingperprint_tag_code_map_.find(tag);
+
+  return it == fingperprint_tag_code_map_.end() ? NONEXIST : it->second;
+}
+
+// Enumerates the values of Chrome-Proxy header and checks if there are

[bengr, 2014/07/16 21:24:48]

Move method comments to the .h.

[xingx, 2014/07/18 17:25:01]

Function removed.

+// fingerprints for Chrome-Proxy header (kTamperDetectFingerprintChromeProxy)
+// and other fingerprints (kTamperDetectFingerprint). If there are, saves them
+// accordingly, removes fingerprint for Chrome-Proxy header from |values| and
+// return true, otherwise return false.
+bool DataReductionProxyTamperDetection::GetTamperDetectionFingerprints(
+    std::vector<std::string>* values,

[bengr, 2014/07/16 21:24:47]

DCHECK that values is non-NULL.

[xingx, 2014/07/18 17:25:02]

Function removed.

+    std::string* chrome_proxy_fingerprint,
+    std::string* other_fingerprints) {
+  int chrome_proxy_fingerprint_index = -1;
+
+  size_t size = values->size();
+  for (size_t i = 0; i < size; ++i) {
+    if ((*values)[i].find(kTamperDetectFingerprintChromeProxy) == 0 &&
+        (*values)[i][strlen(kTamperDetectFingerprintChromeProxy)] == '=') {
+      chrome_proxy_fingerprint_index = i;
+      // Saves Chrome-Proxy fingerprint.
+      *chrome_proxy_fingerprint = (*values)[i].substr(strlen(
+          kTamperDetectFingerprintChromeProxy));
+    }
+    else if ((*values)[i].find(kTamperDetectFingerprints) == 0 &&
+        (*values)[i][strlen(kTamperDetectFingerprints)] == '=') {
+      // Saves other fingerprints.
+      *other_fingerprints = (*values)[i].substr(
+          strlen(kTamperDetectFingerprints));
+    }
+  }
+
+  if (chrome_proxy_fingerprint_index == -1)
+    return false;
+
+  // Erases Chrome-Proxy's fingerprint from Chrome-Proxy header for
+  // later fingerprint calculation.
+  values->erase(values->begin() + chrome_proxy_fingerprint_index);
+  return true;
+}
+
+// Sorts the strings in |values| and concatenates them into a string.
+std::string DataReductionProxyTamperDetection::ValuesToSortedString(
+    std::vector<std::string>* values) {
+  std::string aggregated_values;
+
+  std::sort(values->begin(), values->end());
+  for (size_t i = 0; i < values->size(); ++i)
+    aggregated_values += (*values)[i] + ",";
+  return aggregated_values;
+}
+
+// For a given string, calculates and returns the MD5 hash value of the string.
+std::string DataReductionProxyTamperDetection::GetMD5(
+    const std::string &input) {
+  base::MD5Digest digest;
+  base::MD5Sum(input.c_str(), input.size(), &digest);
+  return std::string((char*)digest.a, ARRAYSIZE_UNSAFE(digest.a));
+}
+
+// For a given |header_name|, gets all its values and returns them as a vector.
+std::vector<std::string> DataReductionProxyTamperDetection::GetHeaderValues(
+    const net::HttpResponseHeaders* headers, const std::string& header_name) {
+  std::vector<std::string> values;
+  std::string value;
+  void* iter = NULL;
+  while (headers->EnumerateHeader(&iter, header_name, &value)) {
+    values.push_back(value);
+  }
+  return values;
+}
+}  // namespace data_reduction_proxy