Component updater must fallback on using HTTP on Windows XPSP2 and below

chrome/browser/component_updater/chrome_component_updater_configurator.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 "chrome/browser/component_updater/chrome_component_updater_configurator.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/strings/string_util.h"
 #include "base/version.h"
+#if defined(OS_WIN)
+#include "base/win/win_util.h"
+#endif  // OS_WIN
 #include "build/build_config.h"
 #include "chrome/browser/component_updater/component_patcher_operation_out_of_process.h"
 #include "chrome/browser/omaha_query_params/chrome_omaha_query_params_delegate.h"
 #include "chrome/common/chrome_version_info.h"
 #include "components/component_updater/component_updater_configurator.h"
 #include "components/component_updater/component_updater_switches.h"
 #include "content/public/browser/browser_thread.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "url/gurl.h"
 
@@ skipping 15 matching lines @@
 // Disables pings. Pings are the requests sent to the update server that report
 // the success or the failure of component install or update attempts.
 extern const char kSwitchDisablePings[] = "disable-pings";
 
 // Sets the URL for updates.
 const char kSwitchUrlSource[] = "url-source";
 
 #define COMPONENT_UPDATER_SERVICE_ENDPOINT \
   "//clients2.google.com/service/update2"
 
-// The default url for the v3 protocol service endpoint.
+// The default URL for the v3 protocol service endpoint. In some cases, the
+// component updater is allowed to fall back to and alternate URL source, if
+// the request to the default URL source fails.
 // The value of |kDefaultUrlSource| can be overridden with
 // --component-updater=url-source=someurl.
 const char kDefaultUrlSource[] = "https:" COMPONENT_UPDATER_SERVICE_ENDPOINT;
+const char kAltUrlSource[] = "http:" COMPONENT_UPDATER_SERVICE_ENDPOINT;
 
 // Disables differential updates.
 const char kSwitchDisableDeltaUpdates[] = "disable-delta-updates";
 
 #if defined(OS_WIN)
 // Disables background downloads.
 const char kSwitchDisableBackgroundDownloads[] = "disable-background-downloads";
 #endif  // defined(OS_WIN)
 
 // Returns true if and only if |test| is contained in |vec|.
 bool HasSwitchValue(const std::vector<std::string>& vec, const char* test) {
   if (vec.empty())
     return 0;
   return (std::find(vec.begin(), vec.end(), test) != vec.end());
 }
 
+// Returns true if falling back on an alternate, unsafe, service URL is
+// allowed. In the fallback case, the security of the component update relies
+// only on the integrity of the CRX payloads, which is self-validating.
+// This is allowed only for some of the pre-Windows Vista versions not including
+// Windows XP SP3. As a side note, pings could be sent to the alternate URL too.
+bool CanUseAltUrlSource() {
+#if defined(OS_WIN)
+  return !base::win::MaybeHasSHA256Support();
+#else
+  return false;
+#endif  // OS_WIN
+}
+
 // If there is an element of |vec| of the form |test|=.*, returns the right-
 // hand side of that assignment. Otherwise, returns an empty string.
 // The right-hand side may contain additional '=' characters, allowing for
 // further nesting of switch arguments.
 std::string GetSwitchArgument(const std::vector<std::string>& vec,
                               const char* test) {
   if (vec.empty())
     return std::string();
   for (std::vector<std::string>::const_iterator it = vec.begin();
        it != vec.end();
@@ skipping 40 matching lines @@
       GetSingleThreadTaskRunner() const OVERRIDE;
 
  private:
   net::URLRequestContextGetter* url_request_getter_;
   std::string extra_info_;
   GURL url_source_override_;
   bool fast_update_;
   bool pings_enabled_;
   bool deltas_enabled_;
   bool background_downloads_enabled_;
+  bool fallback_to_alt_source_url_enabled_;
 };
 
 ChromeConfigurator::ChromeConfigurator(
     const CommandLine* cmdline,
     net::URLRequestContextGetter* url_request_getter)
     : url_request_getter_(url_request_getter),
       fast_update_(false),
       pings_enabled_(false),
       deltas_enabled_(false),
-      background_downloads_enabled_(false) {
+      background_downloads_enabled_(false),
+      fallback_to_alt_source_url_enabled_(false) {
   // Parse comma-delimited debug flags.
   std::vector<std::string> switch_values;
   Tokenize(cmdline->GetSwitchValueASCII(switches::kComponentUpdater),
            ",",
            &switch_values);
   fast_update_ = HasSwitchValue(switch_values, kSwitchFastUpdate);
   pings_enabled_ = !HasSwitchValue(switch_values, kSwitchDisablePings);
   deltas_enabled_ = !HasSwitchValue(switch_values, kSwitchDisableDeltaUpdates);
 
 #if defined(OS_WIN)
   background_downloads_enabled_ =
       !HasSwitchValue(switch_values, kSwitchDisableBackgroundDownloads);
 #else
   background_downloads_enabled_ = false;
 #endif
 
   const std::string switch_url_source =
       GetSwitchArgument(switch_values, kSwitchUrlSource);
   if (!switch_url_source.empty()) {
     url_source_override_ = GURL(switch_url_source);
     DCHECK(url_source_override_.is_valid());
   }
 
   if (HasSwitchValue(switch_values, kSwitchRequestParam))
     extra_info_ += "testrequest=\"1\"";
+
+  fallback_to_alt_source_url_enabled_ = CanUseAltUrlSource();
 }
 
 int ChromeConfigurator::InitialDelay() const {
   return fast_update_ ? 1 : (6 * kDelayOneMinute);
 }
 
 int ChromeConfigurator::NextCheckDelay() {
   return fast_update_ ? 3 : (6 * kDelayOneHour);
 }
 
@@ skipping 12 matching lines @@
 int ChromeConfigurator::OnDemandDelay() const {
   return fast_update_ ? 2 : (30 * kDelayOneMinute);
 }
 
 std::vector<GURL> ChromeConfigurator::UpdateUrl() const {
   std::vector<GURL> urls;
   if (url_source_override_.is_valid()) {
     urls.push_back(GURL(url_source_override_));
   } else {
     urls.push_back(GURL(kDefaultUrlSource));
+    if (fallback_to_alt_source_url_enabled_) {
+      urls.push_back(GURL(kAltUrlSource));
+    }
   }
   return urls;
 }
 
 std::vector<GURL> ChromeConfigurator::PingUrl() const {
   return pings_enabled_ ? UpdateUrl() : std::vector<GURL>();
 }
 
 base::Version ChromeConfigurator::GetBrowserVersion() const {
   return base::Version(chrome::VersionInfo().Version());
@@ skipping 52 matching lines @@
 
 }  // namespace
 
 Configurator* MakeChromeComponentUpdaterConfigurator(
     const base::CommandLine* cmdline,
     net::URLRequestContextGetter* context_getter) {
   return new ChromeConfigurator(cmdline, context_getter);
 }
 
 }  // namespace component_updater