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/windows_version.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 Windows XP systems up to and including SP2. As a
+// side note, pings could be sent to the alternate URL too.
+bool CanUseAltUrlSource() {
+#if defined(OS_WIN)
+  const base::win::OSInfo* os_info = base::win::OSInfo::GetInstance();

[cpu_(ooo_6.6-7.5), 2014/09/17 21:28:18]

no need to cache with os_info. GetInstance has it cached.

[Sorin Jianu, 2014/09/17 21:45:35]

Agreed on caching. 
The local variable is to make the call site prettier. Plus, it might save a
function call to GetInstance, since that stuff is not inlined and might or might
not get PGO.

I could rewrite the code if you'd like me to.

+  if (os_info->version() != base::win::VERSION_XP)

[waffles, 2014/09/17 21:26:45]

Do we need to do anything for VERSION_SERVER_2003 (includes 64-bit XP)?

[cpu_(ooo_6.6-7.5), 2014/09/17 21:28:18]

use (version() < base::win::VERSION_VISTA)

[Sorin Jianu, 2014/09/17 21:29:06]

We could, I hope cpu@ helps me clarify the condition.

[Sorin Jianu, 2014/09/17 21:45:36]

Will it be possible that catches some other previous versions that we want to
support but the condition rejects?

There is also a test for the SP. The way the code is written makes the SP test
apply to XP only. With this proposed change, the SP applies to anything less
than VISTA. 

This might be a pedantic observation. I will make the change if needed.

+    return false;
+  if (os_info->service_pack().major >= 3)
+    return false;
+  return true;
+#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