Add UMA to report Preferences File Corruption

chrome/browser/prefs/pref_metrics_service.cc

Index: chrome/browser/prefs/pref_metrics_service.cc
diff --git a/chrome/browser/prefs/pref_metrics_service.cc b/chrome/browser/prefs/pref_metrics_service.cc
index a437c8c6db9b1bbd69f797558fe156d6d62959bc..d27e96fd532b76480bec1440e3aa3b5ce230c201 100644
--- a/chrome/browser/prefs/pref_metrics_service.cc
+++ b/chrome/browser/prefs/pref_metrics_service.cc
@@ -5,9 +5,17 @@
 #include "chrome/browser/prefs/pref_metrics_service.h"
 
 #include "base/bind.h"
+#include "base/json/json_string_value_serializer.h"
+#include "base/md5.h"
 #include "base/metrics/histogram.h"
+#include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/browser_shutdown.h"
+#include "chrome/browser/extensions/api/music_manager_private/device_id.h"

[Mattias Nissler (ping if slow), 2013/08/15 10:14:51]

I'd consider this a layering violation. chrome/browser/prefs/ should definitely
not depend on extensions.

[bbudge, 2013/08/15 17:33:49]

This appears to be the only way to get a unique per-device id. Perhaps another
CL is needed to expose this more widely?

[Mattias Nissler (ping if slow), 2013/08/20 12:53:54]

That'd be appreciated. Can you file a bug and put a TODO?

[bbudge, 2013/08/20 18:17:50]

Done.

+#include "chrome/browser/extensions/extension_prefs.h"
 #include "chrome/browser/prefs/pref_service_syncable.h"
+#include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/prefs/session_startup_pref.h"
 #include "chrome/browser/prefs/synced_pref_change_registrar.h"
 #include "chrome/browser/profiles/incognito_helpers.h"
@@ -18,21 +26,68 @@
 
 namespace {
 
-// Converts a host name into a domain name for easier matching.
-std::string GetDomainFromHost(const std::string& host) {
-  return net::registry_controlled_domains::GetDomainAndRegistry(
-      host,
-      net::registry_controlled_domains::EXCLUDE_PRIVATE_REGISTRIES);
-}
-
 const int kSessionStartupPrefValueMax = SessionStartupPref::kPrefValueMax;
 
+// In order to detect changes to Preferences that happen outside of Chrome, we
+// save selected prefs in Local Settings. When Chrome is started up, we compare

[Mattias Nissler (ping if slow), 2013/08/15 10:14:51]

local state, here and below

[bbudge, 2013/08/15 17:33:49]

Done.

+// the saved values against the values observed in the user's Preferences file.
+// We add a dictionary of dictionaries to Local Settings to hold the saved
+// values, grouped by profile. To make the system faster and more resistant to

[Mattias Nissler (ping if slow), 2013/08/15 10:14:51]

I don't think hashing makes things faster, given that calculating the hashes
actually takes considerable time.

[bbudge, 2013/08/15 17:33:49]

I was thinking of I/O and comparing values, but I will remove it as the main
point is to discourage spoofing.

+// spoofing, each preference value is hashed with its path and the device id.
+const char kProfilePreferenceHashes[] = "profile.preference_hashes";
+
+// These preferences must be kept in sync with the TrackedPreference enum in
+// tools/metrics/histograms/histograms.xml. To add a new preference, append it
+// to the array and add a corresponding value to the histogram enum.
+const char* kTrackedPrefs[] = {
+  prefs::kShowHomeButton,
+  prefs::kHomePageIsNewTabPage,
+  prefs::kHomePage,
+  prefs::kRestoreOnStartup,
+  prefs::kURLsToRestoreOnStartup,
+  extensions::ExtensionPrefs::kExtensionsPref,

[Mattias Nissler (ping if slow), 2013/08/15 10:14:51]

FWIW, this should be defined in pref_names.{h,cc} as well. Not your fault, feel
free to ignore this comment :)

[bbudge, 2013/08/15 17:33:49]

Perhaps a separate CL.

+};
+
+const int kTrackedPrefsCount = arraysize(kTrackedPrefs);
+
+bool BrowserShuttingDown() {
+  return browser_shutdown::GetShutdownType() != browser_shutdown::NOT_VALID;
+}
+
 }  // namespace
 
 PrefMetricsService::PrefMetricsService(Profile* profile)
-    : profile_(profile) {
+    : weak_factory_(this),
+      profile_(profile) {
   RecordLaunchPrefs();
 
+  // Make sure local state is initialized.
+  g_browser_process->local_state();

[Mattias Nissler (ping if slow), 2013/08/15 10:14:51]

This shouldn't be required, local state gets initialized on browser startup.

[bbudge, 2013/08/15 17:33:49]

I thought it might fix some tests that are crashing because profile name isn't
registered in settings. Unfortunately, it doesn't. Removed.

+
+#if !defined(OS_ANDROID)
+  // We need the machine id to compute pref value hashes. Fetch that, and then
+  // call CheckTrackedPreferences in the callback.
+  extensions::api::DeviceId::GetDeviceId(
+      "PrefMetricsService",  // non-empty string to obfuscate the device id.
+      Bind(&PrefMetricsService::GetDeviceIdCallback,
+           weak_factory_.GetWeakPtr()));
+#else
+  // Android has no GetDeviceId.
+  CheckTrackedPreferences();
+#endif  // !defined(OS_ANDROID)
+
+  // It's tricky to save preference value hashes on browser shutdown. Instead,
+  // register for notifications when tracked preferences change so we can update
+  // the hashes in Local Settings.
+  pref_registrar_.Init(profile_->GetPrefs());
+  for (size_t i = 0; i < arraysize(kTrackedPrefs); ++i) {
+    pref_registrar_.Add(
+        kTrackedPrefs[i],
+        base::Bind(&PrefMetricsService::UpdateTrackedPreference,
+                   weak_factory_.GetWeakPtr(),
+                   kTrackedPrefs[i]));
+  }
+
   PrefServiceSyncable* prefs = PrefServiceSyncable::FromProfile(profile_);
   synced_pref_change_registrar_.reset(new SyncedPrefChangeRegistrar(prefs));
 
@@ -62,6 +117,13 @@ void PrefMetricsService::RecordLaunchPrefs() {
   }
 }
 
+// static
+void PrefMetricsService::RegisterPrefs(PrefRegistrySimple* registry) {
+  // Register the top level dictionary to map profile names to dictionaries of
+  // tracked preferences.
+  registry->RegisterDictionaryPref(kProfilePreferenceHashes);
+}
+
 void PrefMetricsService::RegisterSyncedPrefObservers() {
   LogHistogramValueCallback booleanHandler = base::Bind(
       &PrefMetricsService::LogBooleanPrefChange, base::Unretained(this));
@@ -139,6 +201,112 @@ void PrefMetricsService::LogListPrefChange(
   }
 }
 
+void PrefMetricsService::GetDeviceIdCallback(const std::string& device_id) {
+  device_id_ = device_id;
+  CheckTrackedPreferences();
+}
+
+void PrefMetricsService::CheckTrackedPreferences() {
+  PrefService* local_state = g_browser_process->local_state();
+  const base::DictionaryValue* profiles =
+      local_state->GetDictionary(kProfilePreferenceHashes);
+  DCHECK(profiles);
+  // Get the hashed prefs dictionary if it exists. If it doesn't, it will be
+  // created if we set preference values below.
+  const base::DictionaryValue* hashed_prefs = NULL;
+  profiles->GetDictionary(profile_->GetProfileName(), &hashed_prefs);
+  const PrefService* pref_service = profile_->GetPrefs();
+  for (size_t i = 0; i < arraysize(kTrackedPrefs); ++i) {
+    const base::Value* value =
+        pref_service->GetUserPrefValue(kTrackedPrefs[i]);
+    if (value) {
+      std::string value_hash = GetHashedPrefValue(kTrackedPrefs[i], value);
+      std::string last_hash;
+      if (hashed_prefs &&
+          hashed_prefs->GetString(kTrackedPrefs[i], &last_hash)) {
+        if (value_hash != last_hash) {
+          // Record that the preference changed from its last value.
+          UMA_HISTOGRAM_ENUMERATION("Settings.TrackedPreferenceChanged",
+              i, arraysize(kTrackedPrefs));
+          UpdateTrackedPreference(kTrackedPrefs[i]);
+        }
+      } else {
+        // Record that we haven't tracked this preference yet, or the hash in
+        // local settings was removed.
+        UMA_HISTOGRAM_ENUMERATION("Settings.TrackedPreferenceInitialized",
+            i, arraysize(kTrackedPrefs));
+        UpdateTrackedPreference(kTrackedPrefs[i]);
+      }
+    } else {
+      // There is no preference set. Remove any hashed value from local settings
+      // and if one was present, record that a pref was removed.
+      if (RemoveTrackedPreference(kTrackedPrefs[i])) {
+        UMA_HISTOGRAM_ENUMERATION("Settings.TrackedPreferenceRemoved",
+            i, arraysize(kTrackedPrefs));
+      }
+    }
+  }
+}
+
+void PrefMetricsService::UpdateTrackedPreference(const char* path) {
+  // Don't try to change local settings during browser shutdown.
+  if (BrowserShuttingDown())
+    return;
+
+  PrefService* pref_service = profile_->GetPrefs();
+  const base::Value* value = pref_service->GetUserPrefValue(path);
+  if (value) {
+    PrefService* local_state = g_browser_process->local_state();
+    DictionaryPrefUpdate update(local_state, kProfilePreferenceHashes);
+    base::DictionaryValue* prefs = update.Get();
+    if (prefs) {
+      prefs->SetString(GetHashedPrefPath(path),
+                       GetHashedPrefValue(path, value));
+    }
+  } else {
+    RemoveTrackedPreference(path);
+  }
+}
+
+bool PrefMetricsService::RemoveTrackedPreference(const char* path) {
+  // Don't try to change local settings during browser shutdown.
+  if (BrowserShuttingDown())
+    return false;
+
+  PrefService* local_state = g_browser_process->local_state();
+  DictionaryPrefUpdate update(local_state, kProfilePreferenceHashes);
+  base::DictionaryValue* prefs = update.Get();
+  if (prefs)
+    return prefs->Remove(GetHashedPrefPath(path), NULL);
+
+  return false;
+}
+
+std::string PrefMetricsService::GetHashedPrefPath(const char* path) {
+  std::string hash_pref_path(profile_->GetProfileName());
+  hash_pref_path.append(".");
+  hash_pref_path.append(path);
+  return hash_pref_path;
+}
+
+std::string PrefMetricsService::GetHashedPrefValue(
+    const char* path,
+    const base::Value* value) {
+  DCHECK(value);
+  std::string value_string;
+  JSONStringValueSerializer serializer(&value_string);
+  serializer.Serialize(*value);
+
+  base::MD5Context context;
+  base::MD5Init(&context);
+  base::MD5Update(&context, device_id_);  // Salt with device id.
+  base::MD5Update(&context, path);        // Salt with pref path.
+  base::MD5Update(&context, value_string);
+  base::MD5Digest digest;
+  base::MD5Final(&digest, &context);
+  return base::MD5DigestToBase16(digest);
+}
+
 // static
 PrefMetricsService::Factory* PrefMetricsService::Factory::GetInstance() {
   return Singleton<PrefMetricsService::Factory>::get();