SettingsProvider: exclude secure_frp_mode from resets

When RescueParty detects that a system process is crashing frequently,
it tries to recover in various ways, such as by resetting all settings.
Unfortunately, this included resetting the secure_frp_mode setting,
which is the means by which the system keeps track of whether the
Factory Reset Protection (FRP) challenge has been passed yet.  With this
setting reset, some FRP restrictions went away and it became possible to
bypass FRP by setting a new lockscreen credential.

Fix this by excluding secure_frp_mode from resets.

Note: currently this bug isn't reproducible on 'main' due to ag/23727749
disabling much of RescueParty, but that is a temporary change.

Bug: 253043065
Test: With ag/23727749 reverted and with my fix to prevent
      com.android.settings from crashing *not* applied, tried repeatedly
      setting lockscreen credential while in FRP mode, using the
      smartlock setup activity launched by intent via adb.  Verified
      that although RescueParty is still triggered after 5 attempts,
      secure_frp_mode is no longer reset (its value remains "1").
Test: Verified that secure_frp_mode still gets changed from 1 to 0 when
      FRP is passed legitimately.
Test: atest com.android.providers.settings.SettingsProviderTest
Test: atest android.provider.SettingsProviderTest
Change-Id: Id95ed43b9cc2208090064392bcd5dc012710af93

2 files changed, 38 insertions, 4 deletions

diff --git a/packages/SettingsProvider/src/com/android/providers/settings/SettingsProvider.java b/packages/SettingsProvider/src/com/android/providers/settings/SettingsProvider.java
index d1d745fe2b93..693e2232f168 100644
--- a/packages/SettingsProvider/src/com/android/providers/settings/SettingsProvider.java
+++ b/packages/SettingsProvider/src/com/android/providers/settings/SettingsProvider.java
@@ -3254,6 +3254,15 @@ public class SettingsProvider extends ContentProvider {
             return settingsState.getSettingLocked(name);
         }
 
+        private static boolean shouldExcludeSettingFromReset(Setting setting, String prefix) {
+            // If a prefix was specified, exclude settings whose names don't start with it.
+            if (prefix != null && !setting.getName().startsWith(prefix)) {
+                return true;
+            }
+            // Never reset SECURE_FRP_MODE, as it could be abused to bypass FRP via RescueParty.
+            return Global.SECURE_FRP_MODE.equals(setting.getName());
+        }
+
         public void resetSettingsLocked(int type, int userId, String packageName, int mode,
                 String tag) {
             resetSettingsLocked(type, userId, packageName, mode, tag, /*prefix=*/
@@ -3276,7 +3285,7 @@ public class SettingsProvider extends ContentProvider {
                         Setting setting = settingsState.getSettingLocked(name);
                         if (packageName.equals(setting.getPackageName())) {
                             if ((tag != null && !tag.equals(setting.getTag()))
-                                    || (prefix != null && !setting.getName().startsWith(prefix))) {
+                                    || shouldExcludeSettingFromReset(setting, prefix)) {
                                 continue;
                             }
                             if (settingsState.resetSettingLocked(name)) {
@@ -3297,7 +3306,7 @@ public class SettingsProvider extends ContentProvider {
                         Setting setting = settingsState.getSettingLocked(name);
                         if (!SettingsState.isSystemPackage(getContext(),
                                 setting.getPackageName())) {
-                            if (prefix != null && !setting.getName().startsWith(prefix)) {
+                            if (shouldExcludeSettingFromReset(setting, prefix)) {
                                 continue;
                             }
                             if (settingsState.resetSettingLocked(name)) {
@@ -3318,7 +3327,7 @@ public class SettingsProvider extends ContentProvider {
                         Setting setting = settingsState.getSettingLocked(name);
                         if (!SettingsState.isSystemPackage(getContext(),
                                 setting.getPackageName())) {
-                            if (prefix != null && !setting.getName().startsWith(prefix)) {
+                            if (shouldExcludeSettingFromReset(setting, prefix)) {
                                 continue;
                             }
                             if (setting.isDefaultFromSystem()) {
@@ -3343,7 +3352,7 @@ public class SettingsProvider extends ContentProvider {
                     for (String name : settingsState.getSettingNamesLocked()) {
                         Setting setting = settingsState.getSettingLocked(name);
                         boolean someSettingChanged = false;
-                        if (prefix != null && !setting.getName().startsWith(prefix)) {
+                        if (shouldExcludeSettingFromReset(setting, prefix)) {
                             continue;
                         }
                         if (setting.isDefaultFromSystem()) {
diff --git a/packages/SettingsProvider/test/src/com/android/providers/settings/SettingsProviderTest.java b/packages/SettingsProvider/test/src/com/android/providers/settings/SettingsProviderTest.java
index eaf0dcb9b4e7..a945c33bc20a 100644
--- a/packages/SettingsProvider/test/src/com/android/providers/settings/SettingsProviderTest.java
+++ b/packages/SettingsProvider/test/src/com/android/providers/settings/SettingsProviderTest.java
@@ -464,6 +464,31 @@ public class SettingsProviderTest extends BaseSettingsProviderTest {
         }
     }
 
+    // To prevent FRP bypasses, the SECURE_FRP_MODE setting should not be reset when all other
+    // settings are reset.  But it should still be possible to explicitly set its value.
+    @Test
+    public void testSecureFrpModeSettingCannotBeReset() throws Exception {
+        final String name = Settings.Global.SECURE_FRP_MODE;
+        final String origValue = getSetting(SETTING_TYPE_GLOBAL, name);
+        setSettingViaShell(SETTING_TYPE_GLOBAL, name, "1", false);
+        try {
+            assertEquals("1", getSetting(SETTING_TYPE_GLOBAL, name));
+            for (int type : new int[] { SETTING_TYPE_GLOBAL, SETTING_TYPE_SECURE }) {
+                resetSettingsViaShell(type, Settings.RESET_MODE_UNTRUSTED_DEFAULTS);
+                resetSettingsViaShell(type, Settings.RESET_MODE_UNTRUSTED_CHANGES);
+                resetSettingsViaShell(type, Settings.RESET_MODE_TRUSTED_DEFAULTS);
+            }
+            // The value should still be "1".  It should not have been reset to null.
+            assertEquals("1", getSetting(SETTING_TYPE_GLOBAL, name));
+            // It should still be possible to explicitly set the value to "0".
+            setSettingViaShell(SETTING_TYPE_GLOBAL, name, "0", false);
+            assertEquals("0", getSetting(SETTING_TYPE_GLOBAL, name));
+        } finally {
+            setSettingViaShell(SETTING_TYPE_GLOBAL, name, origValue, false);
+            assertEquals(origValue, getSetting(SETTING_TYPE_GLOBAL, name));
+        }
+    }
+
     private void doTestQueryStringInBracketsViaProviderApiForType(int type) {
         // Make sure we have a clean slate.
         deleteStringViaProviderApi(type, FAKE_SETTING_NAME);