LockSettingsService: reject null keys in setString() et al.

Make the setBoolean(), setLong(), and setString() methods of
ILockSettings throw an exception if the given key is null, rather than
allowing it to be inserted into the locksettings database, where it
previously would cause a crash upon preloading.

This is a small cleanup only; we probably should go further and use an
allowlist of key names.  Still, the ACCESS_KEYGUARD_SECURE_STORAGE
permission is required to call these methods, so there doesn't appear to
be any security impact from the lax input validation.

Bug: 261860102
Test: com.android.server.locksettings
Change-Id: Ic8632068b92182425e78e2f28a1c4016b7af4a3b

services/core/java/com/android/server/locksettings/LockSettingsService.java

@@ -1156,18 +1156,21 @@ public class LockSettingsService extends ILockSettings.Stub {
     @Override
     public void setBoolean(String key, boolean value, int userId) {
         checkWritePermission();
+        Objects.requireNonNull(key);
         mStorage.setBoolean(key, value, userId);
     }
 
     @Override
     public void setLong(String key, long value, int userId) {
         checkWritePermission();
+        Objects.requireNonNull(key);
         mStorage.setLong(key, value, userId);
     }
 
     @Override
     public void setString(String key, String value, int userId) {
         checkWritePermission();
+        Objects.requireNonNull(key);
         mStorage.setString(key, value, userId);
     }
 

services/tests/servicestests/src/com/android/server/locksettings/LockSettingsServiceTests.java

@@ -423,6 +423,21 @@ public class LockSettingsServiceTests extends BaseLockSettingsServiceTests {
         checkPasswordHistoryLength(userId, 3);
     }
 
+    @Test(expected=NullPointerException.class)
+    public void testSetBooleanRejectsNullKey() {
+        mService.setBoolean(null, false, 0);
+    }
+
+    @Test(expected=NullPointerException.class)
+    public void testSetLongRejectsNullKey() {
+        mService.setLong(null, 0, 0);
+    }
+
+    @Test(expected=NullPointerException.class)
+    public void testSetStringRejectsNullKey() {
+        mService.setString(null, "value", 0);
+    }
+
     private void checkPasswordHistoryLength(int userId, int expectedLen) {
         String history = mService.getString(LockPatternUtils.PASSWORD_HISTORY_KEY, "", userId);
         String[] hashes = TextUtils.split(history, LockPatternUtils.PASSWORD_HISTORY_DELIMITER);