Add toggle to allow or disable null algorithms

This adds the allow null algorithms toogle to the Settings UI.

If supported by the smartphone baseband, the toggle allows users to opt
out of null algorithms, unencrypted cellular communication, for all
cellular generations.

This toggle is behind a feature flag that is off by default. It also
requires radio network HAL 2.1 or later to show.

Co-authored-by: Gil Cukierman <cukie@google.com>
Bug: b/237529943
Test: atest NullAlgorithmsPreferenceControllerTest
Test: adb shell device_config put cellular_security
enable_null_cipher_toggle true; // On cuttlefish, you can now see the
toggle in SIM settings.

Change-Id: Ia03cceee5463171ca455fa0624b911e06f222d2d

src/com/android/settings/network/telephony/NullAlgorithmsPreferenceController.java

@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.settings.network.telephony;
+
+import android.content.Context;
+import android.provider.DeviceConfig;
+import android.telephony.TelephonyManager;
+import android.util.Log;
+
+/**
+ * Preference controller for "Allow Null Algorithms"
+ *
+ * <p>This preference controller is toggling null algorithms is not a per-sim operation.
+ */
+public class NullAlgorithmsPreferenceController extends TelephonyTogglePreferenceController {
+
+    // log tags have a char limit of 24 so we can't use the class name
+    private static final String LOG_TAG = "NullAlgosController";
+
+    private TelephonyManager mTelephonyManager;
+
+    /**
+     * Class constructor of "Allow Null Algorithms" toggle.
+     *
+     * @param context of settings
+     * @param key     assigned within UI entry of XML file
+     */
+    public NullAlgorithmsPreferenceController(Context context, String key) {
+        super(context, key);
+        mTelephonyManager = mContext.getSystemService(TelephonyManager.class);
+    }
+
+    /**
+     * Get the {@link com.android.settings.core.BasePreferenceController.AvailabilityStatus} for
+     * this preference given a {@code subId}. This dictates whether the setting is available on
+     * the device, and if it is not, offers some context as to why.
+     */
+    @Override
+    public int getAvailabilityStatus(int subId) {
+        if (mTelephonyManager == null) {
+            Log.w(LOG_TAG,
+                    "Telephony manager not yet initialized. Marking availability as "
+                            + "CONDITIONALLY_UNAVAILABLE");
+            mTelephonyManager = mContext.getSystemService(TelephonyManager.class);
+            return CONDITIONALLY_UNAVAILABLE;
+        }
+
+        if (!DeviceConfig.getBoolean(DeviceConfig.NAMESPACE_CELLULAR_SECURITY,
+                TelephonyManager.PROPERTY_ENABLE_NULL_CIPHER_TOGGLE, false)) {
+            Log.i(LOG_TAG, "Null cipher toggle is disabled by DeviceConfig");
+            return CONDITIONALLY_UNAVAILABLE;
+        }
+
+        try {
+            mTelephonyManager.isNullCipherAndIntegrityPreferenceEnabled();
+        } catch (UnsupportedOperationException e) {
+            Log.i(LOG_TAG, "Null cipher enablement is unsupported: " + e.getMessage());
+            return UNSUPPORTED_ON_DEVICE;
+        }
+
+        return AVAILABLE;
+    }
+
+    /**
+     * Return {@code true} if null algorithms are currently allowed.
+     *
+     * <p><b>NOTE:</b> This method returns the active state of the preference controller and is not
+     * the parameter passed into {@link #setChecked(boolean)}, which is instead the requested future
+     * state.
+     */
+    @Override
+    public boolean isChecked() {
+        return mTelephonyManager.isNullCipherAndIntegrityPreferenceEnabled();
+    }
+
+    /**
+     * Called when a user preference changes on the toggle. We pass this info on to the Telephony
+     * Framework so that the modem can be updated with the user's preference.
+     *
+     * <p>See {@link com.android.settings.core.TogglePreferenceController#setChecked(boolean)} for
+     * details.
+     *
+     * @param isChecked The toggle value that we're being requested to enforce. A value of {@code
+     *                  false} denotes that null ciphers will be disabled by the modem after this
+     *                  function
+     *                  completes, if it is not already.
+     */
+    @Override
+    public boolean setChecked(boolean isChecked) {
+        if (isChecked) {
+            Log.i(LOG_TAG, "Enabling null algorithms");
+        } else {
+            Log.i(LOG_TAG, "Disabling null algorithms");
+        }
+        mTelephonyManager.setNullCipherAndIntegrityEnabled(isChecked);
+        return true;
+    }
+}