networkstack/tethering/TetheringService.java

/*
 * Copyright (C) 2019 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.networkstack.tethering;

import static android.Manifest.permission.ACCESS_NETWORK_STATE;
import static android.Manifest.permission.NETWORK_STACK;
import static android.Manifest.permission.TETHER_PRIVILEGED;
import static android.content.pm.PackageManager.PERMISSION_GRANTED;
import static android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK;
import static android.net.TetheringManager.TETHER_ERROR_NO_ACCESS_TETHERING_PERMISSION;
import static android.net.TetheringManager.TETHER_ERROR_NO_CHANGE_TETHERING_PERMISSION;
import static android.net.TetheringManager.TETHER_ERROR_NO_ERROR;
import static android.net.TetheringManager.TETHER_ERROR_UNSUPPORTED;
import static android.net.dhcp.IDhcpServer.STATUS_UNKNOWN_ERROR;

import android.app.Service;
import android.bluetooth.BluetoothAdapter;
import android.content.Context;
import android.content.Intent;
import android.net.IIntResultListener;
import android.net.INetworkStackConnector;
import android.net.ITetheringConnector;
import android.net.ITetheringEventCallback;
import android.net.NetworkStack;
import android.net.TetheringRequestParcel;
import android.net.dhcp.DhcpServerCallbacks;
import android.net.dhcp.DhcpServingParamsParcel;
import android.net.ip.IpServer;
import android.os.Binder;
import android.os.HandlerThread;
import android.os.IBinder;
import android.os.Looper;
import android.os.RemoteException;
import android.os.ResultReceiver;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.android.internal.annotations.VisibleForTesting;
import com.android.networkstack.apishim.SettingsShimImpl;
import com.android.networkstack.apishim.common.SettingsShim;

import java.io.FileDescriptor;
import java.io.PrintWriter;

/**
 * Android service used to manage tethering.
 *
 * <p>The service returns a binder for the system server to communicate with the tethering.
 */
public class TetheringService extends Service {
    private static final String TAG = TetheringService.class.getSimpleName();

    private TetheringConnector mConnector;
    private SettingsShim mSettingsShim;

    @Override
    public void onCreate() {
        final TetheringDependencies deps = makeTetheringDependencies();
        // The Tethering object needs a fully functional context to start, so this can't be done
        // in the constructor.
        mConnector = new TetheringConnector(makeTethering(deps), TetheringService.this);

        mSettingsShim = SettingsShimImpl.newInstance();
    }

    /**
     * Make a reference to Tethering object.
     */
    @VisibleForTesting
    public Tethering makeTethering(TetheringDependencies deps) {
        return new Tethering(deps);
    }

    @NonNull
    @Override
    public IBinder onBind(Intent intent) {
        return mConnector;
    }

    private static class TetheringConnector extends ITetheringConnector.Stub {
        private final TetheringService mService;
        private final Tethering mTethering;

        TetheringConnector(Tethering tether, TetheringService service) {
            mTethering = tether;
            mService = service;
        }

        @Override
        public void tether(String iface, String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            mTethering.tether(iface, IpServer.STATE_TETHERED, listener);
        }

        @Override
        public void untether(String iface, String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            mTethering.untether(iface, listener);
        }

        @Override
        public void setUsbTethering(boolean enable, String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            mTethering.setUsbTethering(enable, listener);
        }

        @Override
        public void startTethering(TetheringRequestParcel request, String callerPkg,
                String callingAttributionTag, IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg,
                    callingAttributionTag,
                    request.exemptFromEntitlementCheck /* onlyAllowPrivileged */,
                    listener)) {
                return;
            }

            mTethering.startTethering(request, listener);
        }

        @Override
        public void stopTethering(int type, String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            try {
                mTethering.stopTethering(type);
                listener.onResult(TETHER_ERROR_NO_ERROR);
            } catch (RemoteException e) { }
        }

        @Override
        public void requestLatestTetheringEntitlementResult(int type, ResultReceiver receiver,
                boolean showEntitlementUi, String callerPkg, String callingAttributionTag) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, receiver)) return;

            mTethering.requestLatestTetheringEntitlementResult(type, receiver, showEntitlementUi);
        }

        @Override
        public void registerTetheringEventCallback(ITetheringEventCallback callback,
                String callerPkg) {
            try {
                if (!hasTetherAccessPermission()) {
                    callback.onCallbackStopped(TETHER_ERROR_NO_ACCESS_TETHERING_PERMISSION);
                    return;
                }
                mTethering.registerTetheringEventCallback(callback);
            } catch (RemoteException e) { }
        }

        @Override
        public void unregisterTetheringEventCallback(ITetheringEventCallback callback,
                String callerPkg) {
            try {
                if (!hasTetherAccessPermission()) {
                    callback.onCallbackStopped(TETHER_ERROR_NO_ACCESS_TETHERING_PERMISSION);
                    return;
                }
                mTethering.unregisterTetheringEventCallback(callback);
            } catch (RemoteException e) { }
        }

        @Override
        public void stopAllTethering(String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            try {
                mTethering.untetherAll();
                listener.onResult(TETHER_ERROR_NO_ERROR);
            } catch (RemoteException e) { }
        }

        @Override
        public void isTetheringSupported(String callerPkg, String callingAttributionTag,
                IIntResultListener listener) {
            if (checkAndNotifyCommonError(callerPkg, callingAttributionTag, listener)) return;

            try {
                listener.onResult(TETHER_ERROR_NO_ERROR);
            } catch (RemoteException e) { }
        }

        @Override
        protected void dump(@NonNull FileDescriptor fd, @NonNull PrintWriter writer,
                    @Nullable String[] args) {
            mTethering.dump(fd, writer, args);
        }

        private boolean checkAndNotifyCommonError(final String callerPkg,
                final String callingAttributionTag, final IIntResultListener listener) {
            return checkAndNotifyCommonError(callerPkg, callingAttributionTag,
                    false /* onlyAllowPrivileged */, listener);
        }

        private boolean checkAndNotifyCommonError(final String callerPkg,
                final String callingAttributionTag, final boolean onlyAllowPrivileged,
                final IIntResultListener listener) {
            try {
                if (!hasTetherChangePermission(callerPkg, callingAttributionTag,
                        onlyAllowPrivileged)) {
                    listener.onResult(TETHER_ERROR_NO_CHANGE_TETHERING_PERMISSION);
                    return true;
                }
                if (!mTethering.isTetheringSupported()) {
                    listener.onResult(TETHER_ERROR_UNSUPPORTED);
                    return true;
                }
            } catch (RemoteException e) {
                return true;
            }

            return false;
        }

        private boolean checkAndNotifyCommonError(final String callerPkg,
                final String callingAttributionTag, final ResultReceiver receiver) {
            if (!hasTetherChangePermission(callerPkg, callingAttributionTag,
                    false /* onlyAllowPrivileged */)) {
                receiver.send(TETHER_ERROR_NO_CHANGE_TETHERING_PERMISSION, null);
                return true;
            }
            if (!mTethering.isTetheringSupported()) {
                receiver.send(TETHER_ERROR_UNSUPPORTED, null);
                return true;
            }

            return false;
        }

        private boolean hasNetworkStackPermission() {
            return checkCallingOrSelfPermission(NETWORK_STACK)
                    || checkCallingOrSelfPermission(PERMISSION_MAINLINE_NETWORK_STACK);
        }

        private boolean hasTetherPrivilegedPermission() {
            return checkCallingOrSelfPermission(TETHER_PRIVILEGED);
        }

        private boolean checkCallingOrSelfPermission(final String permission) {
            return mService.checkCallingOrSelfPermission(permission) == PERMISSION_GRANTED;
        }

        private boolean hasTetherChangePermission(final String callerPkg,
                final String callingAttributionTag, final boolean onlyAllowPrivileged) {
            if (onlyAllowPrivileged && !hasNetworkStackPermission()) return false;

            if (hasTetherPrivilegedPermission()) return true;

            if (mTethering.isTetherProvisioningRequired()) return false;

            int uid = Binder.getCallingUid();

            // If callerPkg's uid is not same as Binder.getCallingUid(),
            // checkAndNoteWriteSettingsOperation will return false and the operation will be
            // denied.
            return mService.checkAndNoteWriteSettingsOperation(mService, uid, callerPkg,
                    callingAttributionTag, false /* throwException */);
        }

        private boolean hasTetherAccessPermission() {
            if (hasTetherPrivilegedPermission()) return true;

            return mService.checkCallingOrSelfPermission(
                    ACCESS_NETWORK_STATE) == PERMISSION_GRANTED;
        }
    }

    /**
     * Check if the package is a allowed to write settings. This also accounts that such an access
     * happened.
     *
     * @return {@code true} iff the package is allowed to write settings.
     */
    @VisibleForTesting
    boolean checkAndNoteWriteSettingsOperation(@NonNull Context context, int uid,
            @NonNull String callingPackage, @Nullable String callingAttributionTag,
            boolean throwException) {
        return mSettingsShim.checkAndNoteWriteSettingsOperation(context, uid, callingPackage,
                callingAttributionTag, throwException);
    }

    /**
     * An injection method for testing.
     */
    @VisibleForTesting
    public TetheringDependencies makeTetheringDependencies() {
        return new TetheringDependencies() {
            @Override
            public Looper getTetheringLooper() {
                final HandlerThread tetherThread = new HandlerThread("android.tethering");
                tetherThread.start();
                return tetherThread.getLooper();
            }

            @Override
            public Context getContext() {
                return TetheringService.this;
            }

            @Override
            public IpServer.Dependencies getIpServerDependencies() {
                return new IpServer.Dependencies() {
                    @Override
                    public void makeDhcpServer(String ifName, DhcpServingParamsParcel params,
                            DhcpServerCallbacks cb) {
                        try {
                            final INetworkStackConnector service = getNetworkStackConnector();
                            if (service == null) return;

                            service.makeDhcpServer(ifName, params, cb);
                        } catch (RemoteException e) {
                            Log.e(TAG, "Fail to make dhcp server");
                            try {
                                cb.onDhcpServerCreated(STATUS_UNKNOWN_ERROR, null);
                            } catch (RemoteException re) { }
                        }
                    }
                };
            }

            // TODO: replace this by NetworkStackClient#getRemoteConnector after refactoring
            // networkStackClient.
            static final int NETWORKSTACK_TIMEOUT_MS = 60_000;
            private INetworkStackConnector getNetworkStackConnector() {
                IBinder connector;
                try {
                    final long before = System.currentTimeMillis();
                    while ((connector = NetworkStack.getService()) == null) {
                        if (System.currentTimeMillis() - before > NETWORKSTACK_TIMEOUT_MS) {
                            Log.wtf(TAG, "Timeout, fail to get INetworkStackConnector");
                            return null;
                        }
                        Thread.sleep(200);
                    }
                } catch (InterruptedException e) {
                    Log.wtf(TAG, "Interrupted, fail to get INetworkStackConnector");
                    return null;
                }
                return INetworkStackConnector.Stub.asInterface(connector);
            }

            @Override
            public BluetoothAdapter getBluetoothAdapter() {
                return BluetoothAdapter.getDefaultAdapter();
            }
        };
    }
}