src/com/android/providers/media/util/PermissionUtils.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.providers.media.util;

import static android.Manifest.permission.BACKUP;
import static android.Manifest.permission.READ_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_MEDIA_STORAGE;
import static android.app.AppOpsManager.MODE_ALLOWED;
import static android.app.AppOpsManager.OPSTR_LEGACY_STORAGE;
import static android.app.AppOpsManager.OPSTR_READ_EXTERNAL_STORAGE;
import static android.app.AppOpsManager.OPSTR_READ_MEDIA_AUDIO;
import static android.app.AppOpsManager.OPSTR_READ_MEDIA_IMAGES;
import static android.app.AppOpsManager.OPSTR_READ_MEDIA_VIDEO;
import static android.app.AppOpsManager.OPSTR_WRITE_EXTERNAL_STORAGE;
import static android.app.AppOpsManager.OPSTR_WRITE_MEDIA_AUDIO;
import static android.app.AppOpsManager.OPSTR_WRITE_MEDIA_IMAGES;
import static android.app.AppOpsManager.OPSTR_WRITE_MEDIA_VIDEO;
import static android.content.pm.PackageManager.PERMISSION_GRANTED;

import android.app.AppOpsManager;
import android.content.Context;

public class PermissionUtils {
    // Callers must hold both the old and new permissions, so that we can
    // handle obscure cases like when an app targets Q but was installed on
    // a device that was originally running on P before being upgraded to Q.

    public static boolean checkPermissionSystem(Context context,
            int pid, int uid, String packageName) {
        if (uid == android.os.Process.SYSTEM_UID) {
            return true;
        }

        // Special case to speed up when MediaProvider is calling itself; we
        // know it always has system permissions
        if (uid == android.os.Process.myUid()) {
            return true;
        }

        // Determine if caller is holding runtime permission
        final boolean hasStorage = checkPermissionAndAppOp(context, pid,
                uid, packageName, WRITE_EXTERNAL_STORAGE, OPSTR_WRITE_EXTERNAL_STORAGE);

        // We're only willing to give out broad access if they also hold
        // runtime permission; this is a firm CDD requirement
        final boolean hasFull = context
                .checkPermission(WRITE_MEDIA_STORAGE, pid, uid) == PERMISSION_GRANTED;

        return hasFull && hasStorage;
    }

    public static boolean checkPermissionBackup(Context context, int pid, int uid) {
        return context.checkPermission(BACKUP, pid, uid) == PERMISSION_GRANTED;
    }

    public static boolean checkPermissionWriteStorage(Context context,
            int pid, int uid, String packageName) {
        return checkPermissionAndAppOp(context, pid,
                uid, packageName, WRITE_EXTERNAL_STORAGE, OPSTR_WRITE_EXTERNAL_STORAGE);
    }

    public static boolean checkPermissionReadStorage(Context context,
            int pid, int uid, String packageName) {
        return checkPermissionAndAppOp(context, pid,
                uid, packageName, READ_EXTERNAL_STORAGE, OPSTR_READ_EXTERNAL_STORAGE);
    }

    public static boolean checkIsLegacyStorageGranted(Context context, int uid,
            String packageName) {
        return context.getSystemService(AppOpsManager.class)
                .unsafeCheckOp(OPSTR_LEGACY_STORAGE, uid, packageName) == MODE_ALLOWED;
    }

    public static boolean checkPermissionReadAudio(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                READ_EXTERNAL_STORAGE, OPSTR_READ_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_READ_MEDIA_AUDIO);
    }

    public static boolean checkPermissionWriteAudio(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                WRITE_EXTERNAL_STORAGE, OPSTR_WRITE_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_WRITE_MEDIA_AUDIO);
    }

    public static boolean checkPermissionReadVideo(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                READ_EXTERNAL_STORAGE, OPSTR_READ_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_READ_MEDIA_VIDEO);
    }

    public static boolean checkPermissionWriteVideo(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                WRITE_EXTERNAL_STORAGE, OPSTR_WRITE_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_WRITE_MEDIA_VIDEO);
    }

    public static boolean checkPermissionReadImages(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                READ_EXTERNAL_STORAGE, OPSTR_READ_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_READ_MEDIA_IMAGES);
    }

    public static boolean checkPermissionWriteImages(Context context,
            int pid, int uid, String packageName) {
        if (!checkPermissionAndAppOp(context, pid, uid, packageName,
                WRITE_EXTERNAL_STORAGE, OPSTR_WRITE_EXTERNAL_STORAGE)) return false;
        return noteAppOpAllowingLegacy(context, pid, uid, packageName,
                OPSTR_WRITE_MEDIA_IMAGES);
    }

    private static boolean checkPermissionAndAppOp(Context context,
            int pid, int uid, String packageName, String permission, String op) {
        if (context.checkPermission(permission, pid, uid) != PERMISSION_GRANTED) {
            return false;
        }

        final AppOpsManager appOps = context.getSystemService(AppOpsManager.class);
        try {
            appOps.checkPackage(uid, packageName);
        } catch (SecurityException e) {
            return false;
        }

        final int mode = appOps.unsafeCheckOpNoThrow(op, uid, packageName);
        switch (mode) {
            case AppOpsManager.MODE_ALLOWED:
                return true;
            case AppOpsManager.MODE_DEFAULT:
            case AppOpsManager.MODE_IGNORED:
            case AppOpsManager.MODE_ERRORED:
                return false;
            default:
                throw new IllegalStateException(op + " has unknown mode " + mode);
        }
    }

    private static boolean noteAppOpAllowingLegacy(Context context,
            int pid, int uid, String packageName, String op) {
        final AppOpsManager appOps = context.getSystemService(AppOpsManager.class);
        final int mode = appOps.noteOpNoThrow(op, uid, packageName);
        switch (mode) {
            case AppOpsManager.MODE_ALLOWED:
                return true;
            case AppOpsManager.MODE_DEFAULT:
            case AppOpsManager.MODE_IGNORED:
            case AppOpsManager.MODE_ERRORED:
                // Legacy apps technically have the access granted by this op,
                // even when the op is denied
                if ((appOps.unsafeCheckOpNoThrow(OPSTR_LEGACY_STORAGE, uid,
                        packageName) == AppOpsManager.MODE_ALLOWED)) return true;

                return false;
            default:
                throw new IllegalStateException(op + " has unknown mode " + mode);
        }
    }
}