/*
 * Copyright (C) 2018 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.internal.telephony;

import static android.content.pm.PackageManager.PERMISSION_GRANTED;

import android.Manifest;
import android.annotation.Nullable;
import android.app.AppOpsManager;
import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.os.Binder;
import android.os.Build;
import android.os.Process;
import android.os.UserHandle;
import android.permission.PermissionManager;
import android.telephony.SubscriptionManager;
import android.telephony.TelephonyManager;
import android.util.Log;

import com.android.internal.annotations.VisibleForTesting;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

/** Utility class for Telephony permission enforcement. */
public final class TelephonyPermissions {
    private static final String LOG_TAG = "TelephonyPermissions";

    private static final boolean DBG = false;

    /**
     * Whether to disable the new device identifier access restrictions.
     */
    private static final String PROPERTY_DEVICE_IDENTIFIER_ACCESS_RESTRICTIONS_DISABLED =
            "device_identifier_access_restrictions_disabled";

    // Contains a mapping of packages that did not meet the new requirements to access device
    // identifiers and the methods they were attempting to invoke; used to prevent duplicate
    // reporting of packages / methods.
    private static final Map<String, Set<String>> sReportedDeviceIDPackages;
    static {
        sReportedDeviceIDPackages = new HashMap<>();
    }

    private TelephonyPermissions() {}

    /**
     * Check whether the caller (or self, if not processing an IPC) can read phone state.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the
     *       READ_PHONE_STATE runtime permission, or carrier privileges on the given subId.
     *   <li>throw SecurityException: if the caller didn't declare any of these permissions, or, for
     *       apps which support runtime permissions, if the caller does not currently have any of
     *       these permissions.
     *   <li>return false: if the caller lacks all of these permissions and doesn't support runtime
     *       permissions. This implies that the user revoked the ability to read phone state
     *       manually (via AppOps). In this case we can't throw as it would break app compatibility,
     *       so we return false to indicate that the calling function should return dummy data.
     * </ul>
     *
     * <p>Note: for simplicity, this method always returns false for callers using legacy
     * permissions and who have had READ_PHONE_STATE revoked, even if they are carrier-privileged.
     * Such apps should migrate to runtime permissions or stop requiring READ_PHONE_STATE on P+
     * devices.
     *
     * @param subId the subId of the relevant subscription; used to check carrier privileges. May be
     *              {@link SubscriptionManager#INVALID_SUBSCRIPTION_ID} to skip this check for cases
     *              where it isn't relevant (hidden APIs, or APIs which are otherwise okay to leave
     *              inaccesible to carrier-privileged apps).
     */
    public static boolean checkCallingOrSelfReadPhoneState(
            Context context, int subId, String callingPackage, @Nullable String callingFeatureId,
            String message) {
        return checkReadPhoneState(context, subId, Binder.getCallingPid(), Binder.getCallingUid(),
                callingPackage, callingFeatureId, message);
    }

    /** Identical to checkCallingOrSelfReadPhoneState but never throws SecurityException */
    public static boolean checkCallingOrSelfReadPhoneStateNoThrow(
            Context context, int subId, String callingPackage, @Nullable String callingFeatureId,
            String message) {
        try {
            return checkCallingOrSelfReadPhoneState(context, subId, callingPackage,
                    callingFeatureId, message);
        } catch (SecurityException se) {
            return false;
        }
    }

    /**
     * Check whether the app with the given pid/uid can read phone state.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the
     *       READ_PHONE_STATE runtime permission, or carrier privileges on the given subId.
     *   <li>throw SecurityException: if the caller didn't declare any of these permissions, or, for
     *       apps which support runtime permissions, if the caller does not currently have any of
     *       these permissions.
     *   <li>return false: if the caller lacks all of these permissions and doesn't support runtime
     *       permissions. This implies that the user revoked the ability to read phone state
     *       manually (via AppOps). In this case we can't throw as it would break app compatibility,
     *       so we return false to indicate that the calling function should return dummy data.
     * </ul>
     *
     * <p>Note: for simplicity, this method always returns false for callers using legacy
     * permissions and who have had READ_PHONE_STATE revoked, even if they are carrier-privileged.
     * Such apps should migrate to runtime permissions or stop requiring READ_PHONE_STATE on P+
     * devices.
     */
    public static boolean checkReadPhoneState(
            Context context, int subId, int pid, int uid, String callingPackage,
            @Nullable  String callingFeatureId, String message) {
        try {
            context.enforcePermission(
                    android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE, pid, uid, message);

            // SKIP checking for run-time permission since caller has PRIVILEGED permission
            return true;
        } catch (SecurityException privilegedPhoneStateException) {
            try {
                context.enforcePermission(
                        android.Manifest.permission.READ_PHONE_STATE, pid, uid, message);
            } catch (SecurityException phoneStateException) {
                // If we don't have the runtime permission, but do have carrier privileges, that
                // suffices for reading phone state.
                if (SubscriptionManager.isValidSubscriptionId(subId)) {
                    enforceCarrierPrivilege(context, subId, uid, message);
                    return true;
                }
                throw phoneStateException;
            }
        }

        // We have READ_PHONE_STATE permission, so return true as long as the AppOps bit hasn't been
        // revoked.
        AppOpsManager appOps = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
        return appOps.noteOp(AppOpsManager.OPSTR_READ_PHONE_STATE, uid, callingPackage,
                callingFeatureId, null) == AppOpsManager.MODE_ALLOWED;
    }

    /**
     * Check whether the calling packages has carrier privileges for the passing subscription.
     * @return {@code true} if the caller has carrier privileges, {@false} otherwise.
     */
    public static boolean checkCarrierPrivilegeForSubId(Context context, int subId) {
        if (SubscriptionManager.isValidSubscriptionId(subId)
                && getCarrierPrivilegeStatus(context, subId, Binder.getCallingUid())
                == TelephonyManager.CARRIER_PRIVILEGE_STATUS_HAS_ACCESS) {
            return true;
        }
        return false;
    }

    /**
     * Check whether the app with the given pid/uid can read phone state, or has carrier
     * privileges on any active subscription.
     *
     * <p>If the app does not have carrier privilege, this method will return {@code false} instead
     * of throwing a SecurityException. Therefore, the callers cannot tell the difference
     * between M+ apps which declare the runtime permission but do not have it, and pre-M apps
     * which declare the static permission but had access revoked via AppOps. Apps in the former
     * category expect SecurityExceptions; apps in the latter don't. So this method is suitable for
     * use only if the behavior in both scenarios is meant to be identical.
     *
     * @return {@code true} if the app can read phone state or has carrier privilege;
     *         {@code false} otherwise.
     */
    public static boolean checkReadPhoneStateOnAnyActiveSub(Context context, int pid, int uid,
            String callingPackage, @Nullable String callingFeatureId, String message) {
        try {
            context.enforcePermission(
                    android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE, pid, uid, message);

            // SKIP checking for run-time permission since caller has PRIVILEGED permission
            return true;
        } catch (SecurityException privilegedPhoneStateException) {
            try {
                context.enforcePermission(
                        android.Manifest.permission.READ_PHONE_STATE, pid, uid, message);
            } catch (SecurityException phoneStateException) {
                // If we don't have the runtime permission, but do have carrier privileges, that
                // suffices for reading phone state.
                return checkCarrierPrivilegeForAnySubId(context, uid);
            }
        }

        // We have READ_PHONE_STATE permission, so return true as long as the AppOps bit hasn't been
        // revoked.
        AppOpsManager appOps = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
        return appOps.noteOp(AppOpsManager.OPSTR_READ_PHONE_STATE, uid, callingPackage,
                callingFeatureId, null) == AppOpsManager.MODE_ALLOWED;
    }

    /**
     * Check whether the caller (or self, if not processing an IPC) can read device identifiers.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the calling
     *       package passes a DevicePolicyManager Device Owner / Profile Owner device identifier
     *       access check, or the calling package has carrier privileges on any active subscription.
    *   <li>throw SecurityException: if the caller does not meet any of the requirements and is
     *       targeting Q or is targeting pre-Q and does not have the READ_PHONE_STATE permission
     *       or carrier privileges of any active subscription.
     *   <li>return false: if the caller is targeting pre-Q and does have the READ_PHONE_STATE
     *       permission. In this case the caller would expect to have access to the device
     *       identifiers so false is returned instead of throwing a SecurityException to indicate
     *       the calling function should return dummy data.
     * </ul>
     */
    public static boolean checkCallingOrSelfReadDeviceIdentifiers(Context context,
            String callingPackage, @Nullable String callingFeatureId, String message) {
        return checkCallingOrSelfReadDeviceIdentifiers(context,
                SubscriptionManager.INVALID_SUBSCRIPTION_ID, callingPackage, callingFeatureId,
                message);
    }

    /**
     * Check whether the caller (or self, if not processing an IPC) can read device identifiers.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the calling
     *       package passes a DevicePolicyManager Device Owner / Profile Owner device identifier
     *       access check, or the calling package has carrier privileges on any active subscription.
     *   <li>throw SecurityException: if the caller does not meet any of the requirements and is
     *       targeting Q or is targeting pre-Q and does not have the READ_PHONE_STATE permission
     *       or carrier privileges of any active subscription.
     *   <li>return false: if the caller is targeting pre-Q and does have the READ_PHONE_STATE
     *       permission or carrier privileges. In this case the caller would expect to have access
     *       to the device identifiers so false is returned instead of throwing a SecurityException
     *       to indicate the calling function should return dummy data.
     * </ul>
     */
    public static boolean checkCallingOrSelfReadDeviceIdentifiers(Context context, int subId,
            String callingPackage, @Nullable String callingFeatureId, String message) {
        return checkPrivilegedReadPermissionOrCarrierPrivilegePermission(
                context, subId, callingPackage, callingFeatureId, message, true);
    }

    /**
     * Check whether the caller (or self, if not processing an IPC) can read subscriber identifiers.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the calling
     *       package passes a DevicePolicyManager Device Owner / Profile Owner device identifier
     *       access check, or the calling package has carrier privileges on specified subscription.
     *   <li>throw SecurityException: if the caller does not meet any of the requirements and is
     *       targeting Q or is targeting pre-Q and does not have the READ_PHONE_STATE permission.
     *   <li>return false: if the caller is targeting pre-Q and does have the READ_PHONE_STATE
     *       permission. In this case the caller would expect to have access to the device
     *       identifiers so false is returned instead of throwing a SecurityException to indicate
     *       the calling function should return dummy data.
     * </ul>
     */
    public static boolean checkCallingOrSelfReadSubscriberIdentifiers(Context context, int subId,
            String callingPackage, @Nullable String callingFeatureId, String message) {
        return checkPrivilegedReadPermissionOrCarrierPrivilegePermission(
                context, subId, callingPackage, callingFeatureId, message, false);
    }

    /**
     * Checks whether the app with the given pid/uid can read device identifiers.
     *
     * <p>This method behaves in one of the following ways:
     * <ul>
     *   <li>return true: if the caller has the READ_PRIVILEGED_PHONE_STATE permission, the calling
     *       package passes a DevicePolicyManager Device Owner / Profile Owner device identifier
     *       access check; or the calling package has carrier privileges on the specified
     *       subscription; or allowCarrierPrivilegeOnAnySub is true and has carrier privilege on
     *       any active subscription.
     *   <li>throw SecurityException: if the caller does not meet any of the requirements and is
     *       targeting Q or is targeting pre-Q and does not have the READ_PHONE_STATE permission.
     *   <li>return false: if the caller is targeting pre-Q and does have the READ_PHONE_STATE
     *       permission. In this case the caller would expect to have access to the device
     *       identifiers so false is returned instead of throwing a SecurityException to indicate
     *       the calling function should return dummy data.
     * </ul>
     */
    private static boolean checkPrivilegedReadPermissionOrCarrierPrivilegePermission(
            Context context, int subId, String callingPackage, @Nullable String callingFeatureId,
            String message, boolean allowCarrierPrivilegeOnAnySub) {
        int uid = Binder.getCallingUid();
        int pid = Binder.getCallingPid();

        // If the calling package has carrier privileges for specified sub, then allow access.
        if (checkCarrierPrivilegeForSubId(context, subId)) return true;

        // If the calling package has carrier privileges for any subscription
        // and allowCarrierPrivilegeOnAnySub is set true, then allow access.
        if (allowCarrierPrivilegeOnAnySub && checkCarrierPrivilegeForAnySubId(context, uid)) {
            return true;
        }

        PermissionManager permissionManager = (PermissionManager) context.getSystemService(
                Context.PERMISSION_SERVICE);
        if (permissionManager.checkDeviceIdentifierAccess(callingPackage, message, callingFeatureId,
                pid, uid) == PackageManager.PERMISSION_GRANTED) {
            return true;
        }

        return reportAccessDeniedToReadIdentifiers(context, subId, pid, uid, callingPackage,
                message);
    }

    /**
     * Reports a failure when the app with the given pid/uid cannot access the requested identifier.
     *
     * @returns false if the caller is targeting pre-Q and does have the READ_PHONE_STATE
     * permission or carrier privileges.
     * @throws SecurityException if the caller does not meet any of the requirements for the
     *                           requested identifier and is targeting Q or is targeting pre-Q
     *                           and does not have the READ_PHONE_STATE permission or carrier
     *                           privileges.
     */
    private static boolean reportAccessDeniedToReadIdentifiers(Context context, int subId, int pid,
            int uid, String callingPackage, String message) {
        ApplicationInfo callingPackageInfo = null;
        try {
            callingPackageInfo = context.getPackageManager().getApplicationInfoAsUser(
                    callingPackage, 0, UserHandle.getUserHandleForUid(uid));
        } catch (PackageManager.NameNotFoundException e) {
            // If the application info for the calling package could not be found then assume the
            // calling app is a non-preinstalled app to detect any issues with the check
            Log.e(LOG_TAG, "Exception caught obtaining package info for package " + callingPackage,
                    e);
        }
        // The current package should only be reported in StatsLog if it has not previously been
        // reported for the currently invoked device identifier method.
        boolean packageReported = sReportedDeviceIDPackages.containsKey(callingPackage);
        if (!packageReported || !sReportedDeviceIDPackages.get(callingPackage).contains(
                message)) {
            Set invokedMethods;
            if (!packageReported) {
                invokedMethods = new HashSet<String>();
                sReportedDeviceIDPackages.put(callingPackage, invokedMethods);
            } else {
                invokedMethods = sReportedDeviceIDPackages.get(callingPackage);
            }
            invokedMethods.add(message);
            TelephonyCommonStatsLog.write(TelephonyCommonStatsLog.DEVICE_IDENTIFIER_ACCESS_DENIED,
                    callingPackage, message, /* isPreinstalled= */ false, false);
        }
        Log.w(LOG_TAG, "reportAccessDeniedToReadIdentifiers:" + callingPackage + ":" + message + ":"
                + subId);
        // if the target SDK is pre-Q then check if the calling package would have previously
        // had access to device identifiers.
        if (callingPackageInfo != null && (
                callingPackageInfo.targetSdkVersion < Build.VERSION_CODES.Q)) {
            if (context.checkPermission(
                    android.Manifest.permission.READ_PHONE_STATE,
                    pid,
                    uid) == PackageManager.PERMISSION_GRANTED) {
                return false;
            }
            if (checkCarrierPrivilegeForSubId(context, subId)) {
                return false;
            }
        }
        throw new SecurityException(message + ": The user " + uid
                + " does not meet the requirements to access device identifiers.");
    }

    /**
     * Check whether the app with the given pid/uid can read the call log.
     * @return {@code true} if the specified app has the read call log permission and AppOpp granted
     *      to it, {@code false} otherwise.
     */
    public static boolean checkReadCallLog(
            Context context, int subId, int pid, int uid, String callingPackage,
            @Nullable String callingPackageName) {
        if (context.checkPermission(Manifest.permission.READ_CALL_LOG, pid, uid)
                != PERMISSION_GRANTED) {
            // If we don't have the runtime permission, but do have carrier privileges, that
            // suffices for being able to see the call phone numbers.
            if (SubscriptionManager.isValidSubscriptionId(subId)) {
                enforceCarrierPrivilege(context, subId, uid, "readCallLog");
                return true;
            }
            return false;
        }

        // We have READ_CALL_LOG permission, so return true as long as the AppOps bit hasn't been
        // revoked.
        AppOpsManager appOps = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
        return appOps.noteOp(AppOpsManager.OPSTR_READ_CALL_LOG, uid, callingPackage,
                callingPackageName, null) == AppOpsManager.MODE_ALLOWED;
    }

    /**
     * Returns whether the caller can read phone numbers.
     *
     * <p>Besides apps with the ability to read phone state per {@link #checkReadPhoneState}
     * (only prior to R), the default SMS app and apps with READ_SMS or READ_PHONE_NUMBERS
     * can also read phone numbers.
     */
    public static boolean checkCallingOrSelfReadPhoneNumber(
            Context context, int subId, String callingPackage, @Nullable String callingFeatureId,
            String message) {
        return checkReadPhoneNumber(
                context, subId, Binder.getCallingPid(), Binder.getCallingUid(),
                callingPackage, callingFeatureId, message);
    }

    /**
     * Returns whether the caller can read phone numbers.
     *
     * <p>Besides apps with the ability to read phone state per {@link #checkReadPhoneState}
     * (only prior to R), the default SMS app and apps with READ_SMS or READ_PHONE_NUMBERS
     * can also read phone numbers.
     */
    @VisibleForTesting
    public static boolean checkReadPhoneNumber(
            Context context, int subId, int pid, int uid,
            String callingPackage, @Nullable String callingFeatureId, String message) {
        // First, check if the SDK version is below R
        boolean preR = false;
        try {
            ApplicationInfo info = context.getPackageManager().getApplicationInfoAsUser(
                    callingPackage, 0, UserHandle.getUserHandleForUid(Binder.getCallingUid()));
            preR = info.targetSdkVersion <= Build.VERSION_CODES.Q;
        } catch (PackageManager.NameNotFoundException nameNotFoundException) {
        }
        if (preR) {
            // SDK < R allows READ_PHONE_STATE, READ_PRIVILEGED_PHONE_STATE, or carrier privilege
            try {
                return checkReadPhoneState(
                        context, subId, pid, uid, callingPackage, callingFeatureId, message);
            } catch (SecurityException readPhoneStateException) {
            }
        } else {
            // SDK >= R allows READ_PRIVILEGED_PHONE_STATE or carrier privilege
            try {
                context.enforcePermission(
                        android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE, pid, uid, message);
                // Skip checking for runtime permission since caller has privileged permission
                return true;
            } catch (SecurityException readPrivilegedPhoneStateException) {
                if (SubscriptionManager.isValidSubscriptionId(subId)) {
                    try {
                        enforceCarrierPrivilege(context, subId, uid, message);
                        // Skip checking for runtime permission since caller has carrier privilege
                        return true;
                    } catch (SecurityException carrierPrivilegeException) {
                    }
                }
            }
        }

        // Default SMS app can always read it.
        AppOpsManager appOps = (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
        if (appOps.noteOp(AppOpsManager.OPSTR_WRITE_SMS, uid, callingPackage, callingFeatureId,
                null) == AppOpsManager.MODE_ALLOWED) {
            return true;
        }
        // Can be read with READ_SMS too.
        try {
            context.enforcePermission(android.Manifest.permission.READ_SMS, pid, uid, message);
            if (appOps.noteOp(AppOpsManager.OPSTR_READ_SMS, uid, callingPackage,
                    callingFeatureId, null) == AppOpsManager.MODE_ALLOWED) {
                return true;
            }
        } catch (SecurityException readSmsSecurityException) {
        }
        // Can be read with READ_PHONE_NUMBERS too.
        try {
            context.enforcePermission(android.Manifest.permission.READ_PHONE_NUMBERS, pid, uid,
                    message);
            if (appOps.noteOp(AppOpsManager.OPSTR_READ_PHONE_NUMBERS, uid, callingPackage,
                    callingFeatureId, null) == AppOpsManager.MODE_ALLOWED) {
                return true;
            }
        } catch (SecurityException readPhoneNumberSecurityException) {
        }

        throw new SecurityException(message + ": Neither user " + uid
                + " nor current process has " + android.Manifest.permission.READ_PHONE_STATE
                + ", " + android.Manifest.permission.READ_SMS + ", or "
                + android.Manifest.permission.READ_PHONE_NUMBERS);
    }

    /**
     * Ensure the caller (or self, if not processing an IPC) has MODIFY_PHONE_STATE (and is thus a
     * privileged app) or carrier privileges.
     *
     * @throws SecurityException if the caller does not have the required permission/privileges
     */
    public static void enforceCallingOrSelfModifyPermissionOrCarrierPrivilege(
            Context context, int subId, String message) {
        if (context.checkCallingOrSelfPermission(android.Manifest.permission.MODIFY_PHONE_STATE)
                == PERMISSION_GRANTED) {
            return;
        }

        if (DBG) Log.d(LOG_TAG, "No modify permission, check carrier privilege next.");
        enforceCallingOrSelfCarrierPrivilege(context, subId, message);
    }

    /**
     * Ensure the caller (or self, if not processing an IPC) has
     * {@link android.Manifest.permission#READ_PHONE_STATE} or carrier privileges.
     *
     * @throws SecurityException if the caller does not have the required permission/privileges
     */
    public static void enforeceCallingOrSelfReadPhoneStatePermissionOrCarrierPrivilege(
            Context context, int subId, String message) {
        if (context.checkCallingOrSelfPermission(android.Manifest.permission.READ_PHONE_STATE)
                == PERMISSION_GRANTED) {
            return;
        }

        if (DBG) {
            Log.d(LOG_TAG, "No READ_PHONE_STATE permission, check carrier privilege next.");
        }

        enforceCallingOrSelfCarrierPrivilege(context, subId, message);
    }

    /**
     * Ensure the caller (or self, if not processing an IPC) has
     * {@link android.Manifest.permission#READ_PRIVILEGED_PHONE_STATE} or carrier privileges.
     *
     * @throws SecurityException if the caller does not have the required permission/privileges
     */
    public static void enforeceCallingOrSelfReadPrivilegedPhoneStatePermissionOrCarrierPrivilege(
            Context context, int subId, String message) {
        if (context.checkCallingOrSelfPermission(Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
                == PERMISSION_GRANTED) {
            return;
        }

        if (DBG) {
            Log.d(LOG_TAG, "No READ_PRIVILEGED_PHONE_STATE permission, "
                    + "check carrier privilege next.");
        }

        enforceCallingOrSelfCarrierPrivilege(context, subId, message);
    }

    /**
     * Ensure the caller (or self, if not processing an IPC) has
     * {@link android.Manifest.permission#READ_PRIVILEGED_PHONE_STATE} or
     * {@link android.Manifest.permission#READ_PRECISE_PHONE_STATE} or carrier privileges.
     *
     * @throws SecurityException if the caller does not have the required permission/privileges
     */
    public static void enforeceCallingOrSelfReadPrecisePhoneStatePermissionOrCarrierPrivilege(
            Context context, int subId, String message) {
        if (context.checkCallingOrSelfPermission(Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
                == PERMISSION_GRANTED) {
            return;
        }

        if (context.checkCallingOrSelfPermission(Manifest.permission.READ_PRECISE_PHONE_STATE)
                == PERMISSION_GRANTED) {
            return;
        }

        if (DBG) {
            Log.d(LOG_TAG, "No READ_PRIVILEGED_PHONE_STATE nor READ_PRECISE_PHONE_STATE permission"
                    + ", check carrier privilege next.");
        }

        enforceCallingOrSelfCarrierPrivilege(context, subId, message);
    }

    /**
     * Make sure the caller (or self, if not processing an IPC) has carrier privileges.
     *
     * @throws SecurityException if the caller does not have the required privileges
     */
    public static void enforceCallingOrSelfCarrierPrivilege(
            Context context, int subId, String message) {
        // NOTE: It's critical that we explicitly pass the calling UID here rather than call
        // TelephonyManager#hasCarrierPrivileges directly, as the latter only works when called from
        // the phone process. When called from another process, it will check whether that process
        // has carrier privileges instead.
        enforceCarrierPrivilege(context, subId, Binder.getCallingUid(), message);
    }

    private static void enforceCarrierPrivilege(
            Context context, int subId, int uid, String message) {
        if (getCarrierPrivilegeStatus(context, subId, uid)
                != TelephonyManager.CARRIER_PRIVILEGE_STATUS_HAS_ACCESS) {
            if (DBG) Log.e(LOG_TAG, "No Carrier Privilege.");
            throw new SecurityException(message);
        }
    }

    /** Returns whether the provided uid has carrier privileges for any active subscription ID. */
    private static boolean checkCarrierPrivilegeForAnySubId(Context context, int uid) {
        SubscriptionManager sm = (SubscriptionManager) context.getSystemService(
                Context.TELEPHONY_SUBSCRIPTION_SERVICE);
        int[] activeSubIds = sm.getCompleteActiveSubscriptionIdList();
        for (int activeSubId : activeSubIds) {
            if (getCarrierPrivilegeStatus(context, activeSubId, uid)
                    == TelephonyManager.CARRIER_PRIVILEGE_STATUS_HAS_ACCESS) {
                return true;
            }
        }
        return false;
    }

    private static int getCarrierPrivilegeStatus(Context context, int subId, int uid) {
        if (uid == Process.SYSTEM_UID || uid == Process.PHONE_UID) {
            // Skip the check if it's one of these special uids
            return TelephonyManager.CARRIER_PRIVILEGE_STATUS_HAS_ACCESS;
        }
        final long identity = Binder.clearCallingIdentity();
        try {
            TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(
                Context.TELEPHONY_SERVICE);
            return telephonyManager.createForSubscriptionId(subId).getCarrierPrivilegeStatus(uid);
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
    }

    /**
     * Throws if the caller is not of a shell (or root) UID.
     *
     * @param callingUid pass Binder.callingUid().
     */
    public static void enforceShellOnly(int callingUid, String message) {
        if (callingUid == Process.SHELL_UID || callingUid == Process.ROOT_UID) {
            return; // okay
        }

        throw new SecurityException(message + ": Only shell user can call it");
    }
}