android/service/trust/TrustAgentService.java

/**
 * Copyright (C) 2014 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 android.service.trust;

import android.Manifest;
import android.annotation.IntDef;
import android.annotation.NonNull;
import android.annotation.SdkConstant;
import android.annotation.SystemApi;
import android.app.Service;
import android.app.admin.DevicePolicyManager;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.content.pm.ServiceInfo;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.PersistableBundle;
import android.os.RemoteException;
import android.os.UserHandle;
import android.os.UserManager;
import android.util.Log;
import android.util.Slog;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.List;

/**
 * A service that notifies the system about whether it believes the environment of the device
 * to be trusted.
 *
 * <p>Trust agents may only be provided by the platform. It is expected that there is only
 * one trust agent installed on the platform. In the event there is more than one,
 * either trust agent can enable trust.
 * </p>
 *
 * <p>To extend this class, you must declare the service in your manifest file with
 * the {@link android.Manifest.permission#BIND_TRUST_AGENT} permission
 * and include an intent filter with the {@link #SERVICE_INTERFACE} action. For example:</p>
 * <pre>
 * &lt;service android:name=".TrustAgent"
 *          android:label="&#64;string/service_name"
 *          android:permission="android.permission.BIND_TRUST_AGENT">
 *     &lt;intent-filter>
 *         &lt;action android:name="android.service.trust.TrustAgentService" />
 *     &lt;/intent-filter>
 *     &lt;meta-data android:name="android.service.trust.trustagent"
 *          android:value="&#64;xml/trust_agent" />
 * &lt;/service></pre>
 *
 * <p>The associated meta-data file can specify an activity that is accessible through Settings
 * and should allow configuring the trust agent, as defined in
 * {@link android.R.styleable#TrustAgent}. For example:</p>
 *
 * <pre>
 * &lt;trust-agent xmlns:android="http://schemas.android.com/apk/res/android"
 *          android:settingsActivity=".TrustAgentSettings" /></pre>
 *
 * @hide
 */
@SystemApi
public class TrustAgentService extends Service {

    private final String TAG = TrustAgentService.class.getSimpleName() +
            "[" + getClass().getSimpleName() + "]";
    private static final boolean DEBUG = false;

    /**
     * The {@link Intent} that must be declared as handled by the service.
     */
    @SdkConstant(SdkConstant.SdkConstantType.SERVICE_ACTION)
    public static final String SERVICE_INTERFACE
            = "android.service.trust.TrustAgentService";

    /**
     * The name of the {@code meta-data} tag pointing to additional configuration of the trust
     * agent.
     */
    public static final String TRUST_AGENT_META_DATA = "android.service.trust.trustagent";


    /**
     * Flag for {@link #grantTrust(CharSequence, long, int)} indicating that trust is being granted
     * as the direct result of user action - such as solving a security challenge. The hint is used
     * by the system to optimize the experience. Behavior may vary by device and release, so
     * one should only set this parameter if it meets the above criteria rather than relying on
     * the behavior of any particular device or release.
     */
    public static final int FLAG_GRANT_TRUST_INITIATED_BY_USER = 1 << 0;

    /**
     * Flag for {@link #grantTrust(CharSequence, long, int)} indicating that the agent would like
     * to dismiss the keyguard. When using this flag, the {@code TrustAgentService} must ensure
     * it is only set in response to a direct user action with the expectation of dismissing the
     * keyguard.
     */
    public static final int FLAG_GRANT_TRUST_DISMISS_KEYGUARD = 1 << 1;

    /** @hide */
    @Retention(RetentionPolicy.SOURCE)
    @IntDef(flag = true, prefix = { "FLAG_GRANT_TRUST_" }, value = {
            FLAG_GRANT_TRUST_INITIATED_BY_USER,
            FLAG_GRANT_TRUST_DISMISS_KEYGUARD,
    })
    public @interface GrantTrustFlags {}


    /**
     * Int enum indicating that escrow token is active.
     * See {@link #onEscrowTokenStateReceived(long, int)}
     *
     */
    public static final int TOKEN_STATE_ACTIVE = 1;

    /**
     * Int enum indicating that escow token is inactive.
     * See {@link #onEscrowTokenStateReceived(long, int)}
     *
     */
    public static final int TOKEN_STATE_INACTIVE = 0;

    /** @hide */
    @Retention(RetentionPolicy.SOURCE)
    @IntDef(flag = true, prefix = { "TOKEN_STATE_" }, value = {
            TOKEN_STATE_ACTIVE,
            TOKEN_STATE_INACTIVE,
    })
    public @interface TokenState {}

    private static final int MSG_UNLOCK_ATTEMPT = 1;
    private static final int MSG_CONFIGURE = 2;
    private static final int MSG_TRUST_TIMEOUT = 3;
    private static final int MSG_DEVICE_LOCKED = 4;
    private static final int MSG_DEVICE_UNLOCKED = 5;
    private static final int MSG_UNLOCK_LOCKOUT = 6;
    private static final int MSG_ESCROW_TOKEN_ADDED = 7;
    private static final int MSG_ESCROW_TOKEN_STATE_RECEIVED = 8;
    private static final int MSG_ESCROW_TOKEN_REMOVED = 9;

    private static final String EXTRA_TOKEN = "token";
    private static final String EXTRA_TOKEN_HANDLE = "token_handle";
    private static final String EXTRA_USER_HANDLE = "user_handle";
    private static final String EXTRA_TOKEN_STATE = "token_state";
    private static final String EXTRA_TOKEN_REMOVED_RESULT = "token_removed_result";
    /**
     * Class containing raw data for a given configuration request.
     */
    private static final class ConfigurationData {
        final IBinder token;
        final List<PersistableBundle> options;
        ConfigurationData(List<PersistableBundle> opts, IBinder t) {
            options = opts;
            token = t;
        }
    }

    private ITrustAgentServiceCallback mCallback;

    private Runnable mPendingGrantTrustTask;

    private boolean mManagingTrust;

    // Lock used to access mPendingGrantTrustTask and mCallback.
    private final Object mLock = new Object();

    private Handler mHandler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            switch (msg.what) {
                case MSG_UNLOCK_ATTEMPT:
                    onUnlockAttempt(msg.arg1 != 0);
                    break;
                case MSG_UNLOCK_LOCKOUT:
                    onDeviceUnlockLockout(msg.arg1);
                    break;
                case MSG_CONFIGURE: {
                    ConfigurationData data = (ConfigurationData) msg.obj;
                    boolean result = onConfigure(data.options);
                    if (data.token != null) {
                        try {
                            synchronized (mLock) {
                                mCallback.onConfigureCompleted(result, data.token);
                            }
                        } catch (RemoteException e) {
                            onError("calling onSetTrustAgentFeaturesEnabledCompleted()");
                        }
                    }
                    break;
                }
                case MSG_TRUST_TIMEOUT:
                    onTrustTimeout();
                    break;
                case MSG_DEVICE_LOCKED:
                    onDeviceLocked();
                    break;
                case MSG_DEVICE_UNLOCKED:
                    onDeviceUnlocked();
                    break;
                case MSG_ESCROW_TOKEN_ADDED: {
                    Bundle data = msg.getData();
                    byte[] token = data.getByteArray(EXTRA_TOKEN);
                    long handle = data.getLong(EXTRA_TOKEN_HANDLE);
                    UserHandle user = (UserHandle) data.getParcelable(EXTRA_USER_HANDLE);
                    onEscrowTokenAdded(token, handle, user);
                    break;
                }
                case MSG_ESCROW_TOKEN_STATE_RECEIVED: {
                    Bundle data = msg.getData();
                    long handle = data.getLong(EXTRA_TOKEN_HANDLE);
                    int tokenState = data.getInt(EXTRA_TOKEN_STATE, TOKEN_STATE_INACTIVE);
                    onEscrowTokenStateReceived(handle, tokenState);
                    break;
                }
                case MSG_ESCROW_TOKEN_REMOVED: {
                    Bundle data = msg.getData();
                    long handle = data.getLong(EXTRA_TOKEN_HANDLE);
                    boolean success = data.getBoolean(EXTRA_TOKEN_REMOVED_RESULT);
                    onEscrowTokenRemoved(handle, success);
                    break;
                }
            }
        }
    };

    @Override
    public void onCreate() {
        super.onCreate();
        ComponentName component = new ComponentName(this, getClass());
        try {
            ServiceInfo serviceInfo = getPackageManager().getServiceInfo(component, 0 /* flags */);
            if (!Manifest.permission.BIND_TRUST_AGENT.equals(serviceInfo.permission)) {
                throw new IllegalStateException(component.flattenToShortString()
                        + " is not declared with the permission "
                        + "\"" + Manifest.permission.BIND_TRUST_AGENT + "\"");
            }
        } catch (PackageManager.NameNotFoundException e) {
            Log.e(TAG, "Can't get ServiceInfo for " + component.toShortString());
        }
    }

    /**
     * Called after the user attempts to authenticate in keyguard with their device credentials,
     * such as pin, pattern or password.
     *
     * @param successful true if the user successfully completed the challenge.
     */
    public void onUnlockAttempt(boolean successful) {
    }

    /**
     * Called when the timeout provided by the agent expires.  Note that this may be called earlier
     * than requested by the agent if the trust timeout is adjusted by the system or
     * {@link DevicePolicyManager}.  The agent is expected to re-evaluate the trust state and only
     * call {@link #grantTrust(CharSequence, long, boolean)} if the trust state should be
     * continued.
     */
    public void onTrustTimeout() {
    }

    /**
     * Called when the device enters a state where a PIN, pattern or
     * password must be entered to unlock it.
     */
    public void onDeviceLocked() {
    }

    /**
     * Called when the device leaves a state where a PIN, pattern or
     * password must be entered to unlock it.
     */
    public void onDeviceUnlocked() {
    }

    /**
     * Called when the device enters a temporary unlock lockout.
     *
     * <p>This occurs when the user has consecutively failed to unlock the device too many times,
     * and must wait until a timeout has passed to perform another attempt. The user may then only
     * use strong authentication mechanisms (PIN, pattern or password) to unlock the device.
     * Calls to {@link #grantTrust(CharSequence, long, int)} will be ignored until the user has
     * unlocked the device and {@link #onDeviceUnlocked()} is called.
     *
     * @param timeoutMs The amount of time, in milliseconds, that needs to elapse before the user
     *    can attempt to unlock the device again.
     */
    public void onDeviceUnlockLockout(long timeoutMs) {
    }

    /**
     * Called when an escrow token is added for user userId.
     *
     * @param token the added token
     * @param handle the handle to the corresponding internal synthetic password. A user is unlocked
     * by presenting both handle and escrow token.
     * @param user the user to which the escrow token is added.
     *
     */
    public void onEscrowTokenAdded(byte[] token, long handle, UserHandle user) {
    }

    /**
     * Called when an escrow token state is received upon request.
     *
     * @param handle the handle to the internal synthetic password.
     * @param state the state of the requested escrow token, see {@link TokenState}.
     *
     */
    public void onEscrowTokenStateReceived(long handle, @TokenState int tokenState) {
    }

    /**
     * Called when an escrow token is removed.
     *
     * @param handle the handle to the removed the synthetic password.
     * @param successful whether the removing operaiton is achieved.
     *
     */
    public void onEscrowTokenRemoved(long handle, boolean successful) {
    }

    private void onError(String msg) {
        Slog.v(TAG, "Remote exception while " + msg);
    }

    /**
     * Called when device policy admin wants to enable specific options for agent in response to
     * {@link DevicePolicyManager#setKeyguardDisabledFeatures(ComponentName, int)} and
     * {@link DevicePolicyManager#setTrustAgentConfiguration(ComponentName, ComponentName,
     * PersistableBundle)}.
     * <p>Agents that support configuration options should overload this method and return 'true'.
     *
     * @param options The aggregated list of options or an empty list if no restrictions apply.
     * @return true if it supports configuration options.
     */
    public boolean onConfigure(List<PersistableBundle> options) {
        return false;
    }

    /**
     * Call to grant trust on the device.
     *
     * @param message describes why the device is trusted, e.g. "Trusted by location".
     * @param durationMs amount of time in milliseconds to keep the device in a trusted state.
     *    Trust for this agent will automatically be revoked when the timeout expires unless
     *    extended by a subsequent call to this function. The timeout is measured from the
     *    invocation of this function as dictated by {@link SystemClock#elapsedRealtime())}.
     *    For security reasons, the value should be no larger than necessary.
     *    The value may be adjusted by the system as necessary to comply with a policy controlled
     *    by the system or {@link DevicePolicyManager} restrictions. See {@link #onTrustTimeout()}
     *    for determining when trust expires.
     * @param initiatedByUser this is a hint to the system that trust is being granted as the
     *    direct result of user action - such as solving a security challenge. The hint is used
     *    by the system to optimize the experience. Behavior may vary by device and release, so
     *    one should only set this parameter if it meets the above criteria rather than relying on
     *    the behavior of any particular device or release. Corresponds to
     *    {@link #FLAG_GRANT_TRUST_INITIATED_BY_USER}.
     * @throws IllegalStateException if the agent is not currently managing trust.
     *
     * @deprecated use {@link #grantTrust(CharSequence, long, int)} instead.
     */
    @Deprecated
    public final void grantTrust(
            final CharSequence message, final long durationMs, final boolean initiatedByUser) {
        grantTrust(message, durationMs, initiatedByUser ? FLAG_GRANT_TRUST_INITIATED_BY_USER : 0);
    }

    /**
     * Call to grant trust on the device.
     *
     * @param message describes why the device is trusted, e.g. "Trusted by location".
     * @param durationMs amount of time in milliseconds to keep the device in a trusted state.
     *    Trust for this agent will automatically be revoked when the timeout expires unless
     *    extended by a subsequent call to this function. The timeout is measured from the
     *    invocation of this function as dictated by {@link SystemClock#elapsedRealtime())}.
     *    For security reasons, the value should be no larger than necessary.
     *    The value may be adjusted by the system as necessary to comply with a policy controlled
     *    by the system or {@link DevicePolicyManager} restrictions. See {@link #onTrustTimeout()}
     *    for determining when trust expires.
     * @param flags TBDocumented
     * @throws IllegalStateException if the agent is not currently managing trust.
     */
    public final void grantTrust(
            final CharSequence message, final long durationMs, @GrantTrustFlags final int flags) {
        synchronized (mLock) {
            if (!mManagingTrust) {
                throw new IllegalStateException("Cannot grant trust if agent is not managing trust."
                        + " Call setManagingTrust(true) first.");
            }
            if (mCallback != null) {
                try {
                    mCallback.grantTrust(message.toString(), durationMs, flags);
                } catch (RemoteException e) {
                    onError("calling enableTrust()");
                }
            } else {
                // Remember trust has been granted so we can effectively grant it once the service
                // is bound.
                mPendingGrantTrustTask = new Runnable() {
                    @Override
                    public void run() {
                        grantTrust(message, durationMs, flags);
                    }
                };
            }
        }
    }

    /**
     * Call to revoke trust on the device.
     */
    public final void revokeTrust() {
        synchronized (mLock) {
            if (mPendingGrantTrustTask != null) {
                mPendingGrantTrustTask = null;
            }
            if (mCallback != null) {
                try {
                    mCallback.revokeTrust();
                } catch (RemoteException e) {
                    onError("calling revokeTrust()");
                }
            }
        }
    }

    /**
     * Call to notify the system if the agent is ready to manage trust.
     *
     * This property is not persistent across recreating the service and defaults to false.
     * Therefore this method is typically called when initializing the agent in {@link #onCreate}.
     *
     * @param managingTrust indicates if the agent would like to manage trust.
     */
    public final void setManagingTrust(boolean managingTrust) {
        synchronized (mLock) {
            if (mManagingTrust != managingTrust) {
                mManagingTrust = managingTrust;
                if (mCallback != null) {
                    try {
                        mCallback.setManagingTrust(managingTrust);
                    } catch (RemoteException e) {
                        onError("calling setManagingTrust()");
                    }
                }
            }
        }
    }

    /**
     * Call to add an escrow token to derive a synthetic password. A synthetic password is an
     * alternaive to the user-set password/pin/pattern in order to unlock encrypted disk. An escrow
     * token can be taken and internally derive the synthetic password. The new added token will not
     * be acivated until the user input the correct PIN/Passcode/Password once.
     *
     * Result will be return by callback {@link #onEscrowTokenAdded(long, int)}
     *
     * @param token an escrow token of high entropy.
     * @param user the user which the escrow token will be added to.
     *
     */
    public final void addEscrowToken(byte[] token, UserHandle user) {
        synchronized (mLock) {
            if (mCallback == null) {
                Slog.w(TAG, "Cannot add escrow token if the agent is not connecting to framework");
                throw new IllegalStateException("Trust agent is not connected");
            }
            try {
                mCallback.addEscrowToken(token, user.getIdentifier());
            } catch (RemoteException e) {
                onError("calling addEscrowToken");
            }
        }
    }

    /**
     * Call to check the active state of an escrow token.
     *
     * Result will be return in callback {@link #onEscrowTokenStateReceived(long, boolean)}
     *
     * @param handle the handle of escrow token to the internal synthetic password.
     * @param user the user which the escrow token is added to.
     *
     */
    public final void isEscrowTokenActive(long handle, UserHandle user) {
        synchronized (mLock) {
            if (mCallback == null) {
                Slog.w(TAG, "Cannot add escrow token if the agent is not connecting to framework");
                throw new IllegalStateException("Trust agent is not connected");
            }
            try {
                mCallback.isEscrowTokenActive(handle, user.getIdentifier());
            } catch (RemoteException e) {
                onError("calling isEscrowTokenActive");
            }
        }
    }

    /**
     * Call to remove the escrow token.
     *
     * Result will be return in callback {@link #onEscrowTokenRemoved(long, boolean)}
     *
     * @param handle the handle of escrow tokent to the internal synthetic password.
     * @param user the user id which the escrow token is added to.
     *
     */
    public final void removeEscrowToken(long handle, UserHandle user) {
        synchronized (mLock) {
            if (mCallback == null) {
                Slog.w(TAG, "Cannot add escrow token if the agent is not connecting to framework");
                throw new IllegalStateException("Trust agent is not connected");
            }
            try {
                mCallback.removeEscrowToken(handle, user.getIdentifier());
            } catch (RemoteException e) {
                onError("callling removeEscrowToken");
            }
        }
    }

    /**
     * Call to unlock user's FBE.
     *
     * @param handle the handle of escrow tokent to the internal synthetic password.
     * @param token the escrow token
     * @param user the user about to be unlocked.
     *
     */
    public final void unlockUserWithToken(long handle, byte[] token, UserHandle user) {
        UserManager um = (UserManager) getSystemService(Context.USER_SERVICE);
        if (um.isUserUnlocked(user)) {
            Slog.i(TAG, "User already unlocked");
            return;
        }

        synchronized (mLock) {
            if (mCallback == null) {
                Slog.w(TAG, "Cannot add escrow token if the agent is not connecting to framework");
                throw new IllegalStateException("Trust agent is not connected");
            }
            try {
                mCallback.unlockUserWithToken(handle, token, user.getIdentifier());
            } catch (RemoteException e) {
                onError("calling unlockUserWithToken");
            }
        }
    }

    /**
     * Request showing a transient error message on the keyguard.
     * The message will be visible on the lock screen or always on display if possible but can be
     * overridden by other keyguard events of higher priority - eg. fingerprint auth error.
     * Other trust agents may override your message if posted simultaneously.
     *
     * @param message Message to show.
     */
    public final void showKeyguardErrorMessage(@NonNull CharSequence message) {
        if (message == null) {
            throw new IllegalArgumentException("message cannot be null");
        }
        synchronized (mLock) {
            if (mCallback == null) {
                Slog.w(TAG, "Cannot show message because service is not connected to framework.");
                throw new IllegalStateException("Trust agent is not connected");
            }
            try {
                mCallback.showKeyguardErrorMessage(message);
            } catch (RemoteException e) {
                onError("calling showKeyguardErrorMessage");
            }
        }
    }

    @Override
    public final IBinder onBind(Intent intent) {
        if (DEBUG) Slog.v(TAG, "onBind() intent = " + intent);
        return new TrustAgentServiceWrapper();
    }

    private final class TrustAgentServiceWrapper extends ITrustAgentService.Stub {
        @Override /* Binder API */
        public void onUnlockAttempt(boolean successful) {
            mHandler.obtainMessage(MSG_UNLOCK_ATTEMPT, successful ? 1 : 0, 0).sendToTarget();
        }

        @Override
        public void onUnlockLockout(int timeoutMs) {
            mHandler.obtainMessage(MSG_UNLOCK_LOCKOUT, timeoutMs, 0).sendToTarget();
        }

        @Override /* Binder API */
        public void onTrustTimeout() {
            mHandler.sendEmptyMessage(MSG_TRUST_TIMEOUT);
        }

        @Override /* Binder API */
        public void onConfigure(List<PersistableBundle> args, IBinder token) {
            mHandler.obtainMessage(MSG_CONFIGURE, new ConfigurationData(args, token))
                    .sendToTarget();
        }

        @Override
        public void onDeviceLocked() throws RemoteException {
            mHandler.obtainMessage(MSG_DEVICE_LOCKED).sendToTarget();
        }

        @Override
        public void onDeviceUnlocked() throws RemoteException {
            mHandler.obtainMessage(MSG_DEVICE_UNLOCKED).sendToTarget();
        }

        @Override /* Binder API */
        public void setCallback(ITrustAgentServiceCallback callback) {
            synchronized (mLock) {
                mCallback = callback;
                // The managingTrust property is false implicitly on the server-side, so we only
                // need to set it here if the agent has decided to manage trust.
                if (mManagingTrust) {
                    try {
                        mCallback.setManagingTrust(mManagingTrust);
                    } catch (RemoteException e ) {
                        onError("calling setManagingTrust()");
                    }
                }
                if (mPendingGrantTrustTask != null) {
                    mPendingGrantTrustTask.run();
                    mPendingGrantTrustTask = null;
                }
            }
        }

        @Override
        public void onEscrowTokenAdded(byte[] token, long handle, UserHandle user) {
            Message msg = mHandler.obtainMessage(MSG_ESCROW_TOKEN_ADDED);
            msg.getData().putByteArray(EXTRA_TOKEN, token);
            msg.getData().putLong(EXTRA_TOKEN_HANDLE, handle);
            msg.getData().putParcelable(EXTRA_USER_HANDLE, user);
            msg.sendToTarget();
        }

        public void onTokenStateReceived(long handle, int tokenState) {
            Message msg = mHandler.obtainMessage(MSG_ESCROW_TOKEN_STATE_RECEIVED);
            msg.getData().putLong(EXTRA_TOKEN_HANDLE, handle);
            msg.getData().putInt(EXTRA_TOKEN_STATE, tokenState);
            msg.sendToTarget();
        }

        public void onEscrowTokenRemoved(long handle, boolean successful) {
            Message msg = mHandler.obtainMessage(MSG_ESCROW_TOKEN_REMOVED);
            msg.getData().putLong(EXTRA_TOKEN_HANDLE, handle);
            msg.getData().putBoolean(EXTRA_TOKEN_REMOVED_RESULT, successful);
            msg.sendToTarget();
        }
    }
}