server/backup/PackageManagerBackupAgent.java

/*
 * Copyright (C) 2009 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.server.backup;

import android.app.backup.BackupAgent;
import android.app.backup.BackupDataInput;
import android.app.backup.BackupDataOutput;
import android.content.ComponentName;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.Signature;
import android.os.Build;
import android.os.ParcelFileDescriptor;
import android.util.Slog;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import java.util.Objects;

/**
 * We back up the signatures of each package so that during a system restore,
 * we can verify that the app whose data we think we have matches the app
 * actually resident on the device.
 *
 * Since the Package Manager isn't a proper "application" we just provide a
 * direct IBackupAgent implementation and hand-construct it at need.
 */
public class PackageManagerBackupAgent extends BackupAgent {
    private static final String TAG = "PMBA";
    private static final boolean DEBUG = false;

    // key under which we store global metadata (individual app metadata
    // is stored using the package name as a key)
    private static final String GLOBAL_METADATA_KEY = "@meta@";

    // key under which we store the identity of the user's chosen default home app
    private static final String DEFAULT_HOME_KEY = "@home@";

    // Sentinel: start of state file, followed by a version number
    private static final String STATE_FILE_HEADER = "=state=";
    private static final int STATE_FILE_VERSION = 2;

    // Current version of the saved ancestral-dataset file format
    private static final int ANCESTRAL_RECORD_VERSION = 1;

    private List<PackageInfo> mAllPackages;
    private PackageManager mPackageManager;
    // version & signature info of each app in a restore set
    private HashMap<String, Metadata> mRestoredSignatures;
    // The version info of each backed-up app as read from the state file
    private HashMap<String, Metadata> mStateVersions = new HashMap<String, Metadata>();

    private final HashSet<String> mExisting = new HashSet<String>();
    private int mStoredSdkVersion;
    private String mStoredIncrementalVersion;
    private ComponentName mStoredHomeComponent;
    private long mStoredHomeVersion;
    private ArrayList<byte[]> mStoredHomeSigHashes;

    private boolean mHasMetadata;
    private ComponentName mRestoredHome;
    private long mRestoredHomeVersion;
    private String mRestoredHomeInstaller;
    private ArrayList<byte[]> mRestoredHomeSigHashes;

    // For compactness we store the SHA-256 hash of each app's Signatures
    // rather than the Signature blocks themselves.
    public class Metadata {
        public int versionCode;
        public ArrayList<byte[]> sigHashes;

        Metadata(int version, ArrayList<byte[]> hashes) {
            versionCode = version;
            sigHashes = hashes;
        }
    }

    // We're constructed with the set of applications that are participating
    // in backup.  This set changes as apps are installed & removed.
    PackageManagerBackupAgent(PackageManager packageMgr, List<PackageInfo> packages) {
        init(packageMgr, packages);
    }

    PackageManagerBackupAgent(PackageManager packageMgr) {
        init(packageMgr, null);

        evaluateStorablePackages();
    }

    private void init(PackageManager packageMgr, List<PackageInfo> packages) {
        mPackageManager = packageMgr;
        mAllPackages = packages;
        mRestoredSignatures = null;
        mHasMetadata = false;

        mStoredSdkVersion = Build.VERSION.SDK_INT;
        mStoredIncrementalVersion = Build.VERSION.INCREMENTAL;
    }

    // We will need to refresh our understanding of what is eligible for
    // backup periodically; this entry point serves that purpose.
    public void evaluateStorablePackages() {
        mAllPackages = getStorableApplications(mPackageManager);
    }

    public static List<PackageInfo> getStorableApplications(PackageManager pm) {
        List<PackageInfo> pkgs;
        pkgs = pm.getInstalledPackages(PackageManager.GET_SIGNATURES);
        int N = pkgs.size();
        for (int a = N-1; a >= 0; a--) {
            PackageInfo pkg = pkgs.get(a);
            if (!BackupManagerService.appIsEligibleForBackup(pkg.applicationInfo)) {
                pkgs.remove(a);
            }
        }
        return pkgs;
    }

    public boolean hasMetadata() {
        return mHasMetadata;
    }

    public Metadata getRestoredMetadata(String packageName) {
        if (mRestoredSignatures == null) {
            Slog.w(TAG, "getRestoredMetadata() before metadata read!");
            return null;
        }

        return mRestoredSignatures.get(packageName);
    }

    public Set<String> getRestoredPackages() {
        if (mRestoredSignatures == null) {
            Slog.w(TAG, "getRestoredPackages() before metadata read!");
            return null;
        }

        // This is technically the set of packages on the originating handset
        // that had backup agents at all, not limited to the set of packages
        // that had actually contributed a restore dataset, but it's a
        // close enough approximation for our purposes and does not require any
        // additional involvement by the transport to obtain.
        return mRestoredSignatures.keySet();
    }

    // The backed up data is the signature block for each app, keyed by
    // the package name.
    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
            ParcelFileDescriptor newState) {
        if (DEBUG) Slog.v(TAG, "onBackup()");

        ByteArrayOutputStream outputBuffer = new ByteArrayOutputStream();  // we'll reuse these
        DataOutputStream outputBufferStream = new DataOutputStream(outputBuffer);
        parseStateFile(oldState);

        // If the stored version string differs, we need to re-backup all
        // of the metadata.  We force this by removing everything from the
        // "already backed up" map built by parseStateFile().
        if (mStoredIncrementalVersion == null
                || !mStoredIncrementalVersion.equals(Build.VERSION.INCREMENTAL)) {
            Slog.i(TAG, "Previous metadata " + mStoredIncrementalVersion + " mismatch vs "
                    + Build.VERSION.INCREMENTAL + " - rewriting");
            mExisting.clear();
        }

        long homeVersion = 0;
        ArrayList<byte[]> homeSigHashes = null;
        PackageInfo homeInfo = null;
        String homeInstaller = null;
        ComponentName home = getPreferredHomeComponent();
        if (home != null) {
            try {
                homeInfo = mPackageManager.getPackageInfo(home.getPackageName(),
                        PackageManager.GET_SIGNATURES);
                homeInstaller = mPackageManager.getInstallerPackageName(home.getPackageName());
                homeVersion = homeInfo.versionCode;
                homeSigHashes = hashSignatureArray(homeInfo.signatures);
            } catch (NameNotFoundException e) {
                Slog.w(TAG, "Can't access preferred home info");
                // proceed as though there were no preferred home set
                home = null;
            }
        }

        try {
            // We need to push a new preferred-home-app record if:
            //    1. the version of the home app has changed since our last backup;
            //    2. the home app [or absence] we now use differs from the prior state,
            // OR 3. it looks like we use the same home app + version as before, but
            //       the signatures don't match so we treat them as different apps.
            final boolean needHomeBackup = (homeVersion != mStoredHomeVersion)
                    || !Objects.equals(home, mStoredHomeComponent)
                    || (home != null
                        && !BackupManagerService.signaturesMatch(mStoredHomeSigHashes, homeInfo));
            if (needHomeBackup) {
                if (DEBUG) {
                    Slog.i(TAG, "Home preference changed; backing up new state " + home);
                }
                if (home != null) {
                    outputBufferStream.writeUTF(home.flattenToString());
                    outputBufferStream.writeLong(homeVersion);
                    outputBufferStream.writeUTF(homeInstaller != null ? homeInstaller : "" );
                    writeSignatureHashArray(outputBufferStream, homeSigHashes);
                    writeEntity(data, DEFAULT_HOME_KEY, outputBuffer.toByteArray());
                } else {
                    data.writeEntityHeader(DEFAULT_HOME_KEY, -1);
                }
            }

            /*
             * Global metadata:
             *
             * int SDKversion -- the SDK version of the OS itself on the device
             *                   that produced this backup set.  Used to reject
             *                   backups from later OSes onto earlier ones.
             * String incremental -- the incremental release name of the OS stored in
             *                       the backup set.
             */
            outputBuffer.reset();
            if (!mExisting.contains(GLOBAL_METADATA_KEY)) {
                if (DEBUG) Slog.v(TAG, "Storing global metadata key");
                outputBufferStream.writeInt(Build.VERSION.SDK_INT);
                outputBufferStream.writeUTF(Build.VERSION.INCREMENTAL);
                writeEntity(data, GLOBAL_METADATA_KEY, outputBuffer.toByteArray());
            } else {
                if (DEBUG) Slog.v(TAG, "Global metadata key already stored");
                // don't consider it to have been skipped/deleted
                mExisting.remove(GLOBAL_METADATA_KEY);
            }

            // For each app we have on device, see if we've backed it up yet.  If not,
            // write its signature block to the output, keyed on the package name.
            for (PackageInfo pkg : mAllPackages) {
                String packName = pkg.packageName;
                if (packName.equals(GLOBAL_METADATA_KEY)) {
                    // We've already handled the metadata key; skip it here
                    continue;
                } else {
                    PackageInfo info = null;
                    try {
                        info = mPackageManager.getPackageInfo(packName,
                                PackageManager.GET_SIGNATURES);
                    } catch (NameNotFoundException e) {
                        // Weird; we just found it, and now are told it doesn't exist.
                        // Treat it as having been removed from the device.
                        mExisting.add(packName);
                        continue;
                    }

                    if (mExisting.contains(packName)) {
                        // We have backed up this app before.  Check whether the version
                        // of the backup matches the version of the current app; if they
                        // don't match, the app has been updated and we need to store its
                        // metadata again.  In either case, take it out of mExisting so that
                        // we don't consider it deleted later.
                        mExisting.remove(packName);
                        if (info.versionCode == mStateVersions.get(packName).versionCode) {
                            continue;
                        }
                    }

                    if (info.signatures == null || info.signatures.length == 0)
                    {
                        Slog.w(TAG, "Not backing up package " + packName
                                + " since it appears to have no signatures.");
                        continue;
                    }

                    // We need to store this app's metadata
                    /*
                     * Metadata for each package:
                     *
                     * int version       -- [4] the package's versionCode
                     * byte[] signatures -- [len] flattened signature hash array of the package
                     */

                    // marshal the version code in a canonical form
                    outputBuffer.reset();
                    outputBufferStream.writeInt(info.versionCode);
                    writeSignatureHashArray(outputBufferStream,
                            hashSignatureArray(info.signatures));

                    if (DEBUG) {
                        Slog.v(TAG, "+ writing metadata for " + packName
                                + " version=" + info.versionCode
                                + " entityLen=" + outputBuffer.size());
                    }

                    // Now we can write the backup entity for this package
                    writeEntity(data, packName, outputBuffer.toByteArray());
                }
            }

            // At this point, the only entries in 'existing' are apps that were
            // mentioned in the saved state file, but appear to no longer be present
            // on the device.  Write a deletion entity for them.
            for (String app : mExisting) {
                if (DEBUG) Slog.v(TAG, "- removing metadata for deleted pkg " + app);
                try {
                    data.writeEntityHeader(app, -1);
                } catch (IOException e) {
                    Slog.e(TAG, "Unable to write package deletions!");
                    return;
                }
            }
        } catch (IOException e) {
            // Real error writing data
            Slog.e(TAG, "Unable to write package backup data file!");
            return;
        }

        // Finally, write the new state blob -- just the list of all apps we handled
        writeStateFile(mAllPackages, home, homeVersion, homeSigHashes, newState);
    }

    private static void writeEntity(BackupDataOutput data, String key, byte[] bytes)
            throws IOException {
        data.writeEntityHeader(key, bytes.length);
        data.writeEntityData(bytes, bytes.length);
    }

    // "Restore" here is a misnomer.  What we're really doing is reading back the
    // set of app signatures associated with each backed-up app in this restore
    // image.  We'll use those later to determine what we can legitimately restore.
    public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)
            throws IOException {
        List<ApplicationInfo> restoredApps = new ArrayList<ApplicationInfo>();
        HashMap<String, Metadata> sigMap = new HashMap<String, Metadata>();
        if (DEBUG) Slog.v(TAG, "onRestore()");
        int storedSystemVersion = -1;

        while (data.readNextHeader()) {
            String key = data.getKey();
            int dataSize = data.getDataSize();

            if (DEBUG) Slog.v(TAG, "   got key=" + key + " dataSize=" + dataSize);

            // generic setup to parse any entity data
            byte[] inputBytes = new byte[dataSize];
            data.readEntityData(inputBytes, 0, dataSize);
            ByteArrayInputStream inputBuffer = new ByteArrayInputStream(inputBytes);
            DataInputStream inputBufferStream = new DataInputStream(inputBuffer);

            if (key.equals(GLOBAL_METADATA_KEY)) {
                int storedSdkVersion = inputBufferStream.readInt();
                if (DEBUG) Slog.v(TAG, "   storedSystemVersion = " + storedSystemVersion);
                if (storedSystemVersion > Build.VERSION.SDK_INT) {
                    // returning before setting the sig map means we rejected the restore set
                    Slog.w(TAG, "Restore set was from a later version of Android; not restoring");
                    return;
                }
                mStoredSdkVersion = storedSdkVersion;
                mStoredIncrementalVersion = inputBufferStream.readUTF();
                mHasMetadata = true;
                if (DEBUG) {
                    Slog.i(TAG, "Restore set version " + storedSystemVersion
                            + " is compatible with OS version " + Build.VERSION.SDK_INT
                            + " (" + mStoredIncrementalVersion + " vs "
                            + Build.VERSION.INCREMENTAL + ")");
                }
            } else if (key.equals(DEFAULT_HOME_KEY)) {
                String cn = inputBufferStream.readUTF();
                mRestoredHome = ComponentName.unflattenFromString(cn);
                mRestoredHomeVersion = inputBufferStream.readLong();
                mRestoredHomeInstaller = inputBufferStream.readUTF();
                mRestoredHomeSigHashes = readSignatureHashArray(inputBufferStream);
                if (DEBUG) {
                    Slog.i(TAG, "   read preferred home app " + mRestoredHome
                            + " version=" + mRestoredHomeVersion
                            + " installer=" + mRestoredHomeInstaller
                            + " sig=" + mRestoredHomeSigHashes);
                }
            } else {
                // it's a file metadata record
                int versionCode = inputBufferStream.readInt();
                ArrayList<byte[]> sigs = readSignatureHashArray(inputBufferStream);
                if (DEBUG) {
                    Slog.i(TAG, "   read metadata for " + key
                            + " dataSize=" + dataSize
                            + " versionCode=" + versionCode + " sigs=" + sigs);
                }

                if (sigs == null || sigs.size() == 0) {
                    Slog.w(TAG, "Not restoring package " + key
                            + " since it appears to have no signatures.");
                    continue;
                }

                ApplicationInfo app = new ApplicationInfo();
                app.packageName = key;
                restoredApps.add(app);
                sigMap.put(key, new Metadata(versionCode, sigs));
            }
        }

        // On successful completion, cache the signature map for the Backup Manager to use
        mRestoredSignatures = sigMap;
    }

    private static ArrayList<byte[]> hashSignatureArray(Signature[] sigs) {
        if (sigs == null) {
            return null;
        }

        ArrayList<byte[]> hashes = new ArrayList<byte[]>(sigs.length);
        for (Signature s : sigs) {
            hashes.add(BackupManagerService.hashSignature(s));
        }
        return hashes;
    }

    private static void writeSignatureHashArray(DataOutputStream out, ArrayList<byte[]> hashes)
            throws IOException {
        // the number of entries in the array
        out.writeInt(hashes.size());

        // the hash arrays themselves as length + contents
        for (byte[] buffer : hashes) {
            out.writeInt(buffer.length);
            out.write(buffer);
        }
    }

    private static ArrayList<byte[]> readSignatureHashArray(DataInputStream in) {
        try {
            int num;
            try {
                num = in.readInt();
            } catch (EOFException e) {
                // clean termination
                Slog.w(TAG, "Read empty signature block");
                return null;
            }

            if (DEBUG) Slog.v(TAG, " ... unflatten read " + num);

            // Sensical?
            if (num > 20) {
                Slog.e(TAG, "Suspiciously large sig count in restore data; aborting");
                throw new IllegalStateException("Bad restore state");
            }

            // This could be a "legacy" block of actual signatures rather than their hashes.
            // If this is the case, convert them now.  We judge based on the payload size:
            // if the blocks are all 256 bits (32 bytes) then we take them to be SHA-256 hashes;
            // otherwise we take them to be Signatures.
            boolean nonHashFound = false;
            ArrayList<byte[]> sigs = new ArrayList<byte[]>(num);
            for (int i = 0; i < num; i++) {
                int len = in.readInt();
                byte[] readHash = new byte[len];
                in.read(readHash);
                sigs.add(readHash);
                if (len != 32) {
                    nonHashFound = true;
                }
            }

            if (nonHashFound) {
                ArrayList<byte[]> hashes =
                        new ArrayList<byte[]>(sigs.size());
                for (int i = 0; i < sigs.size(); i++) {
                    Signature s = new Signature(sigs.get(i));
                    hashes.add(BackupManagerService.hashSignature(s));
                }
                sigs = hashes;
            }

            return sigs;
        } catch (IOException e) {
            Slog.e(TAG, "Unable to read signatures");
            return null;
        }
    }

    // Util: parse out an existing state file into a usable structure
    private void parseStateFile(ParcelFileDescriptor stateFile) {
        mExisting.clear();
        mStateVersions.clear();
        mStoredSdkVersion = 0;
        mStoredIncrementalVersion = null;
        mStoredHomeComponent = null;
        mStoredHomeVersion = 0;
        mStoredHomeSigHashes = null;

        // The state file is just the list of app names we have stored signatures for
        // with the exception of the metadata block, to which is also appended the
        // version numbers corresponding with the last time we wrote this PM block.
        // If they mismatch the current system, we'll re-store the metadata key.
        FileInputStream instream = new FileInputStream(stateFile.getFileDescriptor());
        BufferedInputStream inbuffer = new BufferedInputStream(instream);
        DataInputStream in = new DataInputStream(inbuffer);

        try {
            boolean ignoreExisting = false;
            String pkg = in.readUTF();

            // Validate the state file version is sensical to us
            if (pkg.equals(STATE_FILE_HEADER)) {
                int stateVersion = in.readInt();
                if (stateVersion > STATE_FILE_VERSION) {
                    Slog.w(TAG, "Unsupported state file version " + stateVersion
                            + ", redoing from start");
                    return;
                }
                pkg = in.readUTF();
            } else {
                // This is an older version of the state file in which the lead element
                // is not a STATE_FILE_VERSION string.  If that's the case, we want to
                // make sure to write our full backup dataset when given an opportunity.
                // We trigger that by simply not marking the restored package metadata
                // as known-to-exist-in-archive.
                Slog.i(TAG, "Older version of saved state - rewriting");
                ignoreExisting = true;
            }

            // First comes the preferred home app data, if any, headed by the DEFAULT_HOME_KEY tag
            if (pkg.equals(DEFAULT_HOME_KEY)) {
                // flattened component name, version, signature of the home app
                mStoredHomeComponent = ComponentName.unflattenFromString(in.readUTF());
                mStoredHomeVersion = in.readLong();
                mStoredHomeSigHashes = readSignatureHashArray(in);

                pkg = in.readUTF(); // set up for the next block of state
            } else {
                // else no preferred home app on the ancestral device - fall through to the rest
            }

            // After (possible) home app data comes the global metadata block
            if (pkg.equals(GLOBAL_METADATA_KEY)) {
                mStoredSdkVersion = in.readInt();
                mStoredIncrementalVersion = in.readUTF();
                if (!ignoreExisting) {
                    mExisting.add(GLOBAL_METADATA_KEY);
                }
            } else {
                Slog.e(TAG, "No global metadata in state file!");
                return;
            }

            // The global metadata was last; now read all the apps
            while (true) {
                pkg = in.readUTF();
                int versionCode = in.readInt();

                if (!ignoreExisting) {
                    mExisting.add(pkg);
                }
                mStateVersions.put(pkg, new Metadata(versionCode, null));
            }
        } catch (EOFException eof) {
            // safe; we're done
        } catch (IOException e) {
            // whoops, bad state file.  abort.
            Slog.e(TAG, "Unable to read Package Manager state file: " + e);
        }
    }

    private ComponentName getPreferredHomeComponent() {
        return mPackageManager.getHomeActivities(new ArrayList<ResolveInfo>());
    }

    // Util: write out our new backup state file
    private void writeStateFile(List<PackageInfo> pkgs, ComponentName preferredHome,
            long homeVersion, ArrayList<byte[]> homeSigHashes, ParcelFileDescriptor stateFile) {
        FileOutputStream outstream = new FileOutputStream(stateFile.getFileDescriptor());
        BufferedOutputStream outbuf = new BufferedOutputStream(outstream);
        DataOutputStream out = new DataOutputStream(outbuf);

        // by the time we get here we know we've done all our backing up
        try {
            // state file version header
            out.writeUTF(STATE_FILE_HEADER);
            out.writeInt(STATE_FILE_VERSION);

            // If we remembered a preferred home app, record that
            if (preferredHome != null) {
                out.writeUTF(DEFAULT_HOME_KEY);
                out.writeUTF(preferredHome.flattenToString());
                out.writeLong(homeVersion);
                writeSignatureHashArray(out, homeSigHashes);
            }

            // Conclude with the metadata block
            out.writeUTF(GLOBAL_METADATA_KEY);
            out.writeInt(Build.VERSION.SDK_INT);
            out.writeUTF(Build.VERSION.INCREMENTAL);

            // now write all the app names + versions
            for (PackageInfo pkg : pkgs) {
                out.writeUTF(pkg.packageName);
                out.writeInt(pkg.versionCode);
            }

            out.flush();
        } catch (IOException e) {
            Slog.e(TAG, "Unable to write package manager state file!");
        }
    }
}