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Commit 2efd2dbb authored by Christopher Tate's avatar Christopher Tate
Browse files

Support full-backup encryption and global backup password 

If the user has supplied a backup password in Settings, that password
is validated during the full backup process and is used as an encryption
key for encoding the backed-up data itself.  This is the fundamental
mechanism whereby users can secure their data even against malicious
parties getting physical unlocked access to their device.

Technically the user-supplied password is not used as the encryption
key for the backed-up data itself.  What is actually done is that a
random key is generated to use as the raw encryption key.  THAT key,
in turn, is encrypted with the user-supplied password (after random
salting and key expansion with PBKDF2).  The encrypted master key
and a checksum are stored in the backup header.  At restore time,
the user supplies their password, which allows the system to decrypt
the master key, which in turn allows the decryption of the backup
data itself.

The checksum is part of the archive in order to permit validation
of the user-supplied password.  The checksum is the result of running
the user-supplied password through PBKDF2 with a randomly selected
salt.  At restore time, the proposed password is run through PBKDF2
with the salt described by the archive header.  If the result does
not match the archive's stated checksum, then the user has supplied
the wrong decryption password.

Also, suppress backup consideration for a few packages whose
data is either nonexistent or inapplicable across devices or
factory reset operations.

Bug 4901637

Change-Id: Id0cc9d0fdfc046602b129f273d48e23b7a14df36
parent b7d95a46

core/java/android/app/backup/BackupAgent.java

+40 −29
Original line number Diff line number Diff line
@@ -213,13 +213,13 @@ public abstract class BackupAgent extends ContextWrapper { 
    public void onFullBackup(FullBackupDataOutput data) throws IOException {

        ApplicationInfo appInfo = getApplicationInfo();



        String rootDir = new File(appInfo.dataDir).getAbsolutePath();

        String filesDir = getFilesDir().getAbsolutePath();

        String databaseDir = getDatabasePath("foo").getParentFile().getAbsolutePath();

        String sharedPrefsDir = getSharedPrefsFile("foo").getParentFile().getAbsolutePath();

        String cacheDir = getCacheDir().getAbsolutePath();

        String rootDir = new File(appInfo.dataDir).getCanonicalPath();

        String filesDir = getFilesDir().getCanonicalPath();

        String databaseDir = getDatabasePath("foo").getParentFile().getCanonicalPath();

        String sharedPrefsDir = getSharedPrefsFile("foo").getParentFile().getCanonicalPath();

        String cacheDir = getCacheDir().getCanonicalPath();

        String libDir = (appInfo.nativeLibraryDir != null)

                ? new File(appInfo.nativeLibraryDir).getAbsolutePath()

                ? new File(appInfo.nativeLibraryDir).getCanonicalPath()

                : null;



        // Filters, the scan queue, and the set of resulting entities
@@ -271,20 +271,27 @@ public abstract class BackupAgent extends ContextWrapper { 
        String spDir;

        String cacheDir;

        String libDir;

        String filePath;



        ApplicationInfo appInfo = getApplicationInfo();



        mainDir = new File(appInfo.dataDir).getAbsolutePath();

        filesDir = getFilesDir().getAbsolutePath();

        dbDir = getDatabasePath("foo").getParentFile().getAbsolutePath();

        spDir = getSharedPrefsFile("foo").getParentFile().getAbsolutePath();

        cacheDir = getCacheDir().getAbsolutePath();

        libDir = (appInfo.nativeLibraryDir == null) ? null

                : new File(appInfo.nativeLibraryDir).getAbsolutePath();

        try {

            mainDir = new File(appInfo.dataDir).getCanonicalPath();

            filesDir = getFilesDir().getCanonicalPath();

            dbDir = getDatabasePath("foo").getParentFile().getCanonicalPath();

            spDir = getSharedPrefsFile("foo").getParentFile().getCanonicalPath();

            cacheDir = getCacheDir().getCanonicalPath();

            libDir = (appInfo.nativeLibraryDir == null)

                    ? null

                    : new File(appInfo.nativeLibraryDir).getCanonicalPath();



            // Now figure out which well-defined tree the file is placed in, working from

            // most to least specific.  We also specifically exclude the lib and cache dirs.

        String filePath = file.getAbsolutePath();

            filePath = file.getCanonicalPath();

        } catch (IOException e) {

            Log.w(TAG, "Unable to obtain canonical paths");

            return;

        }



        if (filePath.startsWith(cacheDir) || filePath.startsWith(libDir)) {

            Log.w(TAG, "lib and cache files are not backed up");
@@ -334,7 +341,9 @@ public abstract class BackupAgent extends ContextWrapper { 


            while (scanQueue.size() > 0) {

                File file = scanQueue.remove(0);

                String filePath = file.getAbsolutePath();

                String filePath;

                try {

                    filePath = file.getCanonicalPath();



                    // prune this subtree?

                    if (excludes != null && excludes.contains(filePath)) {
@@ -342,7 +351,6 @@ public abstract class BackupAgent extends ContextWrapper { 
                    }



                    // If it's a directory, enqueue its contents for scanning.

                try {

                    StructStat stat = Libcore.os.lstat(filePath);

                    if (OsConstants.S_ISLNK(stat.st_mode)) {

                        if (DEBUG) Log.i(TAG, "Symlink (skipping)!: " + file);
@@ -355,6 +363,9 @@ public abstract class BackupAgent extends ContextWrapper { 
                            }

                        }

                    }

                } catch (IOException e) {

                    if (DEBUG) Log.w(TAG, "Error canonicalizing path of " + file);

                    continue;

                } catch (ErrnoException e) {

                    if (DEBUG) Log.w(TAG, "Error scanning file " + file + " : " + e);

                    continue;
@@ -415,15 +426,15 @@ public abstract class BackupAgent extends ContextWrapper { 


        // Parse out the semantic domains into the correct physical location

        if (domain.equals(FullBackup.DATA_TREE_TOKEN)) {

            basePath = getFilesDir().getAbsolutePath();

            basePath = getFilesDir().getCanonicalPath();

        } else if (domain.equals(FullBackup.DATABASE_TREE_TOKEN)) {

            basePath = getDatabasePath("foo").getParentFile().getAbsolutePath();

            basePath = getDatabasePath("foo").getParentFile().getCanonicalPath();

        } else if (domain.equals(FullBackup.ROOT_TREE_TOKEN)) {

            basePath = new File(getApplicationInfo().dataDir).getAbsolutePath();

            basePath = new File(getApplicationInfo().dataDir).getCanonicalPath();

        } else if (domain.equals(FullBackup.SHAREDPREFS_TREE_TOKEN)) {

            basePath = getSharedPrefsFile("foo").getParentFile().getAbsolutePath();

            basePath = getSharedPrefsFile("foo").getParentFile().getCanonicalPath();

        } else if (domain.equals(FullBackup.CACHE_TREE_TOKEN)) {

            basePath = getCacheDir().getAbsolutePath();

            basePath = getCacheDir().getCanonicalPath();

        } else {

            // Not a supported location

            Log.i(TAG, "Data restored from non-app domain " + domain + ", ignoring");

core/java/android/app/backup/IBackupManager.aidl

+23 −1
Original line number Diff line number Diff line
@@ -110,6 +110,23 @@ interface IBackupManager { 
     */

    boolean isBackupEnabled();



    /**

     * Set the device's backup password.  Returns {@code true} if the password was set

     * successfully, {@code false} otherwise.  Typically a failure means that an incorrect

     * current password was supplied.

     *

     * <p>Callers must hold the android.permission.BACKUP permission to use this method.

     */

    boolean setBackupPassword(in String currentPw, in String newPw);



    /**

     * Reports whether a backup password is currently set.  If not, then a null or empty

     * "current password" argument should be passed to setBackupPassword().

     *

     * <p>Callers must hold the android.permission.BACKUP permission to use this method.

     */

    boolean hasBackupPassword();



    /**

     * Schedule an immediate backup attempt for all pending updates.  This is

     * primarily intended for transports to use when they detect a suitable
@@ -161,9 +178,14 @@ interface IBackupManager { 
     * the same time, the UI supplies a callback Binder for progress notifications during

     * the operation.

     *

     * <p>The password passed by the confirming entity must match the saved backup or

     * full-device encryption password in order to perform a backup.  If a password is

     * supplied for restore, it must match the password used when creating the full

     * backup dataset being used for restore.

     *

     * <p>Callers must hold the android.permission.BACKUP permission to use this method.

     */

    void acknowledgeFullBackupOrRestore(int token, boolean allow,

    void acknowledgeFullBackupOrRestore(int token, boolean allow, in String password,

            IFullBackupRestoreObserver observer);



    /**

packages/BackupRestoreConfirmation/res/layout/confirm_backup.xml

+15 −1
Original line number Diff line number Diff line
@@ -29,11 +29,25 @@ 
              android:layout_marginBottom="30dp"

              android:text="@string/backup_confirm_text" />



    <TextView android:id="@+id/password_desc"

              android:layout_below="@id/confirm_text"

              android:layout_width="wrap_content"

              android:layout_height="wrap_content"

              android:layout_marginBottom="10dp"

              android:text="@string/backup_password_text" />



    <EditText android:id="@+id/password"

              android:layout_below="@id/password_desc"

              android:layout_width="match_parent"

              android:layout_height="wrap_content"

              android:layout_marginBottom="30dp"

              android:password="true" />



    <TextView android:id="@+id/package_name"

              android:layout_width="match_parent"

              android:layout_height="20dp"

              android:layout_marginLeft="30dp"

              android:layout_below="@id/confirm_text"

              android:layout_below="@id/password"

              android:layout_marginBottom="30dp" />



    <Button android:id="@+id/button_allow"

packages/BackupRestoreConfirmation/res/layout/confirm_restore.xml

+15 −1
Original line number Diff line number Diff line
@@ -29,11 +29,25 @@ 
              android:layout_marginBottom="30dp"

              android:text="@string/restore_confirm_text" />



    <TextView android:id="@+id/password_desc"

              android:layout_below="@id/confirm_text"

              android:layout_width="wrap_content"

              android:layout_height="wrap_content"

              android:layout_marginBottom="10dp"

              android:text="@string/restore_password_text" />



    <EditText android:id="@+id/password"

              android:layout_below="@id/password_desc"

              android:layout_width="match_parent"

              android:layout_height="wrap_content"

              android:layout_marginBottom="30dp"

              android:password="true" />



    <TextView android:id="@+id/package_name"

              android:layout_width="match_parent"

              android:layout_height="20dp"

              android:layout_marginLeft="30dp"

              android:layout_below="@id/confirm_text"

              android:layout_below="@id/password"

              android:layout_marginBottom="30dp" />



    <Button android:id="@+id/button_allow"

packages/BackupRestoreConfirmation/res/values/strings.xml

+7 −0
Original line number Diff line number Diff line
@@ -29,4 +29,11 @@ 
    <!-- Button to refuse to allow the requested full restore -->

    <string name="deny_restore_button_label">Do not restore</string>



    <!-- Text for message to user that they must enter their predefined backup password in order to perform this operation. -->

    <string name="backup_password_text">Please enter your predefined backup password below. The full backup will also be encrypted using this password:</string>

    <!-- Text for message to user that they may optionally supply an encryption password to use for a full backup operation. -->

    <string name="backup_password_optional">If you wish to encrypt the full backup data, enter a password below:</string>



    <!-- Text for message to user when performing a full restore operation, explaining that they must enter the password originally used to encrypt the full backup data. -->

    <string name="restore_password_text">If the backup data is encrypted, please enter the password below:</string>

</resources>