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/*
* 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 com.android.server;
import android.Manifest;
import android.app.ActivityManager;
import android.content.Context;
import android.content.pm.PackageManager;
import android.os.Binder;
import android.os.IBinder;
import android.os.RemoteException;
import android.os.SystemProperties;
import android.os.UserHandle;
import android.service.persistentdata.IPersistentDataBlockService;
import android.util.Slog;
import com.android.internal.R;
import libcore.io.IoUtils;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
/**
* Service for reading and writing blocks to a persistent partition.
* This data will live across factory resets not initiated via the Settings UI.
* When a device is factory reset through Settings this data is wiped.
*
* Allows writing one block at a time. Namely, each time
* {@link android.service.persistentdata.IPersistentDataBlockService}.write(byte[] data)
* is called, it will overwite the data that was previously written on the block.
*
* Clients can query the size of the currently written block via
* {@link android.service.persistentdata.IPersistentDataBlockService}.getTotalDataSize().
*
* Clients can any number of bytes from the currently written block up to its total size by invoking
* {@link android.service.persistentdata.IPersistentDataBlockService}.read(byte[] data)
*/
public class PersistentDataBlockService extends SystemService {
private static final String TAG = PersistentDataBlockService.class.getSimpleName();
private static final String PERSISTENT_DATA_BLOCK_PROP = "ro.frp.pst";
private static final int HEADER_SIZE = 8;
// Magic number to mark block device as adhering to the format consumed by this service
private static final int PARTITION_TYPE_MARKER = 0x19901873;
// Limit to 100k as blocks larger than this might cause strain on Binder.
private static final int MAX_DATA_BLOCK_SIZE = 1024 * 100;
public static final int DIGEST_SIZE_BYTES = 32;
private final Context mContext;
private final String mDataBlockFile;
private final Object mLock = new Object();
private int mAllowedUid = -1;
private long mBlockDeviceSize;
public PersistentDataBlockService(Context context) {
super(context);
mContext = context;
mDataBlockFile = SystemProperties.get(PERSISTENT_DATA_BLOCK_PROP);
mBlockDeviceSize = -1; // Load lazily
mAllowedUid = getAllowedUid(UserHandle.USER_OWNER);
}
private int getAllowedUid(int userHandle) {
String allowedPackage = mContext.getResources()
.getString(R.string.config_persistentDataPackageName);
PackageManager pm = mContext.getPackageManager();
int allowedUid = -1;
try {
allowedUid = pm.getPackageUid(allowedPackage, userHandle);
} catch (PackageManager.NameNotFoundException e) {
// not expected
Slog.e(TAG, "not able to find package " + allowedPackage, e);
}
return allowedUid;
}
@Override
public void onStart() {
enforceChecksumValidity();
formatIfOemUnlockEnabled();
publishBinderService(Context.PERSISTENT_DATA_BLOCK_SERVICE, mService);
}
private void formatIfOemUnlockEnabled() {
if (doGetOemUnlockEnabled()) {
synchronized (mLock) {
formatPartitionLocked();
doSetOemUnlockEnabledLocked(true);
}
}
}
private void enforceOemUnlockPermission() {
mContext.enforceCallingOrSelfPermission(
Manifest.permission.OEM_UNLOCK_STATE,
"Can't access OEM unlock state");
}
private void enforceUid(int callingUid) {
if (callingUid != mAllowedUid) {
throw new SecurityException("uid " + callingUid + " not allowed to access PST");
}
}
private void enforceIsOwner() {
if (!Binder.getCallingUserHandle().isOwner()) {
throw new SecurityException("Only the Owner is allowed to change OEM unlock state");
}
}
private int getTotalDataSizeLocked(DataInputStream inputStream) throws IOException {
// skip over checksum
inputStream.skipBytes(DIGEST_SIZE_BYTES);
int totalDataSize;
int blockId = inputStream.readInt();
if (blockId == PARTITION_TYPE_MARKER) {
totalDataSize = inputStream.readInt();
} else {
totalDataSize = 0;
}
return totalDataSize;
}
private long getBlockDeviceSize() {
synchronized (mLock) {
if (mBlockDeviceSize == -1) {
mBlockDeviceSize = nativeGetBlockDeviceSize(mDataBlockFile);
}
}
return mBlockDeviceSize;
}
private boolean enforceChecksumValidity() {
byte[] storedDigest = new byte[DIGEST_SIZE_BYTES];
synchronized (mLock) {
byte[] digest = computeDigestLocked(storedDigest);
if (digest == null || !Arrays.equals(storedDigest, digest)) {
Slog.i(TAG, "Formatting FRP partition...");
formatPartitionLocked();
return false;
}
}
return true;
}
private boolean computeAndWriteDigestLocked() {
byte[] digest = computeDigestLocked(null);
if (digest != null) {
DataOutputStream outputStream;
try {
outputStream = new DataOutputStream(
new FileOutputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available?", e);
return false;
}
try {
outputStream.write(digest, 0, DIGEST_SIZE_BYTES);
outputStream.flush();
} catch (IOException e) {
Slog.e(TAG, "failed to write block checksum", e);
return false;
} finally {
IoUtils.closeQuietly(outputStream);
}
return true;
} else {
return false;
}
}
private byte[] computeDigestLocked(byte[] storedDigest) {
DataInputStream inputStream;
try {
inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available?", e);
return null;
}
MessageDigest md;
try {
md = MessageDigest.getInstance("SHA-256");
} catch (NoSuchAlgorithmException e) {
// won't ever happen -- every implementation is required to support SHA-256
Slog.e(TAG, "SHA-256 not supported?", e);
IoUtils.closeQuietly(inputStream);
return null;
}
try {
if (storedDigest != null && storedDigest.length == DIGEST_SIZE_BYTES) {
inputStream.read(storedDigest);
} else {
inputStream.skipBytes(DIGEST_SIZE_BYTES);
}
int read;
byte[] data = new byte[1024];
md.update(data, 0, DIGEST_SIZE_BYTES); // include 0 checksum in digest
while ((read = inputStream.read(data)) != -1) {
md.update(data, 0, read);
}
} catch (IOException e) {
Slog.e(TAG, "failed to read partition", e);
return null;
} finally {
IoUtils.closeQuietly(inputStream);
}
return md.digest();
}
private void formatPartitionLocked() {
DataOutputStream outputStream;
try {
outputStream = new DataOutputStream(new FileOutputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available?", e);
return;
}
byte[] data = new byte[DIGEST_SIZE_BYTES];
try {
outputStream.write(data, 0, DIGEST_SIZE_BYTES);
outputStream.writeInt(PARTITION_TYPE_MARKER);
outputStream.writeInt(0); // data size
outputStream.flush();
} catch (IOException e) {
Slog.e(TAG, "failed to format block", e);
return;
} finally {
IoUtils.closeQuietly(outputStream);
}
doSetOemUnlockEnabledLocked(false);
computeAndWriteDigestLocked();
}
private void doSetOemUnlockEnabledLocked(boolean enabled) {
FileOutputStream outputStream;
try {
outputStream = new FileOutputStream(new File(mDataBlockFile));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available", e);
return;
}
try {
FileChannel channel = outputStream.getChannel();
channel.position(getBlockDeviceSize() - 1);
ByteBuffer data = ByteBuffer.allocate(1);
data.put(enabled ? (byte) 1 : (byte) 0);
data.flip();
channel.write(data);
outputStream.flush();
} catch (IOException e) {
Slog.e(TAG, "unable to access persistent partition", e);
return;
} finally {
IoUtils.closeQuietly(outputStream);
}
}
private boolean doGetOemUnlockEnabled() {
DataInputStream inputStream;
try {
inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available");
return false;
}
try {
synchronized (mLock) {
inputStream.skip(getBlockDeviceSize() - 1);
return inputStream.readByte() != 0;
}
} catch (IOException e) {
Slog.e(TAG, "unable to access persistent partition", e);
return false;
} finally {
IoUtils.closeQuietly(inputStream);
}
}
private native long nativeGetBlockDeviceSize(String path);
private native int nativeWipe(String path);
private final IBinder mService = new IPersistentDataBlockService.Stub() {
@Override
public int write(byte[] data) throws RemoteException {
enforceUid(Binder.getCallingUid());
// Need to ensure we don't write over the last byte
long maxBlockSize = getBlockDeviceSize() - HEADER_SIZE - 1;
if (data.length > maxBlockSize) {
// partition is ~500k so shouldn't be a problem to downcast
return (int) -maxBlockSize;
}
DataOutputStream outputStream;
try {
outputStream = new DataOutputStream(new FileOutputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available?", e);
return -1;
}
ByteBuffer headerAndData = ByteBuffer.allocate(data.length + HEADER_SIZE);
headerAndData.putInt(PARTITION_TYPE_MARKER);
headerAndData.putInt(data.length);
headerAndData.put(data);
synchronized (mLock) {
try {
byte[] checksum = new byte[DIGEST_SIZE_BYTES];
outputStream.write(checksum, 0, DIGEST_SIZE_BYTES);
outputStream.write(headerAndData.array());
outputStream.flush();
} catch (IOException e) {
Slog.e(TAG, "failed writing to the persistent data block", e);
return -1;
} finally {
IoUtils.closeQuietly(outputStream);
}
if (computeAndWriteDigestLocked()) {
return data.length;
} else {
return -1;
}
}
}
@Override
public byte[] read() {
enforceUid(Binder.getCallingUid());
if (!enforceChecksumValidity()) {
return new byte[0];
}
DataInputStream inputStream;
try {
inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available?", e);
return null;
}
try {
synchronized (mLock) {
int totalDataSize = getTotalDataSizeLocked(inputStream);
if (totalDataSize == 0) {
return new byte[0];
}
byte[] data = new byte[totalDataSize];
int read = inputStream.read(data, 0, totalDataSize);
if (read < totalDataSize) {
// something went wrong, not returning potentially corrupt data
Slog.e(TAG, "failed to read entire data block. bytes read: " +
read + "/" + totalDataSize);
return null;
}
return data;
}
} catch (IOException e) {
Slog.e(TAG, "failed to read data", e);
return null;
} finally {
try {
inputStream.close();
} catch (IOException e) {
Slog.e(TAG, "failed to close OutputStream");
}
}
}
@Override
public void wipe() {
enforceOemUnlockPermission();
synchronized (mLock) {
int ret = nativeWipe(mDataBlockFile);
if (ret < 0) {
Slog.e(TAG, "failed to wipe persistent partition");
}
}
}
@Override
public void setOemUnlockEnabled(boolean enabled) {
// do not allow monkey to flip the flag
if (ActivityManager.isUserAMonkey()) {
return;
}
enforceOemUnlockPermission();
enforceIsOwner();
synchronized (mLock) {
doSetOemUnlockEnabledLocked(enabled);
computeAndWriteDigestLocked();
}
}
@Override
public boolean getOemUnlockEnabled() {
enforceOemUnlockPermission();
return doGetOemUnlockEnabled();
}
@Override
public int getDataBlockSize() {
if (mContext.checkCallingPermission(Manifest.permission.ACCESS_PDB_STATE)
!= PackageManager.PERMISSION_GRANTED) {
enforceUid(Binder.getCallingUid());
}
DataInputStream inputStream;
try {
inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile)));
} catch (FileNotFoundException e) {
Slog.e(TAG, "partition not available");
return 0;
}
try {
synchronized (mLock) {
return getTotalDataSizeLocked(inputStream);
}
} catch (IOException e) {
Slog.e(TAG, "error reading data block size");
return 0;
} finally {
IoUtils.closeQuietly(inputStream);
}
}
@Override
public long getMaximumDataBlockSize() {
long actualSize = getBlockDeviceSize() - HEADER_SIZE - 1;
return actualSize <= MAX_DATA_BLOCK_SIZE ? actualSize : MAX_DATA_BLOCK_SIZE;
}
};
}
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