PersistentDataBlockService.java revision 6b0c7acd7f175552d90d1d73b9717ff347158e7d
1/* 2 * Copyright (C) 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package com.android.server; 18 19import android.Manifest; 20import android.app.ActivityManager; 21import android.content.Context; 22import android.content.pm.PackageManager; 23import android.os.Binder; 24import android.os.IBinder; 25import android.os.RemoteException; 26import android.os.SystemProperties; 27import android.os.UserHandle; 28import android.service.persistentdata.IPersistentDataBlockService; 29import android.util.Slog; 30 31import com.android.internal.R; 32 33import libcore.io.IoUtils; 34 35import java.io.DataInputStream; 36import java.io.DataOutputStream; 37import java.io.File; 38import java.io.FileInputStream; 39import java.io.FileNotFoundException; 40import java.io.FileOutputStream; 41import java.io.IOException; 42import java.nio.ByteBuffer; 43import java.nio.channels.FileChannel; 44import java.security.MessageDigest; 45import java.security.NoSuchAlgorithmException; 46import java.util.Arrays; 47 48/** 49 * Service for reading and writing blocks to a persistent partition. 50 * This data will live across factory resets not initiated via the Settings UI. 51 * When a device is factory reset through Settings this data is wiped. 52 * 53 * Allows writing one block at a time. Namely, each time 54 * {@link android.service.persistentdata.IPersistentDataBlockService}.write(byte[] data) 55 * is called, it will overwite the data that was previously written on the block. 56 * 57 * Clients can query the size of the currently written block via 58 * {@link android.service.persistentdata.IPersistentDataBlockService}.getTotalDataSize(). 59 * 60 * Clients can any number of bytes from the currently written block up to its total size by invoking 61 * {@link android.service.persistentdata.IPersistentDataBlockService}.read(byte[] data) 62 */ 63public class PersistentDataBlockService extends SystemService { 64 private static final String TAG = PersistentDataBlockService.class.getSimpleName(); 65 66 private static final String PERSISTENT_DATA_BLOCK_PROP = "ro.frp.pst"; 67 private static final int HEADER_SIZE = 8; 68 // Magic number to mark block device as adhering to the format consumed by this service 69 private static final int PARTITION_TYPE_MARKER = 0x19901873; 70 // Limit to 100k as blocks larger than this might cause strain on Binder. 71 private static final int MAX_DATA_BLOCK_SIZE = 1024 * 100; 72 public static final int DIGEST_SIZE_BYTES = 32; 73 74 private final Context mContext; 75 private final String mDataBlockFile; 76 private final Object mLock = new Object(); 77 78 private int mAllowedUid = -1; 79 private long mBlockDeviceSize; 80 81 public PersistentDataBlockService(Context context) { 82 super(context); 83 mContext = context; 84 mDataBlockFile = SystemProperties.get(PERSISTENT_DATA_BLOCK_PROP); 85 mBlockDeviceSize = -1; // Load lazily 86 mAllowedUid = getAllowedUid(UserHandle.USER_OWNER); 87 } 88 89 private int getAllowedUid(int userHandle) { 90 String allowedPackage = mContext.getResources() 91 .getString(R.string.config_persistentDataPackageName); 92 PackageManager pm = mContext.getPackageManager(); 93 int allowedUid = -1; 94 try { 95 allowedUid = pm.getPackageUid(allowedPackage, userHandle); 96 } catch (PackageManager.NameNotFoundException e) { 97 // not expected 98 Slog.e(TAG, "not able to find package " + allowedPackage, e); 99 } 100 return allowedUid; 101 } 102 103 @Override 104 public void onStart() { 105 enforceChecksumValidity(); 106 publishBinderService(Context.PERSISTENT_DATA_BLOCK_SERVICE, mService); 107 } 108 109 private void enforceOemUnlockPermission() { 110 mContext.enforceCallingOrSelfPermission( 111 Manifest.permission.OEM_UNLOCK_STATE, 112 "Can't access OEM unlock state"); 113 } 114 115 private void enforceUid(int callingUid) { 116 if (callingUid != mAllowedUid) { 117 throw new SecurityException("uid " + callingUid + " not allowed to access PST"); 118 } 119 } 120 121 private void enforceIsOwner() { 122 if (!Binder.getCallingUserHandle().isOwner()) { 123 throw new SecurityException("Only the Owner is allowed to change OEM unlock state"); 124 } 125 } 126 127 private int getTotalDataSizeLocked(DataInputStream inputStream) throws IOException { 128 // skip over checksum 129 inputStream.skipBytes(DIGEST_SIZE_BYTES); 130 131 int totalDataSize; 132 int blockId = inputStream.readInt(); 133 if (blockId == PARTITION_TYPE_MARKER) { 134 totalDataSize = inputStream.readInt(); 135 } else { 136 totalDataSize = 0; 137 } 138 return totalDataSize; 139 } 140 141 private long getBlockDeviceSize() { 142 synchronized (mLock) { 143 if (mBlockDeviceSize == -1) { 144 mBlockDeviceSize = nativeGetBlockDeviceSize(mDataBlockFile); 145 } 146 } 147 148 return mBlockDeviceSize; 149 } 150 151 private boolean enforceChecksumValidity() { 152 byte[] storedDigest = new byte[DIGEST_SIZE_BYTES]; 153 154 synchronized (mLock) { 155 byte[] digest = computeDigestLocked(storedDigest); 156 if (digest == null || !Arrays.equals(storedDigest, digest)) { 157 Slog.i(TAG, "Formatting FRP partition..."); 158 formatPartitionLocked(); 159 return false; 160 } 161 } 162 163 return true; 164 } 165 166 private boolean computeAndWriteDigestLocked() { 167 byte[] digest = computeDigestLocked(null); 168 if (digest != null) { 169 DataOutputStream outputStream; 170 try { 171 outputStream = new DataOutputStream( 172 new FileOutputStream(new File(mDataBlockFile))); 173 } catch (FileNotFoundException e) { 174 Slog.e(TAG, "partition not available?", e); 175 return false; 176 } 177 178 try { 179 outputStream.write(digest, 0, DIGEST_SIZE_BYTES); 180 outputStream.flush(); 181 } catch (IOException e) { 182 Slog.e(TAG, "failed to write block checksum", e); 183 return false; 184 } finally { 185 IoUtils.closeQuietly(outputStream); 186 } 187 return true; 188 } else { 189 return false; 190 } 191 } 192 193 private byte[] computeDigestLocked(byte[] storedDigest) { 194 DataInputStream inputStream; 195 try { 196 inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile))); 197 } catch (FileNotFoundException e) { 198 Slog.e(TAG, "partition not available?", e); 199 return null; 200 } 201 202 MessageDigest md; 203 try { 204 md = MessageDigest.getInstance("SHA-256"); 205 } catch (NoSuchAlgorithmException e) { 206 // won't ever happen -- every implementation is required to support SHA-256 207 Slog.e(TAG, "SHA-256 not supported?", e); 208 IoUtils.closeQuietly(inputStream); 209 return null; 210 } 211 212 try { 213 if (storedDigest != null && storedDigest.length == DIGEST_SIZE_BYTES) { 214 inputStream.read(storedDigest); 215 } else { 216 inputStream.skipBytes(DIGEST_SIZE_BYTES); 217 } 218 219 int read; 220 byte[] data = new byte[1024]; 221 md.update(data, 0, DIGEST_SIZE_BYTES); // include 0 checksum in digest 222 while ((read = inputStream.read(data)) != -1) { 223 md.update(data, 0, read); 224 } 225 } catch (IOException e) { 226 Slog.e(TAG, "failed to read partition", e); 227 return null; 228 } finally { 229 IoUtils.closeQuietly(inputStream); 230 } 231 232 return md.digest(); 233 } 234 235 private void formatPartitionLocked() { 236 DataOutputStream outputStream; 237 try { 238 outputStream = new DataOutputStream(new FileOutputStream(new File(mDataBlockFile))); 239 } catch (FileNotFoundException e) { 240 Slog.e(TAG, "partition not available?", e); 241 return; 242 } 243 244 byte[] data = new byte[DIGEST_SIZE_BYTES]; 245 try { 246 outputStream.write(data, 0, DIGEST_SIZE_BYTES); 247 outputStream.writeInt(PARTITION_TYPE_MARKER); 248 outputStream.writeInt(0); // data size 249 outputStream.flush(); 250 } catch (IOException e) { 251 Slog.e(TAG, "failed to format block", e); 252 return; 253 } finally { 254 IoUtils.closeQuietly(outputStream); 255 } 256 257 doSetOemUnlockEnabledLocked(false); 258 computeAndWriteDigestLocked(); 259 } 260 261 private void doSetOemUnlockEnabledLocked(boolean enabled) { 262 FileOutputStream outputStream; 263 try { 264 outputStream = new FileOutputStream(new File(mDataBlockFile)); 265 } catch (FileNotFoundException e) { 266 Slog.e(TAG, "partition not available", e); 267 return; 268 } 269 270 try { 271 FileChannel channel = outputStream.getChannel(); 272 273 channel.position(getBlockDeviceSize() - 1); 274 275 ByteBuffer data = ByteBuffer.allocate(1); 276 data.put(enabled ? (byte) 1 : (byte) 0); 277 data.flip(); 278 channel.write(data); 279 outputStream.flush(); 280 } catch (IOException e) { 281 Slog.e(TAG, "unable to access persistent partition", e); 282 return; 283 } finally { 284 IoUtils.closeQuietly(outputStream); 285 } 286 } 287 288 private native long nativeGetBlockDeviceSize(String path); 289 private native int nativeWipe(String path); 290 291 private final IBinder mService = new IPersistentDataBlockService.Stub() { 292 @Override 293 public int write(byte[] data) throws RemoteException { 294 enforceUid(Binder.getCallingUid()); 295 296 // Need to ensure we don't write over the last byte 297 long maxBlockSize = getBlockDeviceSize() - HEADER_SIZE - 1; 298 if (data.length > maxBlockSize) { 299 // partition is ~500k so shouldn't be a problem to downcast 300 return (int) -maxBlockSize; 301 } 302 303 DataOutputStream outputStream; 304 try { 305 outputStream = new DataOutputStream(new FileOutputStream(new File(mDataBlockFile))); 306 } catch (FileNotFoundException e) { 307 Slog.e(TAG, "partition not available?", e); 308 return -1; 309 } 310 311 ByteBuffer headerAndData = ByteBuffer.allocate(data.length + HEADER_SIZE); 312 headerAndData.putInt(PARTITION_TYPE_MARKER); 313 headerAndData.putInt(data.length); 314 headerAndData.put(data); 315 316 synchronized (mLock) { 317 try { 318 byte[] checksum = new byte[DIGEST_SIZE_BYTES]; 319 outputStream.write(checksum, 0, DIGEST_SIZE_BYTES); 320 outputStream.write(headerAndData.array()); 321 outputStream.flush(); 322 } catch (IOException e) { 323 Slog.e(TAG, "failed writing to the persistent data block", e); 324 return -1; 325 } finally { 326 IoUtils.closeQuietly(outputStream); 327 } 328 329 if (computeAndWriteDigestLocked()) { 330 return data.length; 331 } else { 332 return -1; 333 } 334 } 335 } 336 337 @Override 338 public byte[] read() { 339 enforceUid(Binder.getCallingUid()); 340 if (!enforceChecksumValidity()) { 341 return new byte[0]; 342 } 343 344 DataInputStream inputStream; 345 try { 346 inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile))); 347 } catch (FileNotFoundException e) { 348 Slog.e(TAG, "partition not available?", e); 349 return null; 350 } 351 352 try { 353 synchronized (mLock) { 354 int totalDataSize = getTotalDataSizeLocked(inputStream); 355 356 if (totalDataSize == 0) { 357 return new byte[0]; 358 } 359 360 byte[] data = new byte[totalDataSize]; 361 int read = inputStream.read(data, 0, totalDataSize); 362 if (read < totalDataSize) { 363 // something went wrong, not returning potentially corrupt data 364 Slog.e(TAG, "failed to read entire data block. bytes read: " + 365 read + "/" + totalDataSize); 366 return null; 367 } 368 return data; 369 } 370 } catch (IOException e) { 371 Slog.e(TAG, "failed to read data", e); 372 return null; 373 } finally { 374 try { 375 inputStream.close(); 376 } catch (IOException e) { 377 Slog.e(TAG, "failed to close OutputStream"); 378 } 379 } 380 } 381 382 @Override 383 public void wipe() { 384 enforceOemUnlockPermission(); 385 386 synchronized (mLock) { 387 int ret = nativeWipe(mDataBlockFile); 388 389 if (ret < 0) { 390 Slog.e(TAG, "failed to wipe persistent partition"); 391 } 392 } 393 } 394 395 @Override 396 public void setOemUnlockEnabled(boolean enabled) { 397 // do not allow monkey to flip the flag 398 if (ActivityManager.isUserAMonkey()) { 399 return; 400 } 401 enforceOemUnlockPermission(); 402 enforceIsOwner(); 403 404 synchronized (mLock) { 405 doSetOemUnlockEnabledLocked(enabled); 406 computeAndWriteDigestLocked(); 407 } 408 } 409 410 @Override 411 public boolean getOemUnlockEnabled() { 412 enforceOemUnlockPermission(); 413 DataInputStream inputStream; 414 try { 415 inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile))); 416 } catch (FileNotFoundException e) { 417 Slog.e(TAG, "partition not available"); 418 return false; 419 } 420 421 try { 422 synchronized (mLock) { 423 inputStream.skip(getBlockDeviceSize() - 1); 424 return inputStream.readByte() != 0; 425 } 426 } catch (IOException e) { 427 Slog.e(TAG, "unable to access persistent partition", e); 428 return false; 429 } finally { 430 IoUtils.closeQuietly(inputStream); 431 } 432 } 433 434 @Override 435 public int getDataBlockSize() { 436 if (mContext.checkCallingPermission(Manifest.permission.ACCESS_PDB_STATE) 437 != PackageManager.PERMISSION_GRANTED) { 438 enforceUid(Binder.getCallingUid()); 439 } 440 441 DataInputStream inputStream; 442 try { 443 inputStream = new DataInputStream(new FileInputStream(new File(mDataBlockFile))); 444 } catch (FileNotFoundException e) { 445 Slog.e(TAG, "partition not available"); 446 return 0; 447 } 448 449 try { 450 synchronized (mLock) { 451 return getTotalDataSizeLocked(inputStream); 452 } 453 } catch (IOException e) { 454 Slog.e(TAG, "error reading data block size"); 455 return 0; 456 } finally { 457 IoUtils.closeQuietly(inputStream); 458 } 459 } 460 461 @Override 462 public long getMaximumDataBlockSize() { 463 long actualSize = getBlockDeviceSize() - HEADER_SIZE - 1; 464 return actualSize <= MAX_DATA_BLOCK_SIZE ? actualSize : MAX_DATA_BLOCK_SIZE; 465 } 466 }; 467} 468