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Prevent writing to FRP partition during factory reset.

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Avoid potential race condition between FRP wipe and write operations
during factory reset by making the FRP partition unwritable after
wipe.

Bug: 30352311
Test: manual
Change-Id: If3f024a1611366c0677a996705724458094fcfad
(cherry picked from commit a629c772f4)
This commit is contained in:
Charles He
2016-11-24 14:05:00 +00:00
parent ce477912a2
commit a9437bd1ca
2 changed files with 19 additions and 6 deletions
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5
core/java/android/service/persistentdata/PersistentDataBlockManager.java
View File

@ -54,6 +54,9 @@ public class PersistentDataBlockManager {
* Returns the number of bytes written or -1 on error. If the block is too big
* to fit on the partition, returns -MAX_BLOCK_SIZE.
*
* {@link #wipe} will block any further {@link #write} operation until reboot,
* in which case -1 will be returned.
*
* @param data the data to write
*/
public int write(byte[] data) {
@ -108,6 +111,8 @@ public class PersistentDataBlockManager {
/**
* Zeroes the previously written block in its entirety. Calling this method
* will erase all data written to the persistent data partition.
* It will also prevent any further {@link #write} operation until reboot,
* in order to prevent a potential race condition. See b/30352311.
*/
public void wipe() {
try {

20
services/core/java/com/android/server/PersistentDataBlockService.java
View File

@ -50,15 +50,14 @@ import java.util.Arrays;
* 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.
* Allows writing one block at a time. Namely, each time {@link IPersistentDataBlockService#write}
* is called, it will overwrite 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().
* {@link IPersistentDataBlockService#getDataBlockSize}
*
* 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)
* Clients can read any number of bytes from the currently written block up to its total size by
* invoking {@link IPersistentDataBlockService#read}
*/
public class PersistentDataBlockService extends SystemService {
private static final String TAG = PersistentDataBlockService.class.getSimpleName();
@ -77,6 +76,7 @@ public class PersistentDataBlockService extends SystemService {
private int mAllowedUid = -1;
private long mBlockDeviceSize;
private boolean mIsWritable = true;
public PersistentDataBlockService(Context context) {
super(context);
@ -345,6 +345,11 @@ public class PersistentDataBlockService extends SystemService {
headerAndData.put(data);
synchronized (mLock) {
if (!mIsWritable) {
IoUtils.closeQuietly(outputStream);
return -1;
}
try {
byte[] checksum = new byte[DIGEST_SIZE_BYTES];
outputStream.write(checksum, 0, DIGEST_SIZE_BYTES);
@ -419,6 +424,9 @@ public class PersistentDataBlockService extends SystemService {
if (ret < 0) {
Slog.e(TAG, "failed to wipe persistent partition");
} else {
mIsWritable = false;
Slog.i(TAG, "persistent partition now wiped and unwritable");
}
}
}