Prevent writing to FRP partition during factory reset.

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

CVE-2017-0498

Change-Id: If3f024a1611366c0677a996705724458094fcfad
(cherry picked from commit a629c772f4a7a5ddf7ff9f78fb19f7ab86c2a9c2)
(cherry picked from commit a9437bd1caeeb38780d920a81bde8cc7ca280fe0)
(cherry picked from commit 1c4d535d0806dbeb6d2fa5cea0373cbd9ab6d33b)

1 files changed, 5 insertions, 0 deletions

diff --git a/core/java/android/service/persistentdata/PersistentDataBlockManager.java b/core/java/android/service/persistentdata/PersistentDataBlockManager.java
index 0ffdf68..10ffe84 100644
--- a/core/java/android/service/persistentdata/PersistentDataBlockManager.java
+++ b/core/java/android/service/persistentdata/PersistentDataBlockManager.java
@@ -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 {