Add a finalizer to LockscreenCredential to wipe the LSKF on GC

Adds a finalizer to the `LockscreenCredential` class, which calls
the `zeroize` method to zeroize the LSKF `byte[]`. This ensures that
`LockscreenCredential` objects that were not closed still have their
data wiped when they are garbage collected.

This is part of an effort to remove instances of the LSKF available
in a RAMdump.

Bug: 320392352
Test: atest com.android.server.locksettings
Change-Id: Id7f1f102cdaa182659e2632bdaf81bd2c46d0f86

1 files changed, 5 insertions, 0 deletions

diff --git a/core/java/com/android/internal/widget/LockscreenCredential.java b/core/java/com/android/internal/widget/LockscreenCredential.java
index 18d5f6db6ac9..54b9a225f944 100644
--- a/core/java/com/android/internal/widget/LockscreenCredential.java
+++ b/core/java/com/android/internal/widget/LockscreenCredential.java
@@ -386,6 +386,11 @@ public class LockscreenCredential implements Parcelable, AutoCloseable {
     }
 
     @Override
+    public void finalize() {
+        zeroize();
+    }
+
+    @Override
     public int hashCode() {
         // Effective Java — Always override hashCode when you override equals
         return Objects.hash(mType, Arrays.hashCode(mCredential), mHasInvalidChars);