From 28d940e33ab78f3561070385c5bb784e0016fa3e Mon Sep 17 00:00:00 2001
From: Marcin Oczeretko <marcinoc@google.com>
Date: Mon, 17 Jan 2022 11:41:37 +0000
Subject: [PATCH] Fix NPE in Binder#getTransactionName

Bug: 214053959
Test: manual

Change-Id: Ie77080d20f638e5e6e0a6ecb255d45bdb12f3c4d
---
 core/java/android/os/Binder.java | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/core/java/android/os/Binder.java b/core/java/android/os/Binder.java
index 429450ce8e5e3..80cf2f87f1d6c 100644
--- a/core/java/android/os/Binder.java
+++ b/core/java/android/os/Binder.java
@@ -311,6 +311,7 @@ public class Binder implements IBinder {
     private final long mObject;
 
     private IInterface mOwner;
+    @Nullable
     private String mDescriptor;
     private volatile String[] mTransactionTraceNames = null;
     private volatile String mSimpleDescriptor = null;
@@ -930,8 +931,8 @@ public class Binder implements IBinder {
                 transactionNames[i] = buf.toString();
                 buf.setLength(0);
             }
-            mTransactionTraceNames = transactionNames;
             mSimpleDescriptor = descriptor;
+            mTransactionTraceNames = transactionNames;
         }
         final int index = transactionCode - FIRST_CALL_TRANSACTION;
         if (index < 0 || index >= mTransactionTraceNames.length) {
@@ -940,13 +941,19 @@ public class Binder implements IBinder {
         return mTransactionTraceNames[index];
     }
 
-    private String getSimpleDescriptor() {
-        final int dot = mDescriptor.lastIndexOf(".");
+    private @NonNull String getSimpleDescriptor() {
+        String descriptor = mDescriptor;
+        if (descriptor == null) {
+            // Just "Binder" to avoid null checks in transaction name tracing.
+            return "Binder";
+        }
+
+        final int dot = descriptor.lastIndexOf(".");
         if (dot > 0) {
             // Strip the package name
-            return mDescriptor.substring(dot + 1);
+            return descriptor.substring(dot + 1);
         }
-        return mDescriptor;
+        return descriptor;
     }
 
     /**