From a929cf01cfb8b6d138c8724d586a8b9de75c0fac Mon Sep 17 00:00:00 2001
From: Nikita Ioffe <ioffe@google.com>
Date: Thu, 3 Jan 2019 13:35:22 +0000
Subject: [PATCH] Add Binder.getCallingUidOrThrow method

Binder.getCallingUidOrThrow is a pure java method which uses
Binder.isHandlingTransaction @CriticalNative method.

Binder.isHandlingTransaction itself is not exposed a public API.

Bug: 62253865
Fix: 62253865
Test: Added a testcase to BinderTest.java to verify ISE is thrown
Change-Id: I93a1b6c24a4747b8b70c32d291b4706b6159a3d0
---
 api/current.txt                               |  1 +
 core/java/android/os/Binder.java              | 24 +++++++++++++++++++
 core/jni/android_util_Binder.cpp              |  7 ++++++
 .../coretests/src/android/os/BinderTest.java  |  9 +++++++
 4 files changed, 41 insertions(+)

diff --git a/api/current.txt b/api/current.txt
index faf7c24c83fee..6c66fcd1d2a5d 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -33698,6 +33698,7 @@ package android.os {
     method public static final void flushPendingCommands();
     method public static final int getCallingPid();
     method public static final int getCallingUid();
+    method public static final int getCallingUidOrThrow();
     method public static final android.os.UserHandle getCallingUserHandle();
     method public java.lang.String getInterfaceDescriptor();
     method public boolean isBinderAlive();
diff --git a/core/java/android/os/Binder.java b/core/java/android/os/Binder.java
index 9939a3c8f36de..1ebb551df9618 100644
--- a/core/java/android/os/Binder.java
+++ b/core/java/android/os/Binder.java
@@ -272,6 +272,30 @@ public class Binder implements IBinder {
     @CriticalNative
     public static final native int getCallingUid();
 
+    /**
+     * Returns {@code true} if the current thread is currently executing an
+     * incoming transaction.
+     *
+     * @hide
+     */
+    @CriticalNative
+    public static final native boolean isHandlingTransaction();
+
+    /**
+     * Return the Linux uid assigned to the process that sent the transaction
+     * currently being processed.
+     *
+     * @throws IllegalStateException if the current thread is not currently
+     *        executing an incoming transaction.
+     */
+    public static final int getCallingUidOrThrow() {
+        if (!isHandlingTransaction()) {
+            throw new IllegalStateException(
+                  "Thread is not in a binder transcation");
+        }
+        return getCallingUid();
+    }
+
     /**
      * Return the UserHandle assigned to the process that sent you the
      * current transaction that is being processed.  This is the user
diff --git a/core/jni/android_util_Binder.cpp b/core/jni/android_util_Binder.cpp
index 3329e2047085f..f201ceb40ff48 100644
--- a/core/jni/android_util_Binder.cpp
+++ b/core/jni/android_util_Binder.cpp
@@ -875,6 +875,11 @@ static jint android_os_Binder_getCallingUid()
     return IPCThreadState::self()->getCallingUid();
 }
 
+static jboolean android_os_Binder_isHandlingTransaction()
+{
+    return IPCThreadState::self()->isServingCall();
+}
+
 static jlong android_os_Binder_clearCallingIdentity()
 {
     return IPCThreadState::self()->clearCallingIdentity();
@@ -960,6 +965,8 @@ static const JNINativeMethod gBinderMethods[] = {
     // @CriticalNative
     { "getCallingUid", "()I", (void*)android_os_Binder_getCallingUid },
     // @CriticalNative
+    { "isHandlingTransaction", "()Z", (void*)android_os_Binder_isHandlingTransaction },
+    // @CriticalNative
     { "clearCallingIdentity", "()J", (void*)android_os_Binder_clearCallingIdentity },
     { "restoreCallingIdentity", "(J)V", (void*)android_os_Binder_restoreCallingIdentity },
     // @CriticalNative
diff --git a/core/tests/coretests/src/android/os/BinderTest.java b/core/tests/coretests/src/android/os/BinderTest.java
index 534c5cdec259a..6c9c3c111ff82 100644
--- a/core/tests/coretests/src/android/os/BinderTest.java
+++ b/core/tests/coretests/src/android/os/BinderTest.java
@@ -43,4 +43,13 @@ public class BinderTest extends TestCase {
         Binder.restoreCallingWorkSource(token);
         assertEquals(UID, Binder.getCallingWorkSourceUid());
     }
+
+    @SmallTest
+    public void testGetCallingUidOrThrow() throws Exception {
+        try {
+            Binder.getCallingUidOrThrow();
+            throw new AssertionError("IllegalStateException expected");
+        } catch (IllegalStateException expected) {
+        }
+    }
 }