Fix NullPointerException on NsdService

The NsdService will throw a NPE if a new client is registered
with a null INsdManagerCallback object. To avoid this, perform
a null check before registering a new client and throw an
IllegalArgumentException if the callback is null.

Bug: 293285797
Test: atest FrameworksNetTests
Change-Id: Id61e27873591031c3fe383879aee0d40eebc08b3

service-t/src/com/android/server/NsdService.java

@@ -1920,11 +1920,14 @@ public class NsdService extends INsdManager.Stub {
     @Override
     public INsdServiceConnector connect(INsdManagerCallback cb, boolean useJavaBackend) {
         mContext.enforceCallingOrSelfPermission(android.Manifest.permission.INTERNET, "NsdService");
+        final int uid = mDeps.getCallingUid();
+        if (cb == null) {
+            throw new IllegalArgumentException("Unknown client callback from uid=" + uid);
+        }
         if (DBG) Log.d(TAG, "New client connect. useJavaBackend=" + useJavaBackend);
         final INsdServiceConnector connector = new NsdServiceConnector();
         mNsdStateMachine.sendMessage(mNsdStateMachine.obtainMessage(NsdManager.REGISTER_CLIENT,
-                new ConnectorArgs((NsdServiceConnector) connector, cb, useJavaBackend,
+                new ConnectorArgs((NsdServiceConnector) connector, cb, useJavaBackend, uid)));
-                        mDeps.getCallingUid())));
         return connector;
     }
 

tests/unit/java/com/android/server/NsdServiceTest.java

@@ -1585,6 +1585,20 @@ public class NsdServiceTest {
         lockOrder.verify(mMulticastLock).release();
     }
 
+    @Test
+    public void testNullINsdManagerCallback() {
+        final NsdService service = new NsdService(mContext, mHandler, CLEANUP_DELAY_MS, mDeps) {
+            @Override
+            public INsdServiceConnector connect(INsdManagerCallback baseCb,
+                    boolean runNewMdnsBackend) {
+                // Pass null INsdManagerCallback
+                return super.connect(null /* cb */, runNewMdnsBackend);
+            }
+        };
+
+        assertThrows(IllegalArgumentException.class, () -> new NsdManager(mContext, service));
+    }
+
     private void waitForIdle() {
         HandlerUtils.waitForIdle(mHandler, TIMEOUT_MS);
     }