Stop exporting the sync adapter services

app/src/androidTest/java/com/etesync/syncadapter/syncadapter/ExportedComponentsTest.kt

@@ -0,0 +1,53 @@
+package com.etesync.syncadapter.syncadapter
+
+import android.content.ComponentName
+import android.content.Context
+import androidx.test.platform.app.InstrumentationRegistry
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * Guards the exported surface of the sync and account services, as declared in the *merged*
+ * AndroidManifest.xml.
+ *
+ * Sync adapter services must stay unexported: the system server binds them either way (it is
+ * exempt from the exported check), while exporting them hands the ISyncAdapter Binder to any
+ * local app, which can then crash the sync process with a malformed transaction.
+ * See https://github.com/etesync/android/issues/295.
+ */
+class ExportedComponentsTest {
+
+    private val context: Context
+        get() = InstrumentationRegistry.getInstrumentation().targetContext
+
+    private fun isExported(cls: Class<*>) =
+            context.packageManager.getServiceInfo(ComponentName(context, cls), 0).exported
+
+    @Test
+    fun syncAdapterServicesAreNotExported() {
+        for (cls in arrayOf(
+                CalendarsSyncAdapterService::class.java,
+                ContactsSyncAdapterService::class.java,
+                AddressBooksSyncAdapterService::class.java,
+                TasksSyncAdapterService::class.java,
+                TasksOrgSyncAdapterService::class.java)) {
+            assertFalse("${cls.simpleName} must not be exported: any local app could then bind it " +
+                    "and crash the sync process (etesync/android#295)", isExported(cls))
+        }
+    }
+
+    @Test
+    fun accountAuthenticatorServiceIsNotExported() {
+        assertFalse("AccountAuthenticatorService is bound by the system and must not be exported",
+                isExported(AccountAuthenticatorService::class.java))
+    }
+
+    @Test
+    fun nullAuthenticatorServiceIsExported() {
+        // Since Android 11 this one has to stay exported, otherwise Google Contacts doesn't show
+        // the address book accounts.
+        assertTrue("NullAuthenticatorService must stay exported so that other apps can see the " +
+                "address book accounts", isExported(NullAuthenticatorService::class.java))
+    }
+}

app/src/main/AndroidManifest.xml

@@ -89,11 +89,19 @@
                 android:resource="@xml/account_authenticator"/>
         </service>
 
+        <!--
+             Sync adapter services must NOT be exported. They are bound by the system server
+             (SyncManager), which is exempt from the exported check, so the sync framework keeps
+             working without it. Exporting them hands the ISyncAdapter Binder to any local app,
+             which can then crash the sync process with a malformed transaction (NPE in
+             AbstractThreadedSyncAdapter.handleOnUnsyncableAccount).
+             See https://github.com/etesync/android/issues/295.
+        -->
+
         <!-- Normal account -->
         <service
             android:name=".syncadapter.CalendarsSyncAdapterService"
-            android:exported="true"
-            tools:ignore="ExportedService">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.content.SyncAdapter" />
             </intent-filter>
@@ -104,8 +112,7 @@
         </service>
         <service
             android:name=".syncadapter.TasksSyncAdapterService"
-            android:exported="true"
-            tools:ignore="ExportedService">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.content.SyncAdapter"/>
             </intent-filter>
@@ -117,8 +124,7 @@
 
         <service
             android:name=".syncadapter.TasksOrgSyncAdapterService"
-            android:exported="true"
-            tools:ignore="ExportedService">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.content.SyncAdapter"/>
             </intent-filter>
@@ -149,8 +155,7 @@
             android:multiprocess="false"/>
         <service
             android:name=".syncadapter.AddressBooksSyncAdapterService"
-            android:exported="true"
-            tools:ignore="ExportedService">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.content.SyncAdapter"/>
             </intent-filter>
@@ -162,8 +167,7 @@
 
         <service
             android:name=".syncadapter.ContactsSyncAdapterService"
-            android:exported="true"
-            tools:ignore="ExportedService">
+            android:exported="false">
             <intent-filter>
                 <action android:name="android.content.SyncAdapter"/>
             </intent-filter>