Add checks around CONTROL_VPN permission during prepare()

Bug: 284803285
Test: atest
FrameworksNetTests: android.net.connectivity.com.android.server.connectivity.VpnTest
Change-Id: I0a277f6b4e7cd25aff7edad9dd0e89a44dfbf3fe
diff --git a/tests/unit/java/com/android/server/connectivity/VpnTest.java b/tests/unit/java/com/android/server/connectivity/VpnTest.java
index 2d2819c..dc50773 100644
--- a/tests/unit/java/com/android/server/connectivity/VpnTest.java
+++ b/tests/unit/java/com/android/server/connectivity/VpnTest.java
@@ -80,6 +80,7 @@
 import static org.mockito.Mockito.doCallRealMethod;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.inOrder;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
@@ -807,6 +808,32 @@
     }
 
     @Test
+    public void testPrepare_legacyVpnWithoutControlVpn()
+            throws Exception {
+        doThrow(new SecurityException("no CONTROL_VPN")).when(mContext)
+                .enforceCallingOrSelfPermission(eq(CONTROL_VPN), any());
+        final Vpn vpn = createVpn();
+        assertThrows(SecurityException.class,
+                () -> vpn.prepare(null, VpnConfig.LEGACY_VPN, VpnManager.TYPE_VPN_SERVICE));
+
+        // CONTROL_VPN can be held by the caller or another system server process - both are
+        // allowed. Just checking for `enforceCallingPermission` may not be sufficient.
+        verify(mContext, never()).enforceCallingPermission(eq(CONTROL_VPN), any());
+    }
+
+    @Test
+    public void testPrepare_legacyVpnWithControlVpn()
+            throws Exception {
+        doNothing().when(mContext).enforceCallingOrSelfPermission(eq(CONTROL_VPN), any());
+        final Vpn vpn = createVpn();
+        assertTrue(vpn.prepare(null, VpnConfig.LEGACY_VPN, VpnManager.TYPE_VPN_SERVICE));
+
+        // CONTROL_VPN can be held by the caller or another system server process - both are
+        // allowed. Just checking for `enforceCallingPermission` may not be sufficient.
+        verify(mContext, never()).enforceCallingPermission(eq(CONTROL_VPN), any());
+    }
+
+    @Test
     public void testIsAlwaysOnPackageSupported() throws Exception {
         final Vpn vpn = createVpn(PRIMARY_USER.id);