Fix PolicyManager: plugin resolver overrides agent (#121456) (#121540)

Author: prdoyle

libs/entitlement/src/main/java/org/elasticsearch/entitlement/runtime/policy/PolicyManager.java

@@ -398,7 +398,9 @@ private ModuleEntitlements computeEntitlements(Class<?> requestingClass) {
         var pluginName = pluginResolver.apply(requestingClass);
         if (pluginName != null) {
             var pluginEntitlements = pluginsEntitlements.get(pluginName);
-            if (pluginEntitlements != null) {
+            if (pluginEntitlements == null) {
+                return ModuleEntitlements.NONE;
+            } else {
                 final String scopeName;
                 if (requestingModule.isNamed() == false) {
                     scopeName = ALL_UNNAMED;

libs/entitlement/src/test/java/org/elasticsearch/entitlement/runtime/policy/PolicyManagerTests.java

@@ -271,7 +271,7 @@ public void testAgentsEntitlements() throws IOException, ClassNotFoundException
             createEmptyTestServerPolicy(),
             List.of(new CreateClassLoaderEntitlement()),
             Map.of(),
-            c -> "test",
+            c -> c.getPackageName().startsWith(TEST_AGENTS_PACKAGE_NAME) ? null : "test",
             TEST_AGENTS_PACKAGE_NAME,
             NO_ENTITLEMENTS_MODULE
         );
@@ -357,6 +357,22 @@ public void testDuplicateFlagEntitlements() {
         );
     }
 
+    /**
+     * If the plugin resolver tells us a class is in a plugin, don't conclude that it's in an agent.
+     */
+    public void testPluginResolverOverridesAgents() {
+        var policyManager = new PolicyManager(
+            createEmptyTestServerPolicy(),
+            List.of(new CreateClassLoaderEntitlement()),
+            Map.of(),
+            c -> "test", // Insist that the class is in a plugin
+            TEST_AGENTS_PACKAGE_NAME,
+            NO_ENTITLEMENTS_MODULE
+        );
+        ModuleEntitlements notAgentsEntitlements = policyManager.getEntitlements(TestAgent.class);
+        assertThat(notAgentsEntitlements.hasEntitlement(CreateClassLoaderEntitlement.class), is(false));
+    }
+
     private static Class<?> makeClassInItsOwnModule() throws IOException, ClassNotFoundException {
         final Path home = createTempDir();
         Path jar = createMockPluginJar(home);