Use compilation as validation for painless role template (#62845)

Role template validation now performs only compilation if the script is painless. 
It no longer attempts to execute the script with empty input which is problematic. 
The compliation process will catch things like invalid syntax, undefined variables, 
which still provide certain level of protection against ill-defined role templates. 
Behaviour for Mustache script is unchanged.

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/support/mapper/TemplateRoleName.java

@@ -24,7 +24,9 @@ import org.elasticsearch.common.xcontent.XContentParseException;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.script.Script;
 import org.elasticsearch.script.ScriptService;
+import org.elasticsearch.script.TemplateScript;
 import org.elasticsearch.xpack.core.security.authc.support.mapper.expressiondsl.ExpressionModel;
 import org.elasticsearch.xpack.core.security.support.MustacheTemplateEvaluator;
 
@@ -99,7 +101,13 @@ public class TemplateRoleName implements ToXContentObject, Writeable {
 
     public void validate(ScriptService scriptService) {
         try {
-            parseTemplate(scriptService, Collections.emptyMap());
+            final XContentParser parser = XContentHelper.createParser(
+                NamedXContentRegistry.EMPTY, LoggingDeprecationHandler.INSTANCE, template, XContentType.JSON);
+            final Script script = MustacheTemplateEvaluator.parseForScript(parser, Collections.emptyMap());
+            final TemplateScript compiledTemplate = scriptService.compile(script, TemplateScript.CONTEXT).newInstance(script.getParams());
+            if ("mustache".equals(script.getLang())) {
+                compiledTemplate.execute();
+            }
         } catch (IllegalArgumentException e) {
             throw e;
         } catch (IOException e) {

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/support/MustacheTemplateEvaluator.java

@@ -25,7 +25,7 @@ public final class MustacheTemplateEvaluator {
         throw new UnsupportedOperationException("Cannot construct " + MustacheTemplateEvaluator.class);
     }
 
-    public static String evaluate(ScriptService scriptService, XContentParser parser, Map<String, Object> extraParams) throws IOException {
+    public static Script parseForScript(XContentParser parser, Map<String, Object> extraParams) throws IOException {
         Script script = Script.parse(parser);
         // Add the user details to the params
         Map<String, Object> params = new HashMap<>();
@@ -36,6 +36,11 @@ public final class MustacheTemplateEvaluator {
         // Always enforce mustache script lang:
         script = new Script(script.getType(), script.getType() == ScriptType.STORED ? null : "mustache", script.getIdOrCode(),
                 script.getOptions(), params);
+        return script;
+    }
+
+    public static String evaluate(ScriptService scriptService, XContentParser parser, Map<String, Object> extraParams) throws IOException {
+        Script script = parseForScript(parser, extraParams);
         TemplateScript compiledTemplate = scriptService.compile(script, TemplateScript.CONTEXT).newInstance(script.getParams());
         return compiledTemplate.execute();
     }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/authc/support/mapper/TemplateRoleNameTests.java

@@ -20,11 +20,13 @@ import org.elasticsearch.common.xcontent.DeprecationHandler;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
+import org.elasticsearch.script.ScriptEngine;
 import org.elasticsearch.script.ScriptException;
 import org.elasticsearch.script.ScriptMetadata;
 import org.elasticsearch.script.ScriptModule;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.script.StoredScriptSource;
+import org.elasticsearch.script.TemplateScript;
 import org.elasticsearch.script.mustache.MustacheScriptEngine;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.EqualsHashCodeTestUtils;
@@ -35,12 +37,20 @@ import org.hamcrest.Matchers;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.List;
+import java.util.Map;
 
 import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.notNullValue;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.doThrow;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 public class TemplateRoleNameTests extends ESTestCase {
@@ -183,6 +193,44 @@ public class TemplateRoleNameTests extends ESTestCase {
         assertTrue(e.getCause() instanceof ScriptException);
     }
 
+    public void testValidateWillCompileButNotExecutePainlessScript() {
+        final TemplateScript compiledScript = mock(TemplateScript.class);
+        doThrow(new IllegalStateException("Validate should not execute painless script")).when(compiledScript).execute();
+        final TemplateScript.Factory scriptFactory = mock(TemplateScript.Factory.class);
+        when(scriptFactory.newInstance(any())).thenReturn(compiledScript);
+
+        final ScriptEngine scriptEngine = mock(ScriptEngine.class);
+        when(scriptEngine.getType()).thenReturn("painless");
+        when(scriptEngine.compile(eq("valid"), eq("params.metedata.group"), any(), eq(Map.of())))
+            .thenReturn(scriptFactory);
+        final ScriptException scriptException =
+            new ScriptException("exception", new IllegalStateException(), List.of(), "bad syntax", "painless");
+        doThrow(scriptException)
+            .when(scriptEngine).compile(eq("invalid"), eq("bad syntax"), any(), eq(Map.of()));
+
+        final ScriptService scriptService = new ScriptService(Settings.EMPTY,
+            Map.of("painless", scriptEngine), ScriptModule.CORE_CONTEXTS) {
+            @Override
+            protected StoredScriptSource getScriptFromClusterState(String id) {
+                if ("valid".equals(id)) {
+                    return new StoredScriptSource("painless", "params.metedata.group", Map.of());
+                } else {
+                    return new StoredScriptSource("painless", "bad syntax", Map.of());
+                }
+            }
+        };
+        // Validation succeeds if compilation is successful
+        new TemplateRoleName(new BytesArray("{ \"id\":\"valid\" }"), Format.STRING).validate(scriptService);
+        verify(scriptEngine, times(1))
+            .compile(eq("valid"), eq("params.metedata.group"), any(), eq(Map.of()));
+        verify(compiledScript, never()).execute();
+
+        // Validation fails if compilation fails
+        final IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
+            () -> new TemplateRoleName(new BytesArray("{ \"id\":\"invalid\" }"), Format.STRING).validate(scriptService));
+        assertSame(scriptException, e.getCause());
+    }
+
     public void testValidationWillFailWhenInlineScriptIsNotEnabled() {
         final Settings settings = Settings.builder().put("script.allowed_types", ScriptService.ALLOW_NONE).build();
         final ScriptService scriptService = new ScriptService(settings,