Add XSS support for Freemarker prior 2.3.24-incubating

dd-java-agent/instrumentation/freemarker-2.3.9/build.gradle

@@ -0,0 +1,23 @@
+muzzle {
+  fail {
+    name = 'freemarker-2.3.9'
+    group = 'org.freemarker'
+    module = 'freemarker'
+    versions = '[2.3.24-incubating,]'
+    assertInverse = true
+  }
+}
+
+apply from: "$rootDir/gradle/java.gradle"
+
+addTestSuiteForDir('latestDepTest', 'test')
+
+dependencies {
+  compileOnly group: 'org.freemarker', name: 'freemarker', version: '2.3.9'
+
+  testImplementation group: 'org.freemarker', name: 'freemarker', version: '2.3.9'
+
+  testRuntimeOnly project(':dd-java-agent:instrumentation:iast-instrumenter')
+
+  latestDepTestImplementation group: 'org.freemarker', name: 'freemarker', version: '2.3.23'
+}

dd-java-agent/instrumentation/freemarker-2.3.9/src/main/java/datadog/trace/instrumentation/freemarker9/DollarVariableInstrumentation.java

@@ -0,0 +1,81 @@
+package datadog.trace.instrumentation.freemarker9;
+
+import static datadog.trace.agent.tooling.bytebuddy.matcher.ClassLoaderMatchers.hasClassNamed;
+import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
+import static net.bytebuddy.matcher.ElementMatchers.isMethod;
+import static net.bytebuddy.matcher.ElementMatchers.not;
+import static net.bytebuddy.matcher.ElementMatchers.takesArgument;
+
+import com.google.auto.service.AutoService;
+import datadog.trace.agent.tooling.Instrumenter;
+import datadog.trace.agent.tooling.InstrumenterModule;
+import datadog.trace.api.iast.InstrumentationBridge;
+import datadog.trace.api.iast.Sink;
+import datadog.trace.api.iast.VulnerabilityTypes;
+import datadog.trace.api.iast.sink.XssModule;
+import freemarker.core.DollarVariable2_3_9Helper;
+import freemarker.core.Environment;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.matcher.ElementMatcher;
+
+@AutoService(InstrumenterModule.class)
+public class DollarVariableInstrumentation extends InstrumenterModule.Iast
+    implements Instrumenter.ForSingleType {
+  static final String FREEMARKER_CORE = "freemarker.core";
+
+  public DollarVariableInstrumentation() {
+    super("freemarker");
+  }
+
+  @Override
+  public String muzzleDirective() {
+    return "freemarker-2.3.9";
+  }
+
+  static final ElementMatcher.Junction<ClassLoader> NOT_VERSION_PRIOR_2_3_24 =
+      not(hasClassNamed("freemarker.cache.ByteArrayTemplateLoader"));
+
+  @Override
+  public ElementMatcher.Junction<ClassLoader> classLoaderMatcher() {
+    return NOT_VERSION_PRIOR_2_3_24;
+  }
+
+  @Override
+  public String instrumentedType() {
+    return FREEMARKER_CORE + ".DollarVariable";
+  }
+
+  @Override
+  public String[] helperClassNames() {
+    return new String[] {FREEMARKER_CORE + ".DollarVariable2_3_9Helper"};
+  }
+
+  @Override
+  public void methodAdvice(MethodTransformer transformer) {
+    transformer.applyAdvice(
+        named("accept")
+            .and(isMethod())
+            .and(takesArgument(0, named(FREEMARKER_CORE + ".Environment"))),
+        DollarVariableInstrumentation.class.getName() + "$DollarVariableAdvice");
+  }
+
+  public static class DollarVariableAdvice {
+
+    @Advice.OnMethodEnter(suppress = Throwable.class)
+    @Sink(VulnerabilityTypes.XSS)
+    public static void onEnter(
+        @Advice.Argument(0) final Environment environment, @Advice.This final Object self) {
+      if (environment == null || self == null) {
+        return;
+      }
+      final XssModule xssModule = InstrumentationBridge.XSS;
+      if (xssModule == null) {
+        return;
+      }
+      String charSec = DollarVariable2_3_9Helper.fetchCharSec(self, environment);
+      final String templateName = environment.getTemplate().getName();
+      final int line = DollarVariable2_3_9Helper.fetchBeginLine(self);
+      xssModule.onXss(charSec, templateName, line);
+    }
+  }
+}

dd-java-agent/instrumentation/freemarker-2.3.9/src/main/java/freemarker/core/DollarVariable2_3_9Helper.java

@@ -0,0 +1,59 @@
+package freemarker.core;
+
+import freemarker.template.TemplateModelException;
+import java.lang.reflect.Field;
+import java.lang.reflect.UndeclaredThrowableException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public final class DollarVariable2_3_9Helper {
+  private DollarVariable2_3_9Helper() {}
+
+  private static final Logger log = LoggerFactory.getLogger(DollarVariable2_3_9Helper.class);
+
+  private static final Field ESCAPED_EXPRESSION = prepareEscapedExpression();
+
+  private static Field prepareEscapedExpression() {
+    try {
+      Field autoEscape = DollarVariable.class.getDeclaredField("escapedExpression");
+      autoEscape.setAccessible(true);
+      return autoEscape;
+    } catch (Throwable e) {
+      log.debug("Failed to get DollarVariable escapedExpression", e);
+      return null;
+    }
+  }
+
+  public static Expression fetchEscapeExpression(Object object) {
+    if (ESCAPED_EXPRESSION == null || !(object instanceof DollarVariable)) {
+      return null;
+    }
+    try {
+      return (Expression) ESCAPED_EXPRESSION.get(object);
+    } catch (IllegalAccessException e) {
+      throw new UndeclaredThrowableException(e);
+    }
+  }
+
+  public static String fetchCharSec(Object object, Environment environment) {
+    if (!(object instanceof DollarVariable)) {
+      return null;
+    }
+    final Expression expression = DollarVariable2_3_9Helper.fetchEscapeExpression(object);
+    if (expression instanceof BuiltIn) {
+      return null;
+    }
+    try {
+      return environment.getDataModel().get(expression.toString()).toString();
+    } catch (TemplateModelException e) {
+      throw new UndeclaredThrowableException(e);
+    }
+  }
+
+  public static Integer fetchBeginLine(Object object) {
+    if (!(object instanceof DollarVariable)) {
+      return null;
+    }
+    return ((DollarVariable) object).beginLine;
+  }
+}

dd-java-agent/instrumentation/freemarker-2.3.9/src/test/groovy/datadog/trace/instrumentation/freemarker9/DollarVariableInstrumentationTest.groovy

@@ -0,0 +1,38 @@
+package datadog.trace.instrumentation.freemarker9
+
+import datadog.trace.agent.test.AgentTestRunner
+import datadog.trace.api.iast.InstrumentationBridge
+import datadog.trace.api.iast.sink.XssModule
+import freemarker.template.Configuration
+import freemarker.template.SimpleHash
+import freemarker.template.Template
+import freemarker.template.TemplateHashModel
+
+class DollarVariableInstrumentationTest extends AgentTestRunner {
+
+  @Override
+  protected void configurePreAgent() {
+    injectSysConfig('dd.iast.enabled', 'true')
+  }
+
+  void 'test freemarker process'() {
+    given:
+    final module = Mock(XssModule)
+    InstrumentationBridge.registerIastModule(module)
+
+    final Configuration cfg = new Configuration()
+    final Template template = new Template("test", new StringReader("test \${$stringExpression}"), cfg)
+    final TemplateHashModel rootDataModel = new SimpleHash(cfg.getObjectWrapper())
+    rootDataModel.put(stringExpression, expression)
+
+    when:
+    template.process(rootDataModel, Mock(FileWriter))
+
+    then:
+    1 * module.onXss(_, _, _)
+
+    where:
+    stringExpression | expression
+    "test"           | "test"
+  }
+}

settings.gradle

@@ -226,6 +226,7 @@ include ':dd-java-agent:instrumentation:elasticsearch:transport-7.3'
 include ':dd-java-agent:instrumentation:enable-wallclock-profiling'
 include ':dd-java-agent:instrumentation:exception-profiling'
 include ':dd-java-agent:instrumentation:finatra-2.9'
+include ':dd-java-agent:instrumentation:freemarker-2.3.9'
 include ':dd-java-agent:instrumentation:freemarker-2.3.24'
 include ':dd-java-agent:instrumentation:glassfish'
 include ':dd-java-agent:instrumentation:google-http-client'