[8.18] Check hidden frames in entitlements (#127877)

docs/changelog/127877.yaml

@@ -0,0 +1,5 @@
+pr: 127877
+summary: Check hidden frames in entitlements
+area: Infra/Core
+type: bug
+issues: []

libs/entitlement/bridge/src/main/java/org/elasticsearch/entitlement/bridge/Util.java

@@ -10,8 +10,10 @@
 package org.elasticsearch.entitlement.bridge;
 
 import java.util.Optional;
+import java.util.Set;
 
 import static java.lang.StackWalker.Option.RETAIN_CLASS_REFERENCE;
+import static java.lang.StackWalker.Option.SHOW_HIDDEN_FRAMES;
 
 public class Util {
     /**
@@ -23,6 +25,8 @@ public class Util {
     public static final Class<?> NO_CLASS = new Object() {
     }.getClass();
 
+    private static final Set<String> skipInternalPackages = Set.of("java.lang.invoke", "java.lang.reflect", "jdk.internal.reflect");
+
     /**
      * Why would we write this instead of using {@link StackWalker#getCallerClass()}?
      * Because that method throws {@link IllegalCallerException} if called from the "outermost frame",
@@ -32,9 +36,10 @@ public class Util {
      */
     @SuppressWarnings("unused") // Called reflectively from InstrumenterImpl
     public static Class<?> getCallerClass() {
-        Optional<Class<?>> callerClassIfAny = StackWalker.getInstance(RETAIN_CLASS_REFERENCE)
+        Optional<Class<?>> callerClassIfAny = StackWalker.getInstance(Set.of(RETAIN_CLASS_REFERENCE, SHOW_HIDDEN_FRAMES))
             .walk(
                 frames -> frames.skip(2) // Skip this method and its caller
+                    .filter(frame -> skipInternalPackages.contains(frame.getDeclaringClass().getPackageName()) == false)
                     .findFirst()
                     .map(StackWalker.StackFrame::getDeclaringClass)
             );

libs/entitlement/src/main/java/org/elasticsearch/entitlement/runtime/policy/entitlements/FilesEntitlement.java

@@ -182,7 +182,9 @@ private static BaseDir parseBaseDir(String baseDir) {
             case "config" -> BaseDir.CONFIG;
             case "data" -> BaseDir.DATA;
             case "home" -> BaseDir.USER_HOME;
-            // NOTE: shared_repo is _not_ accessible to policy files, only internally
+            // it would be nice to limit this to just ES modules, but we don't have a way to plumb that through to here
+            // however, we still don't document in the error case below that shared_repo is valid
+            case "shared_repo" -> BaseDir.SHARED_REPO;
             default -> throw new PolicyValidationException(
                 "invalid relative directory: " + baseDir + ", valid values: [config, data, home]"
             );

modules/repository-url/src/main/plugin-metadata/entitlement-policy.yaml

@@ -1,2 +1,8 @@
+org.elasticsearch.repository.url:
+  - outbound_network
+  - files:
+      - relative_path: .
+        relative_to: shared_repo
+        mode: read
 org.apache.httpcomponents.httpclient:
   - outbound_network # for URLHttpClient