Ensure clean thread context in MasterService (elastic#114512)

`ThreadContext#stashContext` doesn't guarantee to give a clean thread
context, but it's important we don't allow the callers' thread contexts
to leak into the cluster state update. This commit captures the desired
thread context at startup rather than using `stashContext` when forking
the processor.

Author: DaveCTurner

docs/changelog/114512.yaml

@@ -0,0 +1,5 @@
+pr: 114512
+summary: Ensure clean thread context in `MasterService`
+area: Cluster Coordination
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/cluster/service/MasterService.java

@@ -108,6 +108,7 @@ public class MasterService extends AbstractLifecycleComponent {
 
     protected final ThreadPool threadPool;
     private final TaskManager taskManager;
+    private final ThreadContext.StoredContext clusterStateUpdateContext;
 
     private volatile ExecutorService threadPoolExecutor;
     private final AtomicInteger totalQueueSize = new AtomicInteger();
@@ -128,6 +129,7 @@ public MasterService(Settings settings, ClusterSettings clusterSettings, ThreadP
 
         this.threadPool = threadPool;
         this.taskManager = taskManager;
+        this.clusterStateUpdateContext = getClusterStateUpdateContext(threadPool.getThreadContext());
 
         final var queuesByPriorityBuilder = new EnumMap<Priority, PerPriorityQueue>(Priority.class);
         for (final var priority : Priority.values()) {
@@ -137,6 +139,15 @@ public MasterService(Settings settings, ClusterSettings clusterSettings, ThreadP
         this.unbatchedExecutor = new UnbatchedExecutor();
     }
 
+    private static ThreadContext.StoredContext getClusterStateUpdateContext(ThreadContext threadContext) {
+        try (var ignored = threadContext.newStoredContext()) {
+            // capture the context in which to run all cluster state updates here where we know it to be very clean
+            assert threadContext.isDefaultContext() : "must only create MasterService in a clean ThreadContext";
+            threadContext.markAsSystemContext();
+            return threadContext.newStoredContext();
+        }
+    }
+
     private void setSlowTaskLoggingThreshold(TimeValue slowTaskLoggingThreshold) {
         this.slowTaskLoggingThreshold = slowTaskLoggingThreshold;
     }
@@ -1324,8 +1335,8 @@ private void forkQueueProcessor() {
 
         assert totalQueueSize.get() > 0;
         final var threadContext = threadPool.getThreadContext();
-        try (var ignored = threadContext.stashContext()) {
-            threadContext.markAsSystemContext();
+        try (var ignored = threadContext.newStoredContext()) {
+            clusterStateUpdateContext.restore();
             threadPoolExecutor.execute(queuesProcessor);
         }
     }

server/src/main/java/org/elasticsearch/node/NodeConstruction.java

@@ -268,7 +268,14 @@ static NodeConstruction prepareConstruction(
             constructor.loadLoggingDataProviders();
             TelemetryProvider telemetryProvider = constructor.createTelemetryProvider(settings);
             ThreadPool threadPool = constructor.createThreadPool(settings, telemetryProvider.getMeterRegistry());
-            SettingsModule settingsModule = constructor.validateSettings(initialEnvironment.settings(), settings, threadPool);
+
+            final SettingsModule settingsModule;
+            try (var ignored = threadPool.getThreadContext().newStoredContext()) {
+                // If any deprecated settings are in use then we add warnings to the thread context response headers, but we're not
+                // computing a response here so these headers aren't relevant and eventually just get dropped after possibly leaking into
+                // places they shouldn't. Best to explicitly drop them now to protect against such leakage.
+                settingsModule = constructor.validateSettings(initialEnvironment.settings(), settings, threadPool);
+            }
 
             SearchModule searchModule = constructor.createSearchModule(settingsModule.getSettings(), threadPool, telemetryProvider);
             constructor.createClientAndRegistries(settingsModule.getSettings(), threadPool, searchModule);

server/src/test/java/org/elasticsearch/action/admin/indices/rollover/MetadataRolloverServiceTests.java

@@ -34,6 +34,7 @@
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.IndexVersion;
@@ -63,6 +64,7 @@
 import static org.hamcrest.Matchers.lessThanOrEqualTo;
 import static org.hamcrest.Matchers.nullValue;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class MetadataRolloverServiceTests extends ESTestCase {
 
@@ -833,6 +835,7 @@ public void testRolloverClusterStateForDataStreamNoTemplate() throws Exception {
         final TestTelemetryPlugin telemetryPlugin = new TestTelemetryPlugin();
 
         ThreadPool testThreadPool = mock(ThreadPool.class);
+        when(testThreadPool.getThreadContext()).thenReturn(new ThreadContext(Settings.EMPTY));
         MetadataRolloverService rolloverService = DataStreamTestHelper.getMetadataRolloverService(
             dataStream,
             testThreadPool,

server/src/test/java/org/elasticsearch/action/ingest/ReservedPipelineActionTests.java

@@ -23,6 +23,7 @@
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.concurrent.EsExecutors;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.ingest.FakeProcessor;
 import org.elasticsearch.ingest.IngestInfo;
@@ -81,6 +82,7 @@ public void setup() {
         threadPool = mock(ThreadPool.class);
         when(threadPool.generic()).thenReturn(EsExecutors.DIRECT_EXECUTOR_SERVICE);
         when(threadPool.executor(anyString())).thenReturn(EsExecutors.DIRECT_EXECUTOR_SERVICE);
+        when(threadPool.getThreadContext()).thenReturn(new ThreadContext(Settings.EMPTY));
 
         Client client = mock(Client.class);
         ingestService = new IngestService(

server/src/test/java/org/elasticsearch/cluster/ClusterModuleTests.java

@@ -46,7 +46,6 @@
 import org.elasticsearch.indices.EmptySystemIndices;
 import org.elasticsearch.injection.guice.ModuleTestCase;
 import org.elasticsearch.plugins.ClusterPlugin;
-import org.elasticsearch.tasks.TaskManager;
 import org.elasticsearch.telemetry.TelemetryProvider;
 import org.elasticsearch.test.gateway.TestGatewayAllocator;
 import org.elasticsearch.threadpool.TestThreadPool;
@@ -88,8 +87,8 @@ public void setUp() throws Exception {
         clusterService = new ClusterService(
             Settings.EMPTY,
             new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
-            null,
-            (TaskManager) null
+            threadPool,
+            null
         );
     }
 

server/src/test/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateServiceTests.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.IndexScopedSettings;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.health.node.selection.HealthNodeTaskExecutor;
@@ -77,6 +78,7 @@
 import static org.hamcrest.Matchers.nullValue;
 import static org.hamcrest.Matchers.sameInstance;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
 
 public class MetadataIndexTemplateServiceTests extends ESSingleNodeTestCase {
 
@@ -2473,6 +2475,7 @@ public void testAddIndexTemplateWithDeprecatedComponentTemplate() throws Excepti
 
     private static List<Throwable> putTemplate(NamedXContentRegistry xContentRegistry, PutRequest request) {
         ThreadPool testThreadPool = mock(ThreadPool.class);
+        when(testThreadPool.getThreadContext()).thenReturn(new ThreadContext(Settings.EMPTY));
         ClusterService clusterService = ClusterServiceUtils.createClusterService(testThreadPool);
         MetadataCreateIndexService createIndexService = new MetadataCreateIndexService(
             Settings.EMPTY,

server/src/test/java/org/elasticsearch/cluster/service/MasterServiceTests.java

@@ -69,6 +69,7 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumMap;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
@@ -263,7 +264,15 @@ public void testThreadContext() throws InterruptedException {
             final CountDownLatch latch = new CountDownLatch(1);
 
             try (ThreadContext.StoredContext ignored = threadPool.getThreadContext().stashContext()) {
-                final Map<String, String> expectedHeaders = Collections.singletonMap("test", "test");
+
+                final var expectedHeaders = new HashMap<String, String>();
+                expectedHeaders.put(randomIdentifier(), randomIdentifier());
+                for (final var copiedHeader : Task.HEADERS_TO_COPY) {
+                    if (randomBoolean()) {
+                        expectedHeaders.put(copiedHeader, randomIdentifier());
+                    }
+                }
+
                 final Map<String, List<String>> expectedResponseHeaders = Collections.singletonMap(
                     "testResponse",
                     Collections.singletonList("testResponse")
@@ -1343,7 +1352,6 @@ public void testAcking() {
             .build();
         final var deterministicTaskQueue = new DeterministicTaskQueue();
         final var threadPool = deterministicTaskQueue.getThreadPool();
-        threadPool.getThreadContext().markAsSystemContext();
         try (
             var masterService = createMasterService(
                 true,
@@ -1352,6 +1360,7 @@ public void testAcking() {
                 new StoppableExecutorServiceWrapper(threadPool.generic())
             )
         ) {
+            threadPool.getThreadContext().markAsSystemContext();
 
             final var responseHeaderName = "test-response-header";
 

test/framework/src/main/java/org/elasticsearch/test/AbstractBuilderTestCase.java

@@ -36,6 +36,7 @@
 import org.elasticsearch.common.settings.IndexScopedSettings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.settings.SettingsModule;
+import org.elasticsearch.common.util.concurrent.DeterministicTaskQueue;
 import org.elasticsearch.common.xcontent.LoggingDeprecationHandler;
 import org.elasticsearch.core.IOUtils;
 import org.elasticsearch.env.Environment;
@@ -81,7 +82,6 @@
 import org.elasticsearch.script.ScriptModule;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.search.SearchModule;
-import org.elasticsearch.tasks.TaskManager;
 import org.elasticsearch.test.index.IndexVersionUtils;
 import org.elasticsearch.threadpool.TestThreadPool;
 import org.elasticsearch.transport.RemoteClusterAware;
@@ -432,8 +432,8 @@ private static class ServiceHolder implements Closeable {
             ClusterService clusterService = new ClusterService(
                 Settings.EMPTY,
                 new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS),
-                null,
-                (TaskManager) null
+                new DeterministicTaskQueue().getThreadPool(),
+                null
             );
 
             client = (Client) Proxy.newProxyInstance(

x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MlSingleNodeTestCase.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeValue;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.datastreams.DataStreamsPlugin;
 import org.elasticsearch.index.mapper.extras.MapperExtrasPlugin;
@@ -159,6 +160,7 @@ protected <T> T blockingCall(Consumer<ActionListener<T>> function) throws Except
 
     protected static ThreadPool mockThreadPool() {
         ThreadPool tp = mock(ThreadPool.class);
+        when(tp.getThreadContext()).thenReturn(new ThreadContext(Settings.EMPTY));
         ExecutorService executor = mock(ExecutorService.class);
         doAnswer(invocationOnMock -> {
             ((Runnable) invocationOnMock.getArguments()[0]).run();