UNDERTOW-2424: Prevent connection access-after-free allowed through C…

…hunkedStreamSinkConduit

ChunkedStreamSinkConduit releases underlying connections for reuse via a
conduit listener, however flush calls may still be passed through
after writes are terminated and successfully flushed. This would cause
requests to be clobbered when the connection had already been reused
to send another request, breaking the threading model.

core/src/main/java/io/undertow/conduits/ChunkedStreamSinkConduit.java

@@ -200,6 +200,9 @@ int doWrite(final ByteBuffer src) throws IOException {
 
     @Override
     public void truncateWrites() throws IOException {
+        if (anyAreSet(state, FLAG_FINISHED)) {
+            return;
+        }
         try {
             if (lastChunkBuffer != null) {
                 lastChunkBuffer.close();
@@ -259,6 +262,9 @@ public long transferFrom(final StreamSourceChannel source, final long count, fin
 
     @Override
     public boolean flush() throws IOException {
+        if (anyAreSet(state, FLAG_FINISHED)) {
+            return true;
+        }
         this.state |= FLAG_FIRST_DATA_WRITTEN;
         if (anyAreSet(state, FLAG_WRITES_SHUTDOWN)) {
             if (anyAreSet(state, FLAG_NEXT_SHUTDOWN)) {

core/src/test/java/io/undertow/conduits/ChunkedStreamSinkConduitTest.java

@@ -0,0 +1,177 @@
+/*
+ * JBoss, Home of Professional Open Source.
+ * Copyright 2024 Red Hat, Inc., and individual contributors
+ * as indicated by the @author tags.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package io.undertow.conduits;
+
+import io.undertow.connector.ByteBufferPool;
+import io.undertow.server.DefaultByteBufferPool;
+import io.undertow.testutils.category.UnitTest;
+import io.undertow.util.AbstractAttachable;
+import io.undertow.util.HeaderMap;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.xnio.XnioIoThread;
+import org.xnio.XnioWorker;
+import org.xnio.channels.StreamSourceChannel;
+import org.xnio.conduits.StreamSinkConduit;
+import org.xnio.conduits.WriteReadyHandler;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.charset.StandardCharsets;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicLong;
+
+import static org.junit.Assert.*;
+
+/**
+ * Test case for UNDERTOW-2424.
+ */
+@Category(UnitTest.class)
+public class ChunkedStreamSinkConduitTest {
+
+    @Test
+    public void testChunkedStreamSinkConduit() throws IOException {
+        ByteBufferPool pool = new DefaultByteBufferPool(false, 1024, -1, -1);
+        AtomicLong written = new AtomicLong();
+        AtomicInteger flushes = new AtomicInteger();
+        AtomicInteger listenerInvocations = new AtomicInteger();
+        StreamSinkConduit next = new StreamSinkConduit() {
+
+            @Override
+            public long transferFrom(FileChannel src, long position, long count) throws IOException {
+                written.addAndGet(count);
+                return count;
+            }
+
+            @Override
+            public long transferFrom(StreamSourceChannel source, long count, ByteBuffer throughBuffer) throws IOException {
+                written.addAndGet(count);
+                return count;
+            }
+
+            @Override
+            public int write(ByteBuffer src) {
+                int remaining = src.remaining();
+                src.position(src.position() + remaining);
+                written.addAndGet(remaining);
+                return remaining;
+            }
+
+            @Override
+            public long write(ByteBuffer[] srcs, int offs, int len) throws IOException {
+                long total = 0;
+                for (int i = offs; i < len; i++) {
+                    int written = write(srcs[i]);
+                    if (written == 0) {
+                        break;
+                    }
+                    total += written;
+                }
+                return total;
+            }
+
+            @Override
+            public int writeFinal(ByteBuffer src) throws IOException {
+                return write(src);
+            }
+
+            @Override
+            public long writeFinal(ByteBuffer[] srcs, int offset, int length) throws IOException {
+                return write(srcs, offset, length);
+            }
+
+            @Override
+            public void terminateWrites() {
+            }
+
+            @Override
+            public boolean isWriteShutdown() {
+                return false;
+            }
+
+            @Override
+            public void resumeWrites() {
+            }
+
+            @Override
+            public void suspendWrites() {
+            }
+
+            @Override
+            public void wakeupWrites() {
+            }
+
+            @Override
+            public boolean isWriteResumed() {
+                return false;
+            }
+
+            @Override
+            public void awaitWritable() {
+            }
+
+            @Override
+            public void awaitWritable(long time, TimeUnit timeUnit) {
+
+            }
+
+            @Override
+            public XnioIoThread getWriteThread() {
+                return null;
+            }
+
+            @Override
+            public void setWriteReadyHandler(WriteReadyHandler handler) {
+
+            }
+
+            @Override
+            public void truncateWrites() {
+
+            }
+
+            @Override
+            public boolean flush() {
+                flushes.incrementAndGet();
+                return true;
+            }
+
+            @Override
+            public XnioWorker getWorker() {
+                return null;
+            }
+        };
+        ConduitListener<ChunkedStreamSinkConduit> listener = channel -> listenerInvocations.incrementAndGet();
+        ChunkedStreamSinkConduit conduit = new ChunkedStreamSinkConduit(next, pool, false, false, new HeaderMap(), listener, new AbstractAttachable() {});
+
+        assertEquals(5, conduit.write(ByteBuffer.wrap("Hello".getBytes(StandardCharsets.UTF_8))));
+        assertEquals("Expected 11 bytes to be flushed including chunk headers",  11, written.get());
+        assertEquals(0, flushes.get());
+        conduit.terminateWrites();
+        assertTrue(conduit.flush());
+        int flushesAfterTerminate = flushes.get();
+        assertTrue(conduit.flush());
+        // UNDERTOW-2424: If this isn't the case, invocations from response wrappers may invoke flush on persistent
+        // connections that are already being used to process other requests on other threads.
+        assertEquals("Expected flushing after termination not to have any impact", flushesAfterTerminate, flushes.get());
+        assertEquals(1, listenerInvocations.get());
+    }
+}