From 19f0755c48e998b5b136ca58ea21eb3b54bc7b33 Mon Sep 17 00:00:00 2001
From: Per Minborg <pminborg@openjdk.org>
Date: Wed, 27 Aug 2025 09:41:12 +0000
Subject: [PATCH] 8365203: defineClass with direct buffer can cause
 use-after-free

Reviewed-by: jpai
---
 .../share/classes/java/lang/ClassLoader.java  | 17 +++-
 .../defineClass/TestGuardByteBuffer.java      | 79 +++++++++++++++++++
 2 files changed, 92 insertions(+), 4 deletions(-)
 create mode 100644 test/jdk/java/lang/ClassLoader/defineClass/TestGuardByteBuffer.java

diff --git a/src/java.base/share/classes/java/lang/ClassLoader.java b/src/java.base/share/classes/java/lang/ClassLoader.java
index 6082bc53297..511785a5ac8 100644
--- a/src/java.base/share/classes/java/lang/ClassLoader.java
+++ b/src/java.base/share/classes/java/lang/ClassLoader.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2025, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2019, Azul Systems, Inc. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -52,6 +52,7 @@ import java.util.function.Supplier;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import jdk.internal.access.SharedSecrets;
 import jdk.internal.loader.BootLoader;
 import jdk.internal.loader.BuiltinClassLoader;
 import jdk.internal.loader.ClassLoaders;
@@ -1049,14 +1050,22 @@ public abstract class ClassLoader {
 
         protectionDomain = preDefineClass(name, protectionDomain);
         String source = defineClassSourceLocation(protectionDomain);
-        Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
-        postDefineClass(c, protectionDomain);
-        return c;
+
+        SharedSecrets.getJavaNioAccess().acquireSession(b);
+        try {
+            Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
+            postDefineClass(c, protectionDomain);
+            return c;
+        } finally {
+            SharedSecrets.getJavaNioAccess().releaseSession(b);
+        }
     }
 
     static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,
                                         ProtectionDomain pd, String source);
 
+    // Warning: Before calling this method, the provided ByteBuffer must be guarded
+    //          via JavaNioAccess::(acquire|release)Session
     static native Class<?> defineClass2(ClassLoader loader, String name, java.nio.ByteBuffer b,
                                         int off, int len, ProtectionDomain pd,
                                         String source);
diff --git a/test/jdk/java/lang/ClassLoader/defineClass/TestGuardByteBuffer.java b/test/jdk/java/lang/ClassLoader/defineClass/TestGuardByteBuffer.java
new file mode 100644
index 00000000000..6c12004ee4c
--- /dev/null
+++ b/test/jdk/java/lang/ClassLoader/defineClass/TestGuardByteBuffer.java
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8365203
+ * @summary Tests guarding of ByteBuffers in ClassLoader::defineClass
+ * @run junit TestGuardByteBuffer
+ */
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.foreign.Arena;
+import java.util.HexFormat;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+final class TestGuardByteBuffer {
+
+    @Test
+    void guardCrash() {
+        final byte[] classBytes = getClassBytes(); // get bytes of a valid class
+        final var cl = new ClassLoader() {
+            void tryCrash() {
+                var arena = Arena.ofConfined();
+                var byteBuffer = arena.allocate(classBytes.length).asByteBuffer();
+                // Close the arena underneath
+                arena.close();
+                // expected to always fail because the arena
+                // from which the ByteBuffer was constructed
+                // has been closed
+                assertThrows(IllegalStateException.class,
+                        () -> defineClass(null, byteBuffer, null));
+            }
+        };
+        for (int i = 0; i < 10_000; i++) {
+            cl.tryCrash();
+        }
+    }
+
+    private static byte[] getClassBytes() {
+        // unused. this is here just for reference
+        final String source = """
+                    public class NoOp {}
+                """;
+        // (externally) compiled content of the above "source", represented as hex
+        final String classBytesHex = """
+                cafebabe00000044000d0a000200030700040c000500060100106a6176612f
+                6c616e672f4f626a6563740100063c696e69743e0100032829560700080100
+                044e6f4f70010004436f646501000f4c696e654e756d6265725461626c6501
+                000a536f7572636546696c650100094e6f4f702e6a61766100210007000200
+                0000000001000100050006000100090000001d00010001000000052ab70001
+                b100000001000a000000060001000000010001000b00000002000c
+                """;
+
+        return HexFormat.of().parseHex(classBytesHex.replaceAll("\n", ""));
+    }
+
+}