On Mon, 11 Aug 2025 11:33:19 GMT, Per Minborg <pminb...@openjdk.org> wrote:
> ### Description
> This PR proposes to update the `ClassLoader` implementation to properly guard
> access to the provided `ByteBuffer` when defining a class using
> `defineClass(String, ByteBuffer, ...)`. Specifically, calls to
> `SharedSecrets.getJavaNioAccess().acquireSession(ByteBuffer)` and
> `releaseSession(ByteBuffer)` have been introduced to ensure safe and
> consistent buffer access throughout the native class definition process, even
> in the case of a `ByteBuffer` is backed by a `MemorySegment`.
>
> ### Impact
> This modification is internal to the `ClassLoader` implementation and does
> not affect the public API.
> Improves the robustness and security of class loading from buffers.
>
> ### Testing
> Tier 1, 2, and 3 JDK tests pass on multiple platforms.
I think for the new test introduced, I don't think we should test for a crash.
Instead maybe we can simplify it as follows to assert that a closed `Arena`
doesn't allow a `Class` to be defined from the `ByteBuffer`. I think that will
simplify the test and also make it more deterministic. This is what I had in
mind:
/*
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/*
* @test
* @bug 8365203
* @summary Tests guarding of ByteBuffers in ClassLoader::defineClass
* @run junit GuardByteBuffer
*/
import java.lang.foreign.Arena;
import java.util.HexFormat;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertThrows;
final class GuardByteBuffer {
@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 < 10000; 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", ""));
}
}
-------------
PR Comment: https://git.openjdk.org/jdk/pull/26724#issuecomment-3214529831
