动态附加 Java 代理不起作用

Question

我为编码挑战编写了以下代码。该程序的目的是附加到另一个 java 进程并在程序启动后加载检测引擎。这通常在 Java 中通过在代理 jar 文件中实施 agentmain 方法来完成。我在下面的代码中生成了这一切：

错误出现在 JVM 运行玩具程序上，线索是它认为 Agent class 文件名出于某种原因是 Agent$1。我注释掉了我对 ByteBuddy 的使用，并尝试使用内置库加载代理文件，但它仍然失败。

heartbeat : 373 pid = 21992
heartbeat : 374 pid = 21992
Exception in thread "Attach Listener" java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:491)
    at java.instrument/sun.instrument.InstrumentationImpl.loadClassAndCallAgentmain(InstrumentationImpl.java:513)
Caused by: java.lang.NoClassDefFoundError: Agent
    at Agent.agentmain(Agent.java:8)
    ... 6 more
Caused by: java.lang.ClassNotFoundException: Agent
    ... 7 more
Agent failed to start!

import com.sun.tools.attach.VirtualMachine;
import net.bytebuddy.ByteBuddy;
import net.bytebuddy.agent.ByteBuddyAgent;
import net.bytebuddy.dynamic.loading.ClassReloadingStrategy;
import net.bytebuddy.implementation.FixedValue;

import java.io.*;
import java.lang.instrument.Instrumentation;

import static net.bytebuddy.matcher.ElementMatchers.named;

public class Thief {

    public static void main(String[] args) throws Exception {
        Thief thief = new Thief();

        VirtualMachine jvm = VirtualMachine.attach("21992");
        File agentFile = new File("agent.jar");
        jvm.loadAgent(agentFile.getAbsolutePath());

        //thief.guessSecurityCode("24472");
    }

    public String guessSecurityCode(final String pid) throws Exception {
        File jarFile = createAgent();
        ByteBuddyAgent.attach(jarFile, pid);
        return "0000";
    }

    private static String generateSimpleAgent2() {

        return  "import java.lang.instrument.ClassFileTransformer;" + "\n" +
                "import java.lang.instrument.Instrumentation;" + "\n" +
                "import java.security.ProtectionDomain;" + "\n" +
                "\n\n" +
                "public class Agent {" +"\n" +
                "    public static void agentmain(String argument, Instrumentation inst) {" +"\n" +
                "    }" +"\n" +
                "}" +"\n";
    }

    private static String generateSimpleAgent() {

        return  "import java.lang.instrument.ClassFileTransformer;" + "\n" +
                "import java.lang.instrument.Instrumentation;" + "\n" +
                "import java.security.ProtectionDomain;" + "\n" +
                "\n\n" +
                "public class Agent {" +"\n" +
                "    public static void agentmain(String argument, Instrumentation inst) {" +"\n" +
                "        inst.addTransformer(new ClassFileTransformer() {" +"\n" +
                "            @Override" +"\n" +
                "            public byte[] transform(" +"\n" +
                "                ClassLoader loader," +"\n" +
                "                String className," +"\n" +
                "                Class<?> classBeingRedefined," +"\n" +
                "                ProtectionDomain protectionDomain," +"\n" +
                "                byte[] classFileBuffer) {" +"\n" +
                "            System.out.println(\"transform on : \" +className);" +"\n" +
                "            return classFileBuffer;" +"\n" +
                "            }" +"\n" +
                "        });" +"\n" +
                "    }" +"\n" +
                "}" +"\n";
    }

    private static String generateAgentManifest() {
        return  String.join("\n", "Agent-Class: Agent",
                "Can-Retransform-Classes: true",
                "Can-Redefine-Classes: true",
                "Premain-Class: Agent"
        );
    }

    private static String generateAgentManifest2() {
        return  String.join("\n",
                "Manifest-Version: 1.0",
                "Agent-Class: Agent",
                "Permissions: all-permissions"
        );
    }

    private static String generateTransformer() {
        return String.join("\n",
                "import java.lang.instrument.ClassFileTransformer;",
                "import java.security.ProtectionDomain;",
                "import java.util.Arrays;",
                "public class Transformer implements ClassFileTransformer {",
                "    public byte[] transform(ClassLoader loader, String className, Class<?> cls, ProtectionDomain dom, byte[] buf) {",
                "        return null;",
                "    }",
                "}"
        );
    }

    private static void writeFile(String path, String data) throws IOException {
        final PrintWriter out = new PrintWriter(path);
        out.print(data);
        out.close();
    }

    private static void runCommand(String cmd) throws Exception {
        System.out.println("[commmand] " + cmd);
        String s;
        Process p = Runtime.getRuntime().exec(cmd);
        BufferedReader out = new BufferedReader(new InputStreamReader(p.getInputStream()));
        while ((s = out.readLine()) != null) {
            System.out.println("[out] " + s);
        }
        out = new BufferedReader(new InputStreamReader(p.getErrorStream()));
        while ((s = out.readLine()) != null) {
            System.out.println("[err] " + s);
        }
        p.waitFor();
        System.out.println("[exit status] " + p.exitValue());
        p.destroy();
    }

    private static File createAgent() throws Exception {
        writeFile("Agent.java", generateSimpleAgent2());
        writeFile("Transformer.java", generateTransformer());
        writeFile("manifest.mf", generateAgentManifest2());
        runCommand("javac Agent.java Transformer.java");
        runCommand("jar -cfm agent.jar manifest.mf Agent.class Transformer.class");
        return new File("agent.jar");
    }
}

有人知道我做错了什么吗？

Answer 1

Agent是匿名的class，所以一定是你在这里创建的：

new ClassFileTransformer() { ... }

至于为什么找不到，怎么解决我不知道，或许你可以在引用之前为它生成一个真实的名字class？

Answer 2

与 generateSimpleAgent2() 一起使用。它不会以同样的方式失败，就像您在 ewramner 的回答下的评论中所说的那样。那应该给你一个线索。此外，如果您只是阅读异常并相信它告诉您的内容，您就知道该怎么做。再次：

java.lang.ClassNotFoundException: Agent

即，generateSimpleAgent() 创建两个 class 文件，一个用于代理本身，一个用于其匿名 class。这正是 javac 所期望的。只需检查输出目录，您就会看到它。只需将缺少的 class 文件添加到 JAR 中即可：

runCommand("jar -cfm agent.jar manifest.mf Agent.class Agent.class Transformer.class");

现在带有匿名转换器的代理 class 也可以工作了。我测试了。

动态附加 Java 代理不起作用

Dynamically attaching a Java agent not working

java

jvm

agent

byte-buddy