java finalize 攻击

Java可以通过继承父类并实现finalize，在父类构造器抛出异常后，通过将对象引用记录在一个静态域，使得需要被回收的对象保持存活并可以调用相应方法

现在存在一个被攻击的类，Attacked，在age小于18时，对象的构建会失败

public class Attacked {
    private int age;

    public Attacked(int age) {
        this.age = age;
        if (age < 18) {
            throw new InvalidParameterException("age must great than 18");
        }
    }

    public void drink() {
        System.out.println("I can drink,because my age is: " + age);
    }
}

通过添加一个攻击子对象

public class Attacker extends Attacked {
    static Attacked attacked;
    public Attacker(int age) {
        super(age);
    }

    @Override
    protected void finalize() throws Throwable {
        attacked = this;
    }
}

调用下面方法

    public static void main(String[] args) {
        try {
            new Attacker(10);
        } catch (Exception e) {
        }
        System.gc();
        System.runFinalization();
        attacked.drink();
    }

可以看到，尽管age小于18,依然可以输出，从而得到错误的结果

I can drink,because my age is: 10