.NET: 通过AppDomain级别控制安全策略的例子

这是在课堂上讲的一个小范例。场景是：

1. 我们有一个主程序，它公开了一套API，允许其他开发人员为它设计插件

2. 因为插件不是我们设计的，所以我们需要确保这些插件不会恶意地伤害到用意。为此，我们希望将插件的运行权限降低。

解决方案就是，我们单独用一个AppDomain来运行这些插件，并且在该AppDomain级别单独设置安全策略。

1. API

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace API
{
    public interface IPlugin
    {
        void Run();
    }
}

2. Plugin

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PluginSample
{
    public class Plug:API.IPlugin
    {
        #region IPlugin 成员

        void API.IPlugin.Run()
        {
            MainForm form = new MainForm();
            form.ShowDialog();
        }

        #endregion
    }
}

Plugin中有一个窗体，里面有一个按钮，执行访问注册表的操作

using System;
using System.Windows.Forms;

using Microsoft.Win32;

namespace PluginSample
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            RegistryKey key = Registry.CurrentUser.CreateSubKey("Plugins");
            key.SetValue("Version", "1.0.0");
            key.SetValue("Update", DateTime.Now.ToString());

            MessageBox.Show("操作已经完成");
        }
    }
}

3. 宿主程序

为了实现跨应用程序域的加载，我们设计了一个AssemblyLoader类型

using System;
using System.Linq;

using System.Reflection;

namespace Host_WinForms
{
    [Serializable]
    class AssemblyLoader:MarshalByRefObject
        //必须继承MarshalByRefObject，否则无法实现AppDomain级别的安全控制
    {
        public string[] GetPluginTypeNames(string path) {
            Assembly ass = Assembly.LoadFile(path);
            var query = from type in ass.GetTypes()
                        where type.GetInterface(typeof(API.IPlugin).FullName) != null
                        select type.FullName;

            return query.ToArray();
        }

        public void RunPlugin(string path, string typeName) {
            Assembly ass = Assembly.LoadFile(path);
            API.IPlugin plugin = (API.IPlugin)ass.CreateInstance(typeName);
            plugin.Run();
        }
    }
}

宿主程序有一个MainForm

using System;
using System.Windows.Forms;

using System.IO;
using System.Security.Permissions;
using System.Security.Policy;
using System.Security;

namespace Host_WinForms
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }


        private void Log(string message)
        {
            richTextBox1.AppendText(DateTime.Now.ToString().PadRight(25));
            richTextBox1.AppendText(message);
            richTextBox1.AppendText(Environment.NewLine);
        }

        private void MainForm_Load(object sender, EventArgs e)
        {
            Log("主程序启动");

            Log("主程序域中的程序集:");
            foreach (var item in AppDomain.CurrentDomain.GetAssemblies())
            {
                Log(item.FullName);
            }


            //加载所有的插件（遍历当前目录下面的dll),动态创建菜单项目
            AppDomain plugindomain = AppDomain.CreateDomain("PluginDomain");
            AssemblyLoader loader = (AssemblyLoader)plugindomain.CreateInstanceFromAndUnwrap("Host_WinForms.exe", typeof(AssemblyLoader).FullName);

            foreach (var item in Directory.GetFiles(Environment.CurrentDirectory, "*.dll"))
            {
                foreach (var type in loader.GetPluginTypeNames(item))
                {
                    ToolStripMenuItem menuitem = new ToolStripMenuItem(type);
                    menuitem.Tag = item;
                    menuitem.Click += (o1, e1) =>
                    {
                        //当点击了之后执行有关的插件
                        AppDomain plugindomaintemp = AppDomain.CreateDomain("PluginDomain");

                        PolicyLevel level = PolicyLevel.CreateAppDomainLevel();
                        PermissionSet ps = level.GetNamedPermissionSet("Internet");
                        ps.AddPermission(new FileIOPermission(
                            FileIOPermissionAccess.AllAccess, Environment.CurrentDirectory));
                        level.RootCodeGroup.PolicyStatement = new PolicyStatement(ps);
                        plugindomaintemp.SetAppDomainPolicy(level);

                        try
                        {

                            AssemblyLoader loadertemp = (AssemblyLoader)plugindomaintemp.CreateInstanceFromAndUnwrap(
                                "Host_WinForms.exe", typeof(AssemblyLoader).FullName);

                            ToolStripMenuItem temp = (ToolStripMenuItem)o1;
                            loadertemp.RunPlugin(temp.Tag.ToString(), temp.Text);
                        }
                        catch (Exception ex) {
                            MessageBox.Show(string.Format("运行插件发生如下错误:{0}", ex.Message));
                        }
                        finally
                        {
                            AppDomain.Unload(plugindomaintemp);
                        }
                    };

                    AllPluginMenu.DropDownItems.Add(menuitem);
                }
            }


            AppDomain.Unload(plugindomain);

            Log("主程序域中的程序集:");
            foreach (var item in AppDomain.CurrentDomain.GetAssemblies())
            {
                Log(item.FullName);
            }

        }


    }
}

4. 运行效果