I try to make a simple console modding project in C# where I have my program that contain a list of an abstract class named ElementInGame. I want to be able to create others class that inherit ElementInGame from a .txt file. The class ElementInGame will contain some basic methods (virtual and not virtual). But I don't want these other modded class execute malicious code, I would like that they can only access the methods/properties from the inherited class. Here is my ElementInGame code :
(My C# program #1)
using System;
namespace Modding
{
//The class itself inherit from MarshalByRefObject to be available in 2 differents Domains
public abstract class ElementInGame : MarshalByRefObject
{
public ElementInGame()
{
Console.WriteLine("ElementInGame class created");
}
public virtual int GetNumber()
{
return 10;
}
public void CountToTen()
{
for (int i = 0; i <= 10; i++)
{
Console.WriteLine(i);
}
}
}
}
Then I have my .txt file stored at "C:\program.txt"
(My original .txt file)
using System;
namespace Test
{
public class HelloWorld
{
public HelloWorld()
{
Console.WriteLine("Called Constructor() !");
}
public static int TestMethod()
{
Console.WriteLine("Called TestMethod() !");
return 11;
}
}
}
So I code the main program to read the .txt file, compile it with restrictions, and execute it :
(My C# program #2 in a second .cs file, long code warning)
using System;
using System.CodeDom.Compiler;
using System.IO;
using Microsoft.CSharp;
using System.Reflection;
using System.Security.Permissions;
using System.Security;
using System.Security.Policy;
using System.Runtime.Remoting;
using System.Collections.Generic;
namespace Modding
{
public class Program : MarshalByRefObject
{
public static void Main(string[] args)
{
string assemblyPath = @"C:\program.txt"; // Where the .txt file is stored
string code = File.ReadAllText(assemblyPath); //The code to compile
CompilerResults compile = CompileFromCode(code); //Compile the code in the temporary files
string fullPath = compile.PathToAssembly; //sample : C:\Users\MY_USER_NAME\AppData\Local\Temp\5v2p3qki.dll
string pathWithoutFile = Path.GetDirectoryName(fullPath); //sample : C:\Users\MY_USER_NAME\AppData\Local\Temp
string pathNameOnly = Path.GetFileNameWithoutExtension(fullPath); //sample : 5v2p3qki
Program newDomainInstance = GetOtherProtectedDomainInstance(pathWithoutFile);
newDomainInstance.CallMethod(pathNameOnly, "Test.HelloWorld", "TestMethod", null, null);
newDomainInstance.CreateObject(pathNameOnly,"Test.HelloWorld");
List<ElementInGame> allElement = new List<ElementInGame>();
//allElement.Add ***?***
Console.ReadKey();
}
public static Program GetOtherProtectedDomainInstance(string pathWithoutFile)
{
AppDomainSetup adSetup = new AppDomainSetup();
adSetup.ApplicationBase = pathWithoutFile;
//Set some permissions to avoid malicious code
PermissionSet permSet = new PermissionSet(PermissionState.None);
permSet.AddPermission(new SecurityPermission(SecurityPermissionFlag.Execution));
StrongName fullTrustAssembly = new StrongName(
new StrongNamePublicKeyBlob(typeof(Program).Assembly.GetName().GetPublicKey()),
typeof(Program).Assembly.GetName().Name,
typeof(Program).Assembly.GetName().Version);
AppDomain newDomain = AppDomain.CreateDomain("Sandbox", null, adSetup, permSet, fullTrustAssembly);
ObjectHandle handle = Activator.CreateInstanceFrom(
newDomain, typeof(Program).Assembly.ManifestModule.FullyQualifiedName,
typeof(Program).FullName
);
Program newDomainInstance = (Program)handle.Unwrap();
return newDomainInstance;
}
public static CompilerResults CompileFromCode(string code)
{
//Compile the code in a .dll locate in the temporary files
//The following code is based on https://stackoverflow.com/questions/10314815/trying-to-compile-and-execute-c-sharp-code-programmatically
CompilerParameters CompilerParams = new CompilerParameters();
string outputDirectory = Directory.GetCurrentDirectory();
CompilerParams.GenerateInMemory = false;
CompilerParams.TreatWarningsAsErrors = false;
CompilerParams.GenerateExecutable = false;
CompilerParams.CompilerOptions = "/optimize";
//Adding a reference to the current project to allow the .txt file to inherit the class "ElementInGame" later
string[] references = { "System.dll", Assembly.GetEntryAssembly().Location };
CompilerParams.ReferencedAssemblies.AddRange(references);
CSharpCodeProvider provider = new CSharpCodeProvider();
CompilerResults compile = provider.CompileAssemblyFromSource(CompilerParams, code);
if (compile.Errors.HasErrors)
{
string text = "Compile error: ";
foreach (CompilerError ce in compile.Errors)
{
text += "rn" + ce.ToString();
}
throw new Exception(text);
}
return compile;
}
public static void DisplaySomething()//Useful for later
{
Console.WriteLine("This isn't supposed to be display");
}
//Calling a method from the restricted Domain
public void CallMethod(string assemblyName, string typeName, string entryPoint, object objectToExecute = null, object[] parameters = null)
{
MethodInfo target = Assembly.Load(assemblyName).GetType(typeName).GetMethod(entryPoint);
try
{
target.Invoke(objectToExecute, parameters);
}
catch
{
Console.WriteLine("Security Error with Method " + assemblyName + " namespace : " + typeName + " method : " + entryPoint);
}
}
//Create an instance from the restricted Domain
public void CreateObject(string assemblyName, string typeName)
{
try
{
object o = Assembly.Load(assemblyName).CreateInstance(typeName);
}
catch
{
Console.WriteLine("Security Error with Constructor " + assemblyName + " namespace : " + typeName);
}
}
}
}
For the moment the .txt file don't have any link at all with my C# program. The code work properly and I got the following output :
Called TestMethod() !
Called Constructor() !
Then I edit my code in my .txt file to inherit from Modding.ElementInGame :
(My edited .txt file)
using System;
namespace Test
{
public class HelloWorld : Modding.ElementInGame
{
public HelloWorld() : base()
{
Console.WriteLine("Called Constructor() !");
}
public static int TestMethod()
{
Console.WriteLine("Called TestMethod() !");
return 11;
}
}
}
So I expected an output like :
Called TestMethod() !
ElementInGame class created
Called Constructor() !
But after this change, the program crash with a System.NullReferenceException at when calling the TestMethod : newDomainInstance.CallMethod(pathNameOnly, "Test.HelloWorld", "TestMethod", null, null);
However creating an instance of HelloWorld (the .txt file): newDomainInstance.CreateObject(pathNameOnly,"Test.HelloWorld"); seem to works (no crash, the code stay in the try part when doing the try/catch), but my there is nothings print in my console, so it doesn't work I guess ?
Changing the permission of the AppDomain change nothing.
PermissionSet permSet = new PermissionSet(PermissionState.Unrestricted);
permSet.AddPermission(new SecurityPermission(SecurityPermissionFlag.AllFlags));
So my question is : How can I create and store an instance of the .txt file in my program that inherit from ElementInGame (and add it to the list of ElementInGame) ?
That way I can use from my program the virtual method GetNumber(). I don't want the .txt file have access to the program itself (like calling the method DisplaySomething()), just communicate with ElementInGame.
