Compiling with mono and -nostdlib

Question

I am using Microsoft.CSharp.CSharpCodeProvider to programmatically compile an assembly & run some functions from the external .cs file.

But is there a way to forbid those functions from making any changes to the file system and etc. (I need to run them in some kind of a sandbox)?

I was thinking of adding "-nostdlib" option to the CompilerParameters so the resulting assembly will not be able to access System.IO.File and other classes. But I still need System.Object, System.ValueType, etc.

Right now I am getting these errors:

error CS0518: The predefined type `System.Object' is not defined or imported
error CS0518: The predefined type `System.ValueType' is not defined or imported
error CS0518: The predefined type `System.Attribute' is not defined or imported
error CS0518: The predefined type `System.Int32' is not defined or imported
... (too many of them)

How can I add those classes without those which can seriously harm the system (like System.IO.File, System.IO.Directory, System.Net.(something), System.Threading.(something)? )

Or, maybe there are easier ways? Thank you.

Answer 1

By importing the base System types such as System.Object or System.Int32 you import everything contained along in mscorlib.dll such as System.IO.Stream. You can't simply configure the import to not include some types in the assembly. As far as I know, your only way is to build your own stdlib - or build your own compiler but that's another story.

Hopefully thanks to the Mono project it should not be too difficult. You can pull the latest sources on GitHub. More specifically, have a look at the corlib folder. From that simply remove everything you don't want your users to use. Finally adding your custom mscorlib.dll to the ReferencedAssemblies and setting /nostdlib should be enough.

If you like being hardcore, you can try to achieve that using Cecil. Using this wonderful library you can easily lookup for types, remove them and save the patched assembly.

Another way around would be to inspect your loaded assembly for blacklisted types prior it's execution. It's not so trivial but Cecil can probably help. Have a look at this question : .NET Reflection: Find used types

Whatever you choose, good luck and have fun :)

Answer 2

You should use code access security for this. While you cannot restrict a program's access to the System.IO types without also restricting its access to core types such as System.Object, you can implement a runtime sandbox by restricting what code can do at runtime.

CAS allows you to assign permissions for different types of code to execute based on various types of evidence derived from the user's identity or other source. This allows fine-grained tuning of what code can do. It can be controlled both through imperative (i.e. code-based) and declarative (i.e. attribute-based) mechanisms.

CAS is a big subject and this description is necessarily brief.

Here's Mono's and MSDN's documentation for it.