I have an assembly which is being developed to create a facade around some potentially sensitive functionality and I want to allow a third party to call some of the methods contained within it but not others.
How can I prevent the third party calling unauthorised methods given they will have access to the entire DLL (I'm not concerned about them seeing the code, just executing it)?
This has to be compatible with the .net compact framework so unfortunately using the StrongNameIdentityPermission attribute is not possible.
I think you should ship two Facade implementations, one for 'internal' consumers which exposes all methods and another external that exposes only the sub-set. You can achieve this whilst maintaining only one code base by having two separate build processes. One technique that springs to mind is to use compiler directives to exclude a method from the external build, or mark it internal if it is required by other public methods. If you do ship sensitive methods with internal modifiers you may also want to implement obfuscation.
EDIT
Perhaps it would be cleaner, rather than having directives around each method to use partial classes, define a partial class for the sensitive methods and put the entire class implementation in a directive.
public partial class MyClass
{
public void NonSensitive(){}
}
#if INTERNAL_BUILD
public partial class MyClass
{
public void Sensitive(){}
}
#endif
You can have this partial class in the same or a separate file, which might be a nice level of separation as you could prepend the file name x_Sensitive.cs or similar.
Description
Assuming i understand your question.
You can mark your methods with the internal access modifier to make them not
accessable from other librarys.
But this does not help from security persepective, because it is always possible to run the method using reflection.
The internal keyword is an access modifier for types and type members. Internal types or members are accessible only within files in the same assembly
More Information
MSDN - internal (C# Reference)
If a third party can see the code, then they can run it - there is nothing you do to stop this.
Note however you have an application which is loading 3rd party plugins then you could load plugin assemblies with restrictions that prevent it from using reflection - this would mean that you can mark these methods / classes as internal to prevent plugins from being able to call these methods when loaded as a plugin in your application. Depending on the nature of the sensitive functionality this may or may not be useful to you from a security perspective.
For information on how to do this see How to: Run Partially Trusted Code in a Sandbox
Could you offer the functionality that you want the third party to consume as a Web API? They will not have any access to the source code OR the compiled binaries. They will only be able to see exactly what you want them to see. This would also offer additional security features such as Authentication and Authorization of callers.
Related
In C#, is it possible to restrict who can call a method at compile time?
I've looked into directives, but that didn't work since I can't assign values to symbols.
#define WHO VisualStudioUser.Current // does not work
I also looked into Code Access Security (CAS) but that's runtime enforcement, not compile time.
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
here's more details...
I'm building a framework or a series or assemblies for a team of developers. Because of our software license restrictions, I can only allow a few developers to write code to make a call to some restricted methods. The developers will not have access to the source code of the framework but they'll have access to the compiled framework assemblies.
The quick answer will be: No this isn't possible, and if you need to do it, you're Doing It Wrong.
How would this even work? Does it depend who who's running the code or who wrote it?
Edit There's kind of a way using InternalsVisibleTo and restricting accessing in source control to the assemblies that InternalsVisibleTo is specified for. See Jordão's answer
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
One way is to mark the method private or internal, it won't be callable by anyone outside the assembly. UPDATE: Also take a look at the InternalsVisibleTo attribute, which is used to define which assemblies can "see" internals of your assembly.
Another way is to divide the code you want to distribute from the code you don't want people to call into separate assemblies. Maybe you just share an assembly mostly of interfaces with your users, that they them compile against; and you have a separate assembly with implementations that they shouldn't reference directly. Your internal team would have access to the implementation assembly. This is just a common form of dependency management, the dependency inversion principle.
Draft:
Compile the restricted code into (obfuscated) DLLs: TypeA.dll, TypeB.dll etc.
Define an interface for each type, and compile them into separate DLLs: ITypeA.dll, ITypeB.dll etc.
Create a "guard assembly", and embed all restricted assemblies into it: Guard.dll. This has a ResolveEventHandler, and methods to instantiate different types defined in the embedded restricted DLLs. Instances are returned through their interface.
Developers get the interface DLLs and the Guard.dll. Each developer can get a Guard.dll with special authentication tokens in it. For example, a Guard.dll can be bound to PC, an IP address, a GUID issued to the developer, anything.
The developer can instantiate those types for which she has the proper authentication code, and uses the object instance through an interface.
Sorry this is a bit fuzzy, because it was more than a year ago when I used these techniques. I hope the main idea is clear.
Can you try using Extensible C# developed by ResolveCorp, some of the links for study and implementation are:
http://zef.me/782/extensible-c
http://www.codeproject.com/KB/architecture/DbCwithXCSharp.aspx
http://weblogs.asp.net/nunitaddin/archive/2003/02/14/2412.aspx
http://www.devx.com/dotnet/Article/11579/0/page/5
In my .NET solution, I have two projects: one main project and a project for running tests against the main project. In my project, I have several methods that I'd like to keep "private", but would also like to run tests for. Is there an access method that could limit these functions to just inside of my solution?
You are looking for the InternalsVisibleTo attribute.
This attributes lets you specify other assemblies that should have access to types and methods that are internal to your assembly. So, in your main project AssemblyInfo.cs file (or any other source file), you can specify that your test project is a 'friend assembly' and should have access to the internals of your main project:
[assembly:InternalsVisibleTo("MainProject.Tests")]
On a side note, as pointed out by Alexei, if your MainProject is signed with a strong name key, any 'friend' assembly must also be signed. This is explained here
Although, as mentioned in another comment. Best practice is to test your assembly by using its public API.
You can use InternalsVisibleTo attribute to make internal types and methods visible to selected assemblies.
However, you should try to design your API so that it can be tested using only the public interface.
You should seriously think back about the architecture of your solution. This is a smell that often shows that your class does too much things at once.
A simple fix is to extract this responsibility (those private methods) to another class where they then become public and are testable out of the box...
No, there is no way to limit access to "just solution".
The reason is solution is simply group of projects. One project can be in any number of solutions. So even if you "limit" access to projects included in one solution you/someone else can create another solution that somehow will need to magically get access to methods.
Additionally built assembly does not include any information on what solution it was part of - so there is no information at run time to check access.
To you particular problem - InternalsVisibleTo (as shown in other answers) will give access to internal methods to projects you allow (requires strongly signed assemblies) or refactor your code to avoid need for testing private methods.
Okay, I have a solution I am working on that has 4 different projects in it. One of my projects (a console application) is trying to make reference to some of the classes defined in another project (a library); the only problem is, those called are defined as Internal in the library.
How can I use these Internal classes in other assemblies/projects in the same solution? I added references to the library, but that did not help. It is saying that the protection level is too high (because it is internal, it is only available in that assembly).
You generally shouldn't access something that's internal. That defeats the purpose of declaring it so in the first place. If, however, you do need to...
If you can change the assembly with internal things, either:
Make the classes public, or
Use the InternalsVisibleToAttribute to expose it to just the assemblies you want to.
If you cannot change it, or decide not to, then you can use reflection to access the internal classes. For some portions of what you then do with the class, you should be able to use the dynamic keyword to make access easier and faster than with reflection.
You must use reflection to access the internal classes in other assemblies, but it will be significantly slower and not generally optimizable by the compiler. It's also somewhat complicated.
It is recommended that you expose a public class that wraps your internal classes and methods from the other assembly, or simply switch the internal classes in the other assembly over to public.
Before deploying my project, I would like to set all public methods to internal methods. Does someone know a built-in function in Visual Studio or an external tool to do such tasks?
With some trivial refactoring, ILMerge can work here. ILMerge can merge multiple assemblies into one, and change the accessibility of everything that is not part of the primary assembly to internal. By separating your current project into two projects (a library containing all the code, and a helper executable that does nothing but forward to the real code in the library), you can, after a build, merge them back into a single file, in which all the library bits are no longer public.
If you have properties/methods public for test reasons you should have a look at Brad Wilsons blog: Testable Object Pattern
This way you don't have to switch, everything stays internal in development.
Or have a look at Jon Skeets suggestion on InternalsVisibleTo
I can only think of two reasons you would want to do this:
Security. In this case you have the wrong idea: access modifiers are not a security mechanism. They are a design concern, describing how an API presents itself. Any debugger will still give access to all your methods, regardless of their access modifiers.
You have another assembly that you use during development that should have full access. In this case you can leave everything internal and make it a friend assembly.
I know that C# (and .NET in general) is big on attributes. However, despite the fact I have programmed in C# for many years, I haven't found myself ever using them. Would someone get me started on them, and explain where is the best to use them?
Thanks
From Pro C# 2008 and the .NET 3.5 Platform, Fourth Edition by Andrew Troelsen
Understanding Attributed Programming
One role of a .NET compiler is to generate metadata
descriptions for all defined and referenced types. In addition to this standard metadata contained
within any assembly, the .NET platform provides a way for programmers to embed additional
metadata into an assembly using attributes. In a nutshell, attributes are nothing more than code
annotations that can be applied to a given type (class, interface, structure, etc.), member (property,
method, etc.), assembly, or module.
The idea of annotating code using attributes is not new. COM IDL provided numerous predefined
attributes that allowed developers to describe the types contained within a given COM server.
However, COM attributes were little more than a set of keywords. If a COM developer needed to
create a custom attribute, he or she could do so, but it was referenced in code by a 128-bit number
(GUID), which was cumbersome at best.
Unlike COM IDL attributes (which again were simply keywords), .NET attributes are class types
that extend the abstract System.Attribute base class. As you explore the .NET namespaces, you will
find many predefined attributes that you are able to make use of in your applications. Furthermore,
you are free to build custom attributes to further qualify the behavior of your types by creating a
new type deriving from Attribute.
Understand that when you apply attributes in your code, the embedded metadata is essentially
useless until another piece of software explicitly reflects over the information. If this is not the case,
the blurb of metadata embedded within the assembly is ignored and completely harmless.
Attribute Consumers
As you would guess, the .NET 3.5 Framework SDK ships with numerous utilities that are indeed on
the lookout for various attributes. The C# compiler (csc.exe) itself has been preprogrammed to
discover the presence of various attributes during the compilation cycle. For example, if the C#
compiler encounters the [CLSCompliant] attribute, it will automatically check the attributed item to
ensure it is exposing only CLS-compliant constructs. By way of another example, if the C# compiler
discovers an item attributed with the [Obsolete] attribute, it will display a compiler warning in the
Visual Studio 2008 Error List window.
In addition to development tools, numerous methods in the .NET base class libraries are preprogrammed
to reflect over specific attributes. For example, if you wish to persist the state of an
object to file, all you are required to do is annotate your class with the [Serializable] attribute. If
the Serialize() method of the BinaryFormatter class encounters this attribute, the object is automatically
persisted to file in a compact binary format.
The .NET CLR is also on the prowl for the presence of certain attributes. Perhaps the most
famous .NET attribute is [WebMethod]. If you wish to expose a method via HTTP requests and automatically
encode the method return value as XML, simply apply [WebMethod] to the method and the
CLR handles the details. Beyond web service development, attributes are critical to the operation of
the .NET security system, Windows Communication Foundation, and COM/.NET interoperability
(and so on).
Finally, you are free to build applications that are programmed to reflect over your own custom
attributes as well as any attribute in the .NET base class libraries. By doing so, you are essentially
able to create a set of “keywords” that are understood by a specific set of assemblies.
Applying Attributes in C#
The .NET base class library provides a number of attributes in various
namespaces. Below is a snapshot of some—but by absolutely no means all—predefined
attributes.
A Tiny Sampling of Predefined Attributes
[CLSCompliant]
Enforces the annotated item to conform to the rules of the Common
Language Specification (CLS). Recall that CLS-compliant types are
guaranteed to be used seamlessly across all .NET programming languages.
[DllImport]
Allows .NET code to make calls to any unmanaged C- or C++-based code
library, including the API of the underlying operating system. Do note that
[DllImport] is not used when communicating with COM-based software.
[Obsolete]
Marks a deprecated type or member. If other programmers attempt to use
such an item, they will receive a compiler warning describing the error of
their ways.
[Serializable]
Marks a class or structure as being “serializable,” meaning it is able to persist
its current state into a stream.
[NonSerialized]
Specifies that a given field in a class or structure should not be persisted
during the serialization process.
[WebMethod]
Marks a method as being invokable via HTTP requests and instructs the CLR
to serialize the method return value as XML.
Building Custom Attributes
The first step in building a custom attribute is to create a new class deriving from System.Attribute. Example:
// A custom attribute.
public sealed class VehicleDescriptionAttribute : System.Attribute
{
private string msgData;
public VehicleDescriptionAttribute(string description)
{
msgData = description;
}
public VehicleDescriptionAttribute() { }
public string Description
{
get { return msgData; }
set { msgData = value; }
}
}
As you can see, VehicleDescriptionAttribute maintains a private internal string (msgData)
that can be set using a custom constructor and manipulated using a type property (Description).
Beyond the fact that this class derived from System.Attribute, there is nothing unique to this class
definition.
For security reasons, it is considered a .NET best practice to design all custom attributes as sealed. In
fact, Visual Studio 2008 provides a code snippet named Attribute that will dump out a new System.
Attribute-derived class into your code window.
Attributes get more use in code targeted to other programmers or between distinct parts of a program, rather than code targeted at end users.
For example, you could use attributes to import a dll, indicate how types would interact with visual studio (designer visible, intellisense helps, debugger step-through, etc), how to serialize them, indicate a type is obsolete, describe default values, descriptions, handle COM access, etc.
Those are things that are largely invisible to the end user and that a single programmer could put elsewhere in the source code. But they're useful when only the compiled binary is available and not the source.
I like to use attributes as metadata to my code. We have created some simple attributes that let us tag who wrote what code, when, and why. This lets us have both documented changes in code and in runtime. If there are any exceptions during runtime, we can inspect the callstack, look at any attributes on the methods along the way, and track down the people responsible:
[Author("Erich", "2009/04/06", Comment = "blah blah blah")]
public void MyFunction()
{
...
}
Of course, we could use our source control to look at who checked in what code, but this I've found makes the information more available in the place where you need it. Also, if we ever change source control, that information will not be lost since it is persisted in code.
Attributes are a form of declarative programming, 'similar' to creating your UI in XAML. It 'marks' pieces of code (classes, methods, properties, whatever) with an attribute so that you can later gather all those pieces marked in a specific way and then do something standard with all of them.
Eg. Consider the scenario where you have certain sections of code that you want to run once each time your app starts. In one model of programming (non-attribute) you go to your main method and explicitly call those init methods. With attributes you simply gather all methods which you've marked with your 'init' attribute, and call them via reflection.
The same pattern holds for actions like serialization, persistence and whatnot...
I believe you mean that you do not use (or frequently use) custom defined attributes ?
In my current project, I make heavy use of custom attributes, but, the fact that you need to keep in the back of your mind, is that using attributes should not be a goal on itself.
It is a tool / purpose to get to a given solution.
I sometimes use custom attributes in combination with a weaver like PostSharp, to decorate methods where some weaving should be applied to at compile-time.
In my current project, I also use attributes to decorate certain types with additional info ... But I believe I've posted about this here before:
Cool uses of Attributes or Annotations (CLR or Java)?
I use attributes for the following:
Communicating with a plug-in architecture
Telling another framework what to do with the code (NUnit, for instance)
Adding metadata for use with other code (See PropertyGrid)
Mapping objects to databases (See Castle ActiveRecord)
When writing my own APIs to allow users to communicate metadata
In framework code to tell the debugger to skip over it
Those are off the top of my head. I use them in many other places
Attributes are very good at describing some runtime behaviour of your code that is orthoganal to the code in question. For example, in a class called Customer you would model a customer, right? But you might not want to model or describe the way a Customer object is serialized.
Adding attributes to your Customer class allows you to tell some other part of the runtime how it should deal with your Customer.
MSTest and NUnit makes use of attributes to tell the test framework how it should use classes that define test fixtures.
ASP.NET MVC uses attribute to tell the mvc framework which methods on classes it should treat as controller actions.
So, any place where you have a runtime behaviour that you wish to model attributes can be useful.
Class Attribute definition is available here
ClassInterfaceAttribute : Indicates the type of class interface to be generated for a class exposed to COM, if an interface is generated at all.
ComDefaultInterfaceAttribute : Specifies a default interface to expose to COM. This class cannot be inherited.
ComVisibleAttribute: Controls accessibility of an individual managed type or member, or of all types within an assembly, to COM.