Question

I am working through the Microsoft .Net Framework–Application Development Foundation Training Kit book Chapter 8 Lesson 2: Configuring Application Domains

ShowWinIni being the assembly name for the program I want to execute

object[] hostEvidence = { new Zone(SecurityZone.MyComputer) };
Evidence e = new Evidence(hostEvidence, null);

// Create an AppDomain.
AppDomain d = AppDomain.CreateDomain("New Domain", e);

// Run the assembly
d.ExecuteAssemblyByName("ShowWinIni");

When I execute:

AppDomain d = AppDomain.CreateDomain("New Domain", e);

I get the following message:
“This method implicitly uses CAS policy, which has been obsoleted by the .NET Framework. In order to enable CAS policy for compatibility reasons, please use the NetFx40_LegacySecurityPolicy configuration switch. Please see http://go.microsoft.com/fwlink/?LinkID=155570 for more information.”

I can execute the assembly fine when I create an AppDomain without an Evidence object.

Of course, I visited http://go.microsoft.com/fwlink/?LinkID=155570 but I am still confused as to how to create an application domain with specified privileges.

The next most helpful site I found was http://msdn.microsoft.com/en-us/library/bb763046.aspx but my StrongName object computes to NULL.

StrongName fullTrustAssembly =
     typeof(Program).Assembly.Evidence.GetHostEvidence<StrongName>();

Program being the name of the class implementing all this code.

Thanks in advance for your advice and tips!

Answer 1

I found a way to make the original code example work without having to enable NetFX40_LegacySecurityPolicy.

EvidenceBase[] hostEvidence = { new Zone(SecurityZone.MyComputer) };
Evidence e = new Evidence(hostEvidence, null);

AppDomain d = AppDomain.CreateDomain("New Domain", e);

d.ExecuteAssemblyByName("ShowWinIni");

This will not work if you change the SecurityZone to Internet, it will try to use the obsoleted CAS security policy resulting in a NotSupportedException. What I want is a SecurityException… meaning that the assembly I want to execute does not have the permissions it needs.

To execute an assembly in an AppDomain with restricted permissions, you need to use sandboxing. The best example of sandboxing I found is here:
http://www.simple-talk.com/dotnet/.net-framework/whats-new-in-code-access-security-in-.net-framework-4.0—part-i/

I think that page also explains the changes made to CAS in 4.0 very well!

Many sources, including MSDN, had me convinced I needed to provide a StrongName array when calling:

AppDomain.CreateDomain( string friendlyName,
                        Evidence securityInfo,
                        AppDomainSetup info,
                        PermissionSet grantSet,
                        params StrongName[] fullTrustAssemblies);

As stated in my original post, I was (and still am) having trouble getting a StrongName object instead of null. Turns out I didn’t even need it!

This is my completed example for sandboxing:

Evidence ev = new Evidence();
ev.AddHostEvidence(new Zone(SecurityZone.Internet));
PermissionSet internetPS = SecurityManager.GetStandardSandbox(ev);

AppDomainSetup adSetup = new AppDomainSetup();
adSetup.ApplicationBase = Path.GetFullPath(pathToUntrusted);

AppDomain newDomain = AppDomain.CreateDomain("Sandbox Domain", null, adSetup, internetPS);

newDomain.ExecuteAssemblyByName(untrustedAssembly);

pathToUntrusted = a string representation of the file path to my assembly

untrustedAssembly = a string representation of the assembly name