Why does my .net application require full trust?

Question

I've developed a .net 3.0 application, which is deployed using clickonce.

I'd like to move from full trust to partial trust to ease deployment.

I've tried the "Calculate Permissions" tool in the "Security" tab of my project under visual studio, and the answer is quite clear :

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Microsoft Visual Studio
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This application requires full trust to run correctly.

However, I've not been able to figure out why full trust is required. I've tried to change the security settings to "partial trust", but the application raises a SecurityException immediately upon launch :

System.Security.SecurityException   {"Request failed.", Action= "System.Security.Permissions.SecurityAction.LinkDemand"
   at MyNameSpace.Program.Main(String[] args)
   at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
   at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
   at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel)
   at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly()
   at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData)
   at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext)
   at System.Activator.CreateInstance(ActivationContext activationContext)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

My software probably doesn't need full trust (I only connect to a webserver using https, and access the filesystem only upon user request, for importation/exportation purposes)

How can I figure out why my application requires full trust?

Answer 1

Hrm, just a guess, but is it running off of a network share? .NET seems to assign trust based on the location the code is being run from. If it's from anywhere but your local hard drive then you're going to have security issues.

Answer 2

Without seeing the code for your application, it's impossible to tell. There is something that is requiring full trust in your app that you might have overlooked (perhaps a dependency?).

Answer 3

The exception message is telling you why you can't run with partial trust:

System.Security.Permissions.SecurityAction.LinkDemand

If you copy and paste that into Google, you will find several relevant articles on MSDN that might help you to discover why your application requires full trust.

Answer 4

It seems my problem is caused by the fact that my assembly is strongly signed.

Quoted from msdn

In strong-named assemblies, a LinkDemand is applied to all publicly accessible methods, properties, and events therein to restrict their use to fully trusted callers. To disable this feature, you must apply the AllowPartiallyTrustedCallersAttributeattribute.

I'm adding the needed attribute to my assembly, and I'll let you know how things turn out :

[assembly:AllowPartiallyTrustedCallers]

Update : I've added the attribute to my assemblies, but I'm also using some .net assemblies.

Not all .net assemblies can be used by partially trusted assemblies (here's a list), namely, WCF assemblies (ie System.ServiceModel) is not on the list

However, Microsoft states that it's possible to use WCF in a partial trust environment (see here)

I've tried to remove all the unneeded assemblies from my references, I've used the AllowPartiallyTrustedCallers in all my assemblies, and I'm still stucked...

Answer 5

Microsoft has a tool called permcalc which analyse an assembly and produces a detailed xml output file which looks like this :

<Type Name="MyClass">
<Method Sig="instance void .ctor()">
<Demand>
<PermissionSet version="1" class="System.Security.PermissionSet">
  <IPermission version="1" class="System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" Unrestricted="true" /> 
  <IPermission version="1" class="System.Security.Permissions.ReflectionPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" Unrestricted="true" /> 
...

Answer 6

Your stack-trace does not show the type of permission being demanded.

AllowPartiallyTrustedCallers won't help you in this case. It should be specified on the calling target, e.g. when some partially trusted code calls into your trusted assembly. In your situation you should examine whether your app calls into assemblies that do not have this attribute defined. If yes then your app will need to run in full-trust and won't work in partial trust at all (this is how CAS is enforced and is by design.)

Otherwise use permcalc. It will show you the permissions that should then be enabled in the security settings of the project. However I'm not sure if after including all those perms you will still have "partial trust" or rather full trust with a few stripped-down permissions. This is due to the fact that partial trust is very restrictive (open security.config and look at the enabled permissions!), as far as I know WebPermission is not there (which is needed to send http requests), same with FileIOPermission.

Answer 7

Adding the requirePermission='false' attribute in the app.config's configsections helps a lot :

 <sectionGroup name="system.net" type="System.Net.Configuration.NetSectionGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <section requirePermission="false" name="defaultProxy" type="System.Net.Configuration.DefaultProxySection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
    </sectionGroup>

It made the trick for me !