Implementing .NET Security in C#

-->

Environment: C#, .NET

Since my company, Harrissoft.co.uk, does a lot of .NET consultancy, one of our recent projects required that file i/o access be denied if the user running the application did not have administrator privileges. A lot has been written about the command line utility caspol.exe, however, this can seem a little over the top and quite complex when considering code groups, policy levels and zone management.

I basically wanted to programmatically check whether the user had the relevant permissions by accessing their windows account. Fortunately, .NET provides this through the System.Security.Principal namespace. I also wanted to deny access to particular drives - this is done through the namespace System.Security.Permissions.

Below is a skeleton example, where if the user is not an administrator the contents of a text file cannot be read and displayed in a list box:

try
{
  // By default deny access to the C Drive.....
  CodeAccessPermission UserPermission = 
     new FileIOPermission(FileIOPermissionAccess.AllAccess,@"c:\");

  //Check whether the user is part of the administrator group
  AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);
  WindowsPrincipal principal = (WindowsPrincipal)Thread.CurrentPrincipal;
  WindowsIdentity identity = (WindowsIdentity)principal.Identity;
  
  bIsAdmin = principal.IsInRole(WindowsBuiltInRole.Administrator);

  //It's not, so deny access to the file
  if(!bIsAdmin)
  {
    UserPermission.Deny();
  }
  else
  {
    //Do the read
    din = ReadTheFile.DoTheRead();
  }

  if(!bIsAdmin)
  {
    //Reset deny permissions in  current stack frame
    CodeAccessPermission.RevertDeny();
  }

  //If we got this far .... we read in the file
  String str;
  
  while ((str=din.ReadLine()) != null) 
  {
    listBox1.Items.Add(str);
  }
}
catch (SecurityException exception)
{
  //Failed to pass the security checks - so flag up error to user 
  listBox1.Items.Add("Permission denied accessing file");
}

The zip download file contains the .NET project so you can build and run this example.

If you have any comments on this article please email: simonharris@harrissoft.co.uk

Downloads

Download demo project - 22 Kb


Comments

  • I did'nt see that

    Posted by Legacy on 06/05/2002 12:00am

    Originally posted by: sdfs

    I did'nt see that

    Reply
  • good , very useful

    Posted by Legacy on 04/29/2002 12:00am

    Originally posted by: Transbuerg Tian

    good , very useful

    Reply
Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Live Event Date: December 11, 2014 @ 1:00 p.m. ET / 10:00 a.m. PT Market pressures to move more quickly and develop innovative applications are forcing organizations to rethink how they develop and release applications. The combination of public clouds and physical back-end infrastructures are a means to get applications out faster. However, these hybrid solutions complicate DevOps adoption, with application delivery pipelines that span across complex hybrid cloud and non-cloud environments. Check out this …

  • On-demand Event Event Date: October 29, 2014 It's well understood how critical version control is for code. However, its importance to DevOps isn't always recognized. The 2014 DevOps Survey of Practice shows that one of the key predictors of DevOps success is putting all production environment artifacts into version control. In this webcast, Gene Kim discusses these survey findings and shares woeful tales of artifact management gone wrong! Gene also shares examples of how high-performing DevOps …

Most Popular Programming Stories

More for Developers

RSS Feeds