access rights - Add "Everyone" privilege to folder using C#.NET

Question

I have used the code below to allow Everyone access to a folder:

System.Security.AccessControl.DirectorySecurity sec =
    System.IO.Directory.GetAccessControl(directory, AccessControlSections.All);
FileSystemAccessRule accRule = new FileSystemAccessRule("Everyone",
                                       FileSystemRights.Modify,
                                       AccessControlType.Allow);
sec.AddAccessRule(accRule);    // setACL
sec.ResetAccessRule(accRule);

Now, the Everyone user is added to the folder, but not with any rights assigned. All the read, write, execute etc. checkboxes are not checked.

Answer 1

First thing I want to tell you is how I found this solution. This is probably more important than the answer because file permissions are hard to get correct.

First thing I did was set the permissions I wanted using the Windows dialogs and checkboxes. I added a rule for "Everyone" and ticked all boxes except "Full Control".

Then I wrote this C# code to tell me exactly what parameters I need to duplicate the Windows settings:

string path = @"C:UsersyouDesktopperms"; // path to directory whose settings you have already correctly configured
DirectorySecurity sec = Directory.GetAccessControl(path);
foreach (FileSystemAccessRule acr in sec.GetAccessRules(true, true, typeof(System.Security.Principal.NTAccount))) {
    Console.WriteLine("{0} | {1} | {2} | {3} | {4}", acr.IdentityReference.Value, acr.FileSystemRights, acr.InheritanceFlags, acr.PropagationFlags, acr.AccessControlType);
}

This gave me this line of output:

Everyone | Modify, Synchronize | ContainerInherit, ObjectInherit | None | Allow

So the solution is simple (yet hard to get right if you don't know what to look for!):

DirectorySecurity sec = Directory.GetAccessControl(path);
// Using this instead of the "Everyone" string means we work on non-English systems.
SecurityIdentifier everyone = new SecurityIdentifier(WellKnownSidType.WorldSid, null);
sec.AddAccessRule(new FileSystemAccessRule(everyone, FileSystemRights.Modify | FileSystemRights.Synchronize, InheritanceFlags.ContainerInherit | InheritanceFlags.ObjectInherit, PropagationFlags.None, AccessControlType.Allow));
Directory.SetAccessControl(path, sec);

This will make the checkboxes on the Windows security dialog match what you have already set for your test directory.