Resource Access

All resource access from ASP.NET applications and managed code in general is subject to the following two security layers :

• Code access security . This security layer verifies that all of the code in the current call stack, leading up to and including the resource access code, is authorized to access the resource. An administrator uses code access security policy to grant permissions to assemblies. The permissions determine precisely which resource types the assembly can access. Numerous permission types correspond to the different resource types that can be accessed. These types include the file system, registry, event log, directory services, SQL Server, OLE DB data sources, and network resources.

  For a full list of code access permissions, see Chapter 8, "Code Access Security in Practice."

• Operating System/Platform Security . This security layer verifies that the security context of the requesting thread can access the resource. If the thread is impersonating, then the thread impersonation token is used. If not, then the process token is used and is compared against the access control list (ACL) that is attached to the resource to determine whether or not the requested operation can be performed and the resource can be accessed.

Both checks must succeed for the resource to be successfully accessed. All of the resource types that are exposed by the .NET Framework classes are protected with code access permissions. Figure 9.1 shows a range of common resource types that are accessed by Web applications, as well as the associated code access permission that is required for the access attempt to succeed.

Figure 9.1: Common resource types accessed from ASP.NET Web applications and associated permission types