Files and directories are specified using absolute paths. When accessing files, a security check is performed when the file is created or opened. The security check is not done again unless the file is closed and reopened. Checking permissions when the file is first accessed minimizes the impact of the security check on application performance because opening a file happens only once, while reading and writing can happen multiple times.

The scope of the declaration that is allowed depends on the SecurityAction that is used.

The security information declared by a security attribute is stored in the metadata of the attribute target and is accessed by the system at run time. Security attributes are used only for declarative security. For imperative security, use the corresponding permission class.

Caution:

Unrestricted FileIOPermission grants permission for all paths within a file system, including multiple pathnames that can be used to access a single given file. To Deny access to a file, you must Deny all possible paths to the file. For example, if \\server\share is mapped to the network drive X, to Deny access to \\server\share\file, you must Deny \\server\share\file, X:\file and any other path that you can use to access the file.

The following code example demonstrates how to request FileIOPermission by using the FileIOPermissionAttribute class, indicating that this permission, at a minimum, is required to run the code.

 <Assembly: FileIOPermissionAttribute(SecurityAction.RequestMinimum, _
 All := "C:\example\sample.txt")>
'In Visual Basic, you must specify that you are using the assembly scope when making a request.

[assembly:FileIOPermissionAttribute(SecurityAction.RequestMinimum, All="C:\\example\\sample.txt")]
//In C#, you must specify that you are using the assembly scope when making a request.

[assembly:FileIOPermissionAttribute(SecurityAction::RequestMinimum,All="C:\\example\\sample.txt")];
//In C++, you must specify that you are using the assembly scope when making a request.

The following example shows how to demand that the calling code has unrestricted FileIOPermission. You typically make demands in managed libraries (DLLs) to help protect methods or classes from potentially harmful code.

<FileIOPermissionAttribute(SecurityAction.Demand, _
 Unrestricted := True)> Public Class SampleClass

[FileIOPermissionAttribute(SecurityAction.Demand, Unrestricted=true)]

[FileIOPermissionAttribute(SecurityAction::Demand,Unrestricted=true)]

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

.NET Framework

Reference

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