EnvironmentPermission Class
Controls access to system and user environment variables. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
Environment variable names are designated by one or more case-insensitive name lists separated by semicolons, with separate lists for read and write access to the named variables. Write access includes the ability to create and delete environment variables as well as to change existing values.
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EnvironmentPermission grants permission for access to the environment variable and its value. To deny access to a variable and its value, you must deny access to it and any other variable which contains the same value. For example, to Deny access to the TMP variable and its value, %USERPROFILE%\Local Settings\Temp, you must Deny access to TMP, TEMP, and any other variable that you can use to access that value. A better technique to deal with multiple paths is to use a combination of PermitOnly and Deny. For more information on this subject and the use of PermitOnly with Deny, see "Canonicalization Problems Using Deny" in Using the Deny Method. |
The following code example demonstrates the behavior of the EnvironmentPermission methods.
The example is intended to show how the methods perform if you execute the methods from your code. In general, the methods of permission classes are used by the security infrastructure; they are not typically used in applications.
Imports System Imports System.Security Imports System.Security.Permissions Imports System.Collections Public Class EnvironmentPermissionDemo ' IsSubsetOf determines whether the current permission is a subset of the specified permission. Private Function IsSubsetOfDemo() As Boolean Dim returnValue As Boolean = True Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "windir") Dim envPerm2 As New EnvironmentPermission(EnvironmentPermissionAccess.AllAccess, "TEMP") If envPerm1.IsSubsetOf(envPerm2) Then Console.WriteLine("'windir' is a subset of 'TEMP'" + vbLf) Else Console.WriteLine("windir" + " is not a subset of " + "TEMP" + vbLf) End If envPerm1.SetPathList(EnvironmentPermissionAccess.Read, "TEMP") If envPerm1.IsSubsetOf(envPerm2) Then Console.WriteLine("Read access is a subset of AllAccess" + vbLf) Else Console.WriteLine("Read access is not a subset of AllAccess" + vbLf) End If Return returnValue End Function 'IsSubsetOfDemo ' Union creates a new permission that is the union of the current permission and the specified permission. Private Function UnionDemo() As Boolean Dim returnValue As Boolean = True Dim envIdPerm3 As IPermission Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "windir") Dim envPerm2 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "TEMP") envIdPerm3 = CType(envPerm1.Union(envPerm2), EnvironmentPermission) envIdPerm3 = envPerm1.Union(envPerm2) Console.WriteLine("The union of 'windir' and 'TEMP'" + " = " + _ CType(envIdPerm3, EnvironmentPermission).GetPathList(EnvironmentPermissionAccess.Read).ToString()) Return returnValue End Function 'UnionDemo ' Intersect creates and returns a new permission that is the intersection of ' the current permission and the permission specified. Private Function IntersectDemo() As Boolean Dim envIdPerm3 As IPermission Dim returnValue As Boolean = True Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "windir") Dim envPerm2 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "TEMP") Try envIdPerm3 = CType(envPerm1.Intersect(envPerm2), EnvironmentPermission) If Not (envIdPerm3 Is Nothing) AndAlso Not (CType(envIdPerm3, _ EnvironmentPermission).GetPathList(EnvironmentPermissionAccess.Read) Is Nothing) Then Console.WriteLine("The intersection of " + "windir" + " and " + "TEMP" + _ " = " + CType(envIdPerm3, EnvironmentPermission).GetPathList(EnvironmentPermissionAccess.Read).ToString()) Else Console.WriteLine("The intersection of " + "windir" + " and " + "TEMP" + " is null.") End If Catch e As Exception Console.WriteLine("An exception was thrown for intersection : " + e.Message) returnValue = False End Try Return returnValue End Function 'IntersectDemo 'Copy creates and returns an identical copy of the current permission. Private Function CopyDemo() As Boolean Dim returnValue As Boolean = True Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "windir") Try Dim envPerm2 As EnvironmentPermission = CType(envPerm1.Copy(), EnvironmentPermission) If Not (envPerm2 Is Nothing) Then Console.WriteLine("Result of copy = " + envPerm2.ToString() + vbLf) Else Console.WriteLine("Result of copy is null. " + vbLf) End If Catch e As Exception Console.WriteLine(e) End Try Return returnValue End Function 'CopyDemo ' ToXml creates an XML encoding of the permission and its current state; FromXml reconstructs ' a permission with the specified state from the XML encoding. Private Function ToFromXmlDemo() As Boolean Dim returnValue As Boolean = True Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.Read, "windir") Dim envPerm2 As New EnvironmentPermission(PermissionState.None) envPerm2.FromXml(envPerm1.ToXml()) Console.WriteLine("Result of ToFromXml = " + envPerm2.ToString() + vbLf) Return returnValue End Function 'ToFromXmlDemo ' AddPathList adds access for the specified environment variables to the existing state of the permission. ' SetPathList Sets the specified access to the specified environment variables to the existing state ' of the permission. ' GetPathList gets all environment variables with the specified EnvironmentPermissionAccess. Private Function SetGetPathListDemo() As Boolean Try Console.WriteLine("********************************************************" + vbLf) Console.WriteLine("Creating an EnvironmentPermission with AllAccess rights for 'TMP'") Dim envPerm1 As New EnvironmentPermission(EnvironmentPermissionAccess.AllAccess, "TMP") Console.WriteLine("Adding 'TEMP' to the write access list, and 'windir' to the read access list.") envPerm1.AddPathList(EnvironmentPermissionAccess.Write, "TEMP") envPerm1.AddPathList(EnvironmentPermissionAccess.Read, "windir") Console.WriteLine("Read access list before SetPathList = " + envPerm1.GetPathList(EnvironmentPermissionAccess.Read)) Console.WriteLine("Setting read access to 'TMP'") envPerm1.SetPathList(EnvironmentPermissionAccess.Read, "TMP") Console.WriteLine("Read access list after SetPathList = " + envPerm1.GetPathList(EnvironmentPermissionAccess.Read)) Console.WriteLine("Write access list = " + envPerm1.GetPathList(EnvironmentPermissionAccess.Write)) Console.WriteLine("Write access environment variables = " + envPerm1.GetPathList(EnvironmentPermissionAccess.AllAccess)) Catch e As ArgumentException ' EnvironmentPermissionAccess.AllAccess cannot be used as a parameter for GetPathList. Console.WriteLine("An ArgumentException occurred as a result of using AllAccess. " + _ " This property cannot be used as a parameter in GetPathList, because it represents " + _ "more than one type of environment variable : " + vbLf + e.Message) End Try Return True End Function 'SetGetPathListDemo ' Invoke all demos. Public Function RunDemo() As Boolean Dim ret As Boolean = True Dim retTmp As Boolean ' Call IsSubsetOf demo. retTmp = IsSubsetOfDemo() If retTmp Then Console.Out.WriteLine("IsSubset demo completed successfully.") Else Console.Out.WriteLine("IsSubset demo failed.") End If ret = retTmp AndAlso ret ' Call Union demo. retTmp = UnionDemo() If retTmp Then Console.Out.WriteLine("Union demo completed successfully.") Else Console.Out.WriteLine("Union demo failed.") End If ret = retTmp AndAlso ret ' Call Intersect demo. retTmp = IntersectDemo() If retTmp Then Console.Out.WriteLine("Intersect demo completed successfully.") Else Console.Out.WriteLine("Intersect demo failed.") End If ret = retTmp AndAlso ret ' Call Copy demo. retTmp = CopyDemo() If retTmp Then Console.Out.WriteLine("Copy demo completed successfully.") Else Console.Out.WriteLine("Copy demo failed.") End If ret = retTmp AndAlso ret ' Call ToFromXml demo. retTmp = ToFromXmlDemo() If retTmp Then Console.Out.WriteLine("ToFromXml demo completed successfully.") Else Console.Out.WriteLine("ToFromXml demo failed.") End If ret = retTmp AndAlso ret ' Call SetGetPathList demo. retTmp = SetGetPathListDemo() If retTmp Then Console.Out.WriteLine("SetGetPathList demo completed successfully.") Else Console.Out.WriteLine("SetGetPathList demo failed.") End If ret = retTmp AndAlso ret Return ret End Function 'RunDemo ' Test harness. Public Shared Sub Main(ByVal args() As String) Try Dim democase As New EnvironmentPermissionDemo() Dim ret As Boolean = democase.RunDemo() If ret Then Console.Out.WriteLine("EnvironmentPermission demo completed successfully.") Console.Out.WriteLine("Press the Enter key to exit.") Dim consoleInput As String = Console.ReadLine() System.Environment.ExitCode = 100 Else Console.Out.WriteLine("EnvironmentPermission demo failed.") Console.Out.WriteLine("Press the Enter key to exit.") Dim consoleInput As String = Console.ReadLine() System.Environment.ExitCode = 101 End If Catch e As Exception Console.Out.WriteLine("EnvironmentPermission demo failed.") Console.WriteLine(e.ToString()) Console.Out.WriteLine("Press the Enter key to exit.") Dim consoleInput As String = Console.ReadLine() System.Environment.ExitCode = 101 End Try End Sub 'Main End Class 'EnvironmentPermissionDemo
System.Security.CodeAccessPermission
System.Security.Permissions.EnvironmentPermission
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
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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