System.Security.CodeAccessPermission Class

Summary

Defines the underlying structure of all code access permissions.

C# Syntax:

[Serializable] public abstract class CodeAccessPermission : IPermission, ISecurityEncodable, IStackWalk

Code access permissions use a stack walk to ensure that all callers of the code have been granted a permission. If a permission object is null, it is handled the same as a permission object with the state PermissionState.None.

The call stack is typically represented as growing down, so that methods higher in the call stack call methods lower in the call stack.

Notes to inheritors: When you inherit from CodeAccessPermission, you must override the following members: CodeAccessPermission.Copy, CodeAccessPermission.Intersect, CodeAccessPermission.IsSubsetOf, CodeAccessPermission.ToXml, CodeAccessPermission.FromXml, and CodeAccessPermission.Union. You must also define a constructor that takes a PermissionState as its only parameter.

System.Security Namespace See also:
MSDN: permissions | MSDN: requestingpermissions

System.Security.CodeAccessPermission Member List:

Public Methods

Assert	Asserts that calling code can access the resource identified by the current permission through the code that calls this method, even if callers higher in the stack have not been granted permission to access the resource.
Copy	When implemented by a derived class, creates and returns an identical copy of the current permission object.
Demand	Forces a SecurityException at run time if all callers higher in the call stack have not been granted the permission specified by the current instance.
Deny	Prevents callers higher in the call stack from using the code that calls this method to access the resource specified by the current instance.
Equals (inherited from System.Object)	See base class member description: System.Object.Equals Derived from System.Object, the primary base class for all objects.
FromXml	When overridden in a derived class, reconstructs a security object with a specified state from an XML encoding.
GetHashCode (inherited from System.Object)	See base class member description: System.Object.GetHashCode Derived from System.Object, the primary base class for all objects.
GetType (inherited from System.Object)	See base class member description: System.Object.GetType Derived from System.Object, the primary base class for all objects.
Intersect	When implemented by a derived class, creates and returns a permission that is the intersection of the current permission and the specified permission.
IsSubsetOf	When implemented by a derived class, determines whether the current permission is a subset of the specified permission.
PermitOnly	Prevents callers higher in the call stack from using the code that calls this method to access all resources except for the resource specified by the current instance.
RevertAll	Causes all previous overrides for the current frame to be removed and no longer in effect.
RevertAssert	Causes any previous CodeAccessPermission.Assert for the current frame to be removed and no longer in effect.
RevertDeny	Causes any previous CodeAccessPermission.Deny for the current frame to be removed and no longer in effect.
RevertPermitOnly	Causes any previous CodeAccessPermission.PermitOnly for the current frame to be removed and no longer in effect.
ToString	Overridden: Creates and returns a string representation of the current permission object.
ToXml	When overridden in a derived class, creates an XML encoding of the security object and its current state.
Union	When overridden in a derived class, creates a permission that is the union of the current permission and the specified permission.

Protected Constructors

ctor #1

Default constructor. This constructor is called by derived class constructors to initialize state in this type.

Protected Methods

Finalize (inherited from System.Object)	See base class member description: System.Object.Finalize Derived from System.Object, the primary base class for all objects.
MemberwiseClone (inherited from System.Object)	See base class member description: System.Object.MemberwiseClone Derived from System.Object, the primary base class for all objects.

Hierarchy:

• System.Object
• System.Security.CodeAccessPermission
  • System.Net.DnsPermission
  • System.Net.SocketPermission
  • System.Net.WebPermission
  • System.Security.Permissions.EnvironmentPermission
  • System.Security.Permissions.FileDialogPermission
  • System.Security.Permissions.FileIOPermission
  • System.Security.Permissions.IsolatedStoragePermission
  • System.Security.Permissions.ReflectionPermission
  • System.Security.Permissions.SecurityPermission
  • System.Security.Permissions.SiteIdentityPermission
  • System.Security.Permissions.StrongNameIdentityPermission
  • System.Security.Permissions.UIPermission
  • System.Security.Permissions.UrlIdentityPermission
  • System.Security.Permissions.ZoneIdentityPermission

System.Security.CodeAccessPermission Member Details

Summary:

Default constructor. This constructor is called by derived class constructors to initialize state in this type.

C# Syntax:

protected CodeAccessPermission();

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Summary

Asserts that calling code can access the resource identified by the current permission through the code that calls this method, even if callers higher in the stack have not been granted permission to access the resource.

C# Syntax:

public void Assert();

Exceptions

Exception Type	Condition
SecurityException	The calling code does not have SecurityPermissionFlag.Assertion. -or- There is already an active CodeAccessPermission.Assert for the current frame.

Implements:

IStackWalk.Assert

The call stack is typically represented as growing down, so that methods higher in the call stack call methods lower in the call stack. Calling CodeAccessPermission.Assert prevents a stack walk originating lower in the call stack from proceeding up the call stack beyond the code that calls this method. Therefore, even if callers higher on the call stack do not have the requisite permissions to access a resource, they can still access it through the code that calls this method on the necessary permission. An assertion is effective only if the code that calls CodeAccessPermission.Assert passes the security check for the permission that it is asserting.

The call to CodeAccessPermission.Assert is effective until the calling code returns to its caller. Only one CodeAccessPermission.Assert can be active on a frame. An attempt to call CodeAccessPermission.Assert when an active CodeAccessPermission.Assert exists on the frame results in a SecurityException. Call CodeAccessPermission.RevertAssert or CodeAccessPermission.RevertAll to remove an active CodeAccessPermission.Assert.

CodeAccessPermission.Assert is ignored for a permission not granted because a demand for that permission will not succeed. However, if code lower on the call stack calls CodeAccessPermission.Demand for that permission, a SecurityException is thrown when the stack walk reaches the code that tried to call CodeAccessPermission.Assert. This happens because the code that called CodeAccessPermission.Assert has not been granted the permission, even though it tried to CodeAccessPermission.Assert it.

Because calling CodeAccessPermission.Assert removes the requirement that all code in the call chain must be granted permission to access the specified resource, it can open up security vulnerabilities if used incorrectly or inappropriately. Therefore, it should be used with great caution.

Notes to inheritors: You cannot override this method.

SecurityPermission for the ability to call CodeAccessPermission.Assert. Associated enumeration: SecurityPermissionFlag.Assertion

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Summary

When implemented by a derived class, creates and returns an identical copy of the current permission object.

C# Syntax:

public abstract IPermission Copy();

Return Value:

A copy of the current permission object.

Implements:

IPermission.Copy

A copy of a permission object represents the same access to resources as the original permission object.

Notes to inheritors: You must implement this method in a derived class.

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Summary

Forces a SecurityException at run time if all callers higher in the call stack have not been granted the permission specified by the current instance.

C# Syntax:

public void Demand();

Exceptions

Exception Type	Condition
SecurityException	A caller higher in the call stack does not have the permission specified by the current instance. -or- A caller higher in the call stack has called CodeAccessPermission.Deny on the current permission object.

Implements:

IPermission.Demand

Implements:

IStackWalk.Demand

This method is typically used by secure libraries to ensure that callers have permission to access a resource. For example, a file class in a secure class library calls CodeAccessPermission.Demand for the necessary FileIOPermission before performing a file operation requested by the caller.

The permissions of the code that calls this method are not examined; the check begins from the immediate caller of that code and proceeds up the stack. The call stack is typically represented as growing down, so that methods higher in the call stack call methods lower in the call stack. CodeAccessPermission.Demand succeeds only if no SecurityException is raised.

Notes to inheritors: You cannot override this method.

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Summary

Prevents callers higher in the call stack from using the code that calls this method to access the resource specified by the current instance.

C# Syntax:

public void Deny();

Exceptions

Exception Type	Condition
SecurityException	There is already an active CodeAccessPermission.Deny for the current frame.

Implements:

IStackWalk.Deny

This method prevents callers higher in the call stack from accessing the protected resource through the code that calls this method, even if those callers have been granted permission to access it. The call stack is typically represented as growing down, so that methods higher in the call stack call methods lower in the call stack.

CodeAccessPermission.Deny can limit the liability of the programmer or prevent accidental security vulnerabilities because it prevents the method that calls CodeAccessPermission.Deny from being used to access the resource protected by the denied permission. If a method calls CodeAccessPermission.Deny on a permission, and if a CodeAccessPermission.Demand for that permission is invoked by a caller lower in the call stack, that security check will fail when it reaches the CodeAccessPermission.Deny.

The call to CodeAccessPermission.Deny is effective until the calling code returns to its caller. Only one CodeAccessPermission.Deny can be active on a frame. An attempt to call CodeAccessPermission.Deny when an active CodeAccessPermission.Deny exists on the frame results in a SecurityException. Call CodeAccessPermission.RevertDeny or CodeAccessPermission.RevertAll to remove an active CodeAccessPermission.Deny. CodeAccessPermission.Deny is ignored for a permission not granted because a demand for that permission will not succeed.

Notes to inheritors: You cannot override this method.

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Inherited
See base class member description: System.Object.Equals

C# Syntax:

public virtual bool Equals(    object obj );

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.Finalize

C# Syntax:

~CodeAccessPermission();

For more information on members inherited from System.Object click on the link above.

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Summary

When overridden in a derived class, reconstructs a security object with a specified state from an XML encoding.

C# Syntax:

public abstract void FromXml(    SecurityElement elem );

elem

The XML encoding to use to reconstruct the security object.

Implements:

ISecurityEncodable.FromXml

Custom code that extends security objects needs to implement the CodeAccessPermission.ToXml and CodeAccessPermission.FromXml methods to make the objects security-encodable.

Notes to inheritors: You must implement this method in a derived class.

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Inherited
See base class member description: System.Object.GetHashCode

C# Syntax:

public virtual int GetHashCode();

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.GetType

C# Syntax:

public Type GetType();

For more information on members inherited from System.Object click on the link above.

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Summary

When implemented by a derived class, creates and returns a permission that is the intersection of the current permission and the specified permission.

C# Syntax:

public abstract IPermission Intersect(    IPermission target );

target

A permission to intersect with the current permission. It must be of the same type as the current permission.

Return Value:

A new permission that represents the intersection of the current permission and the specified permission. This new permission is null if the intersection is empty.

Exceptions

Exception Type	Condition
ArgumentException	The target parameter is not null and is not an instance of the same class as the current permission.

Implements:

IPermission.Intersect

The intersection of two permissions is a permission that describes the set of operations they both describe in common. Only a demand that passes both original permissions will pass the intersection.

Notes to inheritors: You must implement this method in a derived class.

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Summary

When implemented by a derived class, determines whether the current permission is a subset of the specified permission.

C# Syntax:

public abstract bool IsSubsetOf(    IPermission target );

target

A permission that is to be tested for the subset relationship. This permission must be of the same type as the current permission.

Return Value:

true if the current permission is a subset of the specified permission; otherwise, false.

Exceptions

Exception Type	Condition
ArgumentException	The target parameter is not of the same type as the current permission.

Implements:

IPermission.IsSubsetOf

The current permission is a subset of the specified permission if the current permission specifies a set of operations that is wholly contained by the specified permission. For example, a permission that represents access to C:\example.txt is a subset of a permission that represents access to C:\. If this method returns true, the current permission represents no more access to the protected resource than does the specified permission.

Notes to inheritors: You must implement this method in a derived class.

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Inherited
See base class member description: System.Object.MemberwiseClone

C# Syntax:

protected object MemberwiseClone();

For more information on members inherited from System.Object click on the link above.

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Summary

Prevents callers higher in the call stack from using the code that calls this method to access all resources except for the resource specified by the current instance.

C# Syntax:

public void PermitOnly();

Exceptions

Exception Type	Condition
SecurityException	There is already an active CodeAccessPermission.PermitOnly for the current frame.

Implements:

IStackWalk.PermitOnly

CodeAccessPermission.PermitOnly is similar to CodeAccessPermission.Deny, in that both cause stack walks to fail when they would otherwise succeed. The difference is that CodeAccessPermission.Deny specifies permissions that will cause the stack walk to fail, but CodeAccessPermission.PermitOnly specifies the only permissions that do not cause the stack walk to fail.

Call this method to ensure that your code can be used to access only the specified resources. The call to CodeAccessPermission.PermitOnly is effective until the calling code returns to its caller. Only one CodeAccessPermission.PermitOnly can be active on a frame. An attempt to call CodeAccessPermission.PermitOnly when an active CodeAccessPermission.PermitOnly exists on the frame results in a SecurityException. Call CodeAccessPermission.RevertPermitOnly or CodeAccessPermission.RevertAll to remove an active CodeAccessPermission.PermitOnly.

CodeAccessPermission.PermitOnly is ignored for a permission not granted because a demand for that permission will not succeed. However, if code lower on the call stack later calls CodeAccessPermission.Demand for that permission, a SecurityException is thrown when the stack walk reaches the code that tried to call CodeAccessPermission.PermitOnly. This is because the code that called CodeAccessPermission.PermitOnly has not been granted the permission, even though it called CodeAccessPermission.PermitOnly for that permission. The call stack is typically represented as growing down, so that methods higher in the call stack call methods lower in the call stack.

Notes to inheritors: You cannot override this method.

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Summary

Causes all previous overrides for the current frame to be removed and no longer in effect.

C# Syntax:

public static void RevertAll();

If there are no overrides ( CodeAccessPermission.Assert, CodeAccessPermission.Deny, or CodeAccessPermission.PermitOnly) for the current frame, this method has no effect.

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Summary

Causes any previous CodeAccessPermission.Assert for the current frame to be removed and no longer in effect.

C# Syntax:

public static void RevertAssert();

If there is no CodeAccessPermission.Assert for the current frame, this method has no effect.

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Summary

Causes any previous CodeAccessPermission.Deny for the current frame to be removed and no longer in effect.

C# Syntax:

public static void RevertDeny();

If there is no CodeAccessPermission.Deny for the current frame, this method has no effect.

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Summary

Causes any previous CodeAccessPermission.PermitOnly for the current frame to be removed and no longer in effect.

C# Syntax:

public static void RevertPermitOnly();

If there is no CodeAccessPermission.PermitOnly for the current frame, this method has no effect.

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Summary

Creates and returns a string representation of the current permission object.

C# Syntax:

public override string ToString();

Return Value:

A string representation of the current permission object.

This method is useful in debugging when you need to display the permission as a string.

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Summary

When overridden in a derived class, creates an XML encoding of the security object and its current state.

C# Syntax:

public abstract SecurityElement ToXml();

Return Value:

An XML encoding of the security object, including any state information.

Implements:

ISecurityEncodable.ToXml

Custom code that extends security objects needs to implement the CodeAccessPermission.ToXml and CodeAccessPermission.FromXml methods to make the objects security-encodable.

Notes to inheritors: You must implement this method in a derived class.

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Summary

When overridden in a derived class, creates a permission that is the union of the current permission and the specified permission.

C# Syntax:

public virtual IPermission Union(    IPermission other );

other

A permission to combine with the current permission. It must be of the same type as the current permission.

Return Value:

A new permission that represents the union of the current permission and the specified permission.

Exceptions

Exception Type	Condition
NotSupportedException	The other parameter is not null. This method is only supported at this level when passed null.

Implements:

IPermission.Union

The result of a call to CodeAccessPermission.Union is a permission that represents all the operations represented by both the current permission and the specified permission. Any demand that passes either permission passes their union.

Notes to inheritors: You must implement this method in a derived class.

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