System.Net.DnsPermission Class

Summary

Controls rights to access Domain Name System (DNS) servers on the network.

C# Syntax:

[Serializable] public sealed class DnsPermission : CodeAccessPermission, IUnrestrictedPermission

The default permissions allow all local and Intranet zone applications to access DNS services, and no DNS permission for Internet zone applications.

System.Net Namespace | SecurityZone

System.Net.DnsPermission Member List:

Public Constructors

ctor #1

Public Methods

Assert (inherited from System.Security.CodeAccessPermission)	See base class member description: System.Security.CodeAccessPermission.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	Overridden: Creates an identical copy of the current permission instance.
Demand (inherited from System.Security.CodeAccessPermission)	See base class member description: System.Security.CodeAccessPermission.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 (inherited from System.Security.CodeAccessPermission)	See base class member description: System.Security.CodeAccessPermission.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	Overridden: Reconstructs a DnsPermission instance 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	Overridden: Creates a permission instance that is the intersection of the current permission instance and the specified permission instance.
IsSubsetOf	Overridden: Determines whether the current permission instance is a subset of the specified permission instance.
IsUnrestricted	Checks the overall permission state of the object.
PermitOnly (inherited from System.Security.CodeAccessPermission)	See base class member description: System.Security.CodeAccessPermission.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.
ToString (inherited from System.Security.CodeAccessPermission)	See base class member description: System.Security.CodeAccessPermission.ToString Creates and returns a string representation of the current permission object.
ToXml	Overridden: Creates an XML encoding of a DnsPermission instance and its current state.
Union	Overridden: Creates a permission instance that is the union of the current permission instance and the specified permission instance.

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.DnsPermission Member Details

Summary

Creates a new instance of the DnsPermission class that either allows unrestricted DNS access or disallows DNS access.

C# Syntax:

public DnsPermission(    PermissionState state );

state

One of the PermissionState values.

If state is PermissionState.Unrestricted the DnsPermission instance passes all demands. If state contains any other value, the DnsPermission instance fails all demands.

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Inherited
See base class member description: System.Security.CodeAccessPermission.Assert

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

Creates an identical copy of the current permission instance.

C# Syntax:

public override IPermission Copy();

Return Value:

A new instance of the DnsPermission class that is an identical copy of the current instance.

Implements:

IPermission.Copy

A copy of a DnsPermission instance provides the same access to DNS servers as the original permission instance.

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Inherited
See base class member description: System.Security.CodeAccessPermission.Demand

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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Inherited
See base class member description: System.Security.CodeAccessPermission.Deny

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:

~DnsPermission();

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

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Summary

Reconstructs a DnsPermission instance from an XML encoding.

C# Syntax:

public override void FromXml(    SecurityElement securityElement );

securityElement

The XML encoding to use to reconstruct the DnsPermission instance.

Exceptions

Exception Type	Condition
ArgumentNullException	securityElement is null -or- securityElement is not a permission element.

Implements:

ISecurityEncodable.FromXml

The DnsPermission.FromXml method reconstructs a DnsPermission instance from an XML encoding defined by SecurityElement class.

Use the DnsPermission.ToXml method to XML-encode the DnsPermission instance, including state information.

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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

Creates a permission instance that is the intersection of the current permission instance and the specified permission instance.

C# Syntax:

public override IPermission Intersect(    IPermission target );

target

The DnsPermission instance to combine with the current instance.

Return Value:

A DnsPermission instance that represents the intersection of the current DnsPermission instance with the specified DnsPermission instance, or null if the intersection is empty.

Exceptions

Exception Type	Condition
ArgumentNullException	target is null.

Implements:

IPermission.Intersect

The DnsPermission.Intersect method returns a DnsPermission instance that allows the access defined by both the current DnsPermission instance and the specified DnsPermission instance. Any demand must pass both permissions to pass their intersection.

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Summary

Determines whether the current permission instance is a subset of the specified permission instance.

C# Syntax:

public override bool IsSubsetOf(    IPermission target );

target

The second DnsPermission instance to be tested for the subset relationship.

Return Value:

false when target.IsUnrestricted() is false; otherwise, true.

Implements:

IPermission.IsSubsetOf

The current DnsPermission instance is a subset of the specified DnsPermission instance if the current DnsPermission instance specifies a set of operations that is wholly contained by the specified DnsPermission instance.

If the DnsPermission.IsSubsetOf method returns true, the current DnsPermission instance allows no more access to DNS servers than does the specified DnsPermission instance.

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Summary

Checks the overall permission state of the object.

C# Syntax:

public bool IsUnrestricted();

Return Value:

true if the DnsPermission instance was created with PermissionState.Unrestricted; otherwise, false.

Implements:

IUnrestrictedPermission.IsUnrestricted

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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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Inherited
See base class member description: System.Security.CodeAccessPermission.PermitOnly

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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Inherited
See base class member description: System.Security.CodeAccessPermission.ToString

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

Creates an XML encoding of a DnsPermission instance and its current state.

C# Syntax:

public override SecurityElement ToXml();

Return Value:

A SecurityElement instance containing an XML-encoded representation of the security object, including state information.

Implements:

ISecurityEncodable.ToXml

The DnsPermission.ToXml method creates a SecurityElement instance to XML-encode a representation of the DnsPermission instance, including state information.

Use DnsPermission.FromXml method to restore the state information from a SecurityElement instance.

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Summary

Creates a permission instance that is the union of the current permission instance and the specified permission instance.

C# Syntax:

public override IPermission Union(    IPermission target );

target

The DnsPermission instance to combine with the current instance.

Return Value:

A DnsPermission instance that represents the union of the current DnsPermission instance with the specified DnsPermission instance.

Exceptions

Exception Type	Condition
ArgumentNullException	target is null.

Implements:

IPermission.Union

The DnsPermission.Union method returns a DnsPermission instance that allows the access defined by either the current DnsPermission instance and the specified DnsPermission instance. Any demand that passes either permission passes their union.

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