CA2123: Override link demands should be identical to base

Artigo
11/04/2016

Item	Value
RuleId	CA2123
Category	Microsoft.Security
Breaking change	Breaking

Cause

A public or protected method in a public type overrides a method or implements an interface, and does not have the same Link Demands as the interface or virtual method.

Note

This rule has been deprecated. For more information, see Deprecated rules.

Rule description

This rule matches a method to its base method, which is either an interface or a virtual method in another type, and then compares the link demands on each. A violation is reported if either the method or the base method has a link demand and the other does not.

If this rule is violated, a malicious caller can bypass the link demand merely by calling the unsecured method.

How to fix violations

To fix a violation of this rule, apply the same link demand to the override method or implementation. If this is not possible, mark the method with a full demand or remove the attribute altogether.

When to suppress warnings

Do not suppress a warning from this rule.

Example

The following example shows various violations of this rule.

using System.Security;
using System.Security.Permissions;
using System;

namespace SecurityRulesLibrary
{
   public interface ITestOverrides
   {  
      [EnvironmentPermissionAttribute(SecurityAction.LinkDemand, Unrestricted=true)]
      Object GetFormat(Type formatType);
   }

   public class OverridesAndSecurity : ITestOverrides
   {
      // Rule violation: The interface has security, and this implementation does not.
      object ITestOverrides.GetFormat(Type formatType)
      {
         return (formatType == typeof(OverridesAndSecurity) ? this : null);
      }

      // These two methods are overridden by DerivedClass and DoublyDerivedClass.
      [EnvironmentPermissionAttribute(SecurityAction.LinkDemand, Unrestricted=true)]
      public virtual void DoSomething()
      {
         Console.WriteLine("Doing something.");
      }

      public virtual void DoSomethingElse()
      {
         Console.WriteLine("Doing some other thing.");
      }
   }

   public class DerivedClass : OverridesAndSecurity, ITestOverrides
   {
      //  Rule violation: The interface has security, and this implementation does not.
      public object GetFormat(Type formatType)
      {
         return (formatType == typeof(OverridesAndSecurity) ? this : null);
      }

      // Rule violation: This does not have security, but the base class version does.
      public override void DoSomething()
      {
         Console.WriteLine("Doing some derived thing.");
      }

      // Rule violation: This has security, but the base class version does not.
      [EnvironmentPermissionAttribute(SecurityAction.LinkDemand, Unrestricted=true)]
      public override void DoSomethingElse()
      {
         Console.WriteLine("Doing some other derived thing.");
      }
   }

   public class DoublyDerivedClass : DerivedClass
   {
      // The OverridesAndSecurity version of this method does not have security. 
      // Base class DerivedClass's version does. 
      // The DoublyDerivedClass version does not violate the rule, but the 
      // DerivedClass version does violate the rule.
      public override void DoSomethingElse()
      {
         Console.WriteLine("Doing some other derived thing.");
      }
   }
}

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