本教程讨论了 .NET Framework 安全性并显示了在 C# 修改安全权限的两种方式：命令性安全和声明性安全。

教程

大多数应用程序和组件开发人员不需完成任何特别的工作就可使用 .NET Framework 安全系统并从它所提供的安全保护中受益。

但“安全库”是一个例外，它要求了解更多深入的知识并对安全系统加以特殊考虑。这些代码表明了安全托管代码与非限制代码之间的界限，后者如本机代码（这超出了 .NET Framework 安全基础结构可以强制的范围）。这些库通常必须受到高度信任才可以工作，它们是托管代码中编程错误会潜在地暴露安全隐患的一个位置。代码访问安全性无法消除人为错误的可能性，但相对于使用几个安全库的大量应用程序代码而言，需要严格审查的代码量将大大减少。

示例

该教程包括下列示例：

• 要求。

  示例 1：强制式安全性

  以下示例使用 .NET Framework 调用拒绝 UnmanagedCode 权限。

  // ImperativeSecurity.csusing System;using System.Security;using System.Security.Permissions;using System.Runtime.InteropServices;class NativeMethods{    // This is a call to unmanaged code. Executing this method requires     // the UnmanagedCode security permission. Without this permission    // an attempt to call this method will throw a SecurityException:    [DllImport("msvcrt.dll")]    public static extern int puts(string str);    [DllImport("msvcrt.dll")]    internal static extern int _flushall();}class MainClass{    private static void CallUnmanagedCodeWithoutPermission()    {        // Create a security permission object to describe the        // UnmanagedCode permission:        SecurityPermission perm =            new SecurityPermission(SecurityPermissionFlag.UnmanagedCode);        // Deny the UnmanagedCode from our current set of permissions.        // Any method that is called on this thread until this method         // returns will be denied access to unmanaged code.        // Even though the CallUnmanagedCodeWithPermission method        // is called from a stack frame that already        // calls Assert for unmanaged code, you still cannot call native        // code. Because you use Deny here, the permission gets         // overwritten.        perm.Deny();        try        {            Console.WriteLine("Attempting to call unmanaged code without permission.");            NativeMethods.puts("Hello World!");            NativeMethods._flushall();            Console.WriteLine("Called unmanaged code without permission. Whoops!");        }        catch (SecurityException)        {            Console.WriteLine("Caught Security Exception attempting to call unmanaged code.");        }    }    private static void CallUnmanagedCodeWithPermission()    {        // Create a security permission object to describe the        // UnmanagedCode permission:        SecurityPermission perm =            new SecurityPermission(SecurityPermissionFlag.UnmanagedCode);        // Check that you have permission to access unmanaged code.        // If you don't have permission to access unmanaged code, then        // this call will throw a SecurityException.        // Even though the CallUnmanagedCodeWithPermission method        // is called from a stack frame that already        // calls Assert for unmanaged code, you still cannot call native        // code. Because you use Deny here, the permission gets         // overwritten.        perm.Assert();        try        {            Console.WriteLine("Attempting to call unmanaged code with permission.");            NativeMethods.puts("Hello World!");            NativeMethods._flushall();            Console.WriteLine("Called unmanaged code with permission.");        }        catch (SecurityException)        {            Console.WriteLine("Caught Security Exception attempting to call unmanaged code. Whoops!");        }    }    public static void Main()     {        // The method itself will call the security permission Deny         // for unmanaged code, which will override the Assert permission        // in this stack frame.        SecurityPermission perm = new             SecurityPermission(SecurityPermissionFlag.UnmanagedCode);        perm.Assert();        CallUnmanagedCodeWithoutPermission();        // The method itself will call the security permission Assert        // for unmanaged code, which will override the Deny permission in        // this stack frame.        perm.Deny();        CallUnmanagedCodeWithPermission();    }}

  输出

  Attempting to call unmanaged code without permission.Caught Security Exception attempting to call unmanaged code.Attempting to call unmanaged code with permission.Hello World!Called unmanaged code with permission.

  示例 2：声明式安全性

  这是使用安全权限属性的同一个示例。

  // DeclarativeSecurity.csusing System;using System.Security;using System.Security.Permissions;using System.Runtime.InteropServices;class NativeMethods{    // This is a call to unmanaged code. Executing this method requires     // the UnmanagedCode security permission. Without this permission,    // an attempt to call this method will throw a SecurityException:    [DllImport("msvcrt.dll")]    public static extern int puts(string str);    [DllImport("msvcrt.dll")]    internal static extern int _flushall();}class MainClass{    // The security permission attached to this method will deny the    // UnmanagedCode permission from the current set of permissions for    // the duration of the call to this method:    // Even though the CallUnmanagedCodeWithoutPermission method is    // called from a stack frame that already calls    // Assert for unmanaged code, you still cannot call native code.    // Because this function is attached with the Deny permission for    // unmanaged code, the permission gets overwritten.    [SecurityPermission(SecurityAction.Deny, Flags =        SecurityPermissionFlag.UnmanagedCode)]    private static void CallUnmanagedCodeWithoutPermission()    {        try        {            Console.WriteLine("Attempting to call unmanaged code without permission.");            NativeMethods.puts("Hello World!");            NativeMethods._flushall();            Console.WriteLine("Called unmanaged code without permission. Whoops!");        }        catch (SecurityException)        {            Console.WriteLine("Caught Security Exception attempting to call unmanaged code.");        }    }    // The security permission attached to this method will force a     // runtime check for the unmanaged code permission whenever    // this method is called. If the caller does not have unmanaged code    // permission, then the call will generate a Security Exception.    // Even though the CallUnmanagedCodeWithPermission method is called    // from a stack frame that already calls    // Deny for unmanaged code, it will not prevent you from calling    // native code. Because this method is attached with the Assert    // permission for unmanaged code, the permission gets overwritten.    [SecurityPermission(SecurityAction.Assert, Flags =        SecurityPermissionFlag.UnmanagedCode)]    private static void CallUnmanagedCodeWithPermission()    {        try        {            Console.WriteLine("Attempting to call unmanaged code with permission.");            NativeMethods.puts("Hello World!");            NativeMethods._flushall();            Console.WriteLine("Called unmanaged code with permission.");        }        catch (SecurityException)        {            Console.WriteLine("Caught Security Exception attempting to call unmanaged code. Whoops!");        }    }    public static void Main()     {        SecurityPermission perm = new            SecurityPermission(SecurityPermissionFlag.UnmanagedCode);        // The method itself is attached with the security permission         // Deny for unmanaged code, which will override        // the Assert permission in this stack frame.        perm.Assert();        CallUnmanagedCodeWithoutPermission();        // The method itself is attached with the security permission        // Assert for unmanaged code, which will override the Deny         // permission in this stack frame.        perm.Deny();        CallUnmanagedCodeWithPermission();    }}

  输出

  Attempting to call unmanaged code without permission.Caught Security Exception attempting to call unmanaged code.Attempting to call unmanaged code with permission.Hello World!Called unmanaged code with permission.

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