SecurityException error when calling CLR function

Question

I have written a simple user defined function in C# that gets the IP address and returns host name against it code is as follows:

public partial class UserDefinedFunctions
{
    [Microsoft.SqlServer.Server.SqlFunction]
    public static SqlString getname(String ipAddress)
    {
        System.Data.SqlClient.SqlClientPermission pSql = new SqlClientPermission(System.Security.Permissions.PermissionState.Unrestricted);
        pSql.Assert();

        System.Security.PermissionSet psql1 = new PermissionSet(System.Security.Permissions.PermissionState.Unrestricted);
        psql1.Assert();

        System.Net.DnsPermission psql = new DnsPermission(System.Security.Permissions.PermissionState.Unrestricted);
        psql.Assert();

        System.Security.Permissions.SecurityPermission psql2 = new SecurityPermission(System.Security.Permissions.PermissionState.Unrestricted);
        psql2.Assert();

        IPHostEntry host = Dns.GetHostEntry(ipAddress);
        return new SqlString(host.HostName.ToString());
    }
}

now I have deployed it but when I try to call this function in sql as: select dbo.getname('10.10.10.10')

It returns this error:

Msg 6522, Level 16, State 2, Line 7
A .NET Framework error occurred during execution of user-defined routine or aggregate "getname": 
System.Security.SecurityException: Request for the permission of type 'System.Security.Permissions.SecurityPermission, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
System.Security.SecurityException: 
   at System.Security.CodeAccessSecurityEngine.CheckNReturnSO(PermissionToken permToken, CodeAccessPermission demand, StackCrawlMark& stackMark, Int32 unrestrictedOverride, Int32 create)
   at System.Security.CodeAccessSecurityEngine.Assert(CodeAccessPermission cap, StackCrawlMark& stackMark)
   at System.Security.CodeAccessPermission.Assert()
   at UserDefinedFunctions.getname(String ipAddress)

I have crawled the internet but found nothing on it. Please suggest.

Answer 1

You must create the assembly with external access permission set. The assembly must also be signed or the database set as trustworthy and the database owner granted the external access assembly permission. The permission and assert code above is not required.

E.g.

using Microsoft.SqlServer.Server;
using System;
using System.Data.SqlTypes;
using System.Net;

public partial class UserDefinedFunctions
{
    [Microsoft.SqlServer.Server.SqlFunction(DataAccess=DataAccessKind.None)]
    public static SqlString getname(String ipAddress)
    {
        IPHostEntry host = Dns.GetHostEntry(ipAddress);
        return new SqlString(host.HostName);
    }
}

Save the code to C:\resolve\resolve.cs and compile it...

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /t:library /out:C:\resolve\resolve.dll C:\resolve\resolve.cs

Copy the .dll to the server if not a local instance. Then create the objects...

USE [master]
GO
CREATE DATABASE [clr]; 
GO
ALTER AUTHORIZATION ON DATABASE::[clr] TO [sa]; 
GO
ALTER DATABASE [clr] SET TRUSTWORTHY ON; 
GO
USE [clr]; 
GO
CREATE ASSEMBLY [assResolve] FROM 'C:\resolve\resolve.dll' 
WITH PERMISSION_SET=EXTERNAL_ACCESS; 
GO
CREATE FUNCTION [fnGetHostName](@ipAddress nvarchar(255)) RETURNS nvarchar(255) 
AS EXTERNAL NAME [assResolve].[UserDefinedFunctions].[getname]; 
GO
SELECT [dbo].[fnGetHostName](N'8.8.8.8') as [host]; 
GO
USE [master]