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SafeHandle.DangerousGetHandle Method

Note: This method is new in the .NET Framework version 2.0.

Returns the value of the handle field.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)

public IntPtr DangerousGetHandle ()
public IntPtr DangerousGetHandle ()
public function DangerousGetHandle () : IntPtr

Return Value

An IntPtr representing the value of the handle field. If the handle has been marked invalid with SetHandleAsInvalid, this method still returns the original handle value, which can be a stale value.

You can use this method to retrieve the actual handle value from an instance of the SafeHandle derived class. This method is needed for backwards compatibility because many properties in the .NET Framework return IntPtr handle types. IntPtr handle types are platform-specific types used to represent a pointer or a handle.

Caution noteCaution

Using the DangerousGetHandle method can pose security risks because, if the handle has been marked as invalid with SetHandleAsInvalid, DangerousGetHandle still returns the original, potentially stale handle value. The returned handle can also be recycled at any point. At best, this means the handle might suddenly stop working. At worst, if the handle or the resource that the handle represents is exposed to untrusted code, this can lead to a recycling security attack on the reused or returned handle. For example, an untrusted caller can query data on the handle just returned and receive information for an entirely unrelated resource.

See the DangerousAddRef and the DangerousRelease methods for more information about using the DangerousGetHandle methodsafely.

The following code example demonstrates how to use the DangerousAddRef, DangerousGetHandle, and DangerousRelease with a custom class, called the MySafeHandle class, that implements the SafeHandle class.

using System;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using System.Runtime.ConstrainedExecution;
using System.Security.Permissions;

namespace SafeHandleExample
{

    sealed class MySafeHandle : SafeHandle
    {
        // Called by P/Invoke when returning SafeHandles
        public MySafeHandle()
            : base(IntPtr.Zero, true)
        {
        }

        
        // If & only if you need to support user-supplied handles
        internal MySafeHandle(IntPtr preexistingHandle, bool ownsHandle)
            : base(IntPtr.Zero, ownsHandle)
        {
            SetHandle(preexistingHandle);
        }

        // Do not provide a finalizer - SafeHandle's critical finalizer will
        // call ReleaseHandle for you.

        public override bool IsInvalid
        {

            get { return IsClosed || handle == IntPtr.Zero; }
        }
   
        [DllImport("kernel32")]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
        private static extern bool CloseHandle(IntPtr handle);

        protected override bool ReleaseHandle()
        {
            return CloseHandle(handle);
        }

        [DllImport("kernel32")]
        public static extern MySafeHandle CreateHandle(int someState);


    }


    public class Example
    {
        static void Main()
        {
		Run();

        }

        [SecurityPermission(SecurityAction.Demand, UnmanagedCode=true)]
        static void Run()
        {
            //Create an instance of MySafeHandle.
            MySafeHandle myHandle = new MySafeHandle();

            // ...Set the handle...
       

            bool mustRelease = false;
            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                myHandle.DangerousAddRef(ref mustRelease);
                IntPtr handleCopy = myHandle.DangerousGetHandle();
                // ... perform operations with handleCopy ...
            }
            finally
            {
                if (mustRelease)
                    myHandle.DangerousRelease();
            }

        }
    }

    
}

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0

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