WdfRequestProbeAndLockUserBufferForRead function (wdfrequest.h)

[Applies to KMDF only]

The WdfRequestProbeAndLockUserBufferForRead method verifies that an I/O request's user-mode buffer is readable, and then it locks the buffer's physical memory pages so drivers in the driver stack can read the buffer.

Syntax

NTSTATUS WdfRequestProbeAndLockUserBufferForRead(
  [in]  WDFREQUEST Request,
  [in]  PVOID      Buffer,
  [in]  size_t     Length,
  [out] WDFMEMORY  *MemoryObject
);

Parameters

[in] Request

A handle to a framework request object.

[in] Buffer

A pointer to the request's input buffer. For more information, see the following Remarks section.

[in] Length

The length, in bytes, of the request's input buffer.

[out] MemoryObject

A pointer to a location that receives a handle to a framework memory object that represents the user input buffer.

Return value

WdfRequestProbeAndLockUserBufferForRead returns STATUS_SUCCESS if the operation succeeds. Otherwise, this method might return one of the following values:

This method might also return other NTSTATUS values.

A bug check occurs if the driver supplies an invalid object handle.

Remarks

Only a top-level driver can call the WdfRequestProbeAndLockUserBufferForRead method, because the method requires the process context of the process that created the I/O request.

The user input buffer typically contains information to be written to the device.

The user-mode buffer that the Buffer parameter specifies can be the buffer that WdfRequestRetrieveUnsafeUserInputBuffer retrieves, or it can be a different user-mode input buffer. For example, an I/O control code that uses the buffered access method might pass a structure that contains an embedded pointer to a user-mode buffer. In such a case, the driver can useWdfRequestProbeAndLockUserBufferForRead to obtain a memory object for the buffer.

The buffer length that the Length parameter specifies must not be larger than the buffer's actual size. Otherwise, drivers can access memory outside of the buffer, which is a security risk.

If WdfRequestProbeAndLockUserBufferForRead returns STATUS_SUCCESS, the driver receives a handle to a framework memory object that represents the user-mode buffer. To access the buffer, the driver must call WdfMemoryGetBuffer.

The framework memory object is automatically released when the driver calls WdfRequestComplete.

For more information about WdfRequestProbeAndLockUserBufferForRead, see Accessing Data Buffers in Framework-Based Drivers.

Examples

The following code example is a shortened version of the EvtIoInCallerContext callback function that the NONPNP sample driver contains. When the callback function receives an I/O request, it determines if the request contains an I/O control code with a transfer type of METHOD_NEITHER. If the request does contain such an I/O control code, the function:

1. Calls WdfRequestRetrieveUnsafeUserInputBuffer and WdfRequestRetrieveUnsafeUserOutputBuffer to obtain the virtual addresses of the request's read and write buffers.
2. Calls WdfRequestProbeAndLockUserBufferForRead and WdfRequestProbeAndLockUserBufferForWrite to probe and lock the buffers and to obtain a handle to a framework memory object that represents each buffer.

VOID
NonPnpEvtIoInCallerContext(
    IN WDFDEVICE  Device,
    IN WDFREQUEST Request
    )
{
    NTSTATUS  status = STATUS_SUCCESS;
    PREQUEST_CONTEXT  reqContext = NULL;
    WDF_OBJECT_ATTRIBUTES  attributes;
    WDF_REQUEST_PARAMETERS  params;
    size_t  inBufLen, outBufLen;
    PVOID  inBuf, outBuf;

    WDF_REQUEST_PARAMETERS_INIT(&params);
    WdfRequestGetParameters(
                            Request,
                            &params
                            );

    //
    // Check to see whether the driver received a METHOD_NEITHER I/O control code.
    // If not, just send the request back to the framework.
    //
    if(!(params.Type == WdfRequestTypeDeviceControl &&
            params.Parameters.DeviceIoControl.IoControlCode ==
                                    IOCTL_NONPNP_METHOD_NEITHER)) {
        status = WdfDeviceEnqueueRequest(
                                         Device,
                                         Request
                                         );
        if( !NT_SUCCESS(status) ) {
            goto End;
        }
        return;
    }

    //
    // The I/O control code is METHOD_NEITHER.
    // First, retrieve the virtual addresses of 
    // the input and output buffers.
    //
    status = WdfRequestRetrieveUnsafeUserInputBuffer(
                                                     Request,
                                                     0,
                                                     &inBuf,
                                                     &inBufLen
                                                     );
    if(!NT_SUCCESS(status)) {
        goto End;
    }
    status = WdfRequestRetrieveUnsafeUserOutputBuffer(
                                                      Request,
                                                      0,
                                                      &outBuf,
                                                      &outBufLen
                                                      );
    if(!NT_SUCCESS(status)) {
       goto End;
    }

    //
    // Next, allocate context space for the request, so that the
    // driver can store handles to the memory objects that will
    // be created for input and output buffers.
    //
    WDF_OBJECT_ATTRIBUTES_INIT_CONTEXT_TYPE(&attributes,
                                        REQUEST_CONTEXT);
    status = WdfObjectAllocateContext(
                                      Request,
                                      &attributes,
                                      &reqContext
                                      );
    if(!NT_SUCCESS(status)) {
        goto End;
    }

    //
    // Next, probe and lock the read and write buffers.
    //
    status = WdfRequestProbeAndLockUserBufferForRead(
                                                     Request,
                                                     inBuf,
                                                     inBufLen,
                                                     &reqContext->InputMemoryBuffer
                                                     );
    if(!NT_SUCCESS(status)) {
        goto End;
    }

    status = WdfRequestProbeAndLockUserBufferForWrite(
                                                      Request,
                                                      outBuf,
                                                      outBufLen,
                                                      &reqContext->OutputMemoryBuffer
                                                      );
    if(!NT_SUCCESS(status)) {
        goto End;
    }

    //
    // Finally, return the request to the framework.
    //
    status = WdfDeviceEnqueueRequest(
                                     Device,
                                     Request
                                     );
    if(!NT_SUCCESS(status)) {
        goto End;
    }
    return;

End:
    WdfRequestComplete(
                       Request,
                       status
                       );
    return;
}

Requirements

See also

WdfMemoryGetBuffer

WdfRequestProbeAndLockUserBufferForWrite

WdfRequestRetrieveUnsafeUserInputBuffer