Printing out Recieved string from DeviceIOControl

NTFSD
1

Hi,
apologies for maybe a noob question, but am just starting with Windows Driver programming.

I am trying to create an IOCTL and communicate with the driver from a user mode application. I am sending a string (char) to KM and printing it out in Windbg. In turn, KM will send another string back (char again) and I want to print it on a Mesage box or window text or anything.

The string I am sending from my user mode application is arriving fine and I can print it out in WinDbg.
However, from the UM application, I cannot see the recieved string in the DeviceIOControl function.

Here is my User Mode function PART:

HANDLE hDevice;
DWORD nb;
CString Windowmessage = L" ";
char texttosend[4] = “arg”; //I am sending this
CHAR pRecievedString[250]; //I am supposed to recieve in this

bool bResult = 0;

Windowmessage.Append(L"Sending meessage to Kernel Mode\r\n");
GetDlgItem(OutputTextboxec)->SetWindowTextW(Windowmessage);

Windowmessage.Append(L"Creating FileIO\r\n");
GetDlgItem(OutputTextboxec)->SetWindowTextW(Windowmessage);

hDevice = CreateFile(
	TEXT("\\\\.\\DOSXXXDeviceName"),			//File Name of File or IO device
	GENERIC_READ | GENERIC_WRITE,		//Desired Access 
	0,							     //share mode (0-prevent other processes from opening a file f they request delete/read/write access)
										//FILE_SHARE_DELETE(0x00000004),FILE_SHARE_READ(0x00000001),FILE_SHARE_WRITE(0x00000002),
	NULL,								//SecurityAttributes
	OPEN_EXISTING,						//CreationDisposition:An action to take on a file or device that exists or does not exist.
	FILE_ATTRIBUTE_NORMAL,				// FlagsAndAttributes
	NULL);								// TemplateFile


Windowmessage.Append(L"Sending Control Command \r\n");
GetDlgItem(OutputTextboxec)->SetWindowTextW(Windowmessage);

ZeroMemory(pRecievedString, sizeof(pRecievedString));

bResult = DeviceIoControl(
			hDevice, IOCTL_ADDEXT,
			&texttosend, sizeof(texttosend),
			pRecievedString, sizeof(pRecievedString) ,
			&nb, NULL);

Windowmessage.Append(L"Add Ext Cmnd sent\r\n");
GetDlgItem(OutputTextboxec)->SetWindowTextW(Windowmessage);
	
_**// I tried a lot of formatting to output PRecievedString here but to no avail. %c outputs rubbish. %s creates a memory error//**_
/*wchar_t op[200] = {L'0'};
swprintf(op, sizeof(op), L"in: % %c %s   \r\n ", pRecievedString, pRecievedString);

Windowmessage.Append(op);
GetDlgItem(OutputTextboxec)->SetWindowTextW(Windowmessage);*/

CloseHandle(hDevice);

}

And here is my Kernel Mode function

RegisterExtension_BufferedIO(PIRP Irp, PIO_STACK_LOCATION pIoStackIrp, ULONG_PTR dwDataWritten)
{
PAGED_CODE();

NTSTATUS status = STATUS_UNSUCCESSFUL;
PCHAR pOutputBuffer, pInputBuffer;
ULONG dwDataRead = 0;
PCHAR pReturnData = "Hello from Kernel Buffered IO";
UINT16 dwDataSize = sizeof("Hello from Kernel Buffered IO");

KdPrint(("->->->In Register Extension Buffered IO\r\n"));

pInputBuffer = Irp->AssociatedIrp.SystemBuffer;
pOutputBuffer = Irp->AssociatedIrp.SystemBuffer;

if (pInputBuffer && pOutputBuffer)
{
	if (IsStringTerminated(pInputBuffer, pIoStackIrp->Parameters.DeviceIoControl.InputBufferLength, dwDataRead))
	{
		KdPrint((" Message from User Mode: %s \r\n", pInputBuffer));
		KdPrint((" Output buffer length: %i >= %i:DataSize to Send to UM? \r\n ", pIoStackIrp->Parameters.DeviceIoControl.OutputBufferLength, dwDataSize));

		if (pIoStackIrp->Parameters.DeviceIoControl.OutputBufferLength >= dwDataSize)
		{

			RtlCopyMemory(pOutputBuffer, pReturnData, dwDataSize);
			KdPrint(("Output Buffer = %s \r\n", pOutputBuffer));   _**//This prints fine but I do not see it in User Mode **_
			dwDataWritten = dwDataSize;
			status = STATUS_SUCCESS;
		}
		else
		{
			dwDataWritten = dwDataSize;
			status = STATUS_BUFFER_TOO_SMALL;
		}
	}
}
return status;

}

I know that something is arriving back cause when I initiate pRecievedString, it prints out rubbish. However if I initiate it and do not call DeviceIOControl I see the initiated string in the TextWindow.

I hope it is just some stupid formatting issue.

thanks in advance for your help.
regards
Mario

2

Not sure if there are other problems, but:

dwDataWritten = dwDataSize;

Doesn’t return anything to the caller. You need PULONG_PTR and a *dwDataWritten. Setting a breakpoint and stepping through your code probably would have been faster…

Also, WHY are you passing strings around like this?

3

@“Scott_Noone_(OSR)” said:
Not sure if there are other problems, but:

dwDataWritten = dwDataSize;

Doesn’t return anything to the caller. You need PULONG_PTR and a *dwDataWritten. Setting a breakpoint and stepping through your code probably would have been faster…

Also, WHY are you passing strings around like this?

Thanks for the reply. As I said I’m new to this and even after a lot of reading I am still thinking with the ‘high level language’ mind. Hence why I am ‘passing strings around’ like this. I do not know how to make sure that something has been sent from Kernel to User mode (and thus can be used by it) ,and vice versa.

4

The first things for you to consider are:

  1. Why are you posting this to the file system development forum? Would not NTDEV be more appropriate? Or are you trying to write a file system or filter?
  2. If you’re not trying to write a file system or filter, you should be using WDF… it’ll make your file much easier.

Peter

5

@“Peter_Viscarola_(OSR)” said:
The first things for you to consider are:

  1. Why are you posting this to the file system development forum? Would not NTDEV be more appropriate? Or are you trying to write a file system or filter?
  2. If you’re not trying to write a file system or filter, you should be using WDF… it’ll make your file much easier.

Peter

HI Peter,
I’m writing a MiniFilter to filter certain operations, but using IOCTL to control it from USER mode. Hence why I posted in NTFS, but on second thoughts, since my question regarded specifically IOCTLs, maybe I should repost it in the NTDEV forum.
My Apologies.

6

You should look at using a Communication Port instead, much easier to deal with than IRPs for a minfilter.

7

@“Scott_Noone_(OSR)” said:
Not sure if there are other problems, but:

dwDataWritten = dwDataSize;

Doesn’t return anything to the caller. You need PULONG_PTR and a *dwDataWritten. Setting a breakpoint and stepping through your code probably would have been faster…

Also, WHY are you passing strings around like this?

Hi Scott, thanks a lot, that was my mistake. using dwDataWritten solved the issue. Need kick up my a** on my pointer knowledge