CreateFile returning success without entry into dispatch

NTDEV
1

Hi,

I have an app that talks to my driver. In one test scenario the app opens a handle to the driver (CreateFile), sends an ioctl and closes the handle. This works correctly as expected with the test running in a loop.

When I run the test for long hours (overnight), I observe that the ioctl call fails with Invalid Handle error. While debugging this I noticed that when the issue is reproduced the CreateFile call is getting completed successfully *without* an entry into driver’s dispatch routine (IRP_MJ_CREATE)!
When I subsequently called ioctl with the handle returned by the CreateFile, I get an Invalid Handle error.

In what scenario the CreateFile gets succeeded without corresponding entry into the dispatch? Will appreciate some tips to debug this further, thanks.

Regards,
Suresh

2

That?s simply not possible. If you have a handle, you have a file object. If you have a file object, it was successfully created. If a file object was created, your create dispatch entry point returned success.

You have some sort of bug like a race condition in your test code.

Peter
OSR
@OSRDrivers

3

How are checking for success after the call to CreateFile? Are you sharing the handle across threads?

Bent from my phone

From: xxxxx@lists.osr.com on behalf of xxxxx@yahoo.com
Sent: Thursday, March 29, 2018 6:39:56 PM
To: Windows System Software Devs Interest List
Subject: [ntdev] CreateFile returning success without entry into dispatch

Hi,

I have an app that talks to my driver. In one test scenario the app opens a handle to the driver (CreateFile), sends an ioctl and closes the handle. This works correctly as expected with the test running in a loop.

When I run the test for long hours (overnight), I observe that the ioctl call fails with Invalid Handle error. While debugging this I noticed that when the issue is reproduced the CreateFile call is getting completed successfully without an entry into driver’s dispatch routine (IRP_MJ_CREATE)!
When I subsequently called ioctl with the handle returned by the CreateFile, I get an Invalid Handle error.

In what scenario the CreateFile gets succeeded without corresponding entry into the dispatch? Will appreciate some tips to debug this further, thanks.

Regards,
Suresh

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4

> How are checking for success after the call to CreateFile?

We are checking for a return value of INVALID_HANDLE_VALUE from CreateFile to deduce a failure, otherwise we treat it as success and proceed to use the returned handle in subsequent call to ioctl.

Are you sharing the handle across threads?

No, it is a single thread which opens, uses and closes the handle in each iteration.

Here is the snapshot of the call:

handle = CreateFile(driver_name,
GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_ALWAYS,
FILE_FLAG_OVERLAPPED,
NULL);
if (INVALID_HANDLE_VALUE == handle) {
handle = NULL;
}
return handle;

5

Wait, isn’t 0 a valid handle?

6

> Wait, isn’t 0 a valid handle?

Oh, is it? Thanks for catching that. We then better return a negative value if CreateFile fails.
However in our current scenario we ARE getting a non-zero handle returned from CreateFile (without an entry into dispatch).

7

No, no… zero is not a valid handle for any practical purpose.

Peter
OSR
@OSRDrivers