[UMDF] DMF_VirtualHidMini fails WriteReport requests on descriptors without Report IDs

[nefarius]

Greetings,

just stumbled upon an interesting issue with the DMF_VirtualHidMini module. I have a device which (for compatibility reasons) doesn't utilize Report IDs in its HID Report Descriptor. It exposes one input, feature and output report. Snippet of Output Report definition in descriptor:

	0x06, 0x00, 0xFF,  //     Usage Page (Vendor Defined 0xFF00)
	0x09, 0x01,        //     Usage (0x01)
	0x75, 0x08,        //     Report Size (8)
	0x95, 0x30,        //     Report Count (48)
	0x91, 0x02,        //     Output (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)

Everything works fine except writing an output report, WriteFile / GetOverlappedResult failed with ERROR_INSUFFICIENT_BUFFER despite the same code working perfectly with the legacy kernel-driver equivalent of my new UMDF-only code, which got me curious.

[2021-02-24 13:11:28.502] [WriteFile] [info] ret=0, lastError=997 (0049) ->  00 02 00 00 00 FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[2021-02-24 13:11:28.502] [GetOverlappedResult] [info] ret=0, lastError=122, bytesWritten=0

I am aware of the trickery necessary to get the Report ID delivered from mshidumdf.sys to the reflector and my driver so I examined the VirtualHidMini_RequestGetHidXferPacket_ToWriteToDevice implementation of DmfU and I think I found a bug:

Accessing the output buffer fails with STATUS_BUFFER_TOO_SMALL and my own callback isn't even invoked, the module answers this request with an error. Assuming that a zero-length buffer is the result of an absence of a Report ID (being effectively 0) I introduced this experimental hack and sure enough, my code works now, I receive the buffer content and the user-land API completes with success:

    // Get report Id from output buffer length.
    //
    ntStatus = WdfRequestRetrieveOutputMemory(Request,
                                              &outputMemory);
    if ( !NT_SUCCESS(ntStatus) && ntStatus != STATUS_BUFFER_TOO_SMALL )
    {
        TraceEvents(TRACE_LEVEL_ERROR, DMF_TRACE, "WdfRequestRetrieveOutputMemory fails: ntStatus=%!STATUS!", ntStatus);
        goto Exit;
    }

    // React to this specific case by assuming 0
    //
    if (ntStatus == STATUS_BUFFER_TOO_SMALL)
    {
        Packet->reportId = 0;
    }
    else
    {
        WdfMemoryGetBuffer(outputMemory,
            &outputBufferLength);
        Packet->reportId = (UCHAR)outputBufferLength;
    }

If my assumptions are correct I'd gladly provide a PR and see this change merged so the framework can handle this edge-case properly as well 😁

Thank you!

[samtertzakian]

Hi, nefarius... We are looking at this now. Thank you for your feedback.

[samtertzakian]

This issue is corrected by Release v.1.1.83.
We have made the above change.
Thank you nefarius.