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Filter Verifier complaining about a completion context

benjibenji Member Posts: 19
edited March 2021 in NTFSD


I'm porting a legacy filter driver that does File Encryption to minifilter.

Lately I started using Driver Verifier (the old legacy driver failed passing it). I went solving various problems thanks to it.

But I'm stuck on this one, I've disabled all my FLT_OPERATION_REGISTRATION Callbacks so now I'm not filtering any I/Os and while I shutdown the computer this message appears :

FILTER VERIFIER WARNING: A filter has set a completion context for a callback data which will be
lost. Probable cause of this is that no post-operation callback was requested
or routine was registered for this operation or the request was being pended
or completed. (Filter = FFFFC902E4C59010 (driver_name_here), Cbd = FFFFC902E8705998)
Break, ignore, zap or remove ? 

In windbg I can print the FLT_CALLBACK_DATA structure and the FLT_IO_PARAMETER_BLOCK and the IO_STATUS_BLOCK :

kd> dt !_flt_callback_data FFFFC902E8705998
   +0x000 Flags            : 2
   +0x008 Thread           : 0xffffc902`e7f40040 _KTHREAD
   +0x010 Iopb             : 0xffffc902`e87059f0 _FLT_IO_PARAMETER_BLOCK
   +0x018 IoStatus         : _IO_STATUS_BLOCK
   +0x028 TagData          : (null) 
   +0x030 QueueLinks       : _LIST_ENTRY [ 0x00000000`00000000 - 0x00000000`00000000 ]
   +0x040 QueueContext     : [2] (null) 
   +0x030 FilterContext    : [4] (null) 
   +0x050 RequestorMode    : 0 ''
kd> dx -id 0,0,ffffc902e2aaf080 -r1 ((FLTMGR!_FLT_IO_PARAMETER_BLOCK *)0xffffc902e87059f0)
((FLTMGR!_FLT_IO_PARAMETER_BLOCK *)0xffffc902e87059f0)                 : 0xffffc902e87059f0 [Type: _FLT_IO_PARAMETER_BLOCK *]
    [+0x000] IrpFlags         : 0x0 [Type: unsigned long]
    [+0x004] MajorFunction    : 0x10 [Type: unsigned char]
    [+0x005] MinorFunction    : 0x0 [Type: unsigned char]
    [+0x006] OperationFlags   : 0x0 [Type: unsigned char]
    [+0x007] Reserved         : 0x0 [Type: unsigned char]
    [+0x008] TargetFileObject : 0x0 [Type: _FILE_OBJECT *]
    [+0x010] TargetInstance   : 0xffffc902e69c1010 [Type: _FLT_INSTANCE *]
    [+0x018] Parameters       [Type: _FLT_PARAMETERS]
kd> dx -id 0,0,ffffc902e2aaf080 -r1 (*((FLTMGR!_IO_STATUS_BLOCK *)0xffffc902e87059b0))
(*((FLTMGR!_IO_STATUS_BLOCK *)0xffffc902e87059b0))                 [Type: _IO_STATUS_BLOCK]
    [+0x000] Status           : -1 [Type: long]
    [+0x000] Pointer          : 0xffffffff [Type: void *]
    [+0x008] Information      : 0x0 [Type: unsigned __int64]

But they are quite empty...

And since I'm not filtering any I/Os where can I be using a FLT_CALLBACK_DATA ?
Without Driver Verifier it goes to shutdown normally (no BSOD or freezes).
If anybody has ever encountered this message ... any help appreciated !

(I also registered some callback in pDriverObject->MajorFunction[] to communicate with the driver, but I don't think it can come from this).

Thank you.


  • rod_widdowsonrod_widdowson Member - All Emails Posts: 1,258

    And you absolutely don't have a IRP_MJ_CONTROL callback registered? Sounds very fishy.

    What is the IOCTL being sent? I'd also chase up the thread in question (if there is one) and see if that suggests anything.

    I think that the !fldkd windbg extension will help you a lot. It will tell you what FltMgr thinks is going on and fltkd.cbd will even find the IRP for you

    FWIW I have never seen this before - which adds to my "very fishy" comment, because the obvious causes are also filtered out by verifier earlier (if you set up the completion context and do not have a post call registered for instance)

  • benjibenji Member Posts: 19

    Perfect ! Thank you so much.

    !fltkd.cbd gave me the answer :

    kd> !fltkd.cbd FFFFCA039BE5FC08
    IRP_CTRL: ffffca039be5fb20  SHUTDOWN (16) [00000002] FastIo
    Flags                    : [10000004] DontCopyParms FixedAlloc
    DeviceObject             : ffffca03964b95d0 "\Device\HarddiskVolume2"
    [... more stuff here ...]

    When I said that I didn't register any Pre-op and Post-op I lied, not on purpose obviously, I registered a pre and post but there were transparent/generic.
    The pre-op returned FLT_PREOP_SUCCESS_WITH_CALLBACK, and I registered it for the IRP_MJ_SHUTDOWN. This was the problem it should not returned this code.

    Again, thank you :)

  • Dejan_MaksimovicDejan_Maksimovic Member - All Emails Posts: 589
    via Email
    I was going to say that (no callback) is not possible, because
    FltRegisterFilter would have failed already :)

    Kind regards, Dejan Maksimovic.
    FS Lead:
  • Sergey_PisarevSergey_Pisarev Member - All Emails Posts: 284

    @Dejan_Maksimovic said:
    I was going to say that (no callback) is not possible, because
    FltRegisterFilter would have failed already :)

    Kind regards, Dejan Maksimovic.
    FS Lead:

    It is definitely possible. You probably shouldn’t do that and at least register unload callback but code like this works:

    return FltRegisterFilter(driver, &fltReg, &minifilter);

  • Dejan_MaksimovicDejan_Maksimovic Member - All Emails Posts: 589
    via Email
    Peculiar, I went with the OperstionCallbacks having just the end marker and
    that fails.
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