NULL Data Pointer Pattern: case study

Here is the promised case study for the previous post about data NULL pointers. The complete dump has this bugcheck:

0: kd> !analyze -v


This is a very common bugcheck.  Usually the exception address pinpoints the driver/function that caused the problem.  Always note this address as well as the link date of the driver/image that contains this address. Some common problems are exception code 0x80000003.  This means a hard coded breakpoint or assertion was hit, but this system was booted /NODEBUG.  This is not supposed to happen as developers should never have hardcoded breakpoints in retail code, but ... If this happens, make sure a debugger gets connected, and the system is booted /DEBUG.  This will let us see why this breakpoint is happening.
Arg1: c0000005, The exception code that was not handled
Arg2: 8081c7c4, The address that the exception occurred at
Arg3: f1b5d730, Trap Frame
Arg4: 00000000


8081c7c4 f6412c02        test    byte ptr [ecx+2Ch],2

TRAP_FRAME:  f1b5d730 -- (.trap 0xfffffffff1b5d730)

0: kd> .trap 0xfffffffff1b5d730
ErrCode = 00000000
eax=8923b008 ebx=00000000 ecx=00000000 edx=8923b008 esi=891312d0 edi=89f0b300
eip=8081c7c4 esp=f1b5d7a4 ebp=f1b5d7a4 iopl=0 nv up ei ng nz ac pe nc
cs=0008 ss=0010 ds=0023 es=0023 fs=0030 gs=0000 efl=00010296
8081c7c4 f6412c02   test    byte ptr [ecx+2Ch],2  ds:0023:0000002c=??

0: kd> kv 100
ChildEBP RetAddr  Args to Child             
f1b5d7a4 f42cdea9 8923b008 89f0b300 8923b008 nt!IoIsOperationSynchronous+0xe
f1b5d7bc 8081df85 89f0b300 8923b008 00000200 driveB!FsdDeviceIoControlFile+0×19
f1b5d7d0 808ed7a9 00000000 f1b5da84 f1b5db6c nt!IofCallDriver+0×45
f1b5da20 f3c3a521 89f0b300 f1b5da84 f1b5da84 nt!IoVolumeDeviceToDosName+0×89
WARNING: Stack unwind information not available. Following frames may be wrong.
f1b5da3c f3c3b58e 00000618 e4e00420 f1b5dad4 driverA+0×18531
f1b5dc3c 8081df85 89f48b48 87fa3008 89140d30 driverA+0×1df4

f1b5dc50 808f5437 87fa3078 89140d30 87fa3008 nt!IofCallDriver+0×45
f1b5dc64 808f61bf 89f48b48 87fa3008 89140d30 nt!IopSynchronousServiceTail+0×10b
f1b5dd00 808eed08 000000f0 00000000 00000000 nt!IopXxxControlFile+0×5e5
f1b5dd34 808897bc 000000f0 00000000 00000000 nt!NtDeviceIoControlFile+0×2a
f1b5dd34 7c8285ec 000000f0 00000000 00000000 nt!KiFastCallEntry+0xfc (TrapFrame @ f1b5dd64)
0856e154 7c826fcb 77e416f5 000000f0 00000000 ntdll!KiFastSystemCallRet
0856e158 77e416f5 000000f0 00000000 00000000 ntdll!NtDeviceIoControlFile+0xc
0856e1bc 6f050c6c 000000f0 5665824c 0856e234 kernel32!DeviceIoControl+0×137

From WDK help we know that the first parameter to IoIsOperationSynchronous is a pointer to an IRP structure:

0: kd> !irp 8923b008
Irp is active with 3 stacks 3 is current (= 0x8923b0c0)
 No Mdl: System buffer=878b7288: Thread 8758a020:  Irp stack trace. 
     cmd  flg cl Device   File     Completion-Context
 [  0, 0]   0  0 00000000 00000000 00000000-00000000   
                     Args: 00000000 00000000 00000000 00000000
 [  0, 0]   0  0 00000000 00000000 00000000-00000000   
                     Args: 00000000 00000000 00000000 00000000
>[  e, 0]   0  0 89f0b300 00000000 00000000-00000000   
                     Args: 00000200 00000000 004d0008 00000000

Disassembling the function shows some pointer dereferencing and we can reconstruct it starting from EBP+8, a pointer to an IRP. 

0: kd> .asm no_code_bytes
Assembly options: no_code_bytes

0: kd> u nt!IoIsOperationSynchronous nt!IoIsOperationSynchronous+0xe
8081c7b6 mov     edi,edi
8081c7b8 push    ebp
8081c7b9 mov     ebp,esp
8081c7bb mov     eax,dword ptr [ebp+8]
8081c7be mov     ecx,dword ptr [eax+60h]
8081c7c1 mov     ecx,dword ptr [ecx+18h]

EAX+60 seems to be a current stack location member of IRP and it is a pointer itself to _IO_STACK_LOCATION structure:

0: kd> dt -r _IRP 8923b008
   +0x000 Type             : 6
   +0x002 Size             : 0x268
   +0x004 MdlAddress       : (null)
   +0x008 Flags            : 0x70
   +0x038 CancelRoutine    : (null)
   +0x03c UserBuffer       : 0xf1b5d814
   +0×040 Tail             : __unnamed
      +0×000 Overlay          : __unnamed
         +0×000 DeviceQueueEntry : _KDEVICE_QUEUE_ENTRY
         +0×000 DriverContext    : [4] (null)
         +0×010 Thread           : 0×8758a020 _ETHREAD
         +0×014 AuxiliaryBuffer  : (null)
         +0×018 ListEntry        : _LIST_ENTRY [ 0×0 - 0×0 ]
         +0×020 CurrentStackLocation : 0×8923b0c0 _IO_STACK_LOCATION

ECX+18 is a pointer to a file object in _IO_STACK_LOCATION structure:

0: kd> dt _IO_STACK_LOCATION 8923b008+60
   +0x000 MajorFunction    : 0xc0 ''
   +0x001 MinorFunction    : 0xb0 ''
   +0x002 Flags            : 0x23 '#'
   +0x003 Control          : 0x89 ''
   +0x004 Parameters       : __unnamed
   +0x014 DeviceObject     : (null)
   +0×018 FileObject       : (null)
   +0×01c CompletionRoutine : (null)
   +0×020 Context          : (null)

2C offset at the crash point test byte ptr [ecx+2Ch],2 is _FILE_OBJECT Flags member:

0: kd> dt _FILE_OBJECT
   +0x000 Type             : Int2B
   +0x002 Size             : Int2B
   +0x004 DeviceObject     : Ptr32 _DEVICE_OBJECT
   +0x008 Vpb              : Ptr32 _VPB
   +0x00c FsContext        : Ptr32 Void
   +0x010 FsContext2       : Ptr32 Void
   +0x014 SectionObjectPointer : Ptr32 _SECTION_OBJECT_POINTERS
   +0x018 PrivateCacheMap  : Ptr32 Void
   +0x01c FinalStatus      : Int4B
   +0x020 RelatedFileObject : Ptr32 _FILE_OBJECT
   +0x024 LockOperation    : UChar
   +0x025 DeletePending    : UChar
   +0x026 ReadAccess       : UChar
   +0x027 WriteAccess      : UChar
   +0x028 DeleteAccess     : UChar
   +0x029 SharedRead       : UChar
   +0x02a SharedWrite      : UChar
   +0x02b SharedDelete     : UChar
   +0×02c Flags            : Uint4B
   +0×030 FileName         : _UNICODE_STRING
   +0×038 CurrentByteOffset : _LARGE_INTEGER
   +0×040 Waiters          : Uint4B
   +0×044 Busy             : Uint4B
   +0×048 LastLock         : Ptr32 Void
   +0×04c Lock             : _KEVENT
   +0×05c Event            : _KEVENT
   +0×06c CompletionContext : Ptr32 _IO_COMPLETION_CONTEXT

So it looks like driverA passed an IRP with NULL File object address to driverB and this is also shown in the output of !irp command above.

- Dmitry Vostokov @ -

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