Q216889: FIX: DCOM95 1.2 or DCOM98 Causes Data Corruption in RPC Calls

Article: Q216889
Product(s): Microsoft Windows 95.x Retail Product
Version(s): 
Operating System(s): 
Keyword(s): kbRPC kbOSWin95fix kbOSWin95sp1fix
Last Modified: 16-MAY-2002

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The information in this article applies to:

- Microsoft Windows 95 
- Microsoft Windows 98 
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SYMPTOMS
========

Under Windows 95 with DCOM95 1.2 update or Windows 98 with DCOM98 update, if you
have a pointer to conformant structure as a field of a complex structure, the
unmarshaling side receives uninitialized data. If the data structure is an [in]
parameter, the server manager routine sees the corruption. If it is an [out]
parameter, the client sees the corruption.

The same problem appears if your RPC application is running on Windows NT 4.0
with Service Pack 4 as documented in the following article in the Microsoft
Knowledge Base:

  Q216766 FIX: Windows NT 4.0 w/ SP4 Causes Data Corruption in RPC Calls

Data Structure:

  typedef struct tagConformantStruct 
  {
     unsigned long        size;
     [size_is(size)] char data[];
  } ConformantStruct;

  typedef enum tagColor
  {
     Red, Blue, Green
  } Color;

  typedef union tagMyUnion switch (Color type) u
  {
     case Red :  long  longArm;
     case Blue:  short shortArm;
     case Green: char  charArm;
  } MyUnion;

  typedef struct tagComplexStruct
  {
     unsigned long numUnions;
     ConformantStruct* pConfStruct; // PROBLEM! pointer to conformant struct.
     [size_is(numUnions)] MyUnion myUnions[]; // Makes the struct complex.
  } ComplexStruct;

CAUSE
=====

A defect in the rpcrt4.dll shipped with Windows NT 4.0 Service Pack 4, (DCOM95
1.2) and DCOM98 prevents the conformant part of the conformant structure to be
marshaled. The unmarshaling side expects the conformant part and unmarshals from
a possibly uninitialized part of the RPC buffer. This causes data corruption.

RESOLUTION
==========

A supported fix is now available from Microsoft, but it is only intended to
correct the problem described in this article and should be applied only to
systems experiencing this specific problem. This fix may receive additional
testing at a later time, to further ensure product quality. Therefore, if you
are not severely affected by this problem, Microsoft recommends that you wait
for the next update that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services
to obtain the fix. For a complete list of Microsoft Product Support Services
phone numbers and information about support costs, please go to the following
address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are normally incurred for support calls may
be canceled, if a Microsoft Support Professional determines that a specific
update will resolve your problem. Normal support costs will apply to additional
support questions and issues that do not qualify for the specific update in
question.

  File name   Version     Date       Time     Size
  --------------------------------------------------------
  RPCRT4.DLL  4.71.3116   03-04-99   7:16a   321,296



STATUS
======

Microsoft has confirmed this to be a problem in DCOM for Microsoft Windows 95,
version 1.2, and DCOM98 for Windows 95 and Windows 98 (included with Microsoft
Visual Studio 6). The fix described in the resolution section should not be
applied to systems which do not have one of these products installed.

MORE INFORMATION
================

For additional information about Windows 98 and Windows 98 Second Edition
hotfixes, click the article number below to view the article in the Microsoft
Knowledge Base:

  Q206071 General Information About Windows 98 and Windows 98 Second Edition
  Hotfixes

For additional information about Windows 95 hotfixes, click the article number
below to view the article in the Microsoft Knowledge Base:

  Q161020 Implementing Windows 95 Updates

Additional query words: conformant complex

======================================================================
Keywords          : kbRPC kbOSWin95fix kbOSWin95sp1fix 
Technology        : kbWin95search kbWin98search kbZNotKeyword3 kbWin98
Version           : :
Issue type        : kbprb

=============================================================================

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