Q158587: 16-Bit Named Pipe File Open Leads to WOW Access Violation

Article: Q158587
Product(s): Microsoft Windows NT
Version(s): winnt:3.5,3.51,4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 09-AUG-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
-------------------------------------------------------------------------------

SUMMARY
=======

When a 16-bit application running under Window NT opens a file as a named pipe,
subsequent reads from that file can result in an access violation (AV) in the
WOW subsystem.

In the third-party test code that exposed this bug, a call to _lread() failed.
(This is a valid possibility; in this case, for example, there was no data
available at the pipe.) However, rather than return the standard failure code of
HFILE_ERROR (-1), a garbage value was returned, indicating success. When
processing was attempted using the garbage data extracted from the buffer
returned by the lread() call, an AV occurred.

CAUSE
=====

The file was opened as a named pipe under the WOW subsystem, but the DOS SFT_
flags in the file handle were not marked to indicate that the handle was for a
named pipe. (When _lread() fails under the WOW subsystem, the DOS subsystem will
make an attempt to carry out the read operation before returning failure to the
application.) When the read-file operation failed in WOW, the DOS emulation
layer incorrectly determined that, since the named pipe flag wasn't set for the
handle, it would deal with the handle as with a disk-based file, leading to the
unexpected result.

RESOLUTION
==========

To solve this problem the WOW code was fixed. When a named pipe file is
opened/created, the named pipe bit is now set in the file handle.

STATUS
======

Microsoft has confirmed this to be a problem in Windows NT versions 3.5, 3.51,
and 4.0. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S.
Service Pack. For information on obtaining the service pack, query on the
following word in the Microsoft Knowledge Base (without the spaces):

  S E R V P A C K


Additional query words: prodnt

======================================================================
Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : winnt:3.5,3.51,4.0
Issue type        : kbbug

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

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.