Microsoft KB Archive/167666

= SNA TN3270 Access Violation, Event ID 5 =

Article ID: 167666

Article Last Modified on 9/22/2005

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APPLIES TO


 * Microsoft SNA Server 3.0 Service Pack 4, when used with:
 * Microsoft Windows NT 4.0
 * Microsoft SNA Server 4.0, when used with:
 * Microsoft Windows NT 4.0
 * Microsoft SNA Server 3.0 Service Pack 2, when used with:
 * Microsoft Windows NT 4.0

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This article was previously published under Q167666





SYMPTOMS
The TN3270 Server service fails abnormally with an access violation and logs the following event to the Windows NT application log:

Event ID: 5

Source: TN3270 Server

Description:

The TN3270E Service has abnormally terminated.

EXPLANATION:

An exception (0xC0000005) has occurred that has caused the TN3270E

Service to terminate.

An entry may be logged in the \Drwtsn32.log file indicating a failure in the Tn3servr.exe process. For example:   -- Application exception occurred: App: exe\tn3servr.DBG Exception number: c0000005 (access violation)

Function: RtlDestroyHeap FAULT -> 77f7ebf f3ab   rep  stosd      es:00194000=??????

*> Stack Back Trace <*

FramePtr        Function Name ntdll!RtlDestroyHeap ntdll!RtlAllocateHeap kernel32!LocalAlloc tn3servr!TnAlloc tn3servr!SMG_CB_Allocate tn3servr!SMGScheduleSessionInitialization tn3servr!TCPSessionTerminate - However, when attached with the NTSD or CDB debugger, the failure may actually occur in the following function:    Function:  RtlpFindAndCommitPages

Stack Back Trace - Function Names ntdll!RtlpFindAndCommitPages+0xde ntdll!RtlpExtendHeap+0x52 ntdll!RtlAllocateHeapSlowly+0x894 ntdll!RtlAllocateHeap+0x67a kernel32!LocalAlloc+0x71 tn3servr!TnAlloc+0xd tn3servr!SMG_CB_Allocate+0xb tn3servr!SMGScheduleSessionInitiali tn3servr!TCPSessionTerminate+0x23d tn3servr!TCPThreadMain+0x1d7 tn3servr!TnMain+0x79 kernel32!BaseThreadStart+0x51



CAUSE
The TN3270 service does not account for the 5-byte TN3270E header when receiving data from a TN3270E client causing the TN3270 service to overwrite the end of the buffer that was allocated for the received data. This results in the application exception described previously.



RESOLUTION
The TN3270 service has been updated to allocate buffers that account for the 5-byte TN3270E header when receiving data from TN3270E clients. The following configuration change to the TN3270 Server successfully resolved the problem at a customer location, therefore it can be used as an interim solution until the fix can be applied.  In SNA Server Manager, go to the TN3270 Server Properties dialog box. Choose the Settings folder. Change the following parameters to the values below:

Default RU Sizes:

Inbound: 2048 (Default is 1024)

Outbound: 4096 (Default is 2048)



This particular customer's host system was sending SNA BIND commands indicating the above maximum secondary and primary RU sizes above. The TN3270 Server Inbound RU size should be set to the maximum secondary RU size indicated by the host system. The TN3270 Server Outbound RU size should be set to the maximum primary RU size indicated by the host system.

Note that the host configuration determines these maximum RU size values for a non-negotiable 3270 session. The host administrator should be contacted to determine these RU sizes. If this is not possible, the host RU sizes can be determined by enabling SNA Server Data Link Control messages, or TN3270 Internal Traces using the SNA Trace too. A BIND command will appear in the TN3270 trace as follows: <pre class="fixed_text"> >04/10 11:09:42.751 (+260 msecs)  Event=TEV_DataFromSNAAsync Thread = 0x000000A5 Session = 0x001F7ED8  Socket = 0x00000390 VCB address=0x001F80AC verb_length=0x0044 verb=0x0052 (RUI)  opcode=0x8003 (READ) sid=0x00020003 correlator=0x001F7ED8  post_handle=0x000003A4 prim_rc=LUA_OK sec_rc=LUA_SEC_RC_OK lu_exp    lua_data_length=0x00000023 lua_message_type=0x31 (LUA_MESSAGE_TYPE_BIND) TH Only   efi=1  oadi=0  daf=FD  oaf=01  snf=9E05 RH REQ SC  fi=1   sdi=0  bci=1  eci=1  (Only) 6B 80 00   dr1=1  dr2=0  ri=0   qri=0  pi=0 bbi=0 ebi=0  cdi=0  csi=0  edi=0  pdi=0 000000 31010303 b1903080 00018889 80000280  *..........hi....* 000010 00000000 00000000 03000006 c2c3c3d7  *............BCCP* 000020 f4f800                               *48. * The BIND command data appears in the data portion of the above message, starting at 0x31 (the BIND command, which is byte 0 of the BIND). The maximum secondary and primary RU sizes appear at offset 10 and 11 (starting at 0 origin) in the above trace:

offset 10 = 0x88 (maximum secondary RU size)

offset 11 = 0x89 (maximum primary RU size)

This value is converted to an actual RU size using the following algorithm (assuming the RU size = 0xMN):

M * (2**N)

Here are some common RU sizes:

0x87 = 1024

0x88 = 2048

0x89 = 4096

<div class="status_section">

STATUS
Microsoft has confirmed this to be a problem in SNA Server version 3.0, 3.0 Service Pack 1, and 3.0 Service Pack 2.

This problem was corrected in the latest SNA Server version 3.0 U.S. Service Pack. For information on obtaining this Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

Keywords: kbbug kbfix kbqfe kbnetwork kbhotfixserver KB167666

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