Microsoft KB Archive/218178

= Access Violation in SNASERVR!SNPUGETC if Invalid Formatted GDS Variable Received =

Article ID: 218178

Article Last Modified on 9/22/2005

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APPLIES TO


 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0

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This article was previously published under Q218178





SYMPTOMS
The SNA Server service (Snaservr.exe) may fail unexpectedly with an access violation in function snpugetc. This failure may occur when receiving an invalid formatted General Data Stream (GDS) variable from a mainframe. If Drwtsn32.exe is configured as the default debugger on the SNA Server system, the Drwtsn32.log file may contain an entry similar to the following when this access violation occurs: Application error: Application: exe\snaservr.dbg (pid=259) 11/26/1998 @ 8:56:47.484       Error: c0000005 (Access violation) Function: snpugetc 0100a5ca 8d4e06          lea     ecx,[esi+0x6] ds:0120ea06=???????? 0100a5cd 2bdd            sub     ebx,ebp 0100a5cf 0fbfef          movsx   ebp,di 0100a5d2 3beb            cmp     ebp,ebx 0100a5d4 7e27            jle     snpugetc+0x4d (0100a5fd) 0100a5d6 85f6            test    esi,esi 0100a5d8 7427            jz      snpugetc+0x51 (0100a601) 0100a5da 668b00          mov     ax,[eax] ds:019dff01=???? 0100a5dd 8b36            mov     esi,[esi] ds:00000000=???????? 0100a5df 662b01          sub     ax,[ecx] ds:019d61f6=010c Fault ->0100a5e2 0fbf5e04        movsx   ebx,word ptr [esi+0x4] ds:0120ea07=???? 0100a5e6 0fbf6e06        movsx   ebp,word ptr [esi+0x6] ds:0120ea07=???? 0100a5ea 8d7c07ff        lea     edi,[edi+eax-0x1] ds:02bee908=????????


 * > Stack Back Trace <*

FramePtr ReturnAd Param#1 Param#2  Param#3  Param#4  Function Name 0118fd2c 0105f212 019d257c a3160e06 002d042c 002d0360 snaservr!snpugetc (FPO: [EBP 0xa3160e06] [2,0,4]) 0118fd94 0105c297 002d0360 0000125d 0118fdf8 01144bdd snaservr!s1pxntur (FPO: [EBP 0x002d042c] [3,19,4])

In addition, an event similar to the following will be logged in the Windows NT Application Event Log:

Event ID: 624

Source: SNA Server

Description: Creating dump file C:\SNA\traces\snadump.log for

SNASERVR.EXE



CAUSE
The access violation is caused when SNA Server receives a badly formatted GDS variable. In this case, the format of the Sign-On GDS variable 0x'1221' sent by the host was invalid.

This problem started to occur with SNA Server 3.0 with the introduction of SNA Server single sign on support, where SNA Server now explicitly parses the user and password data within the Sign-On GDS message.



SNA Server 4.0
To resolve this problem, obtain the latest service pack for SNA Server version 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack

SNA Server 3.0
To resolve this problem, obtain the latest service pack for SNA Server version 3.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

184307 How to Obtain the Latest SNA Server Version 3.0 Service Pack



STATUS
Microsoft has confirmed that this is a problem in SNA Server 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, SNA Server 4.0, 4.0 SP1, 4.0 SP2. This problem was first corrected in SNA Server version 3.0 Service Pack 4 and SNA Server version 4.0 Service Pack 3.



MORE INFORMATION
With Client message trace enabled, you may see output similar to the following: PVI  --- PVI  9A000001->010AF5B1 LU 6.2 PVI                     MSGID:SWAT   MSGTYP:NTEOD  Sense1:0000 PVI                     Sense2:0700 PVI PVI   Header  at address 014D4B00, 14 elements PVI  0B010000 07000000 000E0000 01000301     <................> PVI PVI   Element at address 019D257C, start 13, end 268 PVI  2A0502FF 0003D000 000406F3 F0F10019 PVI  10C4C5E5 C2C7F0F3 F14BC1D7 D7C3C3D3 PVI  F207CE0B 1A0DF500 01002033 1221202F PVI  FF002201 40404040 40404040 E5F0F0F1 PVI  F0F0F0F0 F0F0F0F0 D3D6C7C9 D5404040 PVI  40404040 40404040 40404040 40404040 PVI  40404040 40404040 D9C5C3C5 C9D9C5C3 PVI  C5C9F0F0 F0F0F0F0 F0F0F0F0 40404040 PVI  40404040 40404040 40404040 40404040 PVI  40404040 40404040 40404040 40404040 PVI  40404040 40404040 40404040 40404040 PVI  40404040 40404040 40404040 40404040 PVI  40404040 40404040 40404040 40404040 PVI  F0F0F0F0 F0F0F0F5 40404040 40404040 PVI  40404040 40404040 E4E2D9C9 C4404040 PVI  40404040 40404040 C3F0F0F0 F8F0D5D7

Decoding the data shows the following:

2033 1221 - Sign-on GDS variable of length 2033 (which is much too large).

202F FF00 - Sign-On Request Data of length 202F.

2201 - User ID subfield of length 22.

According to SNA Formats & Protocols, the user ID must be 1-10 bytes, so the only valid lengths are 3-12.

40404040 40404040 E5F0F0F1 F0F0F0F0 F0F0F0F0 D3D6C7C9 D5404040 40404040 - User ID

40404040 40404040 40404040 - This is supposed to be an 00,01 or 02 subfield, which it clearly isn't.

Therefore, the data within the above frame clearly shows incorrect SNA protocol.

Additional query words: SNA trap snpugetc

Keywords: kbbug kbfix kbsna300sp4fix kbsna400sp3fix kbqfe kbhotfixserver KB218178

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