IT18434: AMS INTERCEPTOR MAY DRIVE USER CALLBACK FUNCTION INCORRECTLY AFTER HANDLING INVALID MESSAGE

APAR status

• Closed as program error.

Error description

• When using an asynchronous callback function with MQCB to
  consume an AMS protected message, and because of an error in
  processing the message it is moved to the AMS error queue or
  dead letter queue, the callback function is driven with invalid
  CallType.
  
  The results of this incorrect input to the user-supplied
  callback function will depend on the implementation of the
  callback function.
  
  An MQ trace of the issue shows:
  
  ----}! smqiGetAfter rc=Unknown(2) FunctionTime=10517
  ---} smqiCallbackBefore rc=OK FunctionTime=10590
  --} smqxCallbackBefore rc=OK FunctionTime=10598
  CallType 6 ConsumerState 0 cc=2 rc=2063
  
  If cc=2, then it is expected that the CallType should be 5
  (MQCBCT_EVENT_CALL), as a message is not being delivered to the
  callback function.
  

Local fix

• This issue can be avoided within the application's logic by
  either:
  
  1. Modifying the application to use a synchronous MQGET call
  instead of MQCB.
  
  2. Modifying the callback function to check the CC in the
  callback context, and not attempt to act on the supplied message
  buffer if the CC is 2.
  
  
  Alternatively, ensure that messages placed on the AMS protected
  queues are well-formed, and adhere to the policy used when
  getting from the queue.
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of MQ Advanced Message Security (AMS)
  version 8.0.0.5 who are using an asynchronous consume callback
  to retrieve messages and the message is not consumable.  For
  example, the quality of protection present on the message is not
  sufficient for the quality of protection specified in the
  security policy for the queue.
  
  This also applies to locally-attached (bindings mode) JMS client
  applications making use of JMS message listeners, unless the JMS
  application or connection factory has been configured to run in
  migration mode.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  When the MQ queue manager has a message available for delivery
  to a native asynchronous consumer, and the consumer's queue is
  AMS protected, the AMS interceptor will be invoked to unprotect
  the message before the consumer's registered callback function
  is driven by the queue manager.
  
  If the message cannot be unprotected, or is in contravention of
  the security policy defined on the queue, the interceptor will
  move it to the AMS error queue, or dead letter queue, based on
  the current configuration.
  
  In this case, it is expected that the consumer's callback
  function will be driven with a CallType of MQCBCT_EVENT_CALL,
  allowing the callback function to review the MQ completion code
  and reason code within the callback context, and decide how to
  proceed.
  
  A logic error within this code path, introduced in MQ 8.0.0.5,
  meant that the AMS interceptor failed to set the correct
  CallType for the asynchronous consumer. As a result, the
  consumer's callback function was incorrectly invoked with a
  CallType of MQCBCT_MSG_REMOVED. This implied that a message was
  available for the consumer, but this was not the case. A copy of
  the MQMD of the message was supplied to the callback function,
  but the message buffer was empty, as the message had been moved
  to the error or dead letter queue.
  

Problem conclusion

• The MQ AMS interceptor code has been updated such that the
  asynchronous consumer's callback function is correctly invoked
  with a CallType of MQCBCT_EVENT_CALL when the message intended
  for the consumer was moved to the error or dead letter queue.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v8.0       8.0.0.6
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  WMQ BASE MULTIP

• Fixed component ID

  5724H7251

Applicable component levels

• R800 PSY

     UP