IT37135: Memory exceptions when JSON API calls such as json_object_iter_next are called from user code

APAR status

• Closed as program error.

Error description

• MQ client applications, or user code in exits (example: security
  exits) experience exceptions related to json functions when
  using libraries to work with json data such as libjansson.
  
  An FDC record with Probe ID XC130003 may be written.  This is an
  example of text within such an FDC record.
  
  --------------------------------
  Probe Id          :- XC130003
  Component         :- xehExceptionHandler
  Arith1            :- 11 (0xb)
  Comment1          :- SIGSEGV: address not mapped(0x2b2900000018)
  ------------------------------
  
  O/S Call Stack for current thread, may contain
  
  /opt/mqm/lib64/libmqmcs_r.so(xehExceptionHandler+0x6c1)
  /lib64/libpthread.so.0(+0xf630)
  /opt/mqm/lib64/libmqmcs_r.so(json_object_iter_next+0x3)
  /usr/lib64/libjansson.so.4(+0x2aa5)
  /usr/lib64/libjansson.so.4(json_dumps+0x46)
  

Local fix

Problem summary

• ****************************************************************
  USERS AFFECTED:
  Users who wish to use JSON libraries like libjansson, in the
  same application program as MQ application API libraries.
  
  
  Platforms affected:
  Linux on Power, Linux on x86-64, Linux on zSeries
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  The MQ internal shared library libmqmcs_r.so (and variants)
  exported a larger set of symbols as entry points than was needed
  for the functionality of the library.
  
  Because some json_* symbols were exported as entry points from
  libmqmcs_r.so, they could be found by the runtime linker when
  fixing up symbol links, from other function calls elsewhere in
  the application.
  
  When this happened, the library code in libmqmcs_r.so was
  unlikely always to match the expectations of the caller.  This
  resulted in memory exceptions (SIGSEGV etc.).
  

Problem conclusion

• The exported entry points from libmqmcs_r.so (and variants) are
  now derived from a list of symbols that omits the json_*
  functions.  This ensures that the runtime linker does not fix up
  linkage between application code outside MQ and the json_*
  functions inside libmqmcs_r.so.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.1 LTS   9.1.0.9
  v9.x CD    9.2.4
  
  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

  IBM MQ BASE MP

• Fixed component ID

  5724H7271

Applicable component levels