PK65029: DEDB PROCOPT=GO W/COMPRESSION ROUTINE CAUSED STORAGE OVERLAY WHEN COMPRESSION EXIT USED INVALID LL FOR UNCOMPRESSED DATA MOVE

APAR status

• Closed as program error.

Error description

• Customer application was reading through DEDB area using
  PROCOPT=GO. Area was being REORG'd online at the time.
  The pointer chain being followed was broken and IMS ended
  up referencing data in a buffer that was not a segment.
  However, by bad luck the data at the segment code position
  match the expected segment code so a U1026 was not issued
  at this point. The DB had compression exit defined for the
  segment. The exit was called. It so happened that the LL
  field was very, very, large and the bit representing compression
  in the flag byte following the key field was not set, so
  this appeared to be uncompressed data. The exit the customer
  was using, based on DFSCMPX0 sample source, in this case does
  not check the data LL vs DBD max LL+10 and did an MVCL with
  the bad length. This overlayed the segment work area pointed
  to by EPSTSEG2 and was large enough to overlay an EMHB in the
  EMHB pool. The BMP later abended U1026 SC57 when the residual
  data in the twin forward pointer was used as an RBA and passed
  to DBFMBED0 to retrieve the next segment. The overlay caused
  an abendS0C4 in EMHB pool storage compression shortly thereafter
  due to invalid data in block header ( chain field ).
  DBFCMP10 could check that the LL of a compressed segment is
  no larger than DBD max plus 10, which is the largest a
  compressed segment can be. The sample DFSCMPX0 compression
  exit could also check this.
  

Local fix

• Modify compression exit to verify LL of uncompressed segments
  before moving data to destination field.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: IMSFP V8 with compression exit defined.      *
  ****************************************************************
  * PROBLEM DESCRIPTION: Abends0C4 occurred as a result of an    *
  *                      overlay of the segment workarea         *
  *                      pointed to by EPSTSEG2.                 *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
  Customer application was reading through DEDB area using
  PROCOPT=GO. Area was being REORG'd online at the time.
  The pointer chain being followed was broken and IMS ended
  up referencing data in a buffer that was not a segment.
  However, the data at the segment code position matched the
  expected segment code so a U1026 was not issued at this point.
  The DB had compression exit defined for the segment. The exit
  was called and the LL field was very large. The exit the
  customer was using, in this case did not check the data LL vs
  DBD MAX LL and did an MVCL with the bad length.
  This overlayed the segment work area pointed to by EPSTSEG2
  and was large enough to overlay an EMHB in the EMHB pool.
  The BMP later abended U1026 SC57 when the residual data in the
  twin forward pointer was used as an RBA and passed it to
  DBFMBED0 to retrieve the next segment. The overlay caused an
  abendS0C4 in EMHB pool storage compression shortly thereafter
  due to invalid data in block header ( chain field ).
  DBFCMP10 should check that the LL of a compressed segment is no
  larger than DBD max.
  

Problem conclusion

• AIDS: RIDS/FP RIDS/DEDB FP DEDB
    GEN:
  
  *** END IMS KEYWORDS ***
  **********
  DBFCMP10 *
  **********
  
  DBFCMP10 has been updated in CASE 3 which calls EXPAND exit for
  DBFMCSS9 or DBFMGNR0 to validate the segment LL in the buffer is
  not greater than maximum segment length in the work area before
  we call the exit to expand the segment.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

  PK61101

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

  UK36261

Modules/Macros

• DBFCMP10
  

Fix information

• Fixed component name

  IMS V8

• Fixed component ID

  5655C5600

Applicable component levels

• R801 PSY UK36261

     UP08/05/09 P F805