PQ54076: DURING A PUT FROM AN FTP CLIENT, FIN SENT ON DATA CONNECTION IF CLIENT IS TERMINATED

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• If, during a PUT from an FTP OS/390 client to a remote
  host, the FTP client is suddently terminated - the TCPIP stack
  will send to the remote server a FIN.
   Termination of the FTP client can be for a number of reasons,
  but a common reason is that while a data transfer was in
  progress and data was being transferred on the data connection
  from Client to Server, the FTP Client job was cancelled.
   When this occurs, TCPIP sends a FIN to the remote server
  and when FIN is received, remote server does not know that the
  transfer is not complete and processes the FIN as a normal end
  of file.
   It is not until the server attempts to read the next command
  from the client that an error is detected.
   Upon establishing the data connection with the remote server
  for a PUT, FTP should be setting up the connection that a
  reset (RST) is sent if the application goes away.
  .
  Additional Symptoms:
    Client Fails on a put and size of received file is smaller
      than file transferred.
    When server attempts to read next command,
      they will generally get a RC 1121,
       EDC8121I Connection reset.
  .
  Following is a trace on the server where an OS/390 was
  cancelled while transfer in progess. Note failure being
  detected after PUT (ie. store_data) had been processed.
  .
  progressReport:     3317760 bytes transferred
  progressReport:     6451200 bytes transferred
  seq_close_file: close file=
  seq_close_file: file closed
  data_close: shutdown(ds 9)
  dataClose: recv(ds 9) timer(120)
  data_close: close(ds 9)
  store_data: @ exit rc_write=0 ret_code=0
    fio_status=0 abend & reason=000-00 Wrt/Rd ErrorText=
  store_data: @ exit rc_close=0 ret_code=0 abend
    & reason=000-00 Close ErrorText=
  write_smf_record: entering write_smf_record with type 5.
  write_smf_record: return code 0 from smfwr.
  store_data:      9747635 bytes transferred
  get_command: select rc is 1
  get_command: received -1 bytes
  get_command: recv() rc -1: error (1121/76657242)
    - EDC8121I Connection reset.
  end_session: Ending session 000E6350
  parse_cmd : return code -1 from get_command
  main: server thread terminates rc = -1.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of the Communications Server       *
  *                 for OS/390 Release 8 and 10 IP and           *
  *                 for z/OS Version 1 Release 2 IP: FTP         *
  ****************************************************************
  * PROBLEM DESCRIPTION: During a PUT from an FTP OS/390 client  *
  *                      to a remote host, if the client is      *
  *                      suddenly terminated the TCPIP stack     *
  *                      will send a FIN to the remote server.   *
  *                      When the FIN is received, the remote    *
  *                      server does not detect that the         *
  *                      transfer is not complete and processes  *
  *                      the FIN as a normal end of file.        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When data is being sent outbound, PUT from the FTP client
  or GET from the FTP server, if the data connection is
  terminated, the system closes the data connection
  for the FTP application.  This causes a FIN to be sent.  This
  can be misleading on the receiving side, because it may
  interpret the FIN as a valid EOF and not detect any error.  The
  FTP client and server need to set SO_LINGER with a timeout
  value of 0 on the data connection socket, so that the TCP/IP
  stack will generate a reset if the connection is closed by the
  system.  That way the receiving side is notified of the error
  prior to doing the next receive.
  +-------------------------------------------------------------+
  + Please check our Communications Server for OS/390 homepages +
  + for common networking tips and fixes.  The URL for these    +
  + homepages can be found in Informational APAR II11334.       +
  +-------------------------------------------------------------+
  

Problem conclusion

• The FTP client and server have been modified to set SO_LINGER
  with a timeout value of zero on that data connection.  Prior to
  a normal close of the data connection, the server and client
  will set SO_LINGER off, so that a reset is not generated by
  the TCP/IP stack for normal close.
  
  * Cross Reference between External and Internal Names
  EZAFTPSR (FTPDRPLY)  PREFTPCX (EZAFTPCX)  PREFTPLS (EZAFTPLS)
  EZAFTPSR (FTPDRPLY)  PREFTPCX (EZAFTPCX)  PREFTPLS (EZAFTPLS)
  EZAFTPSR (FTPDRPLY)  PREFTPCX (EZAFTPCX)  PREFTPLS (EZAFTPLS)
  

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:

  UQ60836 UQ60837 UQ60838

Modules/Macros

• EZAFTPCX EZAFTPLS EZAFTPSC EZAFTPSR
  

Fix information

• Fixed component name

  TCP/IP V3 MVS

• Fixed component ID

  5655HAL00

Applicable component levels

• R120 PSY UQ60836

     UP02/01/24 P F201

• R380 PSY UQ60837

     UP02/01/24 P F201

• R50A PSY UQ60838

     UP02/01/24 P F201

Fix is available

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