IT38772: Managed File Transfer protocol bridge agent abends due to a NullPointerException during a transfer to an SFTP server.

APAR status

• Closed as program error.

Error description

• An MQ Managed File Transfer protocol bridge agent (PBA) is
  configured to connect to a file server using the SFTP protocol.
  Intermittently, the agent shuts itself down unexpectedly and
  generates an ABEND file
  indicating that a NullPointerException has occurred within the
  method:
  
    com.ibm.wmqfte.jsch.Session.start_discard()
  
  An example of the ABEND file is shown below:
  
  ...
  Thread:    64 (CommandHandlerWorker-0)
  Class:     com.ibm.wmqfte.thread.FTEThread
  Method:    uncaughtException
  Probe:     ABEND_001
  Cause:     java.lang.NullPointerException
  java.lang.NullPointerException
    at
  com.ibm.wmqfte.jsch.Session.start_discard(Session.java:1212)
    at com.ibm.wmqfte.jsch.Session.read(Session.java:1076)
    at com.ibm.wmqfte.jsch.Session.connect(Session.java:356)
    at
  com.ibm.wmqfte.bridge.session.sftp.SFTPConnection.openSession(SF
  TPConnection.java:430)
    at
  com.ibm.wmqfte.bridge.session.sftp.SFTPConnection.connect(SFTPCo
  nnection.java:128)
    at
  com.ibm.wmqfte.bridge.session.sftp.SFTPSession.connect(SFTPSessi
  on.java:169)
    at
  com.ibm.wmqfte.bridge.session.sftp.SessionFactory.createSession(
  SessionFactory.java:98)
    at
  com.ibm.wmqfte.bridge.endpoint.BridgeEndPoint.createSession(Brid
  geEndPoint.java:92)
    at com.ibm.wmqfte.bridge.Bridge.createSession(Bridge.java:355)
    at
  com.ibm.wmqfte.bridge.utils.BridgeSessionContainer.getSession(Br
  igeSessionContainer.java:130)
    at
  com.ibm.wmqfte.bridge.session.BridgeSessionContainerManager.getS
  ession(BridgeSessionContainerManager.java:140)
    at
  com.ibm.wmqfte.io.bridge.BridgeFileImpl.getSession(BridgeFileImp
  l.java:769)
    at
  com.ibm.wmqfte.io.bridge.BridgeFileImpl.<init>(BridgeFileImpl.ja
  va:152)
    at
  com.ibm.wmqfte.io.bridge.BridgeFileFactoryHelperImpl.newFTEFile(
  BridgeFileFactoryHelperImpl.java:115)
    at
  com.ibm.wmqfte.io.FTEFileFactory.newFTEFile(FTEFileFactory.java:
  244)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTETransferItemGenerator.generate
  TransferItemPairs(FTETransferItemGenerator.java:123)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerSAXParser$FTEIte
  mHandler.generateItemListPairs(FTECommandHandlerSAXParser.java:9
  12)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerSAXParser$FTEIte
  mHandler.endElement(FTECommandHandlerSAXParser.java:765)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerSAXParser$FTETra
  nsferSetHandler.endElement(FTECommandHandlerSAXParser.java:537)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerSAXParser$FTESAX
  Handler.endElement(FTECommandHandlerSAXParser.java:311)
    at
  org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown
  Source)
    at
  org.apache.xerces.impl.xs.XMLSchemaValidator.endElement(Unknown
  Source)
    at
  org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanEndElement(U
  nknown Source)
    at
  org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentCo
  ntentDispatcher.dispatch(Unknown Source)
    at
  org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocume
  nt(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown
  Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown
  Source)
    at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
    at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown
  Source)
    at
  org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown
   Source)
    at org.apache.xerces.jaxp.SAXParserImpl.parse(Unknown Source)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerSAXParser.parser
  XML(FTECommandHandlerSAXParser.java:1744)
    at
  com.ibm.wmqfte.cmdhandler.impl.MessageHandlerImpl.externalMessag
  eHandler(MessageHandlerImpl.java:209)
    at
  com.ibm.wmqfte.cmdhandler.impl.MessageHandlerImpl.processCommand
  (MessageHandlerImpl.java:167)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerWorkerThread.pro
  cessCommand(FTECommandHandlerWorkerThread.java:282)
    at
  com.ibm.wmqfte.cmdhandler.impl.FTECommandHandlerWorkerThread.run
  (FTECommandHandlerWorkerThread.java:173)
    at java.lang.Thread.run(Thread.java:820)
    at com.ibm.wmqfte.thread.FTEThread.run(FTEThread.java:70)
  

Local fix

• Resolve why the SFTP server is returning a null key during the
  SSL handshake.
  The agent will get restarted by the MFT process controller and
  there is no manual intervention needed to bring it back to a
  running status.
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of IBM MQ 9.2 Managed File Transfer,
  who have protocol bridge agents (PBAs) that connect to a file
  server using the SFTP protocol.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  MQ Managed File Transfer 9.2 protocol bridge agents (PBAs) use a
  fork of the third-party JSch library when communicating with
  file servers using the SFTP protocol. If the JSch code receives
  some invalid data from a file server while performing a managed
  transfer, then it will discard that data before throwing an
  internal exception. As a result of the internal exception, the
  managed transfer will be marked as "Failed".
  
  Now, if the JSch code received some invalid data during an SFTP
  key exchange while connecting to a file server, it incorrectly
  assumed that the cipher required to read that data had already
  been initialized. When it then tried to use the cipher, a
  NullPointerException would be generated within the internal
  method:
  
    com.ibm.wmqfte.jsch.Session.start_discard()
  
  This caused the agent to generate an ABEND file containing the
  following information:
  
  ...
  Method:     uncaughtException
  Probe:      ABEND_001
  Cause:      java.lang.NullPointerException
  java.lang.NullPointerException
  	at
  com.ibm.wmqfte.jsch.Session.start_discard(Session.java:1212)
  	at com.ibm.wmqfte.jsch.Session.read(Session.java:1076)
  	at com.ibm.wmqfte.jsch.Session.connect(Session.java:356)
  ...
  
  and then shut itself down.
  

Problem conclusion

• The fork of the JSch library used by MQ 9.2 Managed File
  Transfer has been updated so to check if the cipher needed to
  read any invalid data that has been received during an SFTP key
  exchange is initialized before trying to use it. This allows the
  managed transfer that is in progress when the invalid data is
  received to complete and be marked as "Failed", and prevents the
  agent from stopping unexpectedly.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.2 LTS   9.2.0.5
  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

  MQ BASE V9.2

• Fixed component ID

  5724H7281

Applicable component levels