PH20788: ULB IS NOT HANDLING MBUFS CORRECTLY

APAR status

• Closed as program error.

Error description

• a) mbufs received from collocated clients do not contain the
  ethernet headers but ULB assumes they do and overwrites memory
  where the ethernet headers normally exist.
  
  b) ULB is
  attempting to modify the ethernet headers for packets forwarded
  to collocated servers and it should not (packets should be
  passed to collocated server unchanged).
  
  c) ULB is not
  handling mbuf reads correct and assumes all required data is in
  the first mbuf which may not be the case
  
  d) ULB handles some
  pings without forwarding to backend servers (NAT defined
  servers for example). ULB is not responding correctly because
  it attempts to read the entire payload which is typically not
  in a single mbuf.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  IBM WebSphere Application Server Load       *
  *                  Balancer for IPv4 and IPv6 users on AIX     *
  ****************************************************************
  * PROBLEM DESCRIPTION: Users could experience hangs or         *
  *                      crashes on the ULB system.              *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The Load Balancer for IPv4 and IPv6 intercepts network traffic
  at the kernel level which means it reads packets from the
  adapter level rather than from IP. As such, the data is stored
  in mbuf structures rather than a contiguous data stream. The
  load balancer must handle the data structures in a different
  manner to ensure it does not corrupt the data structure or
  access memory which is out of bounds.
  

Problem conclusion

• Code was corrected to ensure LB AIX code handles data stored
  in mbufs correctly.
  
  Fix levels:
     8.5.5.18
     9.0.5.4
  

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

  WS EDGE LB IPV4

• Fixed component ID

  5724H8812

Applicable component levels