[Bug 1616213] Re: Core dump on multipathd shutdown - trusty 14.04.4

[Launchpad Bug Tracker]

This bug was fixed in the package multipath-tools - 0.4.9-3ubuntu7.15

---------------
multipath-tools (0.4.9-3ubuntu7.15) trusty; urgency=medium

  * d/p/0047-Add-existing-multipath-devices-to-wwids-file-on.patch:
    Fix multipathd which does not update /etc/multipath/wwids file
    when reconfigure is invoked. (LP: #1621835)

  [ Dragan Stancevic ]
  * d/p/0048-multipathd-delay-free-pathvec.patch :
    Fix SEGV on multipathd shutdown (LP: #1616213)

  [ Nishanth Aravamudan ]
  * debian/patches/fix_use_after_free.patch: Fix use-after-free bugs.
    Thanks to Christof Schmitt <christof.schmitt at de.ibm.com> and
    Benjamin Marzinski <bmarzins at redhat.com>.  Closes LP:  #1628723.

 -- Louis Bouchard <louis.bouchard at ubuntu.com>  Mon, 12 Sep 2016
10:43:19 +0200

** Changed in: multipath-tools (Ubuntu Trusty)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1616213

Title:
  Core dump on multipathd shutdown - trusty 14.04.4

Status in multipath-tools package in Ubuntu:
  Invalid
Status in multipath-tools source package in Trusty:
  Fix Released

Bug description:
  [Impact]

   * During "service multipath-tools stop" multipath daemon
     is trying to cleanup and shut down several concurrent
     threads. At times depending on a race condition between
     two threads, one thread might free resources that are still
     used by another thread.

     This is causing the multipathd to dump crash core on
     stop events.

   * Fix should be backported to trusty to avoid more support
     issues being filed.

   * This change delays freeing resources that another thread is
     still using.

  [Test Case]

   * install multipath-tools, create a basic multipath.conf with
     devices under management. Run: "service multipath-tools start"
     run I/O on devices and keep the system CPU busy, then run
     "service multipath-tools stop".

  [Regression Potential]

   * There should be no regression potential with this change,
     this problem happens on the exit path and we are only delaying
     a free call.

  [Original Description]

  On ubuntu trusty 14.04.4 in multipath-tools version 0.4.9-3ubuntu7.14
  there is bug in multipathd on shutdown.

  The code will access pathvec pointer which is a valid address:

  Reading symbols from /sbin/multipathd...Reading symbols from /usr/lib/debug//sbin/multipathd...done.
  done.
  [New LWP 41631]
  [New LWP 41584]
  [New LWP 41633]
  [New LWP 41632]
  [New LWP 41582]
  [New LWP 41583]
  [Thread debugging using libthread_db enabled]
  Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
  Core was generated by `/sbin/multipathd'.
  Program terminated with signal SIGSEGV, Segmentation fault.
  #0 0x00000000004075db in checkerloop (ap=0x1b81040) at main.c:1150

  1150	vector_foreach_slot (vecs->pathvec, pp, i) {
  (gdb) list
  1145	pthread_cleanup_push(cleanup_lock, &vecs->lock);
  1146	lock(vecs->lock);
  1147	condlog(4, "tick");
  1148
  1149	if (vecs->pathvec) {
  1150	vector_foreach_slot (vecs->pathvec, pp, i) {
  1151	check_path(vecs, pp);
  1152	}
  1153	}
  1154	if (vecs->mpvec) {

  Pathvec is a valid pointer:
  (gdb) p vecs->pathvec
  $1 = (vector) 0x1b81280

  But the contents of the structure are just garbage:

  (gdb) p *vecs->pathvec
  $2 = {allocated = 1651076143, slot = 0x756e696c2d34365f}
  (gdb)

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