[Bug 1312156] Re: [Precise] Potential for data corruption

[Rafael David Tinoco]

** Description changed:

+ [Impact]
+ 
+  * Pacemaker designated controller can make wrong decisions based on
+ uncleared node status on a rare specific situation. This situation can
+ make the same resource starts on two nodes at the same time, resulting
+ in data corruption.
+ 
+ [Test Case]
+ 
+  * The bug trigger is very hard hard to achieve:
+ 
+ 1) If stonith was successful on fencing a node (any node was fenced).
+ 2) If the target and origin are the same (node killed itself).
+ 3) If we do not have a dc or the fenced node is our dc (our dc killed itself).
+ 4) If the executor is not this node (at least 3 nodes).
+ 5) If this node is elected new DC anytime in the future.
+ 7) If a policy engine was not yet scheduled.
+ 8) If takeover runs before policy engine.
+ 
+  * The bug couldn't be reproduced so far: the patch was made based on a
+ community report (https://www.mail-
+ archive.com/pacemaker at oss.clusterlabs.org/msg19509.html) analyzed by
+ upstream code developer (Andrew Beekhof).
+ 
+ [Regression Potential]
+ 
+  * On logic before commit 82aa2d8d17 the node responsible for fencing
+ (executioner) the dc was responsible also for updating cib. If this
+ update failed (due to a executioner fail, for ex) the dc would be fenced
+ a second time because the cluster would not know about fencing result.
+ On upstream commit 82aa2d8d17, a logic trying to avoid this second dc
+ fencing was introduced. This logic by itself is buggy.
+ 
+  * To minimize any kind of regression, instead of going forward on
+ pacemaker versions, it was decided to go backwards removing only this
+ piece of code.
+ 
+  * It is much more acceptable for SRU to restore old behavior, known to
+ be safe even if it implies killing dc twice, than to backport several
+ pieces of code to implement a logic that was not there on the stable
+ version release.
+ 
+ [Other Info / Original Description]
+ 
  Under certain conditions there is faulty logic in function
  tengine_stonith_notify() which can incorrectly add successfully fenced
  nodes to a list, causing Pacemaker to subsequently erase that node’s
  status section when the next DC (Designated Controller) election occurs.
  With the status section erased, the cluster considers that node is down
  and starts corresponding services on other nodes.  Multiple instances of
  the same service can cause data corruption.
  
  Conditions:
  
  1. fenced node must have been the previous DC and been sufficiently functional to request its own fencing
  2. fencing notification must arrive after the new DC has been elected but before it invokes the policy engine
  
  Pacemaker versions affected:
  
  1.1.6 - 1.1.9
  
  Stable Ubuntu releases affected:
  
  Ubuntu 12.04 LTS
  Ubuntu 12.10 (EOL?)
  
  Fix:
  
  https://github.com/ClusterLabs/pacemaker/commit/f30e1e43
  
  References:
  
  https://www.mail-archive.com/pacemaker@oss.clusterlabs.org/msg19509.html
  http://blog.clusterlabs.org/blog/2014/potential-for-data-corruption-in-pacemaker-1-dot-1-6-through-1-dot-1-9/

-- 
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to pacemaker in Ubuntu.
https://bugs.launchpad.net/bugs/1312156

Title:
  [Precise] Potential for data corruption

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/pacemaker/+bug/1312156/+subscriptions