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[Bug 1364725] Re: logind session ID not used due to race condition

 

r2028 is the revision that caused the crash if the race condition
occurred.

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https://bugs.launchpad.net/bugs/1364725

Title:
  logind session ID not used due to race condition

Status in Light Display Manager:
  Fix Released
Status in Light Display Manager 1.10 series:
  Fix Committed
Status in “lightdm” package in Ubuntu:
  Fix Released
Status in “lightdm” source package in Trusty:
  In Progress
Status in “lightdm” source package in Utopic:
  Fix Released

Bug description:
  [Impact]
  Sometimes a session will fail to get the logind session ID to pass back to the LightDM daemon. This appears to be due to a race using the D-Bus method org.freedesktop.login1.Manager.GetSessionByPID instead of getting the environment variable XDG_SESSION_ID as set in PAM.

  This bug was detected by a bug in LightDM 1.11.7 where the daemon
  would attempt to read both a logind and ConsoleKit ID when this D-Bus
  call failed.

  The solution is to use the XDG_SESSION_ID environment variable and not
  GetSessionByPID() and to fix the passing of the session id(s) from the
  session to the daemon to be unambiguous.

  [Test Case]
  Check the LightDM log always contains lines like:
  [+0.78s] DEBUG: Activating login1 session c1
  for each session.

  [Regression Potential]
  Change is non-trivial and could cause other bugs. Regression tests confirm existing test cases work.

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References