[Bug 1315052] [NEW] lxc-attach from a different login session fails

[Serge Hallyn]

Public bug reported:

When using the cgroup  manager, if an unprivileged user starts a
container from one login session, then ssh's back in and tries lxc-
attach, that will fail.

The workaround for this is simply to start a container under screen or
tmux, then re-attach to that session to lxc-attach.

The proper fix is to use MovePidAbs in lxc-attach to move the current
task to the 'full' (relative to proxy) cgroup of the container.  This
requires a new GetPidCgroupAbs method (which is in cgmanager utopic but
not yet in trusty) to find out the proper cgroup to attach to.

** Affects: cgmanager (Ubuntu)
     Importance: High
         Status: Confirmed

** Affects: lxc (Ubuntu)
     Importance: High
         Status: Triaged

** Affects: cgmanager (Ubuntu Trusty)
     Importance: High
         Status: Fix Committed

** Affects: lxc (Ubuntu Trusty)
     Importance: High
         Status: Confirmed

** Affects: cgmanager (Ubuntu Utopic)
     Importance: High
         Status: Confirmed

** Affects: lxc (Ubuntu Utopic)
     Importance: High
         Status: Triaged

** Also affects: lxc (Ubuntu Trusty)
   Importance: Undecided
       Status: New

** Also affects: lxc (Ubuntu Utopic)
   Importance: Undecided
       Status: New

** Also affects: cgmanager (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: cgmanager (Ubuntu Trusty)
       Status: New => Fix Committed

** Changed in: cgmanager (Ubuntu Trusty)
   Importance: Undecided => High

** Changed in: cgmanager (Ubuntu Utopic)
   Importance: Undecided => High

** Changed in: lxc (Ubuntu Trusty)
   Importance: Undecided => High

** Changed in: lxc (Ubuntu Utopic)
   Importance: Undecided => High

** Changed in: cgmanager (Ubuntu Utopic)
       Status: New => Confirmed

** Changed in: lxc (Ubuntu Trusty)
       Status: New => Confirmed

** Changed in: lxc (Ubuntu Utopic)
       Status: New => Triaged

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https://bugs.launchpad.net/bugs/1315052

Title:
  lxc-attach from a different login session fails

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