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[Seth Forshee <seth.forshee+lp@xxxxxxxxxxxxx>]

The same basic sequence of events happens with and without user
namespaces. init sheds its tty with setsid() but then opens
/dev/console, which as the effect of making /dev/console it's
controlling tty. Later getty also opens /dev/console and tries the
TIOCSCTTY ioctl on the fd. At this point I think the following code in
the kernel handling of that ioctl comes into play:

        if (tty->session) { 
                /* 
                 * This tty is already the controlling 
                 * tty for another session group! 
                 */ 
                if (arg == 1 && capable(CAP_SYS_ADMIN)) { 
                        /* 
                         * Steal it away 
                         */ 
                        read_lock(&tasklist_lock); 
                        session_clear_tty(tty->session); 
                        read_unlock(&tasklist_lock); 
                } else { 
                        ret = -EPERM; 
                        goto unlock; 
                } 
        } 

I.e. getty doesn't have CAP_SYS_ADMIN and thus can't steal the console
from init. I'm not sure what the fix is yet, whether there's something
we can do here which can allow root within a namespace to steal the
console or whether upstart just needs to explicitly shed the console
after opening it.

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https://bugs.launchpad.net/bugs/1263738

Title:
  login console 0 in user namespace container is not configured right

Status in “linux” package in Ubuntu:
  Confirmed
Status in “lxc” package in Ubuntu:
  Triaged
Status in “linux” source package in Trusty:
  Confirmed
Status in “lxc” source package in Trusty:
  Triaged

Bug description:
  When you create a container in a private user namespace, when you start the
  container without the '-d' flag, that console is not properly set up.  Logging in
  gives you

  -bash: no job control in this shell

  and hitting ctrl-c reboots the container.

  Consoles from 'lxc-console -n $container' behave correctly.

  This may be a kernel issue, as discussed here:

  http://lists.linuxcontainers.org/pipermail/lxc-
  devel/2013-October/005843.html

  so also marking this as affecting the kernel.

  This can be worked around, but really needs to be fixed before trusty
  is frozen.

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