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Message #40570
Re: [Bug 1263738] Re: login console 0 in user namespace container is not configured right
Quoting 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.
If it is possible to get to the inode backing the tty at this point
then we should be able to do inode_capable(tty_inode(tty),
CAP_SYS_ADMIN), which should be safe and adquate right?
But I dont' think we can get inode from tty. However we can get the
tty->session which is a struct pid*. So we can check whether we have
ns_capable(ns_of_pid(tty->session), CAP_SYS_ADMIN)
-serge
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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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