[lxc-devel] CGroup Namespaces (v6)

[Alban Crequy]

Hi,

Thanks for the patches!

On 8 December 2015 at 00:06,  <serge.hallyn at ubuntu.com> wrote:
> Hi,
>
> following is a revised set of the CGroup Namespace patchset which Aditya
> Kali has previously sent.  The code can also be found in the cgroupns.v6
> branch of
>
> https://git.kernel.org/cgit/linux/kernel/git/sergeh/linux-security.git/
>
> To summarize the semantics:
>
> 1. CLONE_NEWCGROUP re-uses 0x02000000, which was previously CLONE_STOPPED
>
> 2. unsharing a cgroup namespace makes all your current cgroups your new
> cgroup root.
>
> 3. /proc/pid/cgroup always shows cgroup paths relative to the reader's
> cgroup namespce root.  A task outside of  your cgroup looks like
>
>         8:memory:/../../..
>
> 4. when a task mounts a cgroupfs, the cgroup which shows up as root depends
> on the mounting task's  cgroup namespace.
>
> 5. setns to a cgroup namespace switches your cgroup namespace but not
> your cgroups.
>
> With this, using github.com/hallyn/lxc #2015-11-09/cgns (and
> github.com/hallyn/lxcfs #2015-11-10/cgns) we can start a container in a full
> proper cgroup namespace, avoiding either cgmanager or lxcfs cgroup bind mounts.

I tested cgroupns.v6 with systemd-nspawn + patches from
https://github.com/systemd/systemd/pull/2112 using
unshare(CLONE_NEWCGROUP) booted with
systemd.unified_cgroup_hierarchy=1 in Fedora22. Tested with and
without userns. It worked for me :)

Do you need people to run more tests, with other scenarios?

Do you have patches already for /usr/bin/unshare and /usr/bin/nsenter?

> This is completely backward compatible and will be completely invisible
> to any existing cgroup users (except for those running inside a cgroup
> namespace and looking at /proc/pid/cgroup of tasks outside their
> namespace.)
>
> Changes from V5:
> 1. To get a root dentry for cgroup namespace mount, walk the path from the
>    kernfs root dentry.
>
> Changes from V4:
> 1. Move the FS_USERNS_MOUNT flag to last patch
> 2. Rebase onto cgroup/for-4.5
> 3. Don't non-init user namespaces to bind new subsystems when mounting.
> 4. Address feedback from Tejun (thanks).  Specificaly, not addressed:
>    . kernfs_obtain_root - walking dentry from kernfs root.
>      (I think that's the only piece)
> 5. Dropped unused get_task_cgroup fn/patch.
> 6. Reworked kernfs_path_from_node_locked() to try to simplify the logic.
>    It now finds a common ancestor, walks from the source to it, then back
>    up to the target.
>
> Changes from V3:
> 1. Rebased onto latest cgroup changes.  In particular switch to
>    css_set_lock and ns_common.
> 2. Support all hierarchies.
>
> Changes from V2:
> 1. Added documentation in Documentation/cgroups/namespace.txt
> 2. Fixed a bug that caused crash
> 3. Incorporated some other suggestions from last patchset:
>    - removed use of threadgroup_lock() while creating new cgroupns
>    - use task_lock() instead of rcu_read_lock() while accessing
>      task->nsproxy
>    - optimized setns() to own cgroupns
>    - simplified code around sane-behavior mount option parsing
> 4. Restored ACKs from Serge Hallyn from v1 on few patches that have
>    not changed since then.
>
> Changes from V1:
> 1. No pinning of processes within cgroupns. Tasks can be freely moved
>    across cgroups even outside of their cgroupns-root. Usual DAC/MAC policies
>    apply as before.
> 2. Path in /proc/<pid>/cgroup is now always shown and is relative to
>    cgroupns-root. So path can contain '/..' strings depending on cgroupns-root
>    of the reader and cgroup of <pid>.
> 3. setns() does not require the process to first move under target
>    cgroupns-root.
>
> Changes form RFC (V0):
> 1. setns support for cgroupns
> 2. 'mount -t cgroup cgroup <mntpt>' from inside a cgroupns now
>    mounts the cgroup hierarcy with cgroupns-root as the filesystem root.
> 3. writes to cgroup files outside of cgroupns-root are not allowed
> 4. visibility of /proc/<pid>/cgroup is further restricted by not showing
>    anything if the <pid> is in a sibling cgroupns and its cgroup falls outside
>    your cgroupns-root.
>
>
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