Quoting Aditya Kali (adityakali@xxxxxxxxxx):
> setns on a cgroup namespace is allowed only if
> * task has CAP_SYS_ADMIN in its current user-namespace and
> over the user-namespace associated with target cgroupns.
> * task's current cgroup is descendent of the target cgroupns-root
> cgroup.
What is the point of this?
If I'm a user logged into
/lxc/c1/user.slice/user-1000.slice/session-c12.scope and I start
a container which is in
/lxc/c1/user.slice/user-1000.slice/session-c12.scope/x1
then I will want to be able to enter the container's cgroup.
The container's cgroup root is under my own (satisfying the
below condition0 but my cgroup is not a descendent of the
container's cgroup.
> * target cgroupns-root is same as or deeper than task's current
> cgroupns-root. This is so that the task cannot escape out of its
> cgroupns-root. This also ensures that setns() only makes the task
> get restricted to a deeper cgroup hierarchy.
>
> Signed-off-by: Aditya Kali <adityakali@xxxxxxxxxx>
> ---
> kernel/cgroup_namespace.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 42 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cgroup_namespace.c b/kernel/cgroup_namespace.c
> index c16604f..c612946 100644
> --- a/kernel/cgroup_namespace.c
> +++ b/kernel/cgroup_namespace.c
> @@ -80,8 +80,48 @@ err_out:
>
> static int cgroupns_install(struct nsproxy *nsproxy, void *ns)
> {
> - pr_info("setns not supported for cgroup namespace");
> - return -EINVAL;
> + struct cgroup_namespace *cgroup_ns = ns;
> + struct task_struct *task = current;
> + struct cgroup *cgrp = NULL;
> + int err = 0;
> +
> + if (!ns_capable(current_user_ns(), CAP_SYS_ADMIN) ||
> + !ns_capable(cgroup_ns->user_ns, CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + /* Prevent cgroup changes for this task. */
> + threadgroup_lock(task);
> +
> + cgrp = get_task_cgroup(task);
> +
> + err = -EINVAL;
> + if (!cgroup_on_dfl(cgrp))
> + goto out_unlock;
> +
> + /* Allow switch only if the task's current cgroup is descendant of the
> + * target cgroup_ns->root_cgrp.
> + */
> + if (!cgroup_is_descendant(cgrp, cgroup_ns->root_cgrp))
> + goto out_unlock;
> +
> + /* Only allow setns to a cgroupns root-ed deeper than task's current
> + * cgroupns-root. This will make sure that tasks cannot escape their
> + * cgroupns by attaching to parent cgroupns.
> + */
> + if (!cgroup_is_descendant(cgroup_ns->root_cgrp,
> + task_cgroupns_root(task)))
> + goto out_unlock;
> +
> + err = 0;
> + get_cgroup_ns(cgroup_ns);
> + put_cgroup_ns(nsproxy->cgroup_ns);
> + nsproxy->cgroup_ns = cgroup_ns;
> +
> +out_unlock:
> + threadgroup_unlock(current);
> + if (cgrp)
> + cgroup_put(cgrp);
> + return err;
> }
>
> static void *cgroupns_get(struct task_struct *task)
> --
> 2.1.0.rc2.206.gedb03e5
>
> --
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