root/kernel/ns_cgroup.c

DEFINITIONS

1. cgroup_to_ns
2. ns_cgroup_clone
3. ns_can_attach
4. ns_create
5. ns_destroy

/*
 * ns_cgroup.c - namespace cgroup subsystem
 *
 * Copyright 2006, 2007 IBM Corp
 */

#include <linux/module.h>
#include <linux/cgroup.h>
#include <linux/fs.h>
#include <linux/proc_fs.h>
#include <linux/slab.h>
#include <linux/nsproxy.h>

struct ns_cgroup {
        struct cgroup_subsys_state css;
        spinlock_t lock;
};

struct cgroup_subsys ns_subsys;

static inline struct ns_cgroup *cgroup_to_ns(
                struct cgroup *cgroup)
{
        return container_of(cgroup_subsys_state(cgroup, ns_subsys_id),
                            struct ns_cgroup, css);
}

int ns_cgroup_clone(struct task_struct *task, struct pid *pid)
{
        char name[PROC_NUMBUF];

        snprintf(name, PROC_NUMBUF, "%d", pid_vnr(pid));
        return cgroup_clone(task, &ns_subsys, name);
}

/*
 * Rules:
 *   1. you can only enter a cgroup which is a child of your current
 *     cgroup
 *   2. you can only place another process into a cgroup if
 *     a. you have CAP_SYS_ADMIN
 *     b. your cgroup is an ancestor of task's destination cgroup
 *       (hence either you are in the same cgroup as task, or in an
 *        ancestor cgroup thereof)
 */
static int ns_can_attach(struct cgroup_subsys *ss,
                struct cgroup *new_cgroup, struct task_struct *task)
{
        struct cgroup *orig;

        if (current != task) {
                if (!capable(CAP_SYS_ADMIN))
                        return -EPERM;

                if (!cgroup_is_descendant(new_cgroup))
                        return -EPERM;
        }

        if (atomic_read(&new_cgroup->count) != 0)
                return -EPERM;

        orig = task_cgroup(task, ns_subsys_id);
        if (orig && orig != new_cgroup->parent)
                return -EPERM;

        return 0;
}

/*
 * Rules: you can only create a cgroup if
 *     1. you are capable(CAP_SYS_ADMIN)
 *     2. the target cgroup is a descendant of your own cgroup
 */
static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
                                                struct cgroup *cgroup)
{
        struct ns_cgroup *ns_cgroup;

        if (!capable(CAP_SYS_ADMIN))
                return ERR_PTR(-EPERM);
        if (!cgroup_is_descendant(cgroup))
                return ERR_PTR(-EPERM);

        ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
        if (!ns_cgroup)
                return ERR_PTR(-ENOMEM);
        spin_lock_init(&ns_cgroup->lock);
        return &ns_cgroup->css;
}

static void ns_destroy(struct cgroup_subsys *ss,
                        struct cgroup *cgroup)
{
        struct ns_cgroup *ns_cgroup;

        ns_cgroup = cgroup_to_ns(cgroup);
        kfree(ns_cgroup);
}

struct cgroup_subsys ns_subsys = {
        .name = "ns",
        .can_attach = ns_can_attach,
        .create = ns_create,
        .destroy  = ns_destroy,
        .subsys_id = ns_subsys_id,
};