1/*
2 * ns_cgroup.c - namespace cgroup subsystem
3 *
4 * Copyright 2006, 2007 IBM Corp
5 */
6
7#include <linux/module.h>
8#include <linux/cgroup.h>
9#include <linux/fs.h>
10#include <linux/proc_fs.h>
11#include <linux/slab.h>
12#include <linux/nsproxy.h>
13
14struct ns_cgroup {
15	struct cgroup_subsys_state css;
16};
17
18struct cgroup_subsys ns_subsys;
19
20static inline struct ns_cgroup *cgroup_to_ns(
21		struct cgroup *cgroup)
22{
23	return container_of(cgroup_subsys_state(cgroup, ns_subsys_id),
24			    struct ns_cgroup, css);
25}
26
27int ns_cgroup_clone(struct task_struct *task, struct pid *pid)
28{
29	char name[PROC_NUMBUF];
30
31	snprintf(name, PROC_NUMBUF, "%d", pid_vnr(pid));
32	return cgroup_clone(task, &ns_subsys, name);
33}
34
35/*
36 * Rules:
37 *   1. you can only enter a cgroup which is a descendant of your current
38 *     cgroup
39 *   2. you can only place another process into a cgroup if
40 *     a. you have CAP_SYS_ADMIN
41 *     b. your cgroup is an ancestor of task's destination cgroup
42 *       (hence either you are in the same cgroup as task, or in an
43 *        ancestor cgroup thereof)
44 */
45static int ns_can_attach(struct cgroup_subsys *ss, struct cgroup *new_cgroup,
46			 struct task_struct *task, bool threadgroup)
47{
48	if (current != task) {
49		if (!capable(CAP_SYS_ADMIN))
50			return -EPERM;
51
52		if (!cgroup_is_descendant(new_cgroup, current))
53			return -EPERM;
54	}
55
56	if (!cgroup_is_descendant(new_cgroup, task))
57		return -EPERM;
58
59	if (threadgroup) {
60		struct task_struct *c;
61		rcu_read_lock();
62		list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
63			if (!cgroup_is_descendant(new_cgroup, c)) {
64				rcu_read_unlock();
65				return -EPERM;
66			}
67		}
68		rcu_read_unlock();
69	}
70
71	return 0;
72}
73
74/*
75 * Rules: you can only create a cgroup if
76 *     1. you are capable(CAP_SYS_ADMIN)
77 *     2. the target cgroup is a descendant of your own cgroup
78 */
79static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
80						struct cgroup *cgroup)
81{
82	struct ns_cgroup *ns_cgroup;
83
84	if (!capable(CAP_SYS_ADMIN))
85		return ERR_PTR(-EPERM);
86	if (!cgroup_is_descendant(cgroup, current))
87		return ERR_PTR(-EPERM);
88
89	ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
90	if (!ns_cgroup)
91		return ERR_PTR(-ENOMEM);
92	return &ns_cgroup->css;
93}
94
95static void ns_destroy(struct cgroup_subsys *ss,
96			struct cgroup *cgroup)
97{
98	struct ns_cgroup *ns_cgroup;
99
100	ns_cgroup = cgroup_to_ns(cgroup);
101	kfree(ns_cgroup);
102}
103
104struct cgroup_subsys ns_subsys = {
105	.name = "ns",
106	.can_attach = ns_can_attach,
107	.create = ns_create,
108	.destroy  = ns_destroy,
109	.subsys_id = ns_subsys_id,
110};
111