kernel/ns_cgroup.c

   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/slab.h>
  11
  12 struct ns_cgroup {
  13         struct cgroup_subsys_state css;
  14         spinlock_t lock;
  15 };
  16
  17 struct cgroup_subsys ns_subsys;
  18
  19 static inline struct ns_cgroup *cgroup_to_ns(
  20                 struct cgroup *cgroup)
  21 {
  22         return container_of(cgroup_subsys_state(cgroup, ns_subsys_id),
  23                             struct ns_cgroup, css);
  24 }
  25
  26 int ns_cgroup_clone(struct task_struct *task)
  27 {
  28         return cgroup_clone(task, &ns_subsys);
  29 }
  30
  31 /*
  32  * Rules:
  33  *   1. you can only enter a cgroup which is a child of your current
  34  *     cgroup
  35  *   2. you can only place another process into a cgroup if
  36  *     a. you have CAP_SYS_ADMIN
  37  *     b. your cgroup is an ancestor of task's destination cgroup
  38  *       (hence either you are in the same cgroup as task, or in an
  39  *        ancestor cgroup thereof)
  40  */
  41 static int ns_can_attach(struct cgroup_subsys *ss,
  42                 struct cgroup *new_cgroup, struct task_struct *task)
  43 {
  44         struct cgroup *orig;
  45
  46         if (current != task) {
  47                 if (!capable(CAP_SYS_ADMIN))
  48                         return -EPERM;
  49
  50                 if (!cgroup_is_descendant(new_cgroup))
  51                         return -EPERM;
  52         }
  53
  54         if (atomic_read(&new_cgroup->count) != 0)
  55                 return -EPERM;
  56
  57         orig = task_cgroup(task, ns_subsys_id);
  58         if (orig && orig != new_cgroup->parent)
  59                 return -EPERM;
  60
  61         return 0;
  62 }
  63
  64 /*
  65  * Rules: you can only create a cgroup if
  66  *     1. you are capable(CAP_SYS_ADMIN)
  67  *     2. the target cgroup is a descendant of your own cgroup
  68  */
  69 static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
  70                                                 struct cgroup *cgroup)
  71 {
  72         struct ns_cgroup *ns_cgroup;
  73
  74         if (!capable(CAP_SYS_ADMIN))
  75                 return ERR_PTR(-EPERM);
  76         if (!cgroup_is_descendant(cgroup))
  77                 return ERR_PTR(-EPERM);
  78
  79         ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
  80         if (!ns_cgroup)
  81                 return ERR_PTR(-ENOMEM);
  82         spin_lock_init(&ns_cgroup->lock);
  83         return &ns_cgroup->css;
  84 }
  85
  86 static void ns_destroy(struct cgroup_subsys *ss,
  87                         struct cgroup *cgroup)
  88 {
  89         struct ns_cgroup *ns_cgroup;
  90
  91         ns_cgroup = cgroup_to_ns(cgroup);
  92         kfree(ns_cgroup);
  93 }
  94
  95 struct cgroup_subsys ns_subsys = {
  96         .name = "ns",
  97         .can_attach = ns_can_attach,
  98         .create = ns_create,
  99         .destroy  = ns_destroy,
 100         .subsys_id = ns_subsys_id,
 101 };