kernel/pid_namespace.c

   1 /*
   2  * Pid namespaces
   3  *
   4  * Authors:
   5  *    (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
   6  *    (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
   7  *     Many thanks to Oleg Nesterov for comments and help
   8  *
   9  */
  10
  11 #include <linux/pid.h>
  12 #include <linux/pid_namespace.h>
  13 #include <linux/user_namespace.h>
  14 #include <linux/syscalls.h>
  15 #include <linux/err.h>
  16 #include <linux/acct.h>
  17 #include <linux/slab.h>
  18 #include <linux/proc_ns.h>
  19 #include <linux/reboot.h>
  20 #include <linux/export.h>
  21
  22 struct pid_cache {
  23         int nr_ids;
  24         char name[16];
  25         struct kmem_cache *cachep;
  26         struct list_head list;
  27 };
  28
  29 static LIST_HEAD(pid_caches_lh);
  30 static DEFINE_MUTEX(pid_caches_mutex);
  31 static struct kmem_cache *pid_ns_cachep;
  32
  33 /*
  34  * creates the kmem cache to allocate pids from.
  35  * @nr_ids: the number of numerical ids this pid will have to carry
  36  */
  37
  38 static struct kmem_cache *create_pid_cachep(int nr_ids)
  39 {
  40         struct pid_cache *pcache;
  41         struct kmem_cache *cachep;
  42
  43         mutex_lock(&pid_caches_mutex);
  44         list_for_each_entry(pcache, &pid_caches_lh, list)
  45                 if (pcache->nr_ids == nr_ids)
  46                         goto out;
  47
  48         pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
  49         if (pcache == NULL)
  50                 goto err_alloc;
  51
  52         snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
  53         cachep = kmem_cache_create(pcache->name,
  54                         sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
  55                         0, SLAB_HWCACHE_ALIGN, NULL);
  56         if (cachep == NULL)
  57                 goto err_cachep;
  58
  59         pcache->nr_ids = nr_ids;
  60         pcache->cachep = cachep;
  61         list_add(&pcache->list, &pid_caches_lh);
  62 out:
  63         mutex_unlock(&pid_caches_mutex);
  64         return pcache->cachep;
  65
  66 err_cachep:
  67         kfree(pcache);
  68 err_alloc:
  69         mutex_unlock(&pid_caches_mutex);
  70         return NULL;
  71 }
  72
  73 static void proc_cleanup_work(struct work_struct *work)
  74 {
  75         struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
  76         pid_ns_release_proc(ns);
  77 }
  78
  79 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
  80 #define MAX_PID_NS_LEVEL 32
  81
  82 static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
  83 {
  84         return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
  85 }
  86
  87 static void dec_pid_namespaces(struct ucounts *ucounts)
  88 {
  89         dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
  90 }
  91
  92 static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
  93         struct pid_namespace *parent_pid_ns)
  94 {
  95         struct pid_namespace *ns;
  96         unsigned int level = parent_pid_ns->level + 1;
  97         struct ucounts *ucounts;
  98         int i;
  99         int err;
 100
 101         err = -ENOSPC;
 102         if (level > MAX_PID_NS_LEVEL)
 103                 goto out;
 104         ucounts = inc_pid_namespaces(user_ns);
 105         if (!ucounts)
 106                 goto out;
 107
 108         err = -ENOMEM;
 109         ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
 110         if (ns == NULL)
 111                 goto out_dec;
 112
 113         ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
 114         if (!ns->pidmap[0].page)
 115                 goto out_free;
 116
 117         ns->pid_cachep = create_pid_cachep(level + 1);
 118         if (ns->pid_cachep == NULL)
 119                 goto out_free_map;
 120
 121         err = ns_alloc_inum(&ns->ns);
 122         if (err)
 123                 goto out_free_map;
 124         ns->ns.ops = &pidns_operations;
 125
 126         kref_init(&ns->kref);
 127         ns->level = level;
 128         ns->parent = get_pid_ns(parent_pid_ns);
 129         ns->user_ns = get_user_ns(user_ns);
 130         ns->ucounts = ucounts;
 131         ns->nr_hashed = PIDNS_HASH_ADDING;
 132         INIT_WORK(&ns->proc_work, proc_cleanup_work);
 133
 134         set_bit(0, ns->pidmap[0].page);
 135         atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
 136
 137         for (i = 1; i < PIDMAP_ENTRIES; i++)
 138                 atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
 139
 140         return ns;
 141
 142 out_free_map:
 143         kfree(ns->pidmap[0].page);
 144 out_free:
 145         kmem_cache_free(pid_ns_cachep, ns);
 146 out_dec:
 147         dec_pid_namespaces(ucounts);
 148 out:
 149         return ERR_PTR(err);
 150 }
 151
 152 static void delayed_free_pidns(struct rcu_head *p)
 153 {
 154         struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);
 155
 156         dec_pid_namespaces(ns->ucounts);
 157         put_user_ns(ns->user_ns);
 158
 159         kmem_cache_free(pid_ns_cachep, ns);
 160 }
 161
 162 static void destroy_pid_namespace(struct pid_namespace *ns)
 163 {
 164         int i;
 165
 166         ns_free_inum(&ns->ns);
 167         for (i = 0; i < PIDMAP_ENTRIES; i++)
 168                 kfree(ns->pidmap[i].page);
 169         call_rcu(&ns->rcu, delayed_free_pidns);
 170 }
 171
 172 struct pid_namespace *copy_pid_ns(unsigned long flags,
 173         struct user_namespace *user_ns, struct pid_namespace *old_ns)
 174 {
 175         if (!(flags & CLONE_NEWPID))
 176                 return get_pid_ns(old_ns);
 177         if (task_active_pid_ns(current) != old_ns)
 178                 return ERR_PTR(-EINVAL);
 179         return create_pid_namespace(user_ns, old_ns);
 180 }
 181
 182 static void free_pid_ns(struct kref *kref)
 183 {
 184         struct pid_namespace *ns;
 185
 186         ns = container_of(kref, struct pid_namespace, kref);
 187         destroy_pid_namespace(ns);
 188 }
 189
 190 void put_pid_ns(struct pid_namespace *ns)
 191 {
 192         struct pid_namespace *parent;
 193
 194         while (ns != &init_pid_ns) {
 195                 parent = ns->parent;
 196                 if (!kref_put(&ns->kref, free_pid_ns))
 197                         break;
 198                 ns = parent;
 199         }
 200 }
 201 EXPORT_SYMBOL_GPL(put_pid_ns);
 202
 203 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 204 {
 205         int nr;
 206         int rc;
 207         struct task_struct *task, *me = current;
 208         int init_pids = thread_group_leader(me) ? 1 : 2;
 209
 210         /* Don't allow any more processes into the pid namespace */
 211         disable_pid_allocation(pid_ns);
 212
 213         /*
 214          * Ignore SIGCHLD causing any terminated children to autoreap.
 215          * This speeds up the namespace shutdown, plus see the comment
 216          * below.
 217          */
 218         spin_lock_irq(&me->sighand->siglock);
 219         me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
 220         spin_unlock_irq(&me->sighand->siglock);
 221
 222         /*
 223          * The last thread in the cgroup-init thread group is terminating.
 224          * Find remaining pid_ts in the namespace, signal and wait for them
 225          * to exit.
 226          *
 227          * Note:  This signals each threads in the namespace - even those that
 228          *        belong to the same thread group, To avoid this, we would have
 229          *        to walk the entire tasklist looking a processes in this
 230          *        namespace, but that could be unnecessarily expensive if the
 231          *        pid namespace has just a few processes. Or we need to
 232          *        maintain a tasklist for each pid namespace.
 233          *
 234          */
 235         read_lock(&tasklist_lock);
 236         nr = next_pidmap(pid_ns, 1);
 237         while (nr > 0) {
 238                 rcu_read_lock();
 239
 240                 task = pid_task(find_vpid(nr), PIDTYPE_PID);
 241                 if (task && !__fatal_signal_pending(task))
 242                         send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
 243
 244                 rcu_read_unlock();
 245
 246                 nr = next_pidmap(pid_ns, nr);
 247         }
 248         read_unlock(&tasklist_lock);
 249
 250         /*
 251          * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
 252          * sys_wait4() will also block until our children traced from the
 253          * parent namespace are detached and become EXIT_DEAD.
 254          */
 255         do {
 256                 clear_thread_flag(TIF_SIGPENDING);
 257                 rc = sys_wait4(-1, NULL, __WALL, NULL);
 258         } while (rc != -ECHILD);
 259
 260         /*
 261          * sys_wait4() above can't reap the EXIT_DEAD children but we do not
 262          * really care, we could reparent them to the global init. We could
 263          * exit and reap ->child_reaper even if it is not the last thread in
 264          * this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
 265          * pid_ns can not go away until proc_kill_sb() drops the reference.
 266          *
 267          * But this ns can also have other tasks injected by setns()+fork().
 268          * Again, ignoring the user visible semantics we do not really need
 269          * to wait until they are all reaped, but they can be reparented to
 270          * us and thus we need to ensure that pid->child_reaper stays valid
 271          * until they all go away. See free_pid()->wake_up_process().
 272          *
 273          * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
 274          * if reparented.
 275          */
 276         for (;;) {
 277                 set_current_state(TASK_UNINTERRUPTIBLE);
 278                 if (pid_ns->nr_hashed == init_pids)
 279                         break;
 280                 schedule();
 281         }
 282         __set_current_state(TASK_RUNNING);
 283
 284         if (pid_ns->reboot)
 285                 current->signal->group_exit_code = pid_ns->reboot;
 286
 287         acct_exit_ns(pid_ns);
 288         return;
 289 }
 290
 291 #ifdef CONFIG_CHECKPOINT_RESTORE
 292 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 293                 void __user *buffer, size_t *lenp, loff_t *ppos)
 294 {
 295         struct pid_namespace *pid_ns = task_active_pid_ns(current);
 296         struct ctl_table tmp = *table;
 297
 298         if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
 299                 return -EPERM;
 300
 301         /*
 302          * Writing directly to ns' last_pid field is OK, since this field
 303          * is volatile in a living namespace anyway and a code writing to
 304          * it should synchronize its usage with external means.
 305          */
 306
 307         tmp.data = &pid_ns->last_pid;
 308         return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 309 }
 310
 311 extern int pid_max;
 312 static int zero = 0;
 313 static struct ctl_table pid_ns_ctl_table[] = {
 314         {
 315                 .procname = "ns_last_pid",
 316                 .maxlen = sizeof(int),
 317                 .mode = 0666, /* permissions are checked in the handler */
 318                 .proc_handler = pid_ns_ctl_handler,
 319                 .extra1 = &zero,
 320                 .extra2 = &pid_max,
 321         },
 322         { }
 323 };
 324 static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
 325 #endif  /* CONFIG_CHECKPOINT_RESTORE */
 326
 327 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 328 {
 329         if (pid_ns == &init_pid_ns)
 330                 return 0;
 331
 332         switch (cmd) {
 333         case LINUX_REBOOT_CMD_RESTART2:
 334         case LINUX_REBOOT_CMD_RESTART:
 335                 pid_ns->reboot = SIGHUP;
 336                 break;
 337
 338         case LINUX_REBOOT_CMD_POWER_OFF:
 339         case LINUX_REBOOT_CMD_HALT:
 340                 pid_ns->reboot = SIGINT;
 341                 break;
 342         default:
 343                 return -EINVAL;
 344         }
 345
 346         read_lock(&tasklist_lock);
 347         force_sig(SIGKILL, pid_ns->child_reaper);
 348         read_unlock(&tasklist_lock);
 349
 350         do_exit(0);
 351
 352         /* Not reached */
 353         return 0;
 354 }
 355
 356 static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
 357 {
 358         return container_of(ns, struct pid_namespace, ns);
 359 }
 360
 361 static struct ns_common *pidns_get(struct task_struct *task)
 362 {
 363         struct pid_namespace *ns;
 364
 365         rcu_read_lock();
 366         ns = task_active_pid_ns(task);
 367         if (ns)
 368                 get_pid_ns(ns);
 369         rcu_read_unlock();
 370
 371         return ns ? &ns->ns : NULL;
 372 }
 373
 374 static void pidns_put(struct ns_common *ns)
 375 {
 376         put_pid_ns(to_pid_ns(ns));
 377 }
 378
 379 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 380 {
 381         struct pid_namespace *active = task_active_pid_ns(current);
 382         struct pid_namespace *ancestor, *new = to_pid_ns(ns);
 383
 384         if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
 385             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 386                 return -EPERM;
 387
 388         /*
 389          * Only allow entering the current active pid namespace
 390          * or a child of the current active pid namespace.
 391          *
 392          * This is required for fork to return a usable pid value and
 393          * this maintains the property that processes and their
 394          * children can not escape their current pid namespace.
 395          */
 396         if (new->level < active->level)
 397                 return -EINVAL;
 398
 399         ancestor = new;
 400         while (ancestor->level > active->level)
 401                 ancestor = ancestor->parent;
 402         if (ancestor != active)
 403                 return -EINVAL;
 404
 405         put_pid_ns(nsproxy->pid_ns_for_children);
 406         nsproxy->pid_ns_for_children = get_pid_ns(new);
 407         return 0;
 408 }
 409
 410 static struct ns_common *pidns_get_parent(struct ns_common *ns)
 411 {
 412         struct pid_namespace *active = task_active_pid_ns(current);
 413         struct pid_namespace *pid_ns, *p;
 414
 415         /* See if the parent is in the current namespace */
 416         pid_ns = p = to_pid_ns(ns)->parent;
 417         for (;;) {
 418                 if (!p)
 419                         return ERR_PTR(-EPERM);
 420                 if (p == active)
 421                         break;
 422                 p = p->parent;
 423         }
 424
 425         return &get_pid_ns(pid_ns)->ns;
 426 }
 427
 428 static struct user_namespace *pidns_owner(struct ns_common *ns)
 429 {
 430         return to_pid_ns(ns)->user_ns;
 431 }
 432
 433 const struct proc_ns_operations pidns_operations = {
 434         .name           = "pid",
 435         .type           = CLONE_NEWPID,
 436         .get            = pidns_get,
 437         .put            = pidns_put,
 438         .install        = pidns_install,
 439         .owner          = pidns_owner,
 440         .get_parent     = pidns_get_parent,
 441 };
 442
 443 static __init int pid_namespaces_init(void)
 444 {
 445         pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
 446
 447 #ifdef CONFIG_CHECKPOINT_RESTORE
 448         register_sysctl_paths(kern_path, pid_ns_ctl_table);
 449 #endif
 450         return 0;
 451 }
 452
 453 __initcall(pid_namespaces_init);