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/cred.h>
  16 #include <linux/err.h>
  17 #include <linux/acct.h>
  18 #include <linux/slab.h>
  19 #include <linux/proc_ns.h>
  20 #include <linux/reboot.h>
  21 #include <linux/export.h>
  22 #include <linux/sched/task.h>
  23 #include <linux/sched/signal.h>
  24 #include <linux/idr.h>
  25
  26 static DEFINE_MUTEX(pid_caches_mutex);
  27 static struct kmem_cache *pid_ns_cachep;
  28 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
  29 #define MAX_PID_NS_LEVEL 32
  30 /* Write once array, filled from the beginning. */
  31 static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];
  32
  33 /*
  34  * creates the kmem cache to allocate pids from.
  35  * @level: pid namespace level
  36  */
  37
  38 static struct kmem_cache *create_pid_cachep(unsigned int level)
  39 {
  40         /* Level 0 is init_pid_ns.pid_cachep */
  41         struct kmem_cache **pkc = &pid_cache[level - 1];
  42         struct kmem_cache *kc;
  43         char name[4 + 10 + 1];
  44         unsigned int len;
  45
  46         kc = READ_ONCE(*pkc);
  47         if (kc)
  48                 return kc;
  49
  50         snprintf(name, sizeof(name), "pid_%u", level + 1);
  51         len = sizeof(struct pid) + level * sizeof(struct upid);
  52         mutex_lock(&pid_caches_mutex);
  53         /* Name collision forces to do allocation under mutex. */
  54         if (!*pkc)
  55                 *pkc = kmem_cache_create(name, len, 0, SLAB_HWCACHE_ALIGN, 0);
  56         mutex_unlock(&pid_caches_mutex);
  57         /* current can fail, but someone else can succeed. */
  58         return READ_ONCE(*pkc);
  59 }
  60
  61 static void proc_cleanup_work(struct work_struct *work)
  62 {
  63         struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
  64         pid_ns_release_proc(ns);
  65 }
  66
  67 static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
  68 {
  69         return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
  70 }
  71
  72 static void dec_pid_namespaces(struct ucounts *ucounts)
  73 {
  74         dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
  75 }
  76
  77 static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
  78         struct pid_namespace *parent_pid_ns)
  79 {
  80         struct pid_namespace *ns;
  81         unsigned int level = parent_pid_ns->level + 1;
  82         struct ucounts *ucounts;
  83         int err;
  84
  85         err = -EINVAL;
  86         if (!in_userns(parent_pid_ns->user_ns, user_ns))
  87                 goto out;
  88
  89         err = -ENOSPC;
  90         if (level > MAX_PID_NS_LEVEL)
  91                 goto out;
  92         ucounts = inc_pid_namespaces(user_ns);
  93         if (!ucounts)
  94                 goto out;
  95
  96         err = -ENOMEM;
  97         ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
  98         if (ns == NULL)
  99                 goto out_dec;
 100
 101         idr_init(&ns->idr);
 102
 103         ns->pid_cachep = create_pid_cachep(level);
 104         if (ns->pid_cachep == NULL)
 105                 goto out_free_idr;
 106
 107         err = ns_alloc_inum(&ns->ns);
 108         if (err)
 109                 goto out_free_idr;
 110         ns->ns.ops = &pidns_operations;
 111
 112         kref_init(&ns->kref);
 113         ns->level = level;
 114         ns->parent = get_pid_ns(parent_pid_ns);
 115         ns->user_ns = get_user_ns(user_ns);
 116         ns->ucounts = ucounts;
 117         ns->pid_allocated = PIDNS_ADDING;
 118         INIT_WORK(&ns->proc_work, proc_cleanup_work);
 119
 120         return ns;
 121
 122 out_free_idr:
 123         idr_destroy(&ns->idr);
 124         kmem_cache_free(pid_ns_cachep, ns);
 125 out_dec:
 126         dec_pid_namespaces(ucounts);
 127 out:
 128         return ERR_PTR(err);
 129 }
 130
 131 static void delayed_free_pidns(struct rcu_head *p)
 132 {
 133         struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);
 134
 135         dec_pid_namespaces(ns->ucounts);
 136         put_user_ns(ns->user_ns);
 137
 138         kmem_cache_free(pid_ns_cachep, ns);
 139 }
 140
 141 static void destroy_pid_namespace(struct pid_namespace *ns)
 142 {
 143         ns_free_inum(&ns->ns);
 144
 145         idr_destroy(&ns->idr);
 146         call_rcu(&ns->rcu, delayed_free_pidns);
 147 }
 148
 149 struct pid_namespace *copy_pid_ns(unsigned long flags,
 150         struct user_namespace *user_ns, struct pid_namespace *old_ns)
 151 {
 152         if (!(flags & CLONE_NEWPID))
 153                 return get_pid_ns(old_ns);
 154         if (task_active_pid_ns(current) != old_ns)
 155                 return ERR_PTR(-EINVAL);
 156         return create_pid_namespace(user_ns, old_ns);
 157 }
 158
 159 static void free_pid_ns(struct kref *kref)
 160 {
 161         struct pid_namespace *ns;
 162
 163         ns = container_of(kref, struct pid_namespace, kref);
 164         destroy_pid_namespace(ns);
 165 }
 166
 167 void put_pid_ns(struct pid_namespace *ns)
 168 {
 169         struct pid_namespace *parent;
 170
 171         while (ns != &init_pid_ns) {
 172                 parent = ns->parent;
 173                 if (!kref_put(&ns->kref, free_pid_ns))
 174                         break;
 175                 ns = parent;
 176         }
 177 }
 178 EXPORT_SYMBOL_GPL(put_pid_ns);
 179
 180 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 181 {
 182         int nr;
 183         int rc;
 184         struct task_struct *task, *me = current;
 185         int init_pids = thread_group_leader(me) ? 1 : 2;
 186         struct pid *pid;
 187
 188         /* Don't allow any more processes into the pid namespace */
 189         disable_pid_allocation(pid_ns);
 190
 191         /*
 192          * Ignore SIGCHLD causing any terminated children to autoreap.
 193          * This speeds up the namespace shutdown, plus see the comment
 194          * below.
 195          */
 196         spin_lock_irq(&me->sighand->siglock);
 197         me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
 198         spin_unlock_irq(&me->sighand->siglock);
 199
 200         /*
 201          * The last thread in the cgroup-init thread group is terminating.
 202          * Find remaining pid_ts in the namespace, signal and wait for them
 203          * to exit.
 204          *
 205          * Note:  This signals each threads in the namespace - even those that
 206          *        belong to the same thread group, To avoid this, we would have
 207          *        to walk the entire tasklist looking a processes in this
 208          *        namespace, but that could be unnecessarily expensive if the
 209          *        pid namespace has just a few processes. Or we need to
 210          *        maintain a tasklist for each pid namespace.
 211          *
 212          */
 213         rcu_read_lock();
 214         read_lock(&tasklist_lock);
 215         nr = 2;
 216         idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
 217                 task = pid_task(pid, PIDTYPE_PID);
 218                 if (task && !__fatal_signal_pending(task))
 219                         send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
 220         }
 221         read_unlock(&tasklist_lock);
 222         rcu_read_unlock();
 223
 224         /*
 225          * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
 226          * kernel_wait4() will also block until our children traced from the
 227          * parent namespace are detached and become EXIT_DEAD.
 228          */
 229         do {
 230                 clear_thread_flag(TIF_SIGPENDING);
 231                 rc = kernel_wait4(-1, NULL, __WALL, NULL);
 232         } while (rc != -ECHILD);
 233
 234         /*
 235          * kernel_wait4() above can't reap the EXIT_DEAD children but we do not
 236          * really care, we could reparent them to the global init. We could
 237          * exit and reap ->child_reaper even if it is not the last thread in
 238          * this pid_ns, free_pid(pid_allocated == 0) calls proc_cleanup_work(),
 239          * pid_ns can not go away until proc_kill_sb() drops the reference.
 240          *
 241          * But this ns can also have other tasks injected by setns()+fork().
 242          * Again, ignoring the user visible semantics we do not really need
 243          * to wait until they are all reaped, but they can be reparented to
 244          * us and thus we need to ensure that pid->child_reaper stays valid
 245          * until they all go away. See free_pid()->wake_up_process().
 246          *
 247          * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
 248          * if reparented.
 249          */
 250         for (;;) {
 251                 set_current_state(TASK_INTERRUPTIBLE);
 252                 if (pid_ns->pid_allocated == init_pids)
 253                         break;
 254                 schedule();
 255         }
 256         __set_current_state(TASK_RUNNING);
 257
 258         if (pid_ns->reboot)
 259                 current->signal->group_exit_code = pid_ns->reboot;
 260
 261         acct_exit_ns(pid_ns);
 262         return;
 263 }
 264
 265 #ifdef CONFIG_CHECKPOINT_RESTORE
 266 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 267                 void __user *buffer, size_t *lenp, loff_t *ppos)
 268 {
 269         struct pid_namespace *pid_ns = task_active_pid_ns(current);
 270         struct ctl_table tmp = *table;
 271         int ret, next;
 272
 273         if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
 274                 return -EPERM;
 275
 276         /*
 277          * Writing directly to ns' last_pid field is OK, since this field
 278          * is volatile in a living namespace anyway and a code writing to
 279          * it should synchronize its usage with external means.
 280          */
 281
 282         next = idr_get_cursor(&pid_ns->idr) - 1;
 283
 284         tmp.data = &next;
 285         ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 286         if (!ret && write)
 287                 idr_set_cursor(&pid_ns->idr, next + 1);
 288
 289         return ret;
 290 }
 291
 292 extern int pid_max;
 293 static int zero = 0;
 294 static struct ctl_table pid_ns_ctl_table[] = {
 295         {
 296                 .procname = "ns_last_pid",
 297                 .maxlen = sizeof(int),
 298                 .mode = 0666, /* permissions are checked in the handler */
 299                 .proc_handler = pid_ns_ctl_handler,
 300                 .extra1 = &zero,
 301                 .extra2 = &pid_max,
 302         },
 303         { }
 304 };
 305 static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
 306 #endif  /* CONFIG_CHECKPOINT_RESTORE */
 307
 308 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 309 {
 310         if (pid_ns == &init_pid_ns)
 311                 return 0;
 312
 313         switch (cmd) {
 314         case LINUX_REBOOT_CMD_RESTART2:
 315         case LINUX_REBOOT_CMD_RESTART:
 316                 pid_ns->reboot = SIGHUP;
 317                 break;
 318
 319         case LINUX_REBOOT_CMD_POWER_OFF:
 320         case LINUX_REBOOT_CMD_HALT:
 321                 pid_ns->reboot = SIGINT;
 322                 break;
 323         default:
 324                 return -EINVAL;
 325         }
 326
 327         read_lock(&tasklist_lock);
 328         force_sig(SIGKILL, pid_ns->child_reaper);
 329         read_unlock(&tasklist_lock);
 330
 331         do_exit(0);
 332
 333         /* Not reached */
 334         return 0;
 335 }
 336
 337 static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
 338 {
 339         return container_of(ns, struct pid_namespace, ns);
 340 }
 341
 342 static struct ns_common *pidns_get(struct task_struct *task)
 343 {
 344         struct pid_namespace *ns;
 345
 346         rcu_read_lock();
 347         ns = task_active_pid_ns(task);
 348         if (ns)
 349                 get_pid_ns(ns);
 350         rcu_read_unlock();
 351
 352         return ns ? &ns->ns : NULL;
 353 }
 354
 355 static struct ns_common *pidns_for_children_get(struct task_struct *task)
 356 {
 357         struct pid_namespace *ns = NULL;
 358
 359         task_lock(task);
 360         if (task->nsproxy) {
 361                 ns = task->nsproxy->pid_ns_for_children;
 362                 get_pid_ns(ns);
 363         }
 364         task_unlock(task);
 365
 366         if (ns) {
 367                 read_lock(&tasklist_lock);
 368                 if (!ns->child_reaper) {
 369                         put_pid_ns(ns);
 370                         ns = NULL;
 371                 }
 372                 read_unlock(&tasklist_lock);
 373         }
 374
 375         return ns ? &ns->ns : NULL;
 376 }
 377
 378 static void pidns_put(struct ns_common *ns)
 379 {
 380         put_pid_ns(to_pid_ns(ns));
 381 }
 382
 383 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 384 {
 385         struct pid_namespace *active = task_active_pid_ns(current);
 386         struct pid_namespace *ancestor, *new = to_pid_ns(ns);
 387
 388         if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
 389             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 390                 return -EPERM;
 391
 392         /*
 393          * Only allow entering the current active pid namespace
 394          * or a child of the current active pid namespace.
 395          *
 396          * This is required for fork to return a usable pid value and
 397          * this maintains the property that processes and their
 398          * children can not escape their current pid namespace.
 399          */
 400         if (new->level < active->level)
 401                 return -EINVAL;
 402
 403         ancestor = new;
 404         while (ancestor->level > active->level)
 405                 ancestor = ancestor->parent;
 406         if (ancestor != active)
 407                 return -EINVAL;
 408
 409         put_pid_ns(nsproxy->pid_ns_for_children);
 410         nsproxy->pid_ns_for_children = get_pid_ns(new);
 411         return 0;
 412 }
 413
 414 static struct ns_common *pidns_get_parent(struct ns_common *ns)
 415 {
 416         struct pid_namespace *active = task_active_pid_ns(current);
 417         struct pid_namespace *pid_ns, *p;
 418
 419         /* See if the parent is in the current namespace */
 420         pid_ns = p = to_pid_ns(ns)->parent;
 421         for (;;) {
 422                 if (!p)
 423                         return ERR_PTR(-EPERM);
 424                 if (p == active)
 425                         break;
 426                 p = p->parent;
 427         }
 428
 429         return &get_pid_ns(pid_ns)->ns;
 430 }
 431
 432 static struct user_namespace *pidns_owner(struct ns_common *ns)
 433 {
 434         return to_pid_ns(ns)->user_ns;
 435 }
 436
 437 const struct proc_ns_operations pidns_operations = {
 438         .name           = "pid",
 439         .type           = CLONE_NEWPID,
 440         .get            = pidns_get,
 441         .put            = pidns_put,
 442         .install        = pidns_install,
 443         .owner          = pidns_owner,
 444         .get_parent     = pidns_get_parent,
 445 };
 446
 447 const struct proc_ns_operations pidns_for_children_operations = {
 448         .name           = "pid_for_children",
 449         .real_ns_name   = "pid",
 450         .type           = CLONE_NEWPID,
 451         .get            = pidns_for_children_get,
 452         .put            = pidns_put,
 453         .install        = pidns_install,
 454         .owner          = pidns_owner,
 455         .get_parent     = pidns_get_parent,
 456 };
 457
 458 static __init int pid_namespaces_init(void)
 459 {
 460         pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
 461
 462 #ifdef CONFIG_CHECKPOINT_RESTORE
 463         register_sysctl_paths(kern_path, pid_ns_ctl_table);
 464 #endif
 465         return 0;
 466 }
 467
 468 __initcall(pid_namespaces_init);