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 struct pid_cache {
  27         int nr_ids;
  28         char name[16];
  29         struct kmem_cache *cachep;
  30         struct list_head list;
  31 };
  32
  33 static LIST_HEAD(pid_caches_lh);
  34 static DEFINE_MUTEX(pid_caches_mutex);
  35 static struct kmem_cache *pid_ns_cachep;
  36
  37 /*
  38  * creates the kmem cache to allocate pids from.
  39  * @nr_ids: the number of numerical ids this pid will have to carry
  40  */
  41
  42 static struct kmem_cache *create_pid_cachep(int nr_ids)
  43 {
  44         struct pid_cache *pcache;
  45         struct kmem_cache *cachep;
  46
  47         mutex_lock(&pid_caches_mutex);
  48         list_for_each_entry(pcache, &pid_caches_lh, list)
  49                 if (pcache->nr_ids == nr_ids)
  50                         goto out;
  51
  52         pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
  53         if (pcache == NULL)
  54                 goto err_alloc;
  55
  56         snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
  57         cachep = kmem_cache_create(pcache->name,
  58                         sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
  59                         0, SLAB_HWCACHE_ALIGN, NULL);
  60         if (cachep == NULL)
  61                 goto err_cachep;
  62
  63         pcache->nr_ids = nr_ids;
  64         pcache->cachep = cachep;
  65         list_add(&pcache->list, &pid_caches_lh);
  66 out:
  67         mutex_unlock(&pid_caches_mutex);
  68         return pcache->cachep;
  69
  70 err_cachep:
  71         kfree(pcache);
  72 err_alloc:
  73         mutex_unlock(&pid_caches_mutex);
  74         return NULL;
  75 }
  76
  77 static void proc_cleanup_work(struct work_struct *work)
  78 {
  79         struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
  80         pid_ns_release_proc(ns);
  81 }
  82
  83 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
  84 #define MAX_PID_NS_LEVEL 32
  85
  86 static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
  87 {
  88         return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
  89 }
  90
  91 static void dec_pid_namespaces(struct ucounts *ucounts)
  92 {
  93         dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
  94 }
  95
  96 static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
  97         struct pid_namespace *parent_pid_ns)
  98 {
  99         struct pid_namespace *ns;
 100         unsigned int level = parent_pid_ns->level + 1;
 101         struct ucounts *ucounts;
 102         int err;
 103
 104         err = -EINVAL;
 105         if (!in_userns(parent_pid_ns->user_ns, user_ns))
 106                 goto out;
 107
 108         err = -ENOSPC;
 109         if (level > MAX_PID_NS_LEVEL)
 110                 goto out;
 111         ucounts = inc_pid_namespaces(user_ns);
 112         if (!ucounts)
 113                 goto out;
 114
 115         err = -ENOMEM;
 116         ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
 117         if (ns == NULL)
 118                 goto out_dec;
 119
 120         idr_init(&ns->idr);
 121
 122         ns->pid_cachep = create_pid_cachep(level + 1);
 123         if (ns->pid_cachep == NULL)
 124                 goto out_free_idr;
 125
 126         err = ns_alloc_inum(&ns->ns);
 127         if (err)
 128                 goto out_free_idr;
 129         ns->ns.ops = &pidns_operations;
 130
 131         kref_init(&ns->kref);
 132         ns->level = level;
 133         ns->parent = get_pid_ns(parent_pid_ns);
 134         ns->user_ns = get_user_ns(user_ns);
 135         ns->ucounts = ucounts;
 136         ns->pid_allocated = PIDNS_ADDING;
 137         INIT_WORK(&ns->proc_work, proc_cleanup_work);
 138
 139         return ns;
 140
 141 out_free_idr:
 142         idr_destroy(&ns->idr);
 143         kmem_cache_free(pid_ns_cachep, ns);
 144 out_dec:
 145         dec_pid_namespaces(ucounts);
 146 out:
 147         return ERR_PTR(err);
 148 }
 149
 150 static void delayed_free_pidns(struct rcu_head *p)
 151 {
 152         struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);
 153
 154         dec_pid_namespaces(ns->ucounts);
 155         put_user_ns(ns->user_ns);
 156
 157         kmem_cache_free(pid_ns_cachep, ns);
 158 }
 159
 160 static void destroy_pid_namespace(struct pid_namespace *ns)
 161 {
 162         ns_free_inum(&ns->ns);
 163
 164         idr_destroy(&ns->idr);
 165         call_rcu(&ns->rcu, delayed_free_pidns);
 166 }
 167
 168 struct pid_namespace *copy_pid_ns(unsigned long flags,
 169         struct user_namespace *user_ns, struct pid_namespace *old_ns)
 170 {
 171         if (!(flags & CLONE_NEWPID))
 172                 return get_pid_ns(old_ns);
 173         if (task_active_pid_ns(current) != old_ns)
 174                 return ERR_PTR(-EINVAL);
 175         return create_pid_namespace(user_ns, old_ns);
 176 }
 177
 178 static void free_pid_ns(struct kref *kref)
 179 {
 180         struct pid_namespace *ns;
 181
 182         ns = container_of(kref, struct pid_namespace, kref);
 183         destroy_pid_namespace(ns);
 184 }
 185
 186 void put_pid_ns(struct pid_namespace *ns)
 187 {
 188         struct pid_namespace *parent;
 189
 190         while (ns != &init_pid_ns) {
 191                 parent = ns->parent;
 192                 if (!kref_put(&ns->kref, free_pid_ns))
 193                         break;
 194                 ns = parent;
 195         }
 196 }
 197 EXPORT_SYMBOL_GPL(put_pid_ns);
 198
 199 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 200 {
 201         int nr;
 202         int rc;
 203         struct task_struct *task, *me = current;
 204         int init_pids = thread_group_leader(me) ? 1 : 2;
 205         struct pid *pid;
 206
 207         /* Don't allow any more processes into the pid namespace */
 208         disable_pid_allocation(pid_ns);
 209
 210         /*
 211          * Ignore SIGCHLD causing any terminated children to autoreap.
 212          * This speeds up the namespace shutdown, plus see the comment
 213          * below.
 214          */
 215         spin_lock_irq(&me->sighand->siglock);
 216         me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
 217         spin_unlock_irq(&me->sighand->siglock);
 218
 219         /*
 220          * The last thread in the cgroup-init thread group is terminating.
 221          * Find remaining pid_ts in the namespace, signal and wait for them
 222          * to exit.
 223          *
 224          * Note:  This signals each threads in the namespace - even those that
 225          *        belong to the same thread group, To avoid this, we would have
 226          *        to walk the entire tasklist looking a processes in this
 227          *        namespace, but that could be unnecessarily expensive if the
 228          *        pid namespace has just a few processes. Or we need to
 229          *        maintain a tasklist for each pid namespace.
 230          *
 231          */
 232         rcu_read_lock();
 233         read_lock(&tasklist_lock);
 234         nr = 2;
 235         idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
 236                 task = pid_task(pid, PIDTYPE_PID);
 237                 if (task && !__fatal_signal_pending(task))
 238                         send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
 239         }
 240         read_unlock(&tasklist_lock);
 241         rcu_read_unlock();
 242
 243         /*
 244          * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
 245          * sys_wait4() will also block until our children traced from the
 246          * parent namespace are detached and become EXIT_DEAD.
 247          */
 248         do {
 249                 clear_thread_flag(TIF_SIGPENDING);
 250                 rc = sys_wait4(-1, NULL, __WALL, NULL);
 251         } while (rc != -ECHILD);
 252
 253         /*
 254          * sys_wait4() above can't reap the EXIT_DEAD children but we do not
 255          * really care, we could reparent them to the global init. We could
 256          * exit and reap ->child_reaper even if it is not the last thread in
 257          * this pid_ns, free_pid(pid_allocated == 0) calls proc_cleanup_work(),
 258          * pid_ns can not go away until proc_kill_sb() drops the reference.
 259          *
 260          * But this ns can also have other tasks injected by setns()+fork().
 261          * Again, ignoring the user visible semantics we do not really need
 262          * to wait until they are all reaped, but they can be reparented to
 263          * us and thus we need to ensure that pid->child_reaper stays valid
 264          * until they all go away. See free_pid()->wake_up_process().
 265          *
 266          * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
 267          * if reparented.
 268          */
 269         for (;;) {
 270                 set_current_state(TASK_INTERRUPTIBLE);
 271                 if (pid_ns->pid_allocated == init_pids)
 272                         break;
 273                 schedule();
 274         }
 275         __set_current_state(TASK_RUNNING);
 276
 277         if (pid_ns->reboot)
 278                 current->signal->group_exit_code = pid_ns->reboot;
 279
 280         acct_exit_ns(pid_ns);
 281         return;
 282 }
 283
 284 #ifdef CONFIG_CHECKPOINT_RESTORE
 285 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 286                 void __user *buffer, size_t *lenp, loff_t *ppos)
 287 {
 288         struct pid_namespace *pid_ns = task_active_pid_ns(current);
 289         struct ctl_table tmp = *table;
 290         int ret, next;
 291
 292         if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
 293                 return -EPERM;
 294
 295         /*
 296          * Writing directly to ns' last_pid field is OK, since this field
 297          * is volatile in a living namespace anyway and a code writing to
 298          * it should synchronize its usage with external means.
 299          */
 300
 301         next = idr_get_cursor(&pid_ns->idr) - 1;
 302
 303         tmp.data = &next;
 304         ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 305         if (!ret && write)
 306                 idr_set_cursor(&pid_ns->idr, next + 1);
 307
 308         return ret;
 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 struct ns_common *pidns_for_children_get(struct task_struct *task)
 375 {
 376         struct pid_namespace *ns = NULL;
 377
 378         task_lock(task);
 379         if (task->nsproxy) {
 380                 ns = task->nsproxy->pid_ns_for_children;
 381                 get_pid_ns(ns);
 382         }
 383         task_unlock(task);
 384
 385         if (ns) {
 386                 read_lock(&tasklist_lock);
 387                 if (!ns->child_reaper) {
 388                         put_pid_ns(ns);
 389                         ns = NULL;
 390                 }
 391                 read_unlock(&tasklist_lock);
 392         }
 393
 394         return ns ? &ns->ns : NULL;
 395 }
 396
 397 static void pidns_put(struct ns_common *ns)
 398 {
 399         put_pid_ns(to_pid_ns(ns));
 400 }
 401
 402 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 403 {
 404         struct pid_namespace *active = task_active_pid_ns(current);
 405         struct pid_namespace *ancestor, *new = to_pid_ns(ns);
 406
 407         if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
 408             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 409                 return -EPERM;
 410
 411         /*
 412          * Only allow entering the current active pid namespace
 413          * or a child of the current active pid namespace.
 414          *
 415          * This is required for fork to return a usable pid value and
 416          * this maintains the property that processes and their
 417          * children can not escape their current pid namespace.
 418          */
 419         if (new->level < active->level)
 420                 return -EINVAL;
 421
 422         ancestor = new;
 423         while (ancestor->level > active->level)
 424                 ancestor = ancestor->parent;
 425         if (ancestor != active)
 426                 return -EINVAL;
 427
 428         put_pid_ns(nsproxy->pid_ns_for_children);
 429         nsproxy->pid_ns_for_children = get_pid_ns(new);
 430         return 0;
 431 }
 432
 433 static struct ns_common *pidns_get_parent(struct ns_common *ns)
 434 {
 435         struct pid_namespace *active = task_active_pid_ns(current);
 436         struct pid_namespace *pid_ns, *p;
 437
 438         /* See if the parent is in the current namespace */
 439         pid_ns = p = to_pid_ns(ns)->parent;
 440         for (;;) {
 441                 if (!p)
 442                         return ERR_PTR(-EPERM);
 443                 if (p == active)
 444                         break;
 445                 p = p->parent;
 446         }
 447
 448         return &get_pid_ns(pid_ns)->ns;
 449 }
 450
 451 static struct user_namespace *pidns_owner(struct ns_common *ns)
 452 {
 453         return to_pid_ns(ns)->user_ns;
 454 }
 455
 456 const struct proc_ns_operations pidns_operations = {
 457         .name           = "pid",
 458         .type           = CLONE_NEWPID,
 459         .get            = pidns_get,
 460         .put            = pidns_put,
 461         .install        = pidns_install,
 462         .owner          = pidns_owner,
 463         .get_parent     = pidns_get_parent,
 464 };
 465
 466 const struct proc_ns_operations pidns_for_children_operations = {
 467         .name           = "pid_for_children",
 468         .real_ns_name   = "pid",
 469         .type           = CLONE_NEWPID,
 470         .get            = pidns_for_children_get,
 471         .put            = pidns_put,
 472         .install        = pidns_install,
 473         .owner          = pidns_owner,
 474         .get_parent     = pidns_get_parent,
 475 };
 476
 477 static __init int pid_namespaces_init(void)
 478 {
 479         pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
 480
 481 #ifdef CONFIG_CHECKPOINT_RESTORE
 482         register_sysctl_paths(kern_path, pid_ns_ctl_table);
 483 #endif
 484         return 0;
 485 }
 486
 487 __initcall(pid_namespaces_init);