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Linux/kernel/pid_namespace.c

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  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);
469 

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