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Linux/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);
454 

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