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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/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 pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
 83         struct pid_namespace *parent_pid_ns)
 84 {
 85         struct pid_namespace *ns;
 86         unsigned int level = parent_pid_ns->level + 1;
 87         int i;
 88         int err;
 89 
 90         if (level > MAX_PID_NS_LEVEL) {
 91                 err = -EINVAL;
 92                 goto out;
 93         }
 94 
 95         err = -ENOMEM;
 96         ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
 97         if (ns == NULL)
 98                 goto out;
 99 
100         ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
101         if (!ns->pidmap[0].page)
102                 goto out_free;
103 
104         ns->pid_cachep = create_pid_cachep(level + 1);
105         if (ns->pid_cachep == NULL)
106                 goto out_free_map;
107 
108         err = ns_alloc_inum(&ns->ns);
109         if (err)
110                 goto out_free_map;
111         ns->ns.ops = &pidns_operations;
112 
113         kref_init(&ns->kref);
114         ns->level = level;
115         ns->parent = get_pid_ns(parent_pid_ns);
116         ns->user_ns = get_user_ns(user_ns);
117         ns->nr_hashed = PIDNS_HASH_ADDING;
118         INIT_WORK(&ns->proc_work, proc_cleanup_work);
119 
120         set_bit(0, ns->pidmap[0].page);
121         atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);
122 
123         for (i = 1; i < PIDMAP_ENTRIES; i++)
124                 atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);
125 
126         return ns;
127 
128 out_free_map:
129         kfree(ns->pidmap[0].page);
130 out_free:
131         kmem_cache_free(pid_ns_cachep, ns);
132 out:
133         return ERR_PTR(err);
134 }
135 
136 static void delayed_free_pidns(struct rcu_head *p)
137 {
138         kmem_cache_free(pid_ns_cachep,
139                         container_of(p, struct pid_namespace, rcu));
140 }
141 
142 static void destroy_pid_namespace(struct pid_namespace *ns)
143 {
144         int i;
145 
146         ns_free_inum(&ns->ns);
147         for (i = 0; i < PIDMAP_ENTRIES; i++)
148                 kfree(ns->pidmap[i].page);
149         put_user_ns(ns->user_ns);
150         call_rcu(&ns->rcu, delayed_free_pidns);
151 }
152 
153 struct pid_namespace *copy_pid_ns(unsigned long flags,
154         struct user_namespace *user_ns, struct pid_namespace *old_ns)
155 {
156         if (!(flags & CLONE_NEWPID))
157                 return get_pid_ns(old_ns);
158         if (task_active_pid_ns(current) != old_ns)
159                 return ERR_PTR(-EINVAL);
160         return create_pid_namespace(user_ns, old_ns);
161 }
162 
163 static void free_pid_ns(struct kref *kref)
164 {
165         struct pid_namespace *ns;
166 
167         ns = container_of(kref, struct pid_namespace, kref);
168         destroy_pid_namespace(ns);
169 }
170 
171 void put_pid_ns(struct pid_namespace *ns)
172 {
173         struct pid_namespace *parent;
174 
175         while (ns != &init_pid_ns) {
176                 parent = ns->parent;
177                 if (!kref_put(&ns->kref, free_pid_ns))
178                         break;
179                 ns = parent;
180         }
181 }
182 EXPORT_SYMBOL_GPL(put_pid_ns);
183 
184 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
185 {
186         int nr;
187         int rc;
188         struct task_struct *task, *me = current;
189         int init_pids = thread_group_leader(me) ? 1 : 2;
190 
191         /* Don't allow any more processes into the pid namespace */
192         disable_pid_allocation(pid_ns);
193 
194         /*
195          * Ignore SIGCHLD causing any terminated children to autoreap.
196          * This speeds up the namespace shutdown, plus see the comment
197          * below.
198          */
199         spin_lock_irq(&me->sighand->siglock);
200         me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
201         spin_unlock_irq(&me->sighand->siglock);
202 
203         /*
204          * The last thread in the cgroup-init thread group is terminating.
205          * Find remaining pid_ts in the namespace, signal and wait for them
206          * to exit.
207          *
208          * Note:  This signals each threads in the namespace - even those that
209          *        belong to the same thread group, To avoid this, we would have
210          *        to walk the entire tasklist looking a processes in this
211          *        namespace, but that could be unnecessarily expensive if the
212          *        pid namespace has just a few processes. Or we need to
213          *        maintain a tasklist for each pid namespace.
214          *
215          */
216         read_lock(&tasklist_lock);
217         nr = next_pidmap(pid_ns, 1);
218         while (nr > 0) {
219                 rcu_read_lock();
220 
221                 task = pid_task(find_vpid(nr), PIDTYPE_PID);
222                 if (task && !__fatal_signal_pending(task))
223                         send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
224 
225                 rcu_read_unlock();
226 
227                 nr = next_pidmap(pid_ns, nr);
228         }
229         read_unlock(&tasklist_lock);
230 
231         /*
232          * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
233          * sys_wait4() will also block until our children traced from the
234          * parent namespace are detached and become EXIT_DEAD.
235          */
236         do {
237                 clear_thread_flag(TIF_SIGPENDING);
238                 rc = sys_wait4(-1, NULL, __WALL, NULL);
239         } while (rc != -ECHILD);
240 
241         /*
242          * sys_wait4() above can't reap the EXIT_DEAD children but we do not
243          * really care, we could reparent them to the global init. We could
244          * exit and reap ->child_reaper even if it is not the last thread in
245          * this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
246          * pid_ns can not go away until proc_kill_sb() drops the reference.
247          *
248          * But this ns can also have other tasks injected by setns()+fork().
249          * Again, ignoring the user visible semantics we do not really need
250          * to wait until they are all reaped, but they can be reparented to
251          * us and thus we need to ensure that pid->child_reaper stays valid
252          * until they all go away. See free_pid()->wake_up_process().
253          *
254          * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
255          * if reparented.
256          */
257         for (;;) {
258                 set_current_state(TASK_UNINTERRUPTIBLE);
259                 if (pid_ns->nr_hashed == init_pids)
260                         break;
261                 schedule();
262         }
263         __set_current_state(TASK_RUNNING);
264 
265         if (pid_ns->reboot)
266                 current->signal->group_exit_code = pid_ns->reboot;
267 
268         acct_exit_ns(pid_ns);
269         return;
270 }
271 
272 #ifdef CONFIG_CHECKPOINT_RESTORE
273 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
274                 void __user *buffer, size_t *lenp, loff_t *ppos)
275 {
276         struct pid_namespace *pid_ns = task_active_pid_ns(current);
277         struct ctl_table tmp = *table;
278 
279         if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
280                 return -EPERM;
281 
282         /*
283          * Writing directly to ns' last_pid field is OK, since this field
284          * is volatile in a living namespace anyway and a code writing to
285          * it should synchronize its usage with external means.
286          */
287 
288         tmp.data = &pid_ns->last_pid;
289         return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
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 void pidns_put(struct ns_common *ns)
356 {
357         put_pid_ns(to_pid_ns(ns));
358 }
359 
360 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
361 {
362         struct pid_namespace *active = task_active_pid_ns(current);
363         struct pid_namespace *ancestor, *new = to_pid_ns(ns);
364 
365         if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
366             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
367                 return -EPERM;
368 
369         /*
370          * Only allow entering the current active pid namespace
371          * or a child of the current active pid namespace.
372          *
373          * This is required for fork to return a usable pid value and
374          * this maintains the property that processes and their
375          * children can not escape their current pid namespace.
376          */
377         if (new->level < active->level)
378                 return -EINVAL;
379 
380         ancestor = new;
381         while (ancestor->level > active->level)
382                 ancestor = ancestor->parent;
383         if (ancestor != active)
384                 return -EINVAL;
385 
386         put_pid_ns(nsproxy->pid_ns_for_children);
387         nsproxy->pid_ns_for_children = get_pid_ns(new);
388         return 0;
389 }
390 
391 const struct proc_ns_operations pidns_operations = {
392         .name           = "pid",
393         .type           = CLONE_NEWPID,
394         .get            = pidns_get,
395         .put            = pidns_put,
396         .install        = pidns_install,
397 };
398 
399 static __init int pid_namespaces_init(void)
400 {
401         pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
402 
403 #ifdef CONFIG_CHECKPOINT_RESTORE
404         register_sysctl_paths(kern_path, pid_ns_ctl_table);
405 #endif
406         return 0;
407 }
408 
409 __initcall(pid_namespaces_init);
410 

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