kernel/pid_namespace.c - linux - Git at Google

 /*
  * Pid namespaces
  *
  * Authors:
  *    (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
  *    (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
  *     Many thanks to Oleg Nesterov for comments and help
  *
  */

 #include <linux/pid.h>
 #include <linux/pid_namespace.h>
 #include <linux/user_namespace.h>
 #include <linux/syscalls.h>
 #include <linux/err.h>
 #include <linux/acct.h>
 #include <linux/slab.h>
 #include <linux/proc_ns.h>
 #include <linux/reboot.h>
 #include <linux/export.h>

 struct pid_cache {
 	int nr_ids;
 	char name[16];
 	struct kmem_cache *cachep;
 	struct list_head list;
 };

 static LIST_HEAD(pid_caches_lh);
 static DEFINE_MUTEX(pid_caches_mutex);
 static struct kmem_cache *pid_ns_cachep;

 /*
  * creates the kmem cache to allocate pids from.
  * @nr_ids: the number of numerical ids this pid will have to carry
  */

 static struct kmem_cache *create_pid_cachep(int nr_ids)
 {
 	struct pid_cache *pcache;
 	struct kmem_cache *cachep;

 	mutex_lock(&pid_caches_mutex);
 	list_for_each_entry(pcache, &pid_caches_lh, list)
 		if (pcache->nr_ids == nr_ids)
 			goto out;

 	pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
 	if (pcache == NULL)
 		goto err_alloc;

 	snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
 	cachep = kmem_cache_create(pcache->name,
 			sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
 			0, SLAB_HWCACHE_ALIGN, NULL);
 	if (cachep == NULL)
 		goto err_cachep;

 	pcache->nr_ids = nr_ids;
 	pcache->cachep = cachep;
 	list_add(&pcache->list, &pid_caches_lh);
 out:
 	mutex_unlock(&pid_caches_mutex);
 	return pcache->cachep;

 err_cachep:
 	kfree(pcache);
 err_alloc:
 	mutex_unlock(&pid_caches_mutex);
 	return NULL;
 }

 static void proc_cleanup_work(struct work_struct *work)
 {
 	struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
 	pid_ns_release_proc(ns);
 }

 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
 #define MAX_PID_NS_LEVEL 32

 static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
 {
 	return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
 }

 static void dec_pid_namespaces(struct ucounts *ucounts)
 {
 	dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
 }

 static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns,
 	struct pid_namespace *parent_pid_ns)
 {
 	struct pid_namespace *ns;
 	unsigned int level = parent_pid_ns->level + 1;
 	struct ucounts *ucounts;
 	int i;
 	int err;

 	err = -ENOSPC;
 	if (level > MAX_PID_NS_LEVEL)
 		goto out;
 	ucounts = inc_pid_namespaces(user_ns);
 	if (!ucounts)
 		goto out;

 	err = -ENOMEM;
 	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
 	if (ns == NULL)
 		goto out_dec;

 	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!ns->pidmap[0].page)
 		goto out_free;

 	ns->pid_cachep = create_pid_cachep(level + 1);
 	if (ns->pid_cachep == NULL)
 		goto out_free_map;

 	err = ns_alloc_inum(&ns->ns);
 	if (err)
 		goto out_free_map;
 	ns->ns.ops = &pidns_operations;

 	kref_init(&ns->kref);
 	ns->level = level;
 	ns->parent = get_pid_ns(parent_pid_ns);
 	ns->user_ns = get_user_ns(user_ns);
 	ns->ucounts = ucounts;
 	ns->nr_hashed = PIDNS_HASH_ADDING;
 	INIT_WORK(&ns->proc_work, proc_cleanup_work);

 	set_bit(0, ns->pidmap[0].page);
 	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);

 	for (i = 1; i < PIDMAP_ENTRIES; i++)
 		atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);

 	return ns;

 out_free_map:
 	kfree(ns->pidmap[0].page);
 out_free:
 	kmem_cache_free(pid_ns_cachep, ns);
 out_dec:
 	dec_pid_namespaces(ucounts);
 out:
 	return ERR_PTR(err);
 }

 static void delayed_free_pidns(struct rcu_head *p)
 {
 	struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);

 	dec_pid_namespaces(ns->ucounts);
 	put_user_ns(ns->user_ns);

 	kmem_cache_free(pid_ns_cachep, ns);
 }

 static void destroy_pid_namespace(struct pid_namespace *ns)
 {
 	int i;

 	ns_free_inum(&ns->ns);
 	for (i = 0; i < PIDMAP_ENTRIES; i++)
 		kfree(ns->pidmap[i].page);
 	call_rcu(&ns->rcu, delayed_free_pidns);
 }

 struct pid_namespace *copy_pid_ns(unsigned long flags,
 	struct user_namespace *user_ns, struct pid_namespace *old_ns)
 {
 	if (!(flags & CLONE_NEWPID))
 		return get_pid_ns(old_ns);
 	if (task_active_pid_ns(current) != old_ns)
 		return ERR_PTR(-EINVAL);
 	return create_pid_namespace(user_ns, old_ns);
 }

 static void free_pid_ns(struct kref *kref)
 {
 	struct pid_namespace *ns;

 	ns = container_of(kref, struct pid_namespace, kref);
 	destroy_pid_namespace(ns);
 }

 void put_pid_ns(struct pid_namespace *ns)
 {
 	struct pid_namespace *parent;

 	while (ns != &init_pid_ns) {
 		parent = ns->parent;
 		if (!kref_put(&ns->kref, free_pid_ns))
 			break;
 		ns = parent;
 	}
 }
 EXPORT_SYMBOL_GPL(put_pid_ns);

 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 {
 	int nr;
 	int rc;
 	struct task_struct *task, *me = current;
 	int init_pids = thread_group_leader(me) ? 1 : 2;

 	/* Don't allow any more processes into the pid namespace */
 	disable_pid_allocation(pid_ns);

 	/*
 	 * Ignore SIGCHLD causing any terminated children to autoreap.
 	 * This speeds up the namespace shutdown, plus see the comment
 	 * below.
 	 */
 	spin_lock_irq(&me->sighand->siglock);
 	me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
 	spin_unlock_irq(&me->sighand->siglock);

 	/*
 	 * The last thread in the cgroup-init thread group is terminating.
 	 * Find remaining pid_ts in the namespace, signal and wait for them
 	 * to exit.
 	 *
 	 * Note:  This signals each threads in the namespace - even those that
 	 * 	  belong to the same thread group, To avoid this, we would have
 	 * 	  to walk the entire tasklist looking a processes in this
 	 * 	  namespace, but that could be unnecessarily expensive if the
 	 * 	  pid namespace has just a few processes. Or we need to
 	 * 	  maintain a tasklist for each pid namespace.
 	 *
 	 */
 	read_lock(&tasklist_lock);
 	nr = next_pidmap(pid_ns, 1);
 	while (nr > 0) {
 		rcu_read_lock();

 		task = pid_task(find_vpid(nr), PIDTYPE_PID);
 		if (task && !__fatal_signal_pending(task))
 			send_sig_info(SIGKILL, SEND_SIG_FORCED, task);

 		rcu_read_unlock();

 		nr = next_pidmap(pid_ns, nr);
 	}
 	read_unlock(&tasklist_lock);

 	/*
 	 * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
 	 * sys_wait4() will also block until our children traced from the
 	 * parent namespace are detached and become EXIT_DEAD.
 	 */
 	do {
 		clear_thread_flag(TIF_SIGPENDING);
 		rc = sys_wait4(-1, NULL, __WALL, NULL);
 	} while (rc != -ECHILD);

 	/*
 	 * sys_wait4() above can't reap the EXIT_DEAD children but we do not
 	 * really care, we could reparent them to the global init. We could
 	 * exit and reap ->child_reaper even if it is not the last thread in
 	 * this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
 	 * pid_ns can not go away until proc_kill_sb() drops the reference.
 	 *
 	 * But this ns can also have other tasks injected by setns()+fork().
 	 * Again, ignoring the user visible semantics we do not really need
 	 * to wait until they are all reaped, but they can be reparented to
 	 * us and thus we need to ensure that pid->child_reaper stays valid
 	 * until they all go away. See free_pid()->wake_up_process().
 	 *
 	 * We rely on ignored SIGCHLD, an injected zombie must be autoreaped
 	 * if reparented.
 	 */
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (pid_ns->nr_hashed == init_pids)
 			break;
 		schedule();
 	}
 	__set_current_state(TASK_RUNNING);

 	if (pid_ns->reboot)
 		current->signal->group_exit_code = pid_ns->reboot;

 	acct_exit_ns(pid_ns);
 	return;
 }

 #ifdef CONFIG_CHECKPOINT_RESTORE
 static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp, loff_t *ppos)
 {
 	struct pid_namespace *pid_ns = task_active_pid_ns(current);
 	struct ctl_table tmp = *table;

 	if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
 		return -EPERM;

 	/*
 	 * Writing directly to ns' last_pid field is OK, since this field
 	 * is volatile in a living namespace anyway and a code writing to
 	 * it should synchronize its usage with external means.
 	 */

 	tmp.data = &pid_ns->last_pid;
 	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 }

 extern int pid_max;
 static int zero = 0;
 static struct ctl_table pid_ns_ctl_table[] = {
 	{
 		.procname = "ns_last_pid",
 		.maxlen = sizeof(int),
 		.mode = 0666, /* permissions are checked in the handler */
 		.proc_handler = pid_ns_ctl_handler,
 		.extra1 = &zero,
 		.extra2 = &pid_max,
 	},
 	{ }
 };
 static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
 #endif	/* CONFIG_CHECKPOINT_RESTORE */

 int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
 {
 	if (pid_ns == &init_pid_ns)
 		return 0;

 	switch (cmd) {
 	case LINUX_REBOOT_CMD_RESTART2:
 	case LINUX_REBOOT_CMD_RESTART:
 		pid_ns->reboot = SIGHUP;
 		break;

 	case LINUX_REBOOT_CMD_POWER_OFF:
 	case LINUX_REBOOT_CMD_HALT:
 		pid_ns->reboot = SIGINT;
 		break;
 	default:
 		return -EINVAL;
 	}

 	read_lock(&tasklist_lock);
 	force_sig(SIGKILL, pid_ns->child_reaper);
 	read_unlock(&tasklist_lock);

 	do_exit(0);

 	/* Not reached */
 	return 0;
 }

 static inline struct pid_namespace *to_pid_ns(struct ns_common *ns)
 {
 	return container_of(ns, struct pid_namespace, ns);
 }

 static struct ns_common *pidns_get(struct task_struct *task)
 {
 	struct pid_namespace *ns;

 	rcu_read_lock();
 	ns = task_active_pid_ns(task);
 	if (ns)
 		get_pid_ns(ns);
 	rcu_read_unlock();

 	return ns ? &ns->ns : NULL;
 }

 static void pidns_put(struct ns_common *ns)
 {
 	put_pid_ns(to_pid_ns(ns));
 }

 static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
 {
 	struct pid_namespace *active = task_active_pid_ns(current);
 	struct pid_namespace *ancestor, *new = to_pid_ns(ns);

 	if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) ||
 	    !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
 		return -EPERM;

 	/*
 	 * Only allow entering the current active pid namespace
 	 * or a child of the current active pid namespace.
 	 *
 	 * This is required for fork to return a usable pid value and
 	 * this maintains the property that processes and their
 	 * children can not escape their current pid namespace.
 	 */
 	if (new->level < active->level)
 		return -EINVAL;

 	ancestor = new;
 	while (ancestor->level > active->level)
 		ancestor = ancestor->parent;
 	if (ancestor != active)
 		return -EINVAL;

 	put_pid_ns(nsproxy->pid_ns_for_children);
 	nsproxy->pid_ns_for_children = get_pid_ns(new);
 	return 0;
 }

 static struct ns_common *pidns_get_parent(struct ns_common *ns)
 {
 	struct pid_namespace *active = task_active_pid_ns(current);
 	struct pid_namespace *pid_ns, *p;

 	/* See if the parent is in the current namespace */
 	pid_ns = p = to_pid_ns(ns)->parent;
 	for (;;) {
 		if (!p)
 			return ERR_PTR(-EPERM);
 		if (p == active)
 			break;
 		p = p->parent;
 	}

 	return &get_pid_ns(pid_ns)->ns;
 }

 static struct user_namespace *pidns_owner(struct ns_common *ns)
 {
 	return to_pid_ns(ns)->user_ns;
 }

 const struct proc_ns_operations pidns_operations = {
 	.name		= "pid",
 	.type		= CLONE_NEWPID,
 	.get		= pidns_get,
 	.put		= pidns_put,
 	.install	= pidns_install,
 	.owner		= pidns_owner,
 	.get_parent	= pidns_get_parent,
 };

 static __init int pid_namespaces_init(void)
 {
 	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);

 #ifdef CONFIG_CHECKPOINT_RESTORE
 	register_sysctl_paths(kern_path, pid_ns_ctl_table);
 #endif
 	return 0;
 }

 __initcall(pid_namespaces_init);
	/*
	* Pid namespaces
	*
	* Authors:
	* (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
	* (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
	* Many thanks to Oleg Nesterov for comments and help
	*
	*/

	#include <linux/pid.h>
	#include <linux/pid_namespace.h>
	#include <linux/user_namespace.h>
	#include <linux/syscalls.h>
	#include <linux/err.h>
	#include <linux/acct.h>
	#include <linux/slab.h>
	#include <linux/proc_ns.h>
	#include <linux/reboot.h>
	#include <linux/export.h>

	struct pid_cache {
	int nr_ids;
	char name[16];
	struct kmem_cache *cachep;
	struct list_head list;
	};

	static LIST_HEAD(pid_caches_lh);
	static DEFINE_MUTEX(pid_caches_mutex);
	static struct kmem_cache *pid_ns_cachep;

	/*
	* creates the kmem cache to allocate pids from.
	* @nr_ids: the number of numerical ids this pid will have to carry
	*/

	static struct kmem_cache *create_pid_cachep(int nr_ids)
	{
	struct pid_cache *pcache;
	struct kmem_cache *cachep;

	mutex_lock(&pid_caches_mutex);
	list_for_each_entry(pcache, &pid_caches_lh, list)
	if (pcache->nr_ids == nr_ids)
	goto out;

	pcache = kmalloc(sizeof(struct pid_cache), GFP_KERNEL);
	if (pcache == NULL)
	goto err_alloc;

	snprintf(pcache->name, sizeof(pcache->name), "pid_%d", nr_ids);
	cachep = kmem_cache_create(pcache->name,
	sizeof(struct pid) + (nr_ids - 1) * sizeof(struct upid),
	0, SLAB_HWCACHE_ALIGN, NULL);
	if (cachep == NULL)
	goto err_cachep;

	pcache->nr_ids = nr_ids;
	pcache->cachep = cachep;
	list_add(&pcache->list, &pid_caches_lh);
	out:
	mutex_unlock(&pid_caches_mutex);
	return pcache->cachep;

	err_cachep:
	kfree(pcache);
	err_alloc:
	mutex_unlock(&pid_caches_mutex);
	return NULL;
	}

	static void proc_cleanup_work(struct work_struct *work)
	{
	struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
	pid_ns_release_proc(ns);
	}

	/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
	#define MAX_PID_NS_LEVEL 32

	static struct ucounts inc_pid_namespaces(struct user_namespace ns)
	{
	return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
	}

	static void dec_pid_namespaces(struct ucounts *ucounts)
	{
	dec_ucount(ucounts, UCOUNT_PID_NAMESPACES);
	}

	static struct pid_namespace create_pid_namespace(struct user_namespace user_ns,
	struct pid_namespace *parent_pid_ns)
	{
	struct pid_namespace *ns;
	unsigned int level = parent_pid_ns->level + 1;
	struct ucounts *ucounts;
	int i;
	int err;

	err = -ENOSPC;
	if (level > MAX_PID_NS_LEVEL)
	goto out;
	ucounts = inc_pid_namespaces(user_ns);
	if (!ucounts)
	goto out;

	err = -ENOMEM;
	ns = kmem_cache_zalloc(pid_ns_cachep, GFP_KERNEL);
	if (ns == NULL)
	goto out_dec;

	ns->pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
	if (!ns->pidmap[0].page)
	goto out_free;

	ns->pid_cachep = create_pid_cachep(level + 1);
	if (ns->pid_cachep == NULL)
	goto out_free_map;

	err = ns_alloc_inum(&ns->ns);
	if (err)
	goto out_free_map;
	ns->ns.ops = &pidns_operations;

	kref_init(&ns->kref);
	ns->level = level;
	ns->parent = get_pid_ns(parent_pid_ns);
	ns->user_ns = get_user_ns(user_ns);
	ns->ucounts = ucounts;
	ns->nr_hashed = PIDNS_HASH_ADDING;
	INIT_WORK(&ns->proc_work, proc_cleanup_work);

	set_bit(0, ns->pidmap[0].page);
	atomic_set(&ns->pidmap[0].nr_free, BITS_PER_PAGE - 1);

	for (i = 1; i < PIDMAP_ENTRIES; i++)
	atomic_set(&ns->pidmap[i].nr_free, BITS_PER_PAGE);

	return ns;

	out_free_map:
	kfree(ns->pidmap[0].page);
	out_free:
	kmem_cache_free(pid_ns_cachep, ns);
	out_dec:
	dec_pid_namespaces(ucounts);
	out:
	return ERR_PTR(err);
	}

	static void delayed_free_pidns(struct rcu_head *p)
	{
	struct pid_namespace *ns = container_of(p, struct pid_namespace, rcu);

	dec_pid_namespaces(ns->ucounts);
	put_user_ns(ns->user_ns);

	kmem_cache_free(pid_ns_cachep, ns);
	}

	static void destroy_pid_namespace(struct pid_namespace *ns)
	{
	int i;

	ns_free_inum(&ns->ns);
	for (i = 0; i < PIDMAP_ENTRIES; i++)
	kfree(ns->pidmap[i].page);
	call_rcu(&ns->rcu, delayed_free_pidns);
	}

	struct pid_namespace *copy_pid_ns(unsigned long flags,
	struct user_namespace user_ns, struct pid_namespace old_ns)
	{
	if (!(flags & CLONE_NEWPID))
	return get_pid_ns(old_ns);
	if (task_active_pid_ns(current) != old_ns)
	return ERR_PTR(-EINVAL);
	return create_pid_namespace(user_ns, old_ns);
	}

	static void free_pid_ns(struct kref *kref)
	{
	struct pid_namespace *ns;

	ns = container_of(kref, struct pid_namespace, kref);
	destroy_pid_namespace(ns);
	}

	void put_pid_ns(struct pid_namespace *ns)
	{
	struct pid_namespace *parent;

	while (ns != &init_pid_ns) {
	parent = ns->parent;
	if (!kref_put(&ns->kref, free_pid_ns))
	break;
	ns = parent;
	}
	}
	EXPORT_SYMBOL_GPL(put_pid_ns);

	void zap_pid_ns_processes(struct pid_namespace *pid_ns)
	{
	int nr;
	int rc;
	struct task_struct task, me = current;
	int init_pids = thread_group_leader(me) ? 1 : 2;

	/* Don't allow any more processes into the pid namespace */
	disable_pid_allocation(pid_ns);

	/*
	* Ignore SIGCHLD causing any terminated children to autoreap.
	* This speeds up the namespace shutdown, plus see the comment
	* below.
	*/
	spin_lock_irq(&me->sighand->siglock);
	me->sighand->action[SIGCHLD - 1].sa.sa_handler = SIG_IGN;
	spin_unlock_irq(&me->sighand->siglock);

	/*
	* The last thread in the cgroup-init thread group is terminating.
	* Find remaining pid_ts in the namespace, signal and wait for them
	* to exit.
	*
	* Note: This signals each threads in the namespace - even those that
	* belong to the same thread group, To avoid this, we would have
	* to walk the entire tasklist looking a processes in this
	* namespace, but that could be unnecessarily expensive if the
	* pid namespace has just a few processes. Or we need to
	* maintain a tasklist for each pid namespace.
	*
	*/
	read_lock(&tasklist_lock);
	nr = next_pidmap(pid_ns, 1);
	while (nr > 0) {
	rcu_read_lock();

	task = pid_task(find_vpid(nr), PIDTYPE_PID);
	if (task && !__fatal_signal_pending(task))
	send_sig_info(SIGKILL, SEND_SIG_FORCED, task);

	rcu_read_unlock();

	nr = next_pidmap(pid_ns, nr);
	}
	read_unlock(&tasklist_lock);

	/*
	* Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
	* sys_wait4() will also block until our children traced from the
	* parent namespace are detached and become EXIT_DEAD.
	*/
	do {
	clear_thread_flag(TIF_SIGPENDING);
	rc = sys_wait4(-1, NULL, __WALL, NULL);
	} while (rc != -ECHILD);

	/*
	* sys_wait4() above can't reap the EXIT_DEAD children but we do not
	* really care, we could reparent them to the global init. We could
	* exit and reap ->child_reaper even if it is not the last thread in
	* this pid_ns, free_pid(nr_hashed == 0) calls proc_cleanup_work(),
	* pid_ns can not go away until proc_kill_sb() drops the reference.
	*
	* But this ns can also have other tasks injected by setns()+fork().
	* Again, ignoring the user visible semantics we do not really need
	* to wait until they are all reaped, but they can be reparented to
	* us and thus we need to ensure that pid->child_reaper stays valid
	* until they all go away. See free_pid()->wake_up_process().
	*
	* We rely on ignored SIGCHLD, an injected zombie must be autoreaped
	* if reparented.
	*/
	for (;;) {
	set_current_state(TASK_UNINTERRUPTIBLE);
	if (pid_ns->nr_hashed == init_pids)
	break;
	schedule();
	}
	__set_current_state(TASK_RUNNING);

	if (pid_ns->reboot)
	current->signal->group_exit_code = pid_ns->reboot;

	acct_exit_ns(pid_ns);
	return;
	}

	#ifdef CONFIG_CHECKPOINT_RESTORE
	static int pid_ns_ctl_handler(struct ctl_table *table, int write,
	void __user buffer, size_t lenp, loff_t *ppos)
	{
	struct pid_namespace *pid_ns = task_active_pid_ns(current);
	struct ctl_table tmp = *table;

	if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
	return -EPERM;

	/*
	* Writing directly to ns' last_pid field is OK, since this field
	* is volatile in a living namespace anyway and a code writing to
	* it should synchronize its usage with external means.
	*/

	tmp.data = &pid_ns->last_pid;
	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
	}

	extern int pid_max;
	static int zero = 0;
	static struct ctl_table pid_ns_ctl_table[] = {
	{
	.procname = "ns_last_pid",
	.maxlen = sizeof(int),
	.mode = 0666, /* permissions are checked in the handler */
	.proc_handler = pid_ns_ctl_handler,
	.extra1 = &zero,
	.extra2 = &pid_max,
	},
	{ }
	};
	static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
	#endif /* CONFIG_CHECKPOINT_RESTORE */

	int reboot_pid_ns(struct pid_namespace *pid_ns, int cmd)
	{
	if (pid_ns == &init_pid_ns)
	return 0;

	switch (cmd) {
	case LINUX_REBOOT_CMD_RESTART2:
	case LINUX_REBOOT_CMD_RESTART:
	pid_ns->reboot = SIGHUP;
	break;

	case LINUX_REBOOT_CMD_POWER_OFF:
	case LINUX_REBOOT_CMD_HALT:
	pid_ns->reboot = SIGINT;
	break;
	default:
	return -EINVAL;
	}

	read_lock(&tasklist_lock);
	force_sig(SIGKILL, pid_ns->child_reaper);
	read_unlock(&tasklist_lock);

	do_exit(0);

	/* Not reached */
	return 0;
	}

	static inline struct pid_namespace to_pid_ns(struct ns_common ns)
	{
	return container_of(ns, struct pid_namespace, ns);
	}

	static struct ns_common pidns_get(struct task_struct task)
	{
	struct pid_namespace *ns;

	rcu_read_lock();
	ns = task_active_pid_ns(task);
	if (ns)
	get_pid_ns(ns);
	rcu_read_unlock();

	return ns ? &ns->ns : NULL;
	}

	static void pidns_put(struct ns_common *ns)
	{
	put_pid_ns(to_pid_ns(ns));
	}

	static int pidns_install(struct nsproxy nsproxy, struct ns_common ns)
	{
	struct pid_namespace *active = task_active_pid_ns(current);
	struct pid_namespace ancestor, new = to_pid_ns(ns);

	if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) \|\|
	!ns_capable(current_user_ns(), CAP_SYS_ADMIN))
	return -EPERM;

	/*
	* Only allow entering the current active pid namespace
	* or a child of the current active pid namespace.
	*
	* This is required for fork to return a usable pid value and
	* this maintains the property that processes and their
	* children can not escape their current pid namespace.
	*/
	if (new->level < active->level)
	return -EINVAL;

	ancestor = new;
	while (ancestor->level > active->level)
	ancestor = ancestor->parent;
	if (ancestor != active)
	return -EINVAL;

	put_pid_ns(nsproxy->pid_ns_for_children);
	nsproxy->pid_ns_for_children = get_pid_ns(new);
	return 0;
	}

	static struct ns_common pidns_get_parent(struct ns_common ns)
	{
	struct pid_namespace *active = task_active_pid_ns(current);
	struct pid_namespace pid_ns, p;

	/* See if the parent is in the current namespace */
	pid_ns = p = to_pid_ns(ns)->parent;
	for (;;) {
	if (!p)
	return ERR_PTR(-EPERM);
	if (p == active)
	break;
	p = p->parent;
	}

	return &get_pid_ns(pid_ns)->ns;
	}

	static struct user_namespace pidns_owner(struct ns_common ns)
	{
	return to_pid_ns(ns)->user_ns;
	}

	const struct proc_ns_operations pidns_operations = {
	.name = "pid",
	.type = CLONE_NEWPID,
	.get = pidns_get,
	.put = pidns_put,
	.install = pidns_install,
	.owner = pidns_owner,
	.get_parent = pidns_get_parent,
	};

	static __init int pid_namespaces_init(void)
	{
	pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);

	#ifdef CONFIG_CHECKPOINT_RESTORE
	register_sysctl_paths(kern_path, pid_ns_ctl_table);
	#endif
	return 0;
	}

	__initcall(pid_namespaces_init);