kernel/pid_namespace.c - third_party/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/cred.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>
 #include <linux/sched/task.h>
 #include <linux/sched/signal.h>
 #include <linux/idr.h>

 static DEFINE_MUTEX(pid_caches_mutex);
 static struct kmem_cache *pid_ns_cachep;
 /* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
 #define MAX_PID_NS_LEVEL 32
 /* Write once array, filled from the beginning. */
 static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];

 /*
  * creates the kmem cache to allocate pids from.
  * @level: pid namespace level
  */

 static struct kmem_cache *create_pid_cachep(unsigned int level)
 {
 	/* Level 0 is init_pid_ns.pid_cachep */
 	struct kmem_cache **pkc = &pid_cache[level - 1];
 	struct kmem_cache *kc;
 	char name[4 + 10 + 1];
 	unsigned int len;

 	kc = READ_ONCE(*pkc);
 	if (kc)
 		return kc;

 	snprintf(name, sizeof(name), "pid_%u", level + 1);
 	len = sizeof(struct pid) + level * sizeof(struct upid);
 	mutex_lock(&pid_caches_mutex);
 	/* Name collision forces to do allocation under mutex. */
 	if (!*pkc)
 		*pkc = kmem_cache_create(name, len, 0,
 					 SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT, 0);
 	mutex_unlock(&pid_caches_mutex);
 	/* current can fail, but someone else can succeed. */
 	return READ_ONCE(*pkc);
 }

 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);
 }

 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 err;

 	err = -EINVAL;
 	if (!in_userns(parent_pid_ns->user_ns, user_ns))
 		goto out;

 	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;

 	idr_init(&ns->idr);

 	ns->pid_cachep = create_pid_cachep(level);
 	if (ns->pid_cachep == NULL)
 		goto out_free_idr;

 	err = ns_alloc_inum(&ns->ns);
 	if (err)
 		goto out_free_idr;
 	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->pid_allocated = PIDNS_ADDING;
 	INIT_WORK(&ns->proc_work, proc_cleanup_work);

 	return ns;

 out_free_idr:
 	idr_destroy(&ns->idr);
 	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)
 {
 	ns_free_inum(&ns->ns);

 	idr_destroy(&ns->idr);
 	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;
 	struct pid *pid;

 	/* 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.
 	 *
 	 */
 	rcu_read_lock();
 	read_lock(&tasklist_lock);
 	nr = 2;
 	idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
 		task = pid_task(pid, PIDTYPE_PID);
 		if (task && !__fatal_signal_pending(task))
 			send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
 	}
 	read_unlock(&tasklist_lock);
 	rcu_read_unlock();

 	/*
 	 * Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
 	 * kernel_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 = kernel_wait4(-1, NULL, __WALL, NULL);
 	} while (rc != -ECHILD);

 	/*
 	 * kernel_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(pid_allocated == 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_INTERRUPTIBLE);
 		if (pid_ns->pid_allocated == 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;
 	int ret, next;

 	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.
 	 */

 	next = idr_get_cursor(&pid_ns->idr) - 1;

 	tmp.data = &next;
 	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 	if (!ret && write)
 		idr_set_cursor(&pid_ns->idr, next + 1);

 	return ret;
 }

 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);
 	send_sig(SIGKILL, pid_ns->child_reaper, 1);
 	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 struct ns_common *pidns_for_children_get(struct task_struct *task)
 {
 	struct pid_namespace *ns = NULL;

 	task_lock(task);
 	if (task->nsproxy) {
 		ns = task->nsproxy->pid_ns_for_children;
 		get_pid_ns(ns);
 	}
 	task_unlock(task);

 	if (ns) {
 		read_lock(&tasklist_lock);
 		if (!ns->child_reaper) {
 			put_pid_ns(ns);
 			ns = NULL;
 		}
 		read_unlock(&tasklist_lock);
 	}

 	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,
 };

 const struct proc_ns_operations pidns_for_children_operations = {
 	.name		= "pid_for_children",
 	.real_ns_name	= "pid",
 	.type		= CLONE_NEWPID,
 	.get		= pidns_for_children_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/cred.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>
	#include <linux/sched/task.h>
	#include <linux/sched/signal.h>
	#include <linux/idr.h>

	static DEFINE_MUTEX(pid_caches_mutex);
	static struct kmem_cache *pid_ns_cachep;
	/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
	#define MAX_PID_NS_LEVEL 32
	/* Write once array, filled from the beginning. */
	static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];

	/*
	* creates the kmem cache to allocate pids from.
	* @level: pid namespace level
	*/

	static struct kmem_cache *create_pid_cachep(unsigned int level)
	{
	/* Level 0 is init_pid_ns.pid_cachep */
	struct kmem_cache **pkc = &pid_cache[level - 1];
	struct kmem_cache *kc;
	char name[4 + 10 + 1];
	unsigned int len;

	kc = READ_ONCE(*pkc);
	if (kc)
	return kc;

	snprintf(name, sizeof(name), "pid_%u", level + 1);
	len = sizeof(struct pid) + level * sizeof(struct upid);
	mutex_lock(&pid_caches_mutex);
	/* Name collision forces to do allocation under mutex. */
	if (!*pkc)
	*pkc = kmem_cache_create(name, len, 0,
	SLAB_HWCACHE_ALIGN \| SLAB_ACCOUNT, 0);
	mutex_unlock(&pid_caches_mutex);
	/* current can fail, but someone else can succeed. */
	return READ_ONCE(*pkc);
	}

	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);
	}

	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 err;

	err = -EINVAL;
	if (!in_userns(parent_pid_ns->user_ns, user_ns))
	goto out;

	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;

	idr_init(&ns->idr);

	ns->pid_cachep = create_pid_cachep(level);
	if (ns->pid_cachep == NULL)
	goto out_free_idr;

	err = ns_alloc_inum(&ns->ns);
	if (err)
	goto out_free_idr;
	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->pid_allocated = PIDNS_ADDING;
	INIT_WORK(&ns->proc_work, proc_cleanup_work);

	return ns;

	out_free_idr:
	idr_destroy(&ns->idr);
	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)
	{
	ns_free_inum(&ns->ns);

	idr_destroy(&ns->idr);
	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;
	struct pid *pid;

	/* 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.
	*
	*/
	rcu_read_lock();
	read_lock(&tasklist_lock);
	nr = 2;
	idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
	task = pid_task(pid, PIDTYPE_PID);
	if (task && !__fatal_signal_pending(task))
	send_sig_info(SIGKILL, SEND_SIG_FORCED, task);
	}
	read_unlock(&tasklist_lock);
	rcu_read_unlock();

	/*
	* Reap the EXIT_ZOMBIE children we had before we ignored SIGCHLD.
	* kernel_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 = kernel_wait4(-1, NULL, __WALL, NULL);
	} while (rc != -ECHILD);

	/*
	* kernel_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(pid_allocated == 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_INTERRUPTIBLE);
	if (pid_ns->pid_allocated == 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;
	int ret, next;

	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.
	*/

	next = idr_get_cursor(&pid_ns->idr) - 1;

	tmp.data = &next;
	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
	if (!ret && write)
	idr_set_cursor(&pid_ns->idr, next + 1);

	return ret;
	}

	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);
	send_sig(SIGKILL, pid_ns->child_reaper, 1);
	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 struct ns_common pidns_for_children_get(struct task_struct task)
	{
	struct pid_namespace *ns = NULL;

	task_lock(task);
	if (task->nsproxy) {
	ns = task->nsproxy->pid_ns_for_children;
	get_pid_ns(ns);
	}
	task_unlock(task);

	if (ns) {
	read_lock(&tasklist_lock);
	if (!ns->child_reaper) {
	put_pid_ns(ns);
	ns = NULL;
	}
	read_unlock(&tasklist_lock);
	}

	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,
	};

	const struct proc_ns_operations pidns_for_children_operations = {
	.name = "pid_for_children",
	.real_ns_name = "pid",
	.type = CLONE_NEWPID,
	.get = pidns_for_children_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);