kernel/user.c - kernel/msm - Gitiles

 /*
  * The "user cache".
  *
  * (C) Copyright 1991-2000 Linus Torvalds
  *
  * We have a per-user structure to keep track of how many
  * processes, files etc the user has claimed, in order to be
  * able to have per-user limits for system resources.
  */

 #include <linux/init.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/bitops.h>
 #include <linux/key.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/user_namespace.h>

 /*
  * UID task count cache, to get fast user lookup in "alloc_uid"
  * when changing user ID's (ie setuid() and friends).
  */

 #define UIDHASH_MASK		(UIDHASH_SZ - 1)
 #define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
 #define uidhashentry(ns, uid)	((ns)->uidhash_table + __uidhashfn((uid)))

 static struct kmem_cache *uid_cachep;

 /*
  * The uidhash_lock is mostly taken from process context, but it is
  * occasionally also taken from softirq/tasklet context, when
  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  * But free_uid() is also called with local interrupts disabled, and running
  * local_bh_enable() with local interrupts disabled is an error - we'll run
  * softirq callbacks, and they can unconditionally enable interrupts, and
  * the caller of free_uid() didn't expect that..
  */
 static DEFINE_SPINLOCK(uidhash_lock);

 struct user_struct root_user = {
 	.__count	= ATOMIC_INIT(1),
 	.processes	= ATOMIC_INIT(1),
 	.files		= ATOMIC_INIT(0),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
 #ifdef CONFIG_KEYS
 	.uid_keyring	= &root_user_keyring,
 	.session_keyring = &root_session_keyring,
 #endif
 #ifdef CONFIG_FAIR_USER_SCHED
 	.tg		= &init_task_group,
 #endif
 };

 /*
  * These routines must be called with the uidhash spinlock held!
  */
 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 {
 	hlist_add_head(&up->uidhash_node, hashent);
 }

 static void uid_hash_remove(struct user_struct *up)
 {
 	hlist_del_init(&up->uidhash_node);
 }

 static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
 {
 	struct user_struct *user;
 	struct hlist_node *h;

 	hlist_for_each_entry(user, h, hashent, uidhash_node) {
 		if (user->uid == uid) {
 			atomic_inc(&user->__count);
 			return user;
 		}
 	}

 	return NULL;
 }

 #ifdef CONFIG_FAIR_USER_SCHED

 static void sched_destroy_user(struct user_struct *up)
 {
 	sched_destroy_group(up->tg);
 }

 static int sched_create_user(struct user_struct *up)
 {
 	int rc = 0;

 	up->tg = sched_create_group();
 	if (IS_ERR(up->tg))
 		rc = -ENOMEM;

 	return rc;
 }

 static void sched_switch_user(struct task_struct *p)
 {
 	sched_move_task(p);
 }

 #else	/* CONFIG_FAIR_USER_SCHED */

 static void sched_destroy_user(struct user_struct *up) { }
 static int sched_create_user(struct user_struct *up) { return 0; }
 static void sched_switch_user(struct task_struct *p) { }

 #endif	/* CONFIG_FAIR_USER_SCHED */

 #if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)

 static struct kobject uids_kobject; /* represents /sys/kernel/uids directory */
 static DEFINE_MUTEX(uids_mutex);

 static inline void uids_mutex_lock(void)
 {
 	mutex_lock(&uids_mutex);
 }

 static inline void uids_mutex_unlock(void)
 {
 	mutex_unlock(&uids_mutex);
 }

 /* return cpu shares held by the user */
 static ssize_t cpu_shares_show(struct kset *kset, char *buffer)
 {
 	struct user_struct *up = container_of(kset, struct user_struct, kset);

 	return sprintf(buffer, "%lu\n", sched_group_shares(up->tg));
 }

 /* modify cpu shares held by the user */
 static ssize_t cpu_shares_store(struct kset *kset, const char *buffer,
 				size_t size)
 {
 	struct user_struct *up = container_of(kset, struct user_struct, kset);
 	unsigned long shares;
 	int rc;

 	sscanf(buffer, "%lu", &shares);

 	rc = sched_group_set_shares(up->tg, shares);

 	return (rc ? rc : size);
 }

 static void user_attr_init(struct subsys_attribute *sa, char *name, int mode)
 {
 	sa->attr.name = name;
 	sa->attr.mode = mode;
 	sa->show = cpu_shares_show;
 	sa->store = cpu_shares_store;
 }

 /* Create "/sys/kernel/uids/<uid>" directory and
  *  "/sys/kernel/uids/<uid>/cpu_share" file for this user.
  */
 static int user_kobject_create(struct user_struct *up)
 {
 	struct kset *kset = &up->kset;
 	struct kobject *kobj = &kset->kobj;
 	int error;

 	memset(kset, 0, sizeof(struct kset));
 	kobj->parent = &uids_kobject;	/* create under /sys/kernel/uids dir */
 	kobject_set_name(kobj, "%d", up->uid);
 	kset_init(kset);
 	user_attr_init(&up->user_attr, "cpu_share", 0644);

 	error = kobject_add(kobj);
 	if (error)
 		goto done;

 	error = sysfs_create_file(kobj, &up->user_attr.attr);
 	if (error)
 		kobject_del(kobj);

 	kobject_uevent(kobj, KOBJ_ADD);

 done:
 	return error;
 }

 /* create these in sysfs filesystem:
  * 	"/sys/kernel/uids" directory
  * 	"/sys/kernel/uids/0" directory (for root user)
  * 	"/sys/kernel/uids/0/cpu_share" file (for root user)
  */
 int __init uids_kobject_init(void)
 {
 	int error;

 	/* create under /sys/kernel dir */
 	uids_kobject.parent = &kernel_subsys.kobj;
 	uids_kobject.kset = &kernel_subsys;
 	kobject_set_name(&uids_kobject, "uids");
 	kobject_init(&uids_kobject);

 	error = kobject_add(&uids_kobject);
 	if (!error)
 		error = user_kobject_create(&root_user);

 	return error;
 }

 /* work function to remove sysfs directory for a user and free up
  * corresponding structures.
  */
 static void remove_user_sysfs_dir(struct work_struct *w)
 {
 	struct user_struct *up = container_of(w, struct user_struct, work);
 	struct kobject *kobj = &up->kset.kobj;
 	unsigned long flags;
 	int remove_user = 0;

 	/* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 	 * atomic.
 	 */
 	uids_mutex_lock();

 	local_irq_save(flags);

 	if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 		uid_hash_remove(up);
 		remove_user = 1;
 		spin_unlock_irqrestore(&uidhash_lock, flags);
 	} else {
 		local_irq_restore(flags);
 	}

 	if (!remove_user)
 		goto done;

 	sysfs_remove_file(kobj, &up->user_attr.attr);
 	kobject_uevent(kobj, KOBJ_REMOVE);
 	kobject_del(kobj);

 	sched_destroy_user(up);
 	key_put(up->uid_keyring);
 	key_put(up->session_keyring);
 	kmem_cache_free(uid_cachep, up);

 done:
 	uids_mutex_unlock();
 }

 /* IRQs are disabled and uidhash_lock is held upon function entry.
  * IRQ state (as stored in flags) is restored and uidhash_lock released
  * upon function exit.
  */
 static inline void free_user(struct user_struct *up, unsigned long flags)
 {
 	/* restore back the count */
 	atomic_inc(&up->__count);
 	spin_unlock_irqrestore(&uidhash_lock, flags);

 	INIT_WORK(&up->work, remove_user_sysfs_dir);
 	schedule_work(&up->work);
 }

 #else	/* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */

 static inline int user_kobject_create(struct user_struct *up) { return 0; }
 static inline void uids_mutex_lock(void) { }
 static inline void uids_mutex_unlock(void) { }

 /* IRQs are disabled and uidhash_lock is held upon function entry.
  * IRQ state (as stored in flags) is restored and uidhash_lock released
  * upon function exit.
  */
 static inline void free_user(struct user_struct *up, unsigned long flags)
 {
 	uid_hash_remove(up);
 	spin_unlock_irqrestore(&uidhash_lock, flags);
 	sched_destroy_user(up);
 	key_put(up->uid_keyring);
 	key_put(up->session_keyring);
 	kmem_cache_free(uid_cachep, up);
 }

 #endif

 /*
  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
  * caller must undo that ref with free_uid().
  *
  * If the user_struct could not be found, return NULL.
  */
 struct user_struct *find_user(uid_t uid)
 {
 	struct user_struct *ret;
 	unsigned long flags;
 	struct user_namespace *ns = current->nsproxy->user_ns;

 	spin_lock_irqsave(&uidhash_lock, flags);
 	ret = uid_hash_find(uid, uidhashentry(ns, uid));
 	spin_unlock_irqrestore(&uidhash_lock, flags);
 	return ret;
 }

 void free_uid(struct user_struct *up)
 {
 	unsigned long flags;

 	if (!up)
 		return;

 	local_irq_save(flags);
 	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 		free_user(up, flags);
 	else
 		local_irq_restore(flags);
 }

 struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 {
 	struct hlist_head *hashent = uidhashentry(ns, uid);
 	struct user_struct *up;

 	/* Make uid_hash_find() + user_kobject_create() + uid_hash_insert()
 	 * atomic.
 	 */
 	uids_mutex_lock();

 	spin_lock_irq(&uidhash_lock);
 	up = uid_hash_find(uid, hashent);
 	spin_unlock_irq(&uidhash_lock);

 	if (!up) {
 		struct user_struct *new;

 		new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
 		if (!new)
 			return NULL;
 		new->uid = uid;
 		atomic_set(&new->__count, 1);
 		atomic_set(&new->processes, 0);
 		atomic_set(&new->files, 0);
 		atomic_set(&new->sigpending, 0);
 #ifdef CONFIG_INOTIFY_USER
 		atomic_set(&new->inotify_watches, 0);
 		atomic_set(&new->inotify_devs, 0);
 #endif
 #ifdef CONFIG_POSIX_MQUEUE
 		new->mq_bytes = 0;
 #endif
 		new->locked_shm = 0;

 		if (alloc_uid_keyring(new, current) < 0) {
 			kmem_cache_free(uid_cachep, new);
 			return NULL;
 		}

 		if (sched_create_user(new) < 0) {
 			key_put(new->uid_keyring);
 			key_put(new->session_keyring);
 			kmem_cache_free(uid_cachep, new);
 			return NULL;
 		}

 		if (user_kobject_create(new)) {
 			sched_destroy_user(new);
 			key_put(new->uid_keyring);
 			key_put(new->session_keyring);
 			kmem_cache_free(uid_cachep, new);
 			uids_mutex_unlock();
 			return NULL;
 		}

 		/*
 		 * Before adding this, check whether we raced
 		 * on adding the same user already..
 		 */
 		spin_lock_irq(&uidhash_lock);
 		up = uid_hash_find(uid, hashent);
 		if (up) {
 			/* This case is not possible when CONFIG_FAIR_USER_SCHED
 			 * is defined, since we serialize alloc_uid() using
 			 * uids_mutex. Hence no need to call
 			 * sched_destroy_user() or remove_user_sysfs_dir().
 			 */
 			key_put(new->uid_keyring);
 			key_put(new->session_keyring);
 			kmem_cache_free(uid_cachep, new);
 		} else {
 			uid_hash_insert(new, hashent);
 			up = new;
 		}
 		spin_unlock_irq(&uidhash_lock);

 	}

 	uids_mutex_unlock();

 	return up;
 }

 void switch_uid(struct user_struct *new_user)
 {
 	struct user_struct *old_user;

 	/* What if a process setreuid()'s and this brings the
 	 * new uid over his NPROC rlimit?  We can check this now
 	 * cheaply with the new uid cache, so if it matters
 	 * we should be checking for it.  -DaveM
 	 */
 	old_user = current->user;
 	atomic_inc(&new_user->processes);
 	atomic_dec(&old_user->processes);
 	switch_uid_keyring(new_user);
 	current->user = new_user;
 	sched_switch_user(current);

 	/*
 	 * We need to synchronize with __sigqueue_alloc()
 	 * doing a get_uid(p->user).. If that saw the old
 	 * user value, we need to wait until it has exited
 	 * its critical region before we can free the old
 	 * structure.
 	 */
 	smp_mb();
 	spin_unlock_wait(&current->sighand->siglock);

 	free_uid(old_user);
 	suid_keys(current);
 }

 void release_uids(struct user_namespace *ns)
 {
 	int i;
 	unsigned long flags;
 	struct hlist_head *head;
 	struct hlist_node *nd;

 	spin_lock_irqsave(&uidhash_lock, flags);
 	/*
 	 * collapse the chains so that the user_struct-s will
 	 * be still alive, but not in hashes. subsequent free_uid()
 	 * will free them.
 	 */
 	for (i = 0; i < UIDHASH_SZ; i++) {
 		head = ns->uidhash_table + i;
 		while (!hlist_empty(head)) {
 			nd = head->first;
 			hlist_del_init(nd);
 		}
 	}
 	spin_unlock_irqrestore(&uidhash_lock, flags);

 	free_uid(ns->root_user);
 }

 static int __init uid_cache_init(void)
 {
 	int n;

 	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

 	for(n = 0; n < UIDHASH_SZ; ++n)
 		INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);

 	/* Insert the root user immediately (init already runs as root) */
 	spin_lock_irq(&uidhash_lock);
 	uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 	spin_unlock_irq(&uidhash_lock);

 	return 0;
 }

 module_init(uid_cache_init);
	/*
	* The "user cache".
	*
	* (C) Copyright 1991-2000 Linus Torvalds
	*
	* We have a per-user structure to keep track of how many
	* processes, files etc the user has claimed, in order to be
	* able to have per-user limits for system resources.
	*/

	#include <linux/init.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/bitops.h>
	#include <linux/key.h>
	#include <linux/interrupt.h>
	#include <linux/module.h>
	#include <linux/user_namespace.h>

	/*
	* UID task count cache, to get fast user lookup in "alloc_uid"
	* when changing user ID's (ie setuid() and friends).
	*/

	#define UIDHASH_MASK (UIDHASH_SZ - 1)
	#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
	#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))

	static struct kmem_cache *uid_cachep;

	/*
	* The uidhash_lock is mostly taken from process context, but it is
	* occasionally also taken from softirq/tasklet context, when
	* task-structs get RCU-freed. Hence all locking must be softirq-safe.
	* But free_uid() is also called with local interrupts disabled, and running
	* local_bh_enable() with local interrupts disabled is an error - we'll run
	* softirq callbacks, and they can unconditionally enable interrupts, and
	* the caller of free_uid() didn't expect that..
	*/
	static DEFINE_SPINLOCK(uidhash_lock);

	struct user_struct root_user = {
	.__count = ATOMIC_INIT(1),
	.processes = ATOMIC_INIT(1),
	.files = ATOMIC_INIT(0),
	.sigpending = ATOMIC_INIT(0),
	.locked_shm = 0,
	#ifdef CONFIG_KEYS
	.uid_keyring = &root_user_keyring,
	.session_keyring = &root_session_keyring,
	#endif
	#ifdef CONFIG_FAIR_USER_SCHED
	.tg = &init_task_group,
	#endif
	};

	/*
	* These routines must be called with the uidhash spinlock held!
	*/
	static void uid_hash_insert(struct user_struct up, struct hlist_head hashent)
	{
	hlist_add_head(&up->uidhash_node, hashent);
	}

	static void uid_hash_remove(struct user_struct *up)
	{
	hlist_del_init(&up->uidhash_node);
	}

	static struct user_struct uid_hash_find(uid_t uid, struct hlist_head hashent)
	{
	struct user_struct *user;
	struct hlist_node *h;

	hlist_for_each_entry(user, h, hashent, uidhash_node) {
	if (user->uid == uid) {
	atomic_inc(&user->__count);
	return user;
	}
	}

	return NULL;
	}

	#ifdef CONFIG_FAIR_USER_SCHED

	static void sched_destroy_user(struct user_struct *up)
	{
	sched_destroy_group(up->tg);
	}

	static int sched_create_user(struct user_struct *up)
	{
	int rc = 0;

	up->tg = sched_create_group();
	if (IS_ERR(up->tg))
	rc = -ENOMEM;

	return rc;
	}

	static void sched_switch_user(struct task_struct *p)
	{
	sched_move_task(p);
	}

	#else /* CONFIG_FAIR_USER_SCHED */

	static void sched_destroy_user(struct user_struct *up) { }
	static int sched_create_user(struct user_struct *up) { return 0; }
	static void sched_switch_user(struct task_struct *p) { }

	#endif /* CONFIG_FAIR_USER_SCHED */

	#if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)

	static struct kobject uids_kobject; /* represents /sys/kernel/uids directory */
	static DEFINE_MUTEX(uids_mutex);

	static inline void uids_mutex_lock(void)
	{
	mutex_lock(&uids_mutex);
	}

	static inline void uids_mutex_unlock(void)
	{
	mutex_unlock(&uids_mutex);
	}

	/* return cpu shares held by the user */
	static ssize_t cpu_shares_show(struct kset kset, char buffer)
	{
	struct user_struct *up = container_of(kset, struct user_struct, kset);

	return sprintf(buffer, "%lu\n", sched_group_shares(up->tg));
	}

	/* modify cpu shares held by the user */
	static ssize_t cpu_shares_store(struct kset kset, const char buffer,
	size_t size)
	{
	struct user_struct *up = container_of(kset, struct user_struct, kset);
	unsigned long shares;
	int rc;

	sscanf(buffer, "%lu", &shares);

	rc = sched_group_set_shares(up->tg, shares);

	return (rc ? rc : size);
	}

	static void user_attr_init(struct subsys_attribute sa, char name, int mode)
	{
	sa->attr.name = name;
	sa->attr.mode = mode;
	sa->show = cpu_shares_show;
	sa->store = cpu_shares_store;
	}

	/* Create "/sys/kernel/uids/<uid>" directory and
	* "/sys/kernel/uids/<uid>/cpu_share" file for this user.
	*/
	static int user_kobject_create(struct user_struct *up)
	{
	struct kset *kset = &up->kset;
	struct kobject *kobj = &kset->kobj;
	int error;

	memset(kset, 0, sizeof(struct kset));
	kobj->parent = &uids_kobject; /* create under /sys/kernel/uids dir */
	kobject_set_name(kobj, "%d", up->uid);
	kset_init(kset);
	user_attr_init(&up->user_attr, "cpu_share", 0644);

	error = kobject_add(kobj);
	if (error)
	goto done;

	error = sysfs_create_file(kobj, &up->user_attr.attr);
	if (error)
	kobject_del(kobj);

	kobject_uevent(kobj, KOBJ_ADD);

	done:
	return error;
	}

	/* create these in sysfs filesystem:
	* "/sys/kernel/uids" directory
	* "/sys/kernel/uids/0" directory (for root user)
	* "/sys/kernel/uids/0/cpu_share" file (for root user)
	*/
	int __init uids_kobject_init(void)
	{
	int error;

	/* create under /sys/kernel dir */
	uids_kobject.parent = &kernel_subsys.kobj;
	uids_kobject.kset = &kernel_subsys;
	kobject_set_name(&uids_kobject, "uids");
	kobject_init(&uids_kobject);

	error = kobject_add(&uids_kobject);
	if (!error)
	error = user_kobject_create(&root_user);

	return error;
	}

	/* work function to remove sysfs directory for a user and free up
	* corresponding structures.
	*/
	static void remove_user_sysfs_dir(struct work_struct *w)
	{
	struct user_struct *up = container_of(w, struct user_struct, work);
	struct kobject *kobj = &up->kset.kobj;
	unsigned long flags;
	int remove_user = 0;

	/* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
	* atomic.
	*/
	uids_mutex_lock();

	local_irq_save(flags);

	if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
	uid_hash_remove(up);
	remove_user = 1;
	spin_unlock_irqrestore(&uidhash_lock, flags);
	} else {
	local_irq_restore(flags);
	}

	if (!remove_user)
	goto done;

	sysfs_remove_file(kobj, &up->user_attr.attr);
	kobject_uevent(kobj, KOBJ_REMOVE);
	kobject_del(kobj);

	sched_destroy_user(up);
	key_put(up->uid_keyring);
	key_put(up->session_keyring);
	kmem_cache_free(uid_cachep, up);

	done:
	uids_mutex_unlock();
	}

	/* IRQs are disabled and uidhash_lock is held upon function entry.
	* IRQ state (as stored in flags) is restored and uidhash_lock released
	* upon function exit.
	*/
	static inline void free_user(struct user_struct *up, unsigned long flags)
	{
	/* restore back the count */
	atomic_inc(&up->__count);
	spin_unlock_irqrestore(&uidhash_lock, flags);

	INIT_WORK(&up->work, remove_user_sysfs_dir);
	schedule_work(&up->work);
	}

	#else /* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */

	static inline int user_kobject_create(struct user_struct *up) { return 0; }
	static inline void uids_mutex_lock(void) { }
	static inline void uids_mutex_unlock(void) { }

	/* IRQs are disabled and uidhash_lock is held upon function entry.
	* IRQ state (as stored in flags) is restored and uidhash_lock released
	* upon function exit.
	*/
	static inline void free_user(struct user_struct *up, unsigned long flags)
	{
	uid_hash_remove(up);
	spin_unlock_irqrestore(&uidhash_lock, flags);
	sched_destroy_user(up);
	key_put(up->uid_keyring);
	key_put(up->session_keyring);
	kmem_cache_free(uid_cachep, up);
	}

	#endif

	/*
	* Locate the user_struct for the passed UID. If found, take a ref on it. The
	* caller must undo that ref with free_uid().
	*
	* If the user_struct could not be found, return NULL.
	*/
	struct user_struct *find_user(uid_t uid)
	{
	struct user_struct *ret;
	unsigned long flags;
	struct user_namespace *ns = current->nsproxy->user_ns;

	spin_lock_irqsave(&uidhash_lock, flags);
	ret = uid_hash_find(uid, uidhashentry(ns, uid));
	spin_unlock_irqrestore(&uidhash_lock, flags);
	return ret;
	}

	void free_uid(struct user_struct *up)
	{
	unsigned long flags;

	if (!up)
	return;

	local_irq_save(flags);
	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
	free_user(up, flags);
	else
	local_irq_restore(flags);
	}

	struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
	{
	struct hlist_head *hashent = uidhashentry(ns, uid);
	struct user_struct *up;

	/* Make uid_hash_find() + user_kobject_create() + uid_hash_insert()
	* atomic.
	*/
	uids_mutex_lock();

	spin_lock_irq(&uidhash_lock);
	up = uid_hash_find(uid, hashent);
	spin_unlock_irq(&uidhash_lock);

	if (!up) {
	struct user_struct *new;

	new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
	if (!new)
	return NULL;
	new->uid = uid;
	atomic_set(&new->__count, 1);
	atomic_set(&new->processes, 0);
	atomic_set(&new->files, 0);
	atomic_set(&new->sigpending, 0);
	#ifdef CONFIG_INOTIFY_USER
	atomic_set(&new->inotify_watches, 0);
	atomic_set(&new->inotify_devs, 0);
	#endif
	#ifdef CONFIG_POSIX_MQUEUE
	new->mq_bytes = 0;
	#endif
	new->locked_shm = 0;

	if (alloc_uid_keyring(new, current) < 0) {
	kmem_cache_free(uid_cachep, new);
	return NULL;
	}

	if (sched_create_user(new) < 0) {
	key_put(new->uid_keyring);
	key_put(new->session_keyring);
	kmem_cache_free(uid_cachep, new);
	return NULL;
	}

	if (user_kobject_create(new)) {
	sched_destroy_user(new);
	key_put(new->uid_keyring);
	key_put(new->session_keyring);
	kmem_cache_free(uid_cachep, new);
	uids_mutex_unlock();
	return NULL;
	}

	/*
	* Before adding this, check whether we raced
	* on adding the same user already..
	*/
	spin_lock_irq(&uidhash_lock);
	up = uid_hash_find(uid, hashent);
	if (up) {
	/* This case is not possible when CONFIG_FAIR_USER_SCHED
	* is defined, since we serialize alloc_uid() using
	* uids_mutex. Hence no need to call
	* sched_destroy_user() or remove_user_sysfs_dir().
	*/
	key_put(new->uid_keyring);
	key_put(new->session_keyring);
	kmem_cache_free(uid_cachep, new);
	} else {
	uid_hash_insert(new, hashent);
	up = new;
	}
	spin_unlock_irq(&uidhash_lock);

	}

	uids_mutex_unlock();

	return up;
	}

	void switch_uid(struct user_struct *new_user)
	{
	struct user_struct *old_user;

	/* What if a process setreuid()'s and this brings the
	* new uid over his NPROC rlimit? We can check this now
	* cheaply with the new uid cache, so if it matters
	* we should be checking for it. -DaveM
	*/
	old_user = current->user;
	atomic_inc(&new_user->processes);
	atomic_dec(&old_user->processes);
	switch_uid_keyring(new_user);
	current->user = new_user;
	sched_switch_user(current);

	/*
	* We need to synchronize with __sigqueue_alloc()
	* doing a get_uid(p->user).. If that saw the old
	* user value, we need to wait until it has exited
	* its critical region before we can free the old
	* structure.
	*/
	smp_mb();
	spin_unlock_wait(&current->sighand->siglock);

	free_uid(old_user);
	suid_keys(current);
	}

	void release_uids(struct user_namespace *ns)
	{
	int i;
	unsigned long flags;
	struct hlist_head *head;
	struct hlist_node *nd;

	spin_lock_irqsave(&uidhash_lock, flags);
	/*
	* collapse the chains so that the user_struct-s will
	* be still alive, but not in hashes. subsequent free_uid()
	* will free them.
	*/
	for (i = 0; i < UIDHASH_SZ; i++) {
	head = ns->uidhash_table + i;
	while (!hlist_empty(head)) {
	nd = head->first;
	hlist_del_init(nd);
	}
	}
	spin_unlock_irqrestore(&uidhash_lock, flags);

	free_uid(ns->root_user);
	}

	static int __init uid_cache_init(void)
	{
	int n;

	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
	0, SLAB_HWCACHE_ALIGN\|SLAB_PANIC, NULL);

	for(n = 0; n < UIDHASH_SZ; ++n)
	INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);

	/* Insert the root user immediately (init already runs as root) */
	spin_lock_irq(&uidhash_lock);
	uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
	spin_unlock_irq(&uidhash_lock);

	return 0;
	}

	module_init(uid_cache_init);