/*
   * 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/export.h>

  #include <linux/user_namespace.h>

  /*
   * userns count is 1 for root user, 1 for init_uts_ns,
   * and 1 for... ?
   */

  struct user_namespace init_user_ns = {
  	.kref = {

  		.refcount	= ATOMIC_INIT(3),

  	},

  	.creator = &root_user,

  };
  EXPORT_SYMBOL_GPL(init_user_ns);

  /*
   * 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);

  /* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->user_ns */

  struct user_struct root_user = {

  	.__count	= ATOMIC_INIT(2),

  	.processes	= ATOMIC_INIT(1),
  	.files		= ATOMIC_INIT(0),
  	.sigpending	= ATOMIC_INIT(0),

  	.locked_shm     = 0,

  	.user_ns	= &init_user_ns,

  };

  /*
   * 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);

  	put_user_ns(up->user_ns);

  }

  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;
  }

  /* 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 void free_user(struct user_struct *up, unsigned long flags)

  	__releases(&uidhash_lock)

  {
  	uid_hash_remove(up);
  	spin_unlock_irqrestore(&uidhash_lock, flags);

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

  /*
   * 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_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, *new;

  	spin_lock_irq(&uidhash_lock);

  	up = uid_hash_find(uid, hashent);

  	spin_unlock_irq(&uidhash_lock);

  
  	if (!up) {

  		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);

  		if (!new)
  			goto out_unlock;

  		new->uid = uid;
  		atomic_set(&new->__count, 1);

  		new->user_ns = get_user_ns(ns);

  		/*
  		 * 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) {

  			put_user_ns(ns);

  			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);

  	}

  	return up;

  out_unlock:

  	return NULL;

  }

  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);