/*
   * 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>
  
  /*
   * UID task count cache, to get fast user lookup in "alloc_uid"
   * when changing user ID's (ie setuid() and friends).
   */
  
  #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)
  #define UIDHASH_SZ		(1 << UIDHASH_BITS)
  #define UIDHASH_MASK		(UIDHASH_SZ - 1)
  #define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  #define uidhashentry(uid)	(uidhash_table + __uidhashfn((uid)))
  
  static kmem_cache_t *uid_cachep;
  static struct list_head uidhash_table[UIDHASH_SZ];
  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),
  	.mq_bytes	= 0,
  	.locked_shm     = 0,
  #ifdef CONFIG_KEYS
  	.uid_keyring	= &root_user_keyring,
  	.session_keyring = &root_session_keyring,
  #endif
  };
  
  /*
   * These routines must be called with the uidhash spinlock held!
   */
  static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
  {
  	list_add(&up->uidhash_list, hashent);
  }
  
  static inline void uid_hash_remove(struct user_struct *up)
  {
  	list_del(&up->uidhash_list);
  }
  
  static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
  {
  	struct list_head *up;
  
  	list_for_each(up, hashent) {
  		struct user_struct *user;
  
  		user = list_entry(up, struct user_struct, uidhash_list);
  
  		if(user->uid == uid) {
  			atomic_inc(&user->__count);
  			return user;
  		}
  	}
  
  	return NULL;
  }
  
  /*
   * 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;
  
  	spin_lock(&uidhash_lock);
  	ret = uid_hash_find(uid, uidhashentry(uid));
  	spin_unlock(&uidhash_lock);
  	return ret;
  }
  
  void free_uid(struct user_struct *up)
  {
  	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
  		uid_hash_remove(up);
  		key_put(up->uid_keyring);
  		key_put(up->session_keyring);
  		kmem_cache_free(uid_cachep, up);
  		spin_unlock(&uidhash_lock);
  	}
  }
  
  struct user_struct * alloc_uid(uid_t uid)
  {
  	struct list_head *hashent = uidhashentry(uid);
  	struct user_struct *up;
  
  	spin_lock(&uidhash_lock);
  	up = uid_hash_find(uid, hashent);
  	spin_unlock(&uidhash_lock);
  
  	if (!up) {
  		struct user_struct *new;
  
  		new = kmem_cache_alloc(uid_cachep, SLAB_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
  		atomic_set(&new->inotify_watches, 0);
  		atomic_set(&new->inotify_devs, 0);
  #endif

  
  		new->mq_bytes = 0;
  		new->locked_shm = 0;
  
  		if (alloc_uid_keyring(new) < 0) {
  			kmem_cache_free(uid_cachep, new);
  			return NULL;
  		}
  
  		/*
  		 * Before adding this, check whether we raced
  		 * on adding the same user already..
  		 */
  		spin_lock(&uidhash_lock);
  		up = uid_hash_find(uid, hashent);
  		if (up) {
  			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(&uidhash_lock);
  
  	}
  	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;
  	free_uid(old_user);
  	suid_keys(current);
  }
  
  
  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, NULL);
  
  	for(n = 0; n < UIDHASH_SZ; ++n)
  		INIT_LIST_HEAD(uidhash_table + n);
  
  	/* Insert the root user immediately (init already runs as root) */
  	spin_lock(&uidhash_lock);
  	uid_hash_insert(&root_user, uidhashentry(0));
  	spin_unlock(&uidhash_lock);
  
  	return 0;
  }
  
  module_init(uid_cache_init);