/*
   *  This program is free software; you can redistribute it and/or
   *  modify it under the terms of the GNU General Public License as
   *  published by the Free Software Foundation, version 2 of the
   *  License.
   */
  
  #include <linux/module.h>

  #include <linux/nsproxy.h>

  #include <linux/slab.h>

  #include <linux/user_namespace.h>

  #include <linux/highuid.h>

  #include <linux/cred.h>

  static struct kmem_cache *user_ns_cachep __read_mostly;

  /*

   * Create a new user namespace, deriving the creator from the user in the
   * passed credentials, and replacing that user with the new root user for the
   * new namespace.
   *
   * This is called by copy_creds(), which will finish setting the target task's
   * credentials.

   */

  int create_user_ns(struct cred *new)

  {
  	struct user_namespace *ns;

  	struct user_struct *root_user;

  	int n;

  	ns = kmem_cache_alloc(user_ns_cachep, GFP_KERNEL);

  	if (!ns)

  		return -ENOMEM;

  
  	kref_init(&ns->kref);
  
  	for (n = 0; n < UIDHASH_SZ; ++n)

  		INIT_HLIST_HEAD(ns->uidhash_table + n);

  	/* Alloc new root user.  */
  	root_user = alloc_uid(ns, 0);
  	if (!root_user) {

  		kmem_cache_free(user_ns_cachep, ns);

  		return -ENOMEM;

  	}

  	/* set the new root user in the credentials under preparation */
  	ns->creator = new->user;
  	new->user = root_user;
  	new->uid = new->euid = new->suid = new->fsuid = 0;
  	new->gid = new->egid = new->sgid = new->fsgid = 0;
  	put_group_info(new->group_info);
  	new->group_info = get_group_info(&init_groups);
  #ifdef CONFIG_KEYS
  	key_put(new->request_key_auth);
  	new->request_key_auth = NULL;
  #endif
  	/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */

  	/* root_user holds a reference to ns, our reference can be dropped */
  	put_user_ns(ns);

  	return 0;

  }

  /*
   * Deferred destructor for a user namespace.  This is required because
   * free_user_ns() may be called with uidhash_lock held, but we need to call
   * back to free_uid() which will want to take the lock again.
   */
  static void free_user_ns_work(struct work_struct *work)

  {

  	struct user_namespace *ns =
  		container_of(work, struct user_namespace, destroyer);

  	free_uid(ns->creator);

  	kmem_cache_free(user_ns_cachep, ns);

  }

  
  void free_user_ns(struct kref *kref)
  {
  	struct user_namespace *ns =
  		container_of(kref, struct user_namespace, kref);
  
  	INIT_WORK(&ns->destroyer, free_user_ns_work);
  	schedule_work(&ns->destroyer);
  }

  EXPORT_SYMBOL(free_user_ns);

  
  uid_t user_ns_map_uid(struct user_namespace *to, const struct cred *cred, uid_t uid)
  {
  	struct user_namespace *tmp;
  
  	if (likely(to == cred->user->user_ns))
  		return uid;
  
  
  	/* Is cred->user the creator of the target user_ns
  	 * or the creator of one of it's parents?
  	 */
  	for ( tmp = to; tmp != &init_user_ns;
  	      tmp = tmp->creator->user_ns ) {
  		if (cred->user == tmp->creator) {
  			return (uid_t)0;
  		}
  	}
  
  	/* No useful relationship so no mapping */
  	return overflowuid;
  }
  
  gid_t user_ns_map_gid(struct user_namespace *to, const struct cred *cred, gid_t gid)
  {
  	struct user_namespace *tmp;
  
  	if (likely(to == cred->user->user_ns))
  		return gid;
  
  	/* Is cred->user the creator of the target user_ns
  	 * or the creator of one of it's parents?
  	 */
  	for ( tmp = to; tmp != &init_user_ns;
  	      tmp = tmp->creator->user_ns ) {
  		if (cred->user == tmp->creator) {
  			return (gid_t)0;
  		}
  	}
  
  	/* No useful relationship so no mapping */
  	return overflowgid;
  }

  
  static __init int user_namespaces_init(void)
  {
  	user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
  	return 0;
  }
  module_init(user_namespaces_init);