/* Basic authentication token and access key management
 *
 * Copyright (C) 2004-2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * 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; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/poison.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/workqueue.h>
#include <linux/random.h>
#include <linux/err.h>
#include "internal.h"

static struct kmem_cache        *key_jar;
struct rb_root          key_serial_tree; /* tree of keys indexed by serial */
DEFINE_SPINLOCK(key_serial_lock);

struct rb_root  key_user_tree; /* tree of quota records indexed by UID */
DEFINE_SPINLOCK(key_user_lock);

unsigned int key_quota_root_maxkeys = 200;      /* root's key count quota */
unsigned int key_quota_root_maxbytes = 20000;   /* root's key space quota */
unsigned int key_quota_maxkeys = 200;           /* general key count quota */
unsigned int key_quota_maxbytes = 20000;        /* general key space quota */

static LIST_HEAD(key_types_list);
static DECLARE_RWSEM(key_types_sem);

static void key_cleanup(struct work_struct *work);
static DECLARE_WORK(key_cleanup_task, key_cleanup);

/* we serialise key instantiation and link */
DEFINE_MUTEX(key_construction_mutex);

/* any key who's type gets unegistered will be re-typed to this */
static struct key_type key_type_dead = {
        .name           = "dead",
};

#ifdef KEY_DEBUGGING
void __key_check(const struct key *key)
{
        printk("__key_check: key %p {%08x} should be {%08x}\n",
               key, key->magic, KEY_DEBUG_MAGIC);
        BUG();
}
#endif

/*****************************************************************************/
/*
 * get the key quota record for a user, allocating a new record if one doesn't
 * already exist
 */
struct key_user *key_user_lookup(uid_t uid)
{
        struct key_user *candidate = NULL, *user;
        struct rb_node *parent = NULL;
        struct rb_node **p;

 try_again:
        p = &key_user_tree.rb_node;
        spin_lock(&key_user_lock);

        /* search the tree for a user record with a matching UID */
        while (*p) {
                parent = *p;
                user = rb_entry(parent, struct key_user, node);

                if (uid < user->uid)
                        p = &(*p)->rb_left;
                else if (uid > user->uid)
                        p = &(*p)->rb_right;
                else
                        goto found;
        }

        /* if we get here, we failed to find a match in the tree */
        if (!candidate) {
                /* allocate a candidate user record if we don't already have
                 * one */
                spin_unlock(&key_user_lock);

                user = NULL;
                candidate = kmalloc(sizeof(struct key_user), GFP_KERNEL);
                if (unlikely(!candidate))
                        goto out;

                /* the allocation may have scheduled, so we need to repeat the
                 * search lest someone else added the record whilst we were
                 * asleep */
                goto try_again;
        }

        /* if we get here, then the user record still hadn't appeared on the
         * second pass - so we use the candidate record */
        atomic_set(&candidate->usage, 1);
        atomic_set(&candidate->nkeys, 0);
        atomic_set(&candidate->nikeys, 0);
        candidate->uid = uid;
        candidate->qnkeys = 0;
        candidate->qnbytes = 0;
        spin_lock_init(&candidate->lock);
        mutex_init(&candidate->cons_lock);

        rb_link_node(&candidate->node, parent, p);
        rb_insert_color(&candidate->node, &key_user_tree);
        spin_unlock(&key_user_lock);
        user = candidate;
        goto out;

        /* okay - we found a user record for this UID */
 found:
        atomic_inc(&user->usage);
        spin_unlock(&key_user_lock);
        kfree(candidate);
 out:
        return user;

} /* end key_user_lookup() */

/*****************************************************************************/
/*
 * dispose of a user structure
 */
void key_user_put(struct key_user *user)
{
        if (atomic_dec_and_lock(&user->usage, &key_user_lock)) {
                rb_erase(&user->node, &key_user_tree);
                spin_unlock(&key_user_lock);

                kfree(user);
        }

} /* end key_user_put() */

/*****************************************************************************/
/*
 * assign a key the next unique serial number
 * - these are assigned randomly to avoid security issues through covert
 *   channel problems
 */
static inline void key_alloc_serial(struct key *key)
{
        struct rb_node *parent, **p;
        struct key *xkey;

        /* propose a random serial number and look for a hole for it in the
         * serial number tree */
        do {
                get_random_bytes(&key->serial, sizeof(key->serial));

                key->serial >>= 1; /* negative numbers are not permitted */
        } while (key->serial < 3);

        spin_lock(&key_serial_lock);

attempt_insertion:
        parent = NULL;
        p = &key_serial_tree.rb_node;

        while (*p) {
                parent = *p;
                xkey = rb_entry(parent, struct key, serial_node);

                if (key->serial < xkey->serial)
                        p = &(*p)->rb_left;
                else if (key->serial > xkey->serial)
                        p = &(*p)->rb_right;
                else
                        goto serial_exists;
        }

        /* we've found a suitable hole - arrange for this key to occupy it */
        rb_link_node(&key->serial_node, parent, p);
        rb_insert_color(&key->serial_node, &key_serial_tree);

        spin_unlock(&key_serial_lock);
        return;

        /* we found a key with the proposed serial number - walk the tree from
         * that point looking for the next unused serial number */
serial_exists:
        for (;;) {
                key->serial++;
                if (key->serial < 3) {
                        key->serial = 3;
                        goto attempt_insertion;
                }

                parent = rb_next(parent);
                if (!parent)
                        goto attempt_insertion;

                xkey = rb_entry(parent, struct key, serial_node);
                if (key->serial < xkey->serial)
                        goto attempt_insertion;
        }

} /* end key_alloc_serial() */

/*****************************************************************************/
/*
 * allocate a key of the specified type
 * - update the user's quota to reflect the existence of the key
 * - called from a key-type operation with key_types_sem read-locked by
 *   key_create_or_update()
 *   - this prevents unregistration of the key type
 * - upon return the key is as yet uninstantiated; the caller needs to either
 *   instantiate the key or discard it before returning
 */
struct key *key_alloc(struct key_type *type, const char *desc,
                      uid_t uid, gid_t gid, struct task_struct *ctx,
                      key_perm_t perm, unsigned long flags)
{
        struct key_user *user = NULL;
        struct key *key;
        size_t desclen, quotalen;
        int ret;

        key = ERR_PTR(-EINVAL);
        if (!desc || !*desc)
                goto error;

        desclen = strlen(desc) + 1;
        quotalen = desclen + type->def_datalen;

        /* get hold of the key tracking for this user */
        user = key_user_lookup(uid);
        if (!user)
                goto no_memory_1;

        /* check that the user's quota permits allocation of another key and
         * its description */
        if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
                unsigned maxkeys = (uid == 0) ?
                        key_quota_root_maxkeys : key_quota_maxkeys;
                unsigned maxbytes = (uid == 0) ?
                        key_quota_root_maxbytes : key_quota_maxbytes;

                spin_lock(&user->lock);
                if (!(flags & KEY_ALLOC_QUOTA_OVERRUN)) {
                        if (user->qnkeys + 1 >= maxkeys ||
                            user->qnbytes + quotalen >= maxbytes ||
                            user->qnbytes + quotalen < user->qnbytes)
                                goto no_quota;
                }

                user->qnkeys++;
                user->qnbytes += quotalen;
                spin_unlock(&user->lock);
        }

        /* allocate and initialise the key and its description */
        key = kmem_cache_alloc(key_jar, GFP_KERNEL);
        if (!key)
                goto no_memory_2;

        if (desc) {
                key->description = kmemdup(desc, desclen, GFP_KERNEL);
                if (!key->description)
                        goto no_memory_3;
        }

        atomic_set(&key->usage, 1);
        init_rwsem(&key->sem);
        key->type = type;
        key->user = user;
        key->quotalen = quotalen;
        key->datalen = type->def_datalen;
        key->uid = uid;
        key->gid = gid;
        key->perm = perm;
        key->flags = 0;
        key->expiry = 0;
        key->payload.data = NULL;
        key->security = NULL;

        if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
                key->flags |= 1 << KEY_FLAG_IN_QUOTA;

        memset(&key->type_data, 0, sizeof(key->type_data));

#ifdef KEY_DEBUGGING
        key->magic = KEY_DEBUG_MAGIC;
#endif

        /* let the security module know about the key */
        ret = security_key_alloc(key, ctx, flags);
        if (ret < 0)
                goto security_error;

        /* publish the key by giving it a serial number */
        atomic_inc(&user->nkeys);
        key_alloc_serial(key);

error:
        return key;

security_error:
        kfree(key->description);
        kmem_cache_free(key_jar, key);
        if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
                spin_lock(&user->lock);
                user->qnkeys--;
                user->qnbytes -= quotalen;
                spin_unlock(&user->lock);
        }
        key_user_put(user);
        key = ERR_PTR(ret);
        goto error;

no_memory_3:
        kmem_cache_free(key_jar, key);
no_memory_2:
        if (!(flags & KEY_ALLOC_NOT_IN_QUOTA)) {
                spin_lock(&user->lock);
                user->qnkeys--;
                user->qnbytes -= quotalen;
                spin_unlock(&user->lock);
        }
        key_user_put(user);
no_memory_1:
        key = ERR_PTR(-ENOMEM);
        goto error;

no_quota:
        spin_unlock(&user->lock);
        key_user_put(user);
        key = ERR_PTR(-EDQUOT);
        goto error;

} /* end key_alloc() */

EXPORT_SYMBOL(key_alloc);

/*****************************************************************************/
/*
 * reserve an amount of quota for the key's payload
 */
int key_payload_reserve(struct key *key, size_t datalen)
{
        int delta = (int) datalen - key->datalen;
        int ret = 0;

        key_check(key);

        /* contemplate the quota adjustment */
        if (delta != 0 && test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
                unsigned maxbytes = (key->user->uid == 0) ?
                        key_quota_root_maxbytes : key_quota_maxbytes;

                spin_lock(&key->user->lock);

                if (delta > 0 &&
                    (key->user->qnbytes + delta >= maxbytes ||
                     key->user->qnbytes + delta < key->user->qnbytes)) {
                        ret = -EDQUOT;
                }
                else {
                        key->user->qnbytes += delta;
                        key->quotalen += delta;
                }
                spin_unlock(&key->user->lock);
        }

        /* change the recorded data length if that didn't generate an error */
        if (ret == 0)
                key->datalen = datalen;

        return ret;

} /* end key_payload_reserve() */

EXPORT_SYMBOL(key_payload_reserve);

/*****************************************************************************/
/*
 * instantiate a key and link it into the target keyring atomically
 * - called with the target keyring's semaphore writelocked
 */
static int __key_instantiate_and_link(struct key *key,
                                      const void *data,
                                      size_t datalen,
                                      struct key *keyring,
                                      struct key *instkey)
{
        int ret, awaken;

        key_check(key);
        key_check(keyring);

        awaken = 0;
        ret = -EBUSY;

        mutex_lock(&key_construction_mutex);

        /* can't instantiate twice */
        if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
                /* instantiate the key */
                ret = key->type->instantiate(key, data, datalen);

                if (ret == 0) {
                        /* mark the key as being instantiated */
                        atomic_inc(&key->user->nikeys);
                        set_bit(KEY_FLAG_INSTANTIATED, &key->flags);

                        if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
                                awaken = 1;

                        /* and link it into the destination keyring */
                        if (keyring)
                                ret = __key_link(keyring, key);

                        /* disable the authorisation key */
                        if (instkey)
                                key_revoke(instkey);
                }
        }

        mutex_unlock(&key_construction_mutex);

        /* wake up anyone waiting for a key to be constructed */
        if (awaken)
                wake_up_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT);

        return ret;

} /* end __key_instantiate_and_link() */

/*****************************************************************************/
/*
 * instantiate a key and link it into the target keyring atomically
 */
int key_instantiate_and_link(struct key *key,
                             const void *data,
                             size_t datalen,
                             struct key *keyring,
                             struct key *instkey)
{
        int ret;

        if (keyring)
                down_write(&keyring->sem);

        ret = __key_instantiate_and_link(key, data, datalen, keyring, instkey);

        if (keyring)
                up_write(&keyring->sem);

        return ret;

} /* end key_instantiate_and_link() */

EXPORT_SYMBOL(key_instantiate_and_link);

/*****************************************************************************/
/*
 * negatively instantiate a key and link it into the target keyring atomically
 */
int key_negate_and_link(struct key *key,
                        unsigned timeout,
                        struct key *keyring,
                        struct key *instkey)
{
        struct timespec now;
        int ret, awaken;

        key_check(key);
        key_check(keyring);

        awaken = 0;
        ret = -EBUSY;

        if (keyring)
                down_write(&keyring->sem);

        mutex_lock(&key_construction_mutex);

        /* can't instantiate twice */
        if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
                /* mark the key as being negatively instantiated */
                atomic_inc(&key->user->nikeys);
                set_bit(KEY_FLAG_NEGATIVE, &key->flags);
                set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
                now = current_kernel_time();
                key->expiry = now.tv_sec + timeout;

                if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
                        awaken = 1;

                ret = 0;

                /* and link it into the destination keyring */
                if (keyring)
                        ret = __key_link(keyring, key);

                /* disable the authorisation key */
                if (instkey)
                        key_revoke(instkey);
        }

        mutex_unlock(&key_construction_mutex);

        if (keyring)
                up_write(&keyring->sem);

        /* wake up anyone waiting for a key to be constructed */
        if (awaken)
                wake_up_bit(&key->flags, KEY_FLAG_USER_CONSTRUCT);

        return ret;

} /* end key_negate_and_link() */

EXPORT_SYMBOL(key_negate_and_link);

/*****************************************************************************/
/*
 * do cleaning up in process context so that we don't have to disable
 * interrupts all over the place
 */
static void key_cleanup(struct work_struct *work)
{
        struct rb_node *_n;
        struct key *key;

 go_again:
        /* look for a dead key in the tree */
        spin_lock(&key_serial_lock);

        for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
                key = rb_entry(_n, struct key, serial_node);

                if (atomic_read(&key->usage) == 0)
                        goto found_dead_key;
        }

        spin_unlock(&key_serial_lock);
        return;

 found_dead_key:
        /* we found a dead key - once we've removed it from the tree, we can
         * drop the lock */
        rb_erase(&key->serial_node, &key_serial_tree);
        spin_unlock(&key_serial_lock);

        key_check(key);

        security_key_free(key);

        /* deal with the user's key tracking and quota */
        if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
                spin_lock(&key->user->lock);
                key->user->qnkeys--;
                key->user->qnbytes -= key->quotalen;
                spin_unlock(&key->user->lock);
        }

        atomic_dec(&key->user->nkeys);
        if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
                atomic_dec(&key->user->nikeys);

        key_user_put(key->user);

        /* now throw away the key memory */
        if (key->type->destroy)
                key->type->destroy(key);

        kfree(key->description);

#ifdef KEY_DEBUGGING
        key->magic = KEY_DEBUG_MAGIC_X;
#endif
        kmem_cache_free(key_jar, key);

        /* there may, of course, be more than one key to destroy */
        goto go_again;

} /* end key_cleanup() */

/*****************************************************************************/
/*
 * dispose of a reference to a key
 * - when all the references are gone, we schedule the cleanup task to come and
 *   pull it out of the tree in definite process context
 */
void key_put(struct key *key)
{
        if (key) {
                key_check(key);

                if (atomic_dec_and_test(&key->usage))
                        schedule_work(&key_cleanup_task);
        }

} /* end key_put() */

EXPORT_SYMBOL(key_put);

/*****************************************************************************/
/*
 * find a key by its serial number
 */
struct key *key_lookup(key_serial_t id)
{
        struct rb_node *n;
        struct key *key;

        spin_lock(&key_serial_lock);

        /* search the tree for the specified key */
        n = key_serial_tree.rb_node;
        while (n) {
                key = rb_entry(n, struct key, serial_node);

                if (id < key->serial)
                        n = n->rb_left;
                else if (id > key->serial)
                        n = n->rb_right;
                else
                        goto found;
        }

 not_found:
        key = ERR_PTR(-ENOKEY);
        goto error;

 found:
        /* pretend it doesn't exist if it's dead */
        if (atomic_read(&key->usage) == 0 ||
            test_bit(KEY_FLAG_DEAD, &key->flags) ||
            key->type == &key_type_dead)
                goto not_found;

        /* this races with key_put(), but that doesn't matter since key_put()
         * doesn't actually change the key
         */
        atomic_inc(&key->usage);

 error:
        spin_unlock(&key_serial_lock);
        return key;

} /* end key_lookup() */

/*****************************************************************************/
/*
 * find and lock the specified key type against removal
 * - we return with the sem readlocked
 */
struct key_type *key_type_lookup(const char *type)
{
        struct key_type *ktype;

        down_read(&key_types_sem);

        /* look up the key type to see if it's one of the registered kernel
         * types */
        list_for_each_entry(ktype, &key_types_list, link) {
                if (strcmp(ktype->name, type) == 0)
                        goto found_kernel_type;
        }

        up_read(&key_types_sem);
        ktype = ERR_PTR(-ENOKEY);

 found_kernel_type:
        return ktype;

} /* end key_type_lookup() */

/*****************************************************************************/
/*
 * unlock a key type
 */
void key_type_put(struct key_type *ktype)
{
        up_read(&key_types_sem);

} /* end key_type_put() */

/*****************************************************************************/
/*
 * attempt to update an existing key
 * - the key has an incremented refcount
 * - we need to put the key if we get an error
 */
static inline key_ref_t __key_update(key_ref_t key_ref,
                                     const void *payload, size_t plen)
{
        struct key *key = key_ref_to_ptr(key_ref);
        int ret;

        /* need write permission on the key to update it */
        ret = key_permission(key_ref, KEY_WRITE);
        if (ret < 0)
                goto error;

        ret = -EEXIST;
        if (!key->type->update)
                goto error;

        down_write(&key->sem);

        ret = key->type->update(key, payload, plen);
        if (ret == 0)
                /* updating a negative key instantiates it */
                clear_bit(KEY_FLAG_NEGATIVE, &key->flags);

        up_write(&key->sem);

        if (ret < 0)
                goto error;
out:
        return key_ref;

error:
        key_put(key);
        key_ref = ERR_PTR(ret);
        goto out;

} /* end __key_update() */

/*****************************************************************************/
/*
 * search the specified keyring for a key of the same description; if one is
 * found, update it, otherwise add a new one
 */
key_ref_t key_create_or_update(key_ref_t keyring_ref,
                               const char *type,
                               const char *description,
                               const void *payload,
                               size_t plen,
                               key_perm_t perm,
                               unsigned long flags)
{
        struct key_type *ktype;
        struct key *keyring, *key = NULL;
        key_ref_t key_ref;
        int ret;

        /* look up the key type to see if it's one of the registered kernel
         * types */
        ktype = key_type_lookup(type);
        if (IS_ERR(ktype)) {
                key_ref = ERR_PTR(-ENODEV);
                goto error;
        }

        key_ref = ERR_PTR(-EINVAL);
        if (!ktype->match || !ktype->instantiate)
                goto error_2;

        keyring = key_ref_to_ptr(keyring_ref);

        key_check(keyring);

        key_ref = ERR_PTR(-ENOTDIR);
        if (keyring->type != &key_type_keyring)
                goto error_2;

        down_write(&keyring->sem);

        /* if we're going to allocate a new key, we're going to have
         * to modify the keyring */
        ret = key_permission(keyring_ref, KEY_WRITE);
        if (ret < 0) {
                key_ref = ERR_PTR(ret);
                goto error_3;
        }

        /* if it's possible to update this type of key, search for an existing
         * key of the same type and description in the destination keyring and
         * update that instead if possible
         */
        if (ktype->update) {
                key_ref = __keyring_search_one(keyring_ref, ktype, description,
                                               0);
                if (!IS_ERR(key_ref))
                        goto found_matching_key;
        }

        /* if the client doesn't provide, decide on the permissions we want */
        if (perm == KEY_PERM_UNDEF) {
                perm = KEY_POS_VIEW | KEY_POS_SEARCH | KEY_POS_LINK | KEY_POS_SETATTR;
                perm |= KEY_USR_VIEW | KEY_USR_SEARCH | KEY_USR_LINK | KEY_USR_SETATTR;

                if (ktype->read)
                        perm |= KEY_POS_READ | KEY_USR_READ;

                if (ktype == &key_type_keyring || ktype->update)
                        perm |= KEY_USR_WRITE;
        }

        /* allocate a new key */
        key = key_alloc(ktype, description, current->fsuid, current->fsgid,
                        current, perm, flags);
        if (IS_ERR(key)) {
                key_ref = ERR_CAST(key);
                goto error_3;
        }

        /* instantiate it and link it into the target keyring */
        ret = __key_instantiate_and_link(key, payload, plen, keyring, NULL);
        if (ret < 0) {
                key_put(key);
                key_ref = ERR_PTR(ret);
                goto error_3;
        }

        key_ref = make_key_ref(key, is_key_possessed(keyring_ref));

 error_3:
        up_write(&keyring->sem);
 error_2:
        key_type_put(ktype);
 error:
        return key_ref;

 found_matching_key:
        /* we found a matching key, so we're going to try to update it
         * - we can drop the locks first as we have the key pinned
         */
        up_write(&keyring->sem);
        key_type_put(ktype);

        key_ref = __key_update(key_ref, payload, plen);
        goto error;

} /* end key_create_or_update() */

EXPORT_SYMBOL(key_create_or_update);

/*****************************************************************************/
/*
 * update a key
 */
int key_update(key_ref_t key_ref, const void *payload, size_t plen)
{
        struct key *key = key_ref_to_ptr(key_ref);
        int ret;

        key_check(key);

        /* the key must be writable */
        ret = key_permission(key_ref, KEY_WRITE);
        if (ret < 0)
                goto error;

        /* attempt to update it if supported */
        ret = -EOPNOTSUPP;
        if (key->type->update) {
                down_write(&key->sem);

                ret = key->type->update(key, payload, plen);
                if (ret == 0)
                        /* updating a negative key instantiates it */
                        clear_bit(KEY_FLAG_NEGATIVE, &key->flags);

                up_write(&key->sem);
        }

 error:
        return ret;

} /* end key_update() */

EXPORT_SYMBOL(key_update);

/*****************************************************************************/
/*
 * revoke a key
 */
void key_revoke(struct key *key)
{
        key_check(key);

        /* make sure no one's trying to change or use the key when we mark it
         * - we tell lockdep that we might nest because we might be revoking an
         *   authorisation key whilst holding the sem on a key we've just
         *   instantiated
         */
        down_write_nested(&key->sem, 1);
        if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags) &&
            key->type->revoke)
                key->type->revoke(key);

        up_write(&key->sem);

} /* end key_revoke() */

EXPORT_SYMBOL(key_revoke);

/*****************************************************************************/
/*
 * register a type of key
 */
int register_key_type(struct key_type *ktype)
{
        struct key_type *p;
        int ret;

        ret = -EEXIST;
        down_write(&key_types_sem);

        /* disallow key types with the same name */
        list_for_each_entry(p, &key_types_list, link) {
                if (strcmp(p->name, ktype->name) == 0)
                        goto out;
        }

        /* store the type */
        list_add(&ktype->link, &key_types_list);
        ret = 0;

 out:
        up_write(&key_types_sem);
        return ret;

} /* end register_key_type() */

EXPORT_SYMBOL(register_key_type);

/*****************************************************************************/
/*
 * unregister a type of key
 */
void unregister_key_type(struct key_type *ktype)
{
        struct rb_node *_n;
        struct key *key;

        down_write(&key_types_sem);

        /* withdraw the key type */
        list_del_init(&ktype->link);

        /* mark all the keys of this type dead */
        spin_lock(&key_serial_lock);

        for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
                key = rb_entry(_n, struct key, serial_node);

                if (key->type == ktype)
                        key->type = &key_type_dead;
        }

        spin_unlock(&key_serial_lock);

        /* make sure everyone revalidates their keys */
        synchronize_rcu();

        /* we should now be able to destroy the payloads of all the keys of
         * this type with impunity */
        spin_lock(&key_serial_lock);

        for (_n = rb_first(&key_serial_tree); _n; _n = rb_next(_n)) {
                key = rb_entry(_n, struct key, serial_node);

                if (key->type == ktype) {
                        if (ktype->destroy)
                                ktype->destroy(key);
                        memset(&key->payload, KEY_DESTROY, sizeof(key->payload));
                }
        }

        spin_unlock(&key_serial_lock);
        up_write(&key_types_sem);

} /* end unregister_key_type() */

EXPORT_SYMBOL(unregister_key_type);

/*****************************************************************************/
/*
 * initialise the key management stuff
 */
void __init key_init(void)
{
        /* allocate a slab in which we can store keys */
        key_jar = kmem_cache_create("key_jar", sizeof(struct key),
                        0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);

        /* add the special key types */
        list_add_tail(&key_type_keyring.link, &key_types_list);
        list_add_tail(&key_type_dead.link, &key_types_list);
        list_add_tail(&key_type_user.link, &key_types_list);

        /* record the root user tracking */
        rb_link_node(&root_key_user.node,
                     NULL,

                     &key_user_tree.rb_node);

        rb_insert_color(&root_key_user.node,
                        &key_user_tree);

} /* end key_init() */