st: fix race in st_scsi_execute_end

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / security / keys / key.c

/* 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 <linux/user_namespace.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 user_namespace *user_ns)
{
        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 if (user_ns < user->user_ns)
                        p = &(*p)->rb_left;
                else if (user_ns > user->user_ns)
                        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->user_ns = get_user_ns(user_ns);
        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;
}

/*
 * 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);
                put_user_ns(user->user_ns);

                kfree(user);
        }
}

/*
 * Allocate a serial number for a key.  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;
        }
}

/**
 * key_alloc - Allocate a key of the specified type.
 * @type: The type of key to allocate.
 * @desc: The key description to allow the key to be searched out.
 * @uid: The owner of the new key.
 * @gid: The group ID for the new key's group permissions.
 * @cred: The credentials specifying UID namespace.
 * @perm: The permissions mask of the new key.
 * @flags: Flags specifying quota properties.
 *
 * Allocate a key of the specified type with the attributes given.  The key is
 * returned in an uninstantiated state and the caller needs to instantiate the
 * key before returning.
 *
 * The user's key count quota is updated to reflect the creation of the key and
 * the user's key data quota has the default for the key type reserved.  The
 * instantiation function should amend this as necessary.  If insufficient
 * quota is available, -EDQUOT will be returned.
 *
 * The LSM security modules can prevent a key being created, in which case
 * -EACCES will be returned.
 *
 * Returns a pointer to the new key if successful and an error code otherwise.
 *
 * Note that the caller needs to ensure the key type isn't uninstantiated.
 * Internally this can be done by locking key_types_sem.  Externally, this can
 * be done by either never unregistering the key type, or making sure
 * key_alloc() calls don't race with module unloading.
 */
struct key *key_alloc(struct key_type *type, const char *desc,
                      uid_t uid, gid_t gid, const struct cred *cred,
                      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;

        if (type->vet_description) {
                ret = type->vet_description(desc);
                if (ret < 0) {
                        key = ERR_PTR(ret);
                        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, cred->user->user_ns);
        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, cred, 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;
}
EXPORT_SYMBOL(key_alloc);

/**
 * key_payload_reserve - Adjust data quota reservation for the key's payload
 * @key: The key to make the reservation for.
 * @datalen: The amount of data payload the caller now wants.
 *
 * Adjust the amount of the owning user's key data quota that a key reserves.
 * If the amount is increased, then -EDQUOT may be returned if there isn't
 * enough free quota available.
 *
 * If successful, 0 is returned.
 */
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;
}
EXPORT_SYMBOL(key_payload_reserve);

/*
 * Instantiate a key and link it into the target keyring atomically.  Must be
 * called with the target keyring's semaphore writelocked.  The target key's
 * semaphore need not be locked as instantiation is serialised by
 * key_construction_mutex.
 */
static int __key_instantiate_and_link(struct key *key,
                                      const void *data,
                                      size_t datalen,
                                      struct key *keyring,
                                      struct key *authkey,
                                      unsigned long *_prealloc)
{
        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)
                                __key_link(keyring, key, _prealloc);

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

        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;
}

/**
 * key_instantiate_and_link - Instantiate a key and link it into the keyring.
 * @key: The key to instantiate.
 * @data: The data to use to instantiate the keyring.
 * @datalen: The length of @data.
 * @keyring: Keyring to create a link in on success (or NULL).
 * @authkey: The authorisation token permitting instantiation.
 *
 * Instantiate a key that's in the uninstantiated state using the provided data
 * and, if successful, link it in to the destination keyring if one is
 * supplied.
 *
 * If successful, 0 is returned, the authorisation token is revoked and anyone
 * waiting for the key is woken up.  If the key was already instantiated,
 * -EBUSY will be returned.
 */
int key_instantiate_and_link(struct key *key,
                             const void *data,
                             size_t datalen,
                             struct key *keyring,
                             struct key *authkey)
{
        unsigned long prealloc;
        int ret;

        if (keyring) {
                ret = __key_link_begin(keyring, key->type, key->description,
                                       &prealloc);
                if (ret < 0)
                        return ret;
        }

        ret = __key_instantiate_and_link(key, data, datalen, keyring, authkey,
                                         &prealloc);

        if (keyring)
                __key_link_end(keyring, key->type, prealloc);

        return ret;
}

EXPORT_SYMBOL(key_instantiate_and_link);

/**
 * key_reject_and_link - Negatively instantiate a key and link it into the keyring.
 * @key: The key to instantiate.
 * @timeout: The timeout on the negative key.
 * @error: The error to return when the key is hit.
 * @keyring: Keyring to create a link in on success (or NULL).
 * @authkey: The authorisation token permitting instantiation.
 *
 * Negatively instantiate a key that's in the uninstantiated state and, if
 * successful, set its timeout and stored error and link it in to the
 * destination keyring if one is supplied.  The key and any links to the key
 * will be automatically garbage collected after the timeout expires.
 *
 * Negative keys are used to rate limit repeated request_key() calls by causing
 * them to return the stored error code (typically ENOKEY) until the negative
 * key expires.
 *
 * If successful, 0 is returned, the authorisation token is revoked and anyone
 * waiting for the key is woken up.  If the key was already instantiated,
 * -EBUSY will be returned.
 */
int key_reject_and_link(struct key *key,
                        unsigned timeout,
                        unsigned error,
                        struct key *keyring,
                        struct key *authkey)
{
        unsigned long prealloc;
        struct timespec now;
        int ret, awaken, link_ret = 0;

        key_check(key);
        key_check(keyring);

        awaken = 0;
        ret = -EBUSY;

        if (keyring)
                link_ret = __key_link_begin(keyring, key->type,
                                            key->description, &prealloc);

        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);
                key->type_data.reject_error = -error;
                now = current_kernel_time();
                key->expiry = now.tv_sec + timeout;
                key_schedule_gc(key->expiry + key_gc_delay);

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

                ret = 0;

                /* and link it into the destination keyring */
                if (keyring && link_ret == 0)
                        __key_link(keyring, key, &prealloc);

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

        mutex_unlock(&key_construction_mutex);

        if (keyring)
                __key_link_end(keyring, key->type, prealloc);

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

        return ret == 0 ? link_ret : ret;
}
EXPORT_SYMBOL(key_reject_and_link);

/*
 * Garbage collect keys in process context so that we don't have to disable
 * interrupts all over the place.
 *
 * key_put() schedules this rather than trying to do the cleanup itself, which
 * means key_put() doesn't have to sleep.
 */
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;
}

/**
 * key_put - Discard a reference to a key.
 * @key: The key to discard a reference from.
 *
 * Discard a reference to a key, and when all the references are gone, we
 * schedule the cleanup task to come and pull it out of the tree in process
 * context at some later time.
 */
void key_put(struct key *key)
{
        if (key) {
                key_check(key);

                if (atomic_dec_and_test(&key->usage))
                        schedule_work(&key_cleanup_task);
        }
}
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 is awaiting deletion */
        if (atomic_read(&key->usage) == 0)
                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;
}

/*
 * Find and lock the specified key type against removal.
 *
 * We return with the sem read-locked if successful.  If the type wasn't
 * available -ENOKEY is returned instead.
 */
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;
}

/*
 * Unlock a key type locked by key_type_lookup().
 */
void key_type_put(struct key_type *ktype)
{
        up_read(&key_types_sem);
}

/*
 * Attempt to update an existing key.
 *
 * The key is given to us with an incremented refcount that we need to discard
 * 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;
}

/**
 * key_create_or_update - Update or create and instantiate a key.
 * @keyring_ref: A pointer to the destination keyring with possession flag.
 * @type: The type of key.
 * @description: The searchable description for the key.
 * @payload: The data to use to instantiate or update the key.
 * @plen: The length of @payload.
 * @perm: The permissions mask for a new key.
 * @flags: The quota flags for a new key.
 *
 * Search the destination keyring for a key of the same description and if one
 * is found, update it, otherwise create and instantiate a new one and create a
 * link to it from that keyring.
 *
 * If perm is KEY_PERM_UNDEF then an appropriate key permissions mask will be
 * concocted.
 *
 * Returns a pointer to the new key if successful, -ENODEV if the key type
 * wasn't available, -ENOTDIR if the keyring wasn't a keyring, -EACCES if the
 * caller isn't permitted to modify the keyring or the LSM did not permit
 * creation of the key.
 *
 * On success, the possession flag from the keyring ref will be tacked on to
 * the key ref before it is returned.
 */
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)
{
        unsigned long prealloc;
        const struct cred *cred = current_cred();
        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;

        ret = __key_link_begin(keyring, ktype, description, &prealloc);
        if (ret < 0)
                goto error_2;

        /* 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, cred->fsuid, cred->fsgid, cred,
                        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,
                                         &prealloc);
        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:
        __key_link_end(keyring, ktype, prealloc);
 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
         */
        __key_link_end(keyring, ktype, prealloc);
        key_type_put(ktype);

        key_ref = __key_update(key_ref, payload, plen);
        goto error;
}
EXPORT_SYMBOL(key_create_or_update);

/**
 * key_update - Update a key's contents.
 * @key_ref: The pointer (plus possession flag) to the key.
 * @payload: The data to be used to update the key.
 * @plen: The length of @payload.
 *
 * Attempt to update the contents of a key with the given payload data.  The
 * caller must be granted Write permission on the key.  Negative keys can be
 * instantiated by this method.
 *
 * Returns 0 on success, -EACCES if not permitted and -EOPNOTSUPP if the key
 * type does not support updating.  The key type may return other errors.
 */
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;
}
EXPORT_SYMBOL(key_update);

/**
 * key_revoke - Revoke a key.
 * @key: The key to be revoked.
 *
 * Mark a key as being revoked and ask the type to free up its resources.  The
 * revocation timeout is set and the key and all its links will be
 * automatically garbage collected after key_gc_delay amount of time if they
 * are not manually dealt with first.
 */
void key_revoke(struct key *key)
{
        struct timespec now;
        time_t time;

        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);

        /* set the death time to no more than the expiry time */
        now = current_kernel_time();
        time = now.tv_sec;
        if (key->revoked_at == 0 || key->revoked_at > time) {
                key->revoked_at = time;
                key_schedule_gc(key->revoked_at + key_gc_delay);
        }

        up_write(&key->sem);
}
EXPORT_SYMBOL(key_revoke);

/**
 * register_key_type - Register a type of key.
 * @ktype: The new key type.
 *
 * Register a new key type.
 *
 * Returns 0 on success or -EEXIST if a type of this name already exists.
 */
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;
}
EXPORT_SYMBOL(register_key_type);

/**
 * unregister_key_type - Unregister a type of key.
 * @ktype: The key type.
 *
 * Unregister a key type and mark all the extant keys of this type as dead.
 * Those keys of this type are then destroyed to get rid of their payloads and
 * they and their links will be garbage collected as soon as possible.
 */
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;
                        set_bit(KEY_FLAG_DEAD, &key->flags);
                }
        }

        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);

        key_schedule_gc(0);
}
EXPORT_SYMBOL(unregister_key_type);

/*
 * Initialise the key management state.
 */
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);
}