key.c

linux 内核源代码

		/* 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,
			       unsigned long flags)
{
	struct key_type *ktype;
	struct key *keyring, *key = NULL;
	key_perm_t perm;
	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;
	}

	/* decide on the permissions we want */
	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_PTR(PTR_ERR(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);

	/* record root's user standard keyrings */
	key_check(&root_user_keyring);
	key_check(&root_session_keyring);

	__key_insert_serial(&root_user_keyring);
	__key_insert_serial(&root_session_keyring);

	keyring_publish_name(&root_user_keyring);
	keyring_publish_name(&root_session_keyring);

	/* link the two root keyrings together */
	key_link(&root_session_keyring, &root_user_keyring);

} /* end key_init() */