path: root/security/keys/keyring.c

/* keyring.c: keyring handling
 *
 * Copyright (C) 2004-5 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/sched.h>
#include <linux/slab.h>
#include <linux/seq_file.h>
#include <linux/err.h>
#include <asm/uaccess.h>
#include "internal.h"

/*
 * when plumbing the depths of the key tree, this sets a hard limit set on how
 * deep we're willing to go
 */
#define KEYRING_SEARCH_MAX_DEPTH 6

/*
 * we keep all named keyrings in a hash to speed looking them up
 */
#define KEYRING_NAME_HASH_SIZE	(1 << 5)

static struct list_head	keyring_name_hash[KEYRING_NAME_HASH_SIZE];
static DEFINE_RWLOCK(keyring_name_lock);

static inline unsigned keyring_hash(const char *desc)
{
	unsigned bucket = 0;

	for (; *desc; desc++)
		bucket += (unsigned char) *desc;

	return bucket & (KEYRING_NAME_HASH_SIZE - 1);
}

/*
 * the keyring type definition
 */
static int keyring_instantiate(struct key *keyring,
			       const void *data, size_t datalen);
static int keyring_duplicate(struct key *keyring, const struct key *source);
static int keyring_match(const struct key *keyring, const void *criterion);
static void keyring_destroy(struct key *keyring);
static void keyring_describe(const struct key *keyring, struct seq_file *m);
static long keyring_read(const struct key *keyring,
			 char __user *buffer, size_t buflen);

struct key_type key_type_keyring = {
	.name		= "keyring",
	.def_datalen	= sizeof(struct keyring_list),
	.instantiate	= keyring_instantiate,
	.duplicate	= keyring_duplicate,
	.match		= keyring_match,
	.destroy	= keyring_destroy,
	.describe	= keyring_describe,
	.read		= keyring_read,
};

/*
 * semaphore to serialise link/link calls to prevent two link calls in parallel
 * introducing a cycle
 */
DECLARE_RWSEM(keyring_serialise_link_sem);

/*****************************************************************************/
/*
 * publish the name of a keyring so that it can be found by name (if it has
 * one)
 */
void keyring_publish_name(struct key *keyring)
{
	int bucket;

	if (keyring->description) {
		bucket = keyring_hash(keyring->description);

		write_lock(&keyring_name_lock);

		if (!keyring_name_hash[bucket].next)
			INIT_LIST_HEAD(&keyring_name_hash[bucket]);

		list_add_tail(&keyring->type_data.link,
			      &keyring_name_hash[bucket]);

		write_unlock(&keyring_name_lock);
	}

} /* end keyring_publish_name() */

/*****************************************************************************/
/*
 * initialise a keyring
 * - we object if we were given any data
 */
static int keyring_instantiate(struct key *keyring,
			       const void *data, size_t datalen)
{
	int ret;

	ret = -EINVAL;
	if (datalen == 0) {
		/* make the keyring available by name if it has one */
		keyring_publish_name(keyring);
		ret = 0;
	}

	return ret;

} /* end keyring_instantiate() */

/*****************************************************************************/
/*
 * duplicate the list of subscribed keys from a source keyring into this one
 */
static int keyring_duplicate(struct key *keyring, const struct key *source)
{
	struct keyring_list *sklist, *klist;
	unsigned max;
	size_t size;
	int loop, ret;

	const unsigned limit =
		(PAGE_SIZE - sizeof(*klist)) / sizeof(struct key *);

	ret = 0;

	/* find out how many keys are currently linked */
	rcu_read_lock();
	sklist = rcu_dereference(source->payload.subscriptions);
	max = 0;
	if (sklist)
		max = sklist->nkeys;
	rcu_read_unlock();

	/* allocate a new payload and stuff load with key links */
	if (max > 0) {
		BUG_ON(max > limit);

		max = (max + 3) & ~3;
		if (max > limit)
			max = limit;

		ret = -ENOMEM;
		size = sizeof(*klist) + sizeof(struct key *) * max;
		klist = kmalloc(size, GFP_KERNEL);
		if (!klist)
			goto error;

		/* set links */
		rcu_read_lock();
		sklist = rcu_dereference(source->payload.subscriptions);

		klist->maxkeys = max;
		klist->nkeys = sklist->nkeys