path: root/security/keys/keyring.c

/* Keyring handling
 *
 * Copyright (C) 2004-2005, 2008, 2013 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/export.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/seq_file.h>
#include <linux/err.h>
#include <keys/keyring-type.h>
#include <keys/user-type.h>
#include <linux/assoc_array_priv.h>
#include <linux/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)

/*
 * We mark pointers we pass to the associative array with bit 1 set if
 * they're keyrings and clear otherwise.
 */
#define KEYRING_PTR_SUBTYPE	0x2UL

static inline bool keyring_ptr_is_keyring(const struct assoc_array_ptr *x)
{
	return (unsigned long)x & KEYRING_PTR_SUBTYPE;
}
static inline struct key *keyring_ptr_to_key(const struct assoc_array_ptr *x)
{
	void *object = assoc_array_ptr_to_leaf(x);
	return (struct key *)((unsigned long)object & ~KEYRING_PTR_SUBTYPE);
}
static inline void *keyring_key_to_ptr(struct key *key)
{
	if (key->type == &key_type_keyring)
		return (void *)((unsigned long)key | KEYRING_PTR_SUBTYPE);
	return key;
}

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 key type definition.  Keyrings are simply keys of this type and
 * can be treated as ordinary keys in addition to having their own special
 * operations.
 */
static int keyring_preparse(struct key_preparsed_payload *prep);
static void keyring_free_preparse(struct key_preparsed_payload *prep);
static int keyring_instantiate(struct key *keyring,
			       struct key_preparsed_payload *prep);
static void keyring_revoke(struct key *keyring);
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	= 0,
	.preparse	= keyring_preparse,
	.free_preparse	= keyring_free_preparse,
	.instantiate	= keyring_instantiate,
	.revoke		= keyring_revoke,
	.destroy	= keyring_destroy,
	.describe	= keyring_describe,
	.read		= keyring_read,
};
EXPORT_SYMBOL(key_type_keyring);

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

/*
 * Publish the name of a keyring so that it can be found by name (if it has
 * one).
 */
static 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->name_link,
			      &keyring_name_hash[bucket]);

		write_unlock(&keyring_name_lock);
	}
}

/*
 * Preparse a keyring payload
 */
static int keyring_preparse(struct key_preparsed_payload *prep)
{
	return prep->datalen != 0 ? -EINVAL : 0;
}

/*
 * Free a preparse of a user defined key payload
 */
static void keyring_free_preparse(struct key_preparsed_payload *prep)
{
}

/*
 * Initialise a keyring.
 *
 * Returns 0 on success, -EINVAL if given any data.
 */
static int keyring_instantiate(struct key *keyring,
			       struct key_preparsed_payload *prep)
{
	assoc_array_init(&keyring->keys);
	/* make the keyring available by name if it has one */
	keyring_publish_name(keyring);
	return 0;
}

/*
 * Multiply 64-bits by 32-bits to 96-bits and fold back to 64-bit.  Ideally we'd
 * fold the carry back too, but that requires inline asm.
 */
static u64 mult_64x32_and_fold(u64 x, u32 y)
{
	u64 hi = (u64)(u32)(x >> 32) * y;
	u64 lo = (u64)(u32)(x) * y;
	return lo + ((u64)(u32)hi << 32) + (u32)(hi >> 32);
}

/*
 * Hash a key type and description.
 */
static unsigned long hash_key_type_and_desc(const struct keyring_index_key *index_key)
{
	const unsigned level_shift = ASSOC_ARRAY_LEVEL_STEP;
	const unsigned long fan_mask = ASSOC_ARRAY_FAN_MASK;
	const char *description = index_key->description;
	unsigned long hash, type;
	u32 piece;
	u64 acc;
	int n, desc_len = index_key->desc_len;

	type = (unsigned long)index_key->type;

	acc = mult_64x32_and_fold(type, desc_len + 13);
	acc = mult_64x32_and_fold(acc, 9207);
	for (;;) {
		n = desc_len;
		if (n <= 0)
			break;
		if (n > 4)
			n = 4;
		piece = 0;
		memcpy(&piece, description, n);
		description += n;
		desc_len -= n;
		acc = mult_64x32_and_fold(acc, piece);
		acc = mult_64x32_and_fold(acc, 9207);
	}

	/* Fold the hash down to 32 bits if need be. */
	hash = acc;
	if (ASSOC_ARRAY_KEY_CHUNK_SIZE == 32)
		hash ^= acc >> 32;

	/* Squidge all the keyring