hashtab.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Implementation of the hash table type.
 *
 * Author : Stephen Smalley, <[email protected]>
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include "hashtab.h"
#include "security.h"

static struct kmem_cache *hashtab_node_cachep __ro_after_init;

/*
 * Here we simply round the number of elements up to the nearest power of two.
 * I tried also other options like rounding down or rounding to the closest
 * power of two (up or down based on which is closer), but I was unable to
 * find any significant difference in lookup/insert performance that would
 * justify switching to a different (less intuitive) formula. It could be that
 * a different formula is actually more optimal, but any future changes here
 * should be supported with performance/memory usage data.
 *
 * The total memory used by the htable arrays (only) with Fedora policy loaded
 * is approximately 163 KB at the time of writing.
 */
static u32 hashtab_compute_size(u32 nel)
{
	return nel == 0 ? 0 : roundup_pow_of_two(nel);
}

int hashtab_init(struct hashtab *h, u32 nel_hint)
{
	u32 size = hashtab_compute_size(nel_hint);

	/* should already be zeroed, but better be safe */
	h->nel = 0;
	h->size = 0;
	h->htable = NULL;

	if (size) {
		h->htable = kcalloc(size, sizeof(*h->htable),
				    GFP_KERNEL | __GFP_NOWARN);
		if (!h->htable)
			return -ENOMEM;
		h->size = size;
	}
	return 0;
}

int __hashtab_insert(struct hashtab *h, struct hashtab_node **dst, void *key,
		     void *datum)
{
	struct hashtab_node *newnode;

	newnode = kmem_cache_zalloc(hashtab_node_cachep, GFP_KERNEL);
	if (!newnode)
		return -ENOMEM;
	newnode->key = key;
	newnode->datum = datum;
	newnode->next = *dst;
	*dst = newnode;

	h->nel++;
	return 0;
}

void hashtab_destroy(struct hashtab *h)
{
	u32 i;
	struct hashtab_node *cur, *temp;

	for (i = 0; i < h->size; i++) {
		cur = h->htable[i];
		while (cur) {
			temp = cur;
			cur = cur->next;
			kmem_cache_free(hashtab_node_cachep, temp);
		}
		h->htable[i] = NULL;
	}

	kfree(h->htable);
	h->htable = NULL;
}

int hashtab_map(struct hashtab *h, int (*apply)(void *k, void *d, void *args),
		void *args)
{
	u32 i;
	int ret;
	struct hashtab_node *cur;

	for (i = 0; i < h->size; i++) {
		cur = h->htable[i];
		while (cur) {
			ret = apply(cur->key, cur->datum, args);
			if (ret)
				return ret;
			cur = cur->next;
		}
	}
	return 0;
}

#ifdef CONFIG_SECURITY_SELINUX_DEBUG
void hashtab_stat(struct hashtab *h, struct hashtab_info *info)
{
	u32 i, chain_len, slots_used, max_chain_len;
	u64 chain2_len_sum;
	struct hashtab_node *cur;

	slots_used = 0;
	max_chain_len = 0;
	chain2_len_sum = 0;
	for (i = 0; i < h->size; i++) {
		cur = h->htable[i];
		if (cur) {
			slots_used++;
			chain_len = 0;
			while (cur) {
				chain_len++;
				cur = cur->next;
			}

			if (chain_len > max_chain_len)
				max_chain_len = chain_len;

			chain2_len_sum += (u64)chain_len * chain_len;
		}
	}

	info->slots_used = slots_used;
	info->max_chain_len = max_chain_len;
	info->chain2_len_sum = chain2_len_sum;
}
#endif /* CONFIG_SECURITY_SELINUX_DEBUG */

int hashtab_duplicate(struct hashtab *new, const struct hashtab *orig,
		      int (*copy)(struct hashtab_node *new,
				  const struct hashtab_node *orig, void *args),
		      int (*destroy)(void *k, void *d, void *args), void *args)
{
	const struct hashtab_node *orig_cur;
	struct hashtab_node *cur, *tmp, *tail;
	u32 i;
	int rc;

	memset(new, 0, sizeof(*new));

	new->htable = kcalloc(orig->size, sizeof(*new->htable), GFP_KERNEL);
	if (!new->htable)
		return -ENOMEM;

	new->size = orig->size;

	for (i = 0; i < orig->size; i++) {
		tail = NULL;
		for (orig_cur = orig->htable[i]; orig_cur;
		     orig_cur = orig_cur->next) {
			tmp = kmem_cache_zalloc(hashtab_node_cachep,
						GFP_KERNEL);
			if (!tmp)
				goto error;
			rc = copy(tmp, orig_cur, args);
			if (rc) {
				kmem_cache_free(hashtab_node_cachep, tmp);
				goto error;
			}
			tmp->next = NULL;
			if (!tail)
				new->htable[i] = tmp;
			else
				tail->next = tmp;
			tail = tmp;
			new->nel++;
		}
	}

	return 0;

error:
	for (i = 0; i < new->size; i++) {
		for (cur = new->htable[i]; cur; cur = tmp) {
			tmp = cur->next;
			destroy(cur->key, cur->datum, args);
			kmem_cache_free(hashtab_node_cachep, cur);
		}
	}
	kfree(new->htable);
	memset(new, 0, sizeof(*new));
	return -ENOMEM;
}

void __init hashtab_cache_init(void)
{
	hashtab_node_cachep = KMEM_CACHE(hashtab_node, SLAB_PANIC);
}