linux/security/selinux/ss/hashtab.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Implementation of the hash table type.
 *
 * Author : Stephen Smalley, <sds@tycho.nsa.gov>
 */
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include "hashtab.h"

static struct kmem_cache *hashtab_node_cachep;

/*
 * Here we simply round the number of elements up to the nearest power of two.
 * I tried also other options like rouding 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)
{
	h->size = hashtab_compute_size(nel_hint);
	h->nel = 0;
	if (!h->size)
		return 0;

	h->htable = kcalloc(h->size, sizeof(*h->htable), GFP_KERNEL);
	return h->htable ? 0 : -ENOMEM;
}

int hashtab_insert(struct hashtab *h, void *key, void *datum,
		   struct hashtab_key_params key_params)
{
	u32 hvalue;
	struct hashtab_node *prev, *cur, *newnode;

	cond_resched();

	if (!h->size || h->nel == HASHTAB_MAX_NODES)
		return -EINVAL;

	hvalue = key_params.hash(key) & (h->size - 1);
	prev = NULL;
	cur = h->htable[hvalue];
	while (cur) {
		int cmp = key_params.cmp(key, cur->key);

		if (cmp == 0)
			return -EEXIST;
		if (cmp < 0)
			break;
		prev = cur;
		cur = cur->next;
	}

	newnode = kmem_cache_zalloc(hashtab_node_cachep, GFP_KERNEL);
	if (!newnode)
		return -ENOMEM;
	newnode->key = key;
	newnode->datum = datum;
	if (prev) {
		newnode->next = prev->next;
		prev->next = newnode;
	} else {
		newnode->next = h->htable[hvalue];
		h->htable[hvalue] = newnode;
	}

	h->nel++;
	return 0;
}

void *hashtab_search(struct hashtab *h, const void *key,
		     struct hashtab_key_params key_params)
{
	u32 hvalue;
	struct hashtab_node *cur;

	if (!h->size)
		return NULL;

	hvalue = key_params.hash(key) & (h->size - 1);
	cur = h->htable[hvalue];
	while (cur) {
		int cmp = key_params.cmp(key, cur->key);

		if (cmp == 0)
			return cur->datum;
		if (cmp < 0)
			break;
		cur = cur->next;
	}
	return NULL;
}

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;
}


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

	slots_used = 0;
	max_chain_len = 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;
		}
	}

	info->slots_used = slots_used;
	info->max_chain_len = max_chain_len;
}

void __init hashtab_cache_init(void)
{
		hashtab_node_cachep = kmem_cache_create("hashtab_node",
			sizeof(struct hashtab_node),
			0, SLAB_PANIC, NULL);
}