hashtab.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Implementation of the hash table type.
  4 *
  5 * Author : Stephen Smalley, <stephen.smalley.work@gmail.com>
  6 */
  7
  8#include <linux/kernel.h>
  9#include <linux/slab.h>
 10#include <linux/errno.h>
 11#include "hashtab.h"
 12#include "security.h"
 13
 14static struct kmem_cache *hashtab_node_cachep __ro_after_init;
 15
 16/*
 17 * Here we simply round the number of elements up to the nearest power of two.
 18 * I tried also other options like rounding down or rounding to the closest
 19 * power of two (up or down based on which is closer), but I was unable to
 20 * find any significant difference in lookup/insert performance that would
 21 * justify switching to a different (less intuitive) formula. It could be that
 22 * a different formula is actually more optimal, but any future changes here
 23 * should be supported with performance/memory usage data.
 24 *
 25 * The total memory used by the htable arrays (only) with Fedora policy loaded
 26 * is approximately 163 KB at the time of writing.
 27 */
 28static u32 hashtab_compute_size(u32 nel)
 29{
 30	return nel == 0 ? 0 : roundup_pow_of_two(nel);
 31}
 32
 33int hashtab_init(struct hashtab *h, u32 nel_hint)
 34{
 35	u32 size = hashtab_compute_size(nel_hint);
 36
 37	/* should already be zeroed, but better be safe */
 38	h->nel = 0;
 39	h->size = 0;
 40	h->htable = NULL;
 41
 42	if (size) {
 43		h->htable = kcalloc(size, sizeof(*h->htable),
 44				    GFP_KERNEL | __GFP_NOWARN);
 45		if (!h->htable)
 46			return -ENOMEM;
 47		h->size = size;
 48	}
 49	return 0;
 50}
 51
 52int __hashtab_insert(struct hashtab *h, struct hashtab_node **dst, void *key,
 53		     void *datum)
 54{
 55	struct hashtab_node *newnode;
 56
 57	newnode = kmem_cache_zalloc(hashtab_node_cachep, GFP_KERNEL);
 58	if (!newnode)
 59		return -ENOMEM;
 60	newnode->key = key;
 61	newnode->datum = datum;
 62	newnode->next = *dst;
 63	*dst = newnode;
 64
 65	h->nel++;
 66	return 0;
 67}
 68
 69void hashtab_destroy(struct hashtab *h)
 70{
 71	u32 i;
 72	struct hashtab_node *cur, *temp;
 73
 74	for (i = 0; i < h->size; i++) {
 75		cur = h->htable[i];
 76		while (cur) {
 77			temp = cur;
 78			cur = cur->next;
 79			kmem_cache_free(hashtab_node_cachep, temp);
 80		}
 81		h->htable[i] = NULL;
 82	}
 83
 84	kfree(h->htable);
 85	h->htable = NULL;
 86}
 87
 88int hashtab_map(struct hashtab *h, int (*apply)(void *k, void *d, void *args),
 89		void *args)
 90{
 91	u32 i;
 92	int ret;
 93	struct hashtab_node *cur;
 94
 95	for (i = 0; i < h->size; i++) {
 96		cur = h->htable[i];
 97		while (cur) {
 98			ret = apply(cur->key, cur->datum, args);
 99			if (ret)
100				return ret;
101			cur = cur->next;
102		}
103	}
104	return 0;
105}
106
107#ifdef CONFIG_SECURITY_SELINUX_DEBUG
108void hashtab_stat(struct hashtab *h, struct hashtab_info *info)
109{
110	u32 i, chain_len, slots_used, max_chain_len;
111	u64 chain2_len_sum;
112	struct hashtab_node *cur;
113
114	slots_used = 0;
115	max_chain_len = 0;
116	chain2_len_sum = 0;
117	for (i = 0; i < h->size; i++) {
118		cur = h->htable[i];
119		if (cur) {
120			slots_used++;
121			chain_len = 0;
122			while (cur) {
123				chain_len++;
124				cur = cur->next;
125			}
126
127			if (chain_len > max_chain_len)
128				max_chain_len = chain_len;
129
130			chain2_len_sum += (u64)chain_len * chain_len;
131		}
132	}
133
134	info->slots_used = slots_used;
135	info->max_chain_len = max_chain_len;
136	info->chain2_len_sum = chain2_len_sum;
137}
138#endif /* CONFIG_SECURITY_SELINUX_DEBUG */
139
140int hashtab_duplicate(struct hashtab *new, const struct hashtab *orig,
141		      int (*copy)(struct hashtab_node *new,
142				  const struct hashtab_node *orig, void *args),
143		      int (*destroy)(void *k, void *d, void *args), void *args)
144{
145	const struct hashtab_node *orig_cur;
146	struct hashtab_node *cur, *tmp, *tail;
147	u32 i;
148	int rc;
149
150	memset(new, 0, sizeof(*new));
151
152	new->htable = kcalloc(orig->size, sizeof(*new->htable), GFP_KERNEL);
153	if (!new->htable)
154		return -ENOMEM;
155
156	new->size = orig->size;
157
158	for (i = 0; i < orig->size; i++) {
159		tail = NULL;
160		for (orig_cur = orig->htable[i]; orig_cur;
161		     orig_cur = orig_cur->next) {
162			tmp = kmem_cache_zalloc(hashtab_node_cachep,
163						GFP_KERNEL);
164			if (!tmp)
165				goto error;
166			rc = copy(tmp, orig_cur, args);
167			if (rc) {
168				kmem_cache_free(hashtab_node_cachep, tmp);
169				goto error;
170			}
171			tmp->next = NULL;
172			if (!tail)
173				new->htable[i] = tmp;
174			else
175				tail->next = tmp;
176			tail = tmp;
177			new->nel++;
178		}
179	}
180
181	return 0;
182
183error:
184	for (i = 0; i < new->size; i++) {
185		for (cur = new->htable[i]; cur; cur = tmp) {
186			tmp = cur->next;
187			destroy(cur->key, cur->datum, args);
188			kmem_cache_free(hashtab_node_cachep, cur);
189		}
190	}
191	kfree(new->htable);
192	memset(new, 0, sizeof(*new));
193	return -ENOMEM;
194}
195
196void __init hashtab_cache_init(void)
197{
198	hashtab_node_cachep = KMEM_CACHE(hashtab_node, SLAB_PANIC);
199}