security/selinux/ss/hashtab.c

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