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https://github.com/systemd/systemd.git
synced 2025-01-11 09:18:07 +03:00
hashmap: randomize hash functions a bit
This commit is contained in:
Lennart Poettering
parent
ef7939dfbb
commit
a3b6fafed4
@ -821,7 +821,7 @@ have_myhostname=no
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AC_ARG_ENABLE(myhostname, AS_HELP_STRING([--disable-myhostname], [disable nss-myhostname support]))
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if test "x$enable_myhostname" != "xno"; then
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AC_HEADER_STDC
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AC_CHECK_HEADERS([arpa/inet.h fcntl.h inttypes.h netdb.h netinet/in.h stdlib.h string.h sys/socket.h sys/time.h unistd.h nss.h sys/ioctl.h])
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AC_CHECK_HEADERS([arpa/inet.h fcntl.h inttypes.h netdb.h netinet/in.h stdlib.h string.h sys/socket.h sys/time.h unistd.h nss.h sys/ioctl.h sys/auxv.h])
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AC_C_CONST
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AC_TYPE_SIZE_T
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@ -24,6 +24,10 @@
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#include <string.h>
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#include <errno.h>
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#ifdef HAVE_SYS_AUXV_H
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#include <sys/auxv.h>
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#endif
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#include "util.h"
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#include "hashmap.h"
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#include "macro.h"
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@ -46,6 +50,7 @@ struct Hashmap {
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struct hashmap_entry ** buckets;
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unsigned n_buckets, n_entries;
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unsigned random_xor;
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bool from_pool;
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};
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@ -171,10 +176,15 @@ int uint64_compare_func(const void *_a, const void *_b) {
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return a < b ? -1 : (a > b ? 1 : 0);
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}
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static unsigned bucket_hash(Hashmap *h, const void *p) {
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return (h->hash_func(p) ^ h->random_xor) % h->n_buckets;
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}
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Hashmap *hashmap_new(hash_func_t hash_func, compare_func_t compare_func) {
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bool b;
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Hashmap *h;
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size_t size;
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void *auxv;
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b = is_main_thread();
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@ -204,6 +214,19 @@ Hashmap *hashmap_new(hash_func_t hash_func, compare_func_t compare_func) {
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h->from_pool = b;
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/* Let's randomize our hash functions a bit so that they are
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* harder to guess for clients. For this, start out by cheaply
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* using some bits the kernel passed into the process using
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* the auxiliary vector. If the hashmap grows later on we will
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* rehash everything using a new random XOR mask from
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* /dev/random. */
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#ifdef HAVE_SYS_AUXV_H
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auxv = (void*) getauxval(AT_RANDOM);
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h->random_xor = auxv ? *(unsigned*) auxv : random_u();
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#else
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h->random_xor = random_u();
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#endif
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return h;
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}
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@ -284,8 +307,7 @@ static void remove_entry(Hashmap *h, struct hashmap_entry *e) {
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assert(h);
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assert(e);
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hash = h->hash_func(e->key) % h->n_buckets;
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hash = bucket_hash(h, e->key);
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unlink_entry(h, e, hash);
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if (h->from_pool)
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@ -368,7 +390,6 @@ void hashmap_clear_free_free(Hashmap *h) {
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}
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}
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static struct hashmap_entry *hash_scan(Hashmap *h, unsigned hash, const void *key) {
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struct hashmap_entry *e;
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assert(h);
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@ -382,8 +403,8 @@ static struct hashmap_entry *hash_scan(Hashmap *h, unsigned hash, const void *ke
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}
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static bool resize_buckets(Hashmap *h) {
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unsigned m;
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struct hashmap_entry **n, *i;
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unsigned m, nxor;
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assert(h);
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@ -398,6 +419,11 @@ static bool resize_buckets(Hashmap *h) {
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if (!n)
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return false;
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/* Let's use a different randomized xor value for the
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* extension, so that people cannot guess what we are using
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* here forever */
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nxor = random_u();
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for (i = h->iterate_list_head; i; i = i->iterate_next) {
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unsigned hash, x;
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@ -410,10 +436,10 @@ static bool resize_buckets(Hashmap *h) {
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if (i->bucket_previous)
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i->bucket_previous->bucket_next = i->bucket_next;
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else
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h->buckets[hash % h->n_buckets] = i->bucket_next;
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h->buckets[(hash ^ h->random_xor) % h->n_buckets] = i->bucket_next;
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/* Then, add to new backet table */
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x = hash % m;
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x = (hash ^ nxor) % m;
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i->bucket_next = n[x];
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i->bucket_previous = NULL;
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@ -427,6 +453,7 @@ static bool resize_buckets(Hashmap *h) {
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h->buckets = n;
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h->n_buckets = m;
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h->random_xor = nxor;
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return true;
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}
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@ -437,7 +464,7 @@ int hashmap_put(Hashmap *h, const void *key, void *value) {
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assert(h);
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (e) {
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if (e->value == value)
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@ -446,7 +473,7 @@ int hashmap_put(Hashmap *h, const void *key, void *value) {
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}
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if (resize_buckets(h))
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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if (h->from_pool)
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e = allocate_tile(&first_entry_pool, &first_entry_tile, sizeof(struct hashmap_entry));
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@ -470,7 +497,7 @@ int hashmap_replace(Hashmap *h, const void *key, void *value) {
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assert(h);
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (e) {
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e->key = key;
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@ -487,7 +514,7 @@ int hashmap_update(Hashmap *h, const void *key, void *value) {
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assert(h);
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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return -ENOENT;
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@ -503,7 +530,7 @@ void* hashmap_get(Hashmap *h, const void *key) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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return NULL;
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@ -518,7 +545,7 @@ void* hashmap_get2(Hashmap *h, const void *key, void **key2) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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return NULL;
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@ -535,12 +562,8 @@ bool hashmap_contains(Hashmap *h, const void *key) {
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if (!h)
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return false;
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hash = h->hash_func(key) % h->n_buckets;
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if (!hash_scan(h, hash, key))
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return false;
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return true;
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hash = bucket_hash(h, key);
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return !!hash_scan(h, hash, key);
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}
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void* hashmap_remove(Hashmap *h, const void *key) {
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@ -551,9 +574,9 @@ void* hashmap_remove(Hashmap *h, const void *key) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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if (!(e = hash_scan(h, hash, key)))
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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return NULL;
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data = e->value;
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@ -569,11 +592,12 @@ int hashmap_remove_and_put(Hashmap *h, const void *old_key, const void *new_key,
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if (!h)
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return -ENOENT;
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old_hash = h->hash_func(old_key) % h->n_buckets;
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if (!(e = hash_scan(h, old_hash, old_key)))
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old_hash = bucket_hash(h, old_key);
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e = hash_scan(h, old_hash, old_key);
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if (!e)
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return -ENOENT;
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new_hash = h->hash_func(new_key) % h->n_buckets;
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new_hash = bucket_hash(h, new_key);
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if (hash_scan(h, new_hash, new_key))
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return -EEXIST;
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@ -594,12 +618,14 @@ int hashmap_remove_and_replace(Hashmap *h, const void *old_key, const void *new_
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if (!h)
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return -ENOENT;
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old_hash = h->hash_func(old_key) % h->n_buckets;
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if (!(e = hash_scan(h, old_hash, old_key)))
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old_hash = bucket_hash(h, old_key);
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e = hash_scan(h, old_hash, old_key);
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if (!e)
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return -ENOENT;
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new_hash = h->hash_func(new_key) % h->n_buckets;
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if ((k = hash_scan(h, new_hash, new_key)))
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new_hash = bucket_hash(h, new_key);
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k = hash_scan(h, new_hash, new_key);
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if (k)
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if (e != k)
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remove_entry(h, k);
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@ -620,7 +646,7 @@ void* hashmap_remove_value(Hashmap *h, const void *key, void *value) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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@ -711,7 +737,7 @@ void *hashmap_iterate_skip(Hashmap *h, const void *key, Iterator *i) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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@ -820,9 +846,9 @@ int hashmap_merge(Hashmap *h, Hashmap *other) {
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for (e = other->iterate_list_head; e; e = e->iterate_next) {
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int r;
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if ((r = hashmap_put(h, e->key, e->value)) < 0)
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if (r != -EEXIST)
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return r;
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r = hashmap_put(h, e->key, e->value);
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if (r < 0 && r != -EEXIST)
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return r;
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}
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return 0;
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@ -844,13 +870,11 @@ void hashmap_move(Hashmap *h, Hashmap *other) {
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n = e->iterate_next;
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h_hash = h->hash_func(e->key) % h->n_buckets;
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h_hash = bucket_hash(h, e->key);
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if (hash_scan(h, h_hash, e->key))
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continue;
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other_hash = other->hash_func(e->key) % other->n_buckets;
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other_hash = bucket_hash(other, e->key);
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unlink_entry(other, e, other_hash);
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link_entry(h, e, h_hash);
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}
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@ -865,11 +889,11 @@ int hashmap_move_one(Hashmap *h, Hashmap *other, const void *key) {
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assert(h);
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h_hash = h->hash_func(key) % h->n_buckets;
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h_hash = bucket_hash(h, key);
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if (hash_scan(h, h_hash, key))
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return -EEXIST;
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other_hash = other->hash_func(key) % other->n_buckets;
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other_hash = bucket_hash(other, key);
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e = hash_scan(other, other_hash, key);
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if (!e)
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return -ENOENT;
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@ -925,7 +949,7 @@ void *hashmap_next(Hashmap *h, const void *key) {
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if (!h)
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return NULL;
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hash = h->hash_func(key) % h->n_buckets;
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hash = bucket_hash(h, key);
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e = hash_scan(h, hash, key);
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if (!e)
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return NULL;
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@ -2424,6 +2424,25 @@ fallback:
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return random() * RAND_MAX + random();
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}
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unsigned random_u(void) {
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_cleanup_close_ int fd;
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unsigned u;
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ssize_t r;
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fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
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if (fd < 0)
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goto fallback;
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r = loop_read(fd, &u, sizeof(u), true);
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if (r != sizeof(u))
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goto fallback;
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return u;
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fallback:
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return random() * RAND_MAX + random();
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}
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void rename_process(const char name[8]) {
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assert(name);
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@ -253,6 +253,7 @@ int make_null_stdio(void);
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int make_console_stdio(void);
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unsigned long long random_ull(void);
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unsigned random_u(void);
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/* For basic lookup tables with strictly enumerated entries */
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#define __DEFINE_STRING_TABLE_LOOKUP(name,type,scope) \
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