ee76b0979f
siphash24() is wildly used by projects nowadays. It's certainly slower then our djb hashing that we used before. But quite likely it's fast enough for us, given how wildly it is used. I think it would be hard to profile NetworkManager to show that the performance of hash tables is the issue, be it with djb or siphash24. Certainly with siphash24() it's much harder to exploit the hashing algorithm to cause worst case hash operations (provided that the seed is kept private). Does this better resistance against a denial of service matter for us? Probably not, but let's better be safe then sorry. Note that systemd's implementation uses a different seed for each hash table (at least, after the hash table grows to a certain size). We don't do that and use only one global seed.
120 lines
2.8 KiB
C
120 lines
2.8 KiB
C
/* -*- Mode: C; tab-width: 4; indent-tabs-mode: t; c-basic-offset: 4 -*- */
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/* NetworkManager -- Network link manager
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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* Boston, MA 02110-1301 USA.
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*
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* (C) Copyright 2017 Red Hat, Inc.
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*/
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#include "nm-default.h"
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#include "nm-hash-utils.h"
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#include <stdint.h>
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#include "nm-shared-utils.h"
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#include "nm-random-utils.h"
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/*****************************************************************************/
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#define HASH_KEY_SIZE 16u
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#define HASH_KEY_SIZE_GUINT ((HASH_KEY_SIZE + sizeof (guint) - 1) / sizeof (guint))
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G_STATIC_ASSERT (sizeof (guint) * HASH_KEY_SIZE_GUINT >= HASH_KEY_SIZE);
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static const guint8 *
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_get_hash_key (void)
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{
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static const guint8 *volatile global_seed = NULL;
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const guint8 *g;
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g = global_seed;
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if (G_UNLIKELY (g == NULL)) {
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/* the returned hash is aligned to guin64, hence, it is save
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* to use it as guint* or guint64* pointer. */
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static union {
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guint8 v8[HASH_KEY_SIZE];
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} g_arr _nm_alignas (guint64);
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static gsize g_lock;
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if (g_once_init_enter (&g_lock)) {
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nm_utils_random_bytes (g_arr.v8, sizeof (g_arr.v8));
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g_atomic_pointer_compare_and_exchange (&global_seed, NULL, g_arr.v8);
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g = g_arr.v8;
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g_once_init_leave (&g_lock, 1);
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} else {
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g = global_seed;
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nm_assert (g);
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}
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}
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return g;
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}
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void
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nm_hash_init (NMHashState *state, guint static_seed)
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{
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const guint8 *g;
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guint seed[HASH_KEY_SIZE_GUINT];
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nm_assert (state);
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g = _get_hash_key ();
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memcpy (seed, g, HASH_KEY_SIZE);
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seed[0] ^= static_seed;
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siphash24_init (&state->_state, (const guint8 *) seed);
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}
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guint
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nm_hash_str (const char *str)
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{
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NMHashState h;
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if (str) {
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nm_hash_init (&h, 1867854211u);
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nm_hash_update_str (&h, str);
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} else
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nm_hash_init (&h, 842995561u);
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return nm_hash_complete (&h);
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}
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guint
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nm_str_hash (gconstpointer str)
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{
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return nm_hash_str (str);
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}
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guint
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nm_hash_ptr (gconstpointer ptr)
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{
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guint h;
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h = ((const guint *) _get_hash_key ())[0];
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if (sizeof (ptr) <= sizeof (guint))
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h = h ^ ((guint) ((uintptr_t) ptr));
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else
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h = h ^ ((guint) (((uintptr_t) ptr) >> 32)) ^ ((guint) ((uintptr_t) ptr));
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return h ?: 2907677551u;
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}
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guint
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nm_direct_hash (gconstpointer ptr)
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{
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return nm_hash_ptr (ptr);
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}
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