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https://gitlab.freedesktop.org/NetworkManager/NetworkManager.git
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6fbd280b35
When using siphash24(), the hash value depends on the hashed input and the key from _get_hash_key(). If the input is static, so is also the result of siphash24(), albeit the bits are scrabbled more. Add a nm_hash_static() to get such a static key, but without actually doing siphash24(). The static key is also xored with a static_seed. For that, also mangle the first byte of the hash key using siphash24() itself. That is, because nm_hash_static() only uses the first guint of the random key. Hence, we want that this first guint has all the entropy of the entire key. We use siphash24() itself, to mangle all bits of the 16 byte key into the first guint.
152 lines
4 KiB
C
152 lines
4 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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/* the returned hash is aligned to guin64, hence, it is safe
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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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const guint8 *g;
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struct siphash siph_state;
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uint64_t h;
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guint *p;
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g = global_seed;
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if (G_LIKELY (g != NULL)) {
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nm_assert (g == g_arr.v8);
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return g;
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}
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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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/* use siphash() of the key-size, to mangle the first guint. Otherwise,
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* the first guint has only the entropy that nm_utils_random_bytes()
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* generated for the first 4 bytes and relies on a good random generator. */
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siphash24_init (&siph_state, g_arr.v8);
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siphash24_compress (g_arr.v8, sizeof (g_arr.v8), &siph_state);
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h = siphash24_finalize (&siph_state);
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p = (guint *) g_arr.v8;
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if (sizeof (guint) < sizeof (h))
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*p = *p ^ ((guint) (h & 0xFFFFFFFFu)) ^ ((guint) (h >> 32));
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else
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*p = *p ^ ((guint) (h & 0xFFFFFFFFu));
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g_atomic_pointer_compare_and_exchange (&global_seed, NULL, g_arr.v8);
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g_once_init_leave (&g_lock, 1);
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}
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nm_assert (global_seed == g_arr.v8);
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return g_arr.v8;
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}
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guint
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nm_hash_static (guint static_seed)
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{
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/* note that we only xor the static_seed with the key.
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* We don't use siphash24(), which would mix the bits better.
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* Note that this doesn't matter, because static_seed is not
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* supposed to be a value that you are hashing (for that, use
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* full siphash24()).
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* Instead, different callers may set a different static_seed
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* so that nm_hash_str(NULL) != nm_hash_ptr(NULL).
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*
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* Also, ensure that we don't return zero.
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*/
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return ((*((const guint *) _get_hash_key ())) ^ static_seed)
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?: static_seed ?: 3679500967u;
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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) (((guint64) (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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