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72b4139700
Recent discussions have illustrated the potential for DOS attacks with the hash table implementations used by most languages and libraries. https://lwn.net/Articles/474912/ libvirt has an internal hash table impl, and uses hash tables for a variety of purposes. The hash key generation code is pretty simple and thus not strongly collision resistant. This patch replaces the current libvirt hash key generator with the (public domain) Murmurhash3 code. In addition every hash table now gets a random seed value which is used to perturb the hashing code. This should make it impossible to mount any practical attack against libvirt hashing code. * bootstrap.conf: Import bitrotate module * src/Makefile.am: Add virhashcode.[ch] * src/util/util.c: Make virRandom() return a fixed 32 bit integer value. * src/util/hash.c, src/util/hash.h, src/util/cgroup.c: Replace hash code generation with a call to virHashCodeGen() * src/util/virhashcode.h, src/util/virhashcode.c: Add a new virHashCodeGen() API using the Murmurhash3 algorithm.
124 lines
2.8 KiB
C
124 lines
2.8 KiB
C
/*
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* virhashcode.c: hash code generation
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*
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* Copyright (C) 2012 Red Hat, Inc.
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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 2.1 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 Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* The hash code generation is based on the public domain MurmurHash3 from Austin Appleby:
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* http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
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*
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* We use only the 32 bit variant because the 2 produce different results while
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* we need to produce the same result regardless of the architecture as
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* clients can be both 64 or 32 bit at the same time.
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*/
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#include <config.h>
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#include "virhashcode.h"
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#include "bitrotate.h"
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/* slower than original but handles platforms that do only aligned reads */
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__attribute__((always_inline))
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static uint32_t getblock(const uint8_t *p, int i)
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{
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uint32_t r;
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size_t size = sizeof(r);
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memcpy(&r, &p[i * size], size);
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return r;
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}
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/*
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* Finalization mix - force all bits of a hash block to avalanche
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*/
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__attribute__((always_inline))
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static uint32_t fmix(uint32_t h)
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{
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h ^= h >> 16;
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h *= 0x85ebca6b;
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h ^= h >> 13;
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h *= 0xc2b2ae35;
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h ^= h >> 16;
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return h;
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}
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uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed)
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{
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const uint8_t *blocks;
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const uint8_t *tail;
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size_t nblocks;
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uint32_t h1;
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uint32_t k1;
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uint32_t c1;
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uint32_t c2;
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size_t i;
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blocks = (const uint8_t *)key;
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nblocks = len / 4;
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h1 = seed;
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c1 = 0xcc9e2d51;
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c2 = 0x1b873593;
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/* body */
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for (i = 0; i < nblocks; i++) {
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k1 = getblock(blocks, i);
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k1 *= c1;
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k1 = rotl32(k1, 15);
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k1 *= c2;
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h1 ^= k1;
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h1 = rotl32(h1, 13);
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h1 = h1 * 5 + 0xe6546b64;
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}
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/* tail */
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tail = (const uint8_t *)key + nblocks * 4;
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k1 = 0;
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switch (len & 3) {
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case 3:
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k1 ^= tail[2] << 16;
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/* fallthrough */
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case 2:
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k1 ^= tail[1] << 8;
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/* fallthrough */
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case 1:
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k1 ^= tail[0];
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k1 *= c1;
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k1 = rotl32(k1, 15);
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k1 *= c2;
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h1 ^= k1;
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/* fallthrough */
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default:
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break;
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}
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/* finalization */
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h1 ^= len;
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h1 = fmix(h1);
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return h1;
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}
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