Replace hashing algorithm with murmurhash

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.

bootstrap.conf

@@ -23,6 +23,7 @@ accept
 areadlink
 base64
 bind
+bitrotate
 byteswap
 c-ctype
 c-strcase

src/Makefile.am

@@ -90,6 +90,7 @@ UTIL_SOURCES =							\
 		util/xml.c util/xml.h				\
 		util/virterror.c util/virterror_internal.h	\
 		util/virhash.c util/virhash.h			\
+		util/virhashcode.c util/virhashcode.h           \
 		util/virkeycode.c util/virkeycode.h		\
 		util/virkeymaps.h				\
 		util/virnetdev.h util/virnetdev.c		\

src/util/cgroup.c

@@ -33,6 +33,7 @@
 #include "logging.h"
 #include "virfile.h"
 #include "virhash.h"
+#include "virhashcode.h"
 
 #define CGROUP_MAX_VAL 512
 
@@ -1636,9 +1637,10 @@ cleanup:
 }
 
 
-static uint32_t virCgroupPidCode(const void *name)
+static uint32_t virCgroupPidCode(const void *name, uint32_t seed)
 {
-    return (uint32_t)(intptr_t)name;
+    unsigned long pid = (unsigned long)(intptr_t)name;
+    return virHashCodeGen(&pid, sizeof(pid), seed);
 }
 static bool virCgroupPidEqual(const void *namea, const void *nameb)
 {

src/util/virhash.c

@@ -28,6 +28,8 @@
 #include "virhash.h"
 #include "memory.h"
 #include "logging.h"
+#include "virhashcode.h"
+#include "virrandom.h"
 
 #define VIR_FROM_THIS VIR_FROM_NONE
 
@@ -57,6 +59,7 @@ struct _virHashEntry {
  */
 struct _virHashTable {
     virHashEntryPtr *table;
+    uint32_t seed;
     size_t size;
     size_t nbElems;
     /* True iff we are iterating over hash entries. */
@@ -70,20 +73,9 @@ struct _virHashTable {
     virHashKeyFree keyFree;
 };
 
-static uint32_t virHashStrCode(const void *name)
+static uint32_t virHashStrCode(const void *name, uint32_t seed)
 {
-    const char *str = name;
-    uint32_t value = 0L;
-    char ch;
-
-    if (str != NULL) {
-        value += 30 * (*str);
-        while ((ch = *str++) != 0) {
-            value =
-                value ^ ((value << 5) + (value >> 3) + (uint32_t) ch);
-        }
-    }
-    return value;
+    return virHashCodeGen(name, strlen(name), seed);
 }
 
 static bool virHashStrEqual(const void *namea, const void *nameb)
@@ -105,7 +97,7 @@ static void virHashStrFree(void *name)
 static size_t
 virHashComputeKey(virHashTablePtr table, const void *name)
 {
-    uint32_t value = table->keyCode(name);
+    uint32_t value = table->keyCode(name, table->seed);
     return (value % table->size);
 }
 
@@ -139,6 +131,7 @@ virHashTablePtr virHashCreateFull(ssize_t size,
         return NULL;
     }
 
+    table->seed = virRandomBits(32);
     table->size = size;
     table->nbElems = 0;
     table->dataFree = dataFree;

src/util/virhash.h

@@ -56,12 +56,15 @@ typedef int (*virHashSearcher) (const void *payload, const void *name,
 /**
  * virHashKeyCode:
  * @name: the hash key
+ * @seed: random seed
  *
- * Compute the hash code corresponding to the key @name
+ * Compute the hash code corresponding to the key @name, using
+ * @seed to perturb the hashing algorithm
  *
  * Returns the hash code
  */
-typedef uint32_t (*virHashKeyCode)(const void *name);
+typedef uint32_t (*virHashKeyCode)(const void *name,
+                                   uint32_t seed);
 /**
  * virHashKeyEqual:
  * @namea: the first hash key

src/util/virhashcode.c

+/*
+ * virhashcode.c: hash code generation
+ *
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ * The hash code generation is based on the public domain MurmurHash3 from Austin Appleby:
+ * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
+ *
+ * We use only the 32 bit variant because the 2 produce different results while
+ * we need to produce the same result regardless of the architecture as
+ * clients can be both 64 or 32 bit at the same time.
+ */
+
+#include <config.h>
+
+#include "virhashcode.h"
+#include "bitrotate.h"
+
+/* slower than original but handles platforms that do only aligned reads */
+__attribute__((always_inline))
+static uint32_t getblock(const uint8_t *p, int i)
+{
+    uint32_t r;
+    size_t size = sizeof(r);
+
+    memcpy(&r, &p[i * size], size);
+
+    return r;
+}
+
+/*
+ * Finalization mix - force all bits of a hash block to avalanche
+ */
+__attribute__((always_inline))
+static uint32_t fmix(uint32_t h)
+{
+    h ^= h >> 16;
+    h *= 0x85ebca6b;
+    h ^= h >> 13;
+    h *= 0xc2b2ae35;
+    h ^= h >> 16;
+
+    return h;
+}
+
+
+uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed)
+{
+    const uint8_t *blocks;
+    const uint8_t *tail;
+    size_t nblocks;
+    uint32_t h1;
+    uint32_t k1;
+    uint32_t c1;
+    uint32_t c2;
+    size_t i;
+
+    blocks = (const uint8_t *)key;
+    nblocks = len / 4;
+    h1 = seed;
+    c1 = 0xcc9e2d51;
+    c2 = 0x1b873593;
+
+    /* body */
+
+    for (i = 0; i < nblocks; i++) {
+
+        k1 = getblock(blocks, i);
+
+        k1 *= c1;
+        k1 = rotl32(k1, 15);
+        k1 *= c2;
+
+        h1 ^= k1;
+        h1 = rotl32(h1, 13);
+        h1 = h1 * 5 + 0xe6546b64;
+    }
+
+    /* tail */
+
+    tail = (const uint8_t *)key + nblocks * 4;
+
+    k1 = 0;
+
+    switch (len & 3) {
+    case 3:
+        k1 ^= tail[2] << 16;
+        /* fallthrough */
+    case 2:
+        k1 ^= tail[1] << 8;
+        /* fallthrough */
+    case 1:
+        k1 ^= tail[0];
+        k1 *= c1;
+        k1 = rotl32(k1, 15);
+        k1 *= c2;
+        h1 ^= k1;
+        /* fallthrough */
+    default:
+        break;
+    }
+
+    /* finalization */
+
+    h1 ^= len;
+    h1 = fmix(h1);
+
+    return h1;
+}

src/util/virhashcode.h

+/*
+ * virhashcode.h: hash code generation
+ *
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ * The hash code generation is based on the public domain MurmurHash3 from Austin Appleby:
+ * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
+ *
+ * We use only the 32 bit variant because the 2 produce different result while
+ * we need to produce the same result regardless of the architecture as
+ * clients can be both 64 or 32 bit at the same time.
+ */
+
+#ifndef __VIR_HASH_CODE_H__
+# define __VIR_HASH_CODE_H__
+
+# include "internal.h"
+
+extern uint32_t virHashCodeGen(const void *key, size_t len, uint32_t seed);
+
+#endif /* __VIR_HASH_CODE_H__ */