Randomise hashes by providing a seed.

This is supposed to be a "good enough" approach. Using a crypto quality
function like apr_generate_random_bytes() may be stronger, but this function
may block, so it will be avoided for now.

git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1231605 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 25 insertions, 7 deletions

diff --git a/tables/apr_hash.c b/tables/apr_hash.c
index d64e77941..f899d5156 100644
--- a/tables/apr_hash.c
+++ b/tables/apr_hash.c
@@ -18,6 +18,10 @@
 
 #include "apr_general.h"
 #include "apr_pools.h"
+#include "apr_time.h"
+#if APR_HAVE_STDLIB_H
+#include <stdlib.h>     /* for rand, srand */
+#endif
 
 #include "apr_hash.h"
 
@@ -75,7 +79,7 @@ struct apr_hash_t {
     apr_pool_t          *pool;
     apr_hash_entry_t   **array;
     apr_hash_index_t     iterator;  /* For apr_hash_first(NULL, ...) */
-    unsigned int         count, max;
+    unsigned int         count, max, seed;
     apr_hashfunc_t       hash_func;
     apr_hash_entry_t    *free;  /* List of recycled entries */
 };
@@ -95,13 +99,18 @@ static apr_hash_entry_t **alloc_array(apr_hash_t *ht, unsigned int max)
 APR_DECLARE(apr_hash_t *) apr_hash_make(apr_pool_t *pool)
 {
     apr_hash_t *ht;
+    apr_time_t now = apr_time_now();
+
     ht = apr_palloc(pool, sizeof(apr_hash_t));
     ht->pool = pool;
     ht->free = NULL;
     ht->count = 0;
     ht->max = INITIAL_MAX;
+    srand((unsigned int)((now >> 32) ^ now ^ (apr_uintptr_t)ht));
+    ht->seed = (unsigned int)(rand());
     ht->array = alloc_array(ht, ht->max);
-    ht->hash_func = apr_hashfunc_default;
+    ht->hash_func = NULL;
+
     return ht;
 }
 
@@ -201,10 +210,10 @@ static void expand_array(apr_hash_t *ht)
     ht->max = new_max;
 }
 
-APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *char_key,
-                                                      apr_ssize_t *klen)
+static unsigned int apr_hashfunc_default_internal(const char *char_key,
+                                                  apr_ssize_t *klen,
+                                                  unsigned int hash)
 {
-    unsigned int hash = 0;
     const unsigned char *key = (const unsigned char *)char_key;
     const unsigned char *p;
     apr_ssize_t i;
@@ -246,7 +255,7 @@ APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *char_key,
      *
      *                  -- Ralf S. Engelschall <rse@engelschall.com>
      */
-     
+
     if (*klen == APR_HASH_KEY_STRING) {
         for (p = key; *p; p++) {
             hash = hash * 33 + *p;
@@ -262,6 +271,11 @@ APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *char_key,
     return hash;
 }
 
+APR_DECLARE_NONSTD(unsigned int) apr_hashfunc_default(const char *char_key,
+                                                      apr_ssize_t *klen)
+{
+    return apr_hashfunc_default_internal(char_key, klen, 0);
+}
 
 /*
  * This is where we keep the details of the hash function and control
@@ -280,7 +294,10 @@ static apr_hash_entry_t **find_entry(apr_hash_t *ht,
     apr_hash_entry_t **hep, *he;
     unsigned int hash;
 
-    hash = ht->hash_func(key, &klen);
+    if (ht->hash_func)
+        hash = ht->hash_func(key, &klen);
+    else
+        hash = apr_hashfunc_default_internal(key, &klen, ht->seed);
 
     /* scan linked list */
     for (hep = &ht->array[hash & ht->max], he = *hep;
@@ -322,6 +339,7 @@ APR_DECLARE(apr_hash_t *) apr_hash_copy(apr_pool_t *pool,
     ht->free = NULL;
     ht->count = orig->count;
     ht->max = orig->max;
+    ht->seed = orig->seed;
     ht->hash_func = orig->hash_func;
     ht->array = (apr_hash_entry_t **)((char *)ht + sizeof(apr_hash_t));