tomoyo: improve hash bucket dispersion

When examining the network device name hash, it was discovered that
the low order bits of full_name_hash() are not very well dispersed
across the possible values. When used by filesystem code, this is handled
by folding with the function hash_long().

The only other non-filesystem usage of full_name_hash() at this time
appears to be in TOMOYO. This patch should fix that.

I do not use TOMOYO at this time, so this patch is build tested only.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
index 5f2e332..917f564 100644 (file)
--- a/security/tomoyo/realpath.c
+++ b/security/tomoyo/realpath.c
@@ -13,6 +13,8 @@
 #include <linux/mount.h>
 #include <linux/mnt_namespace.h>
 #include <linux/fs_struct.h>
+#include <linux/hash.h>
+
 #include "common.h"
 #include "realpath.h"
 
@@ -263,7 +265,8 @@ static unsigned int tomoyo_quota_for_savename;
  * table. Frequency of appending strings is very low. So we don't need
  * large (e.g. 64k) hash size. 256 will be sufficient.
  */
-#define TOMOYO_MAX_HASH 256
+#define TOMOYO_HASH_BITS  8
+#define TOMOYO_MAX_HASH (1u<<TOMOYO_HASH_BITS)
 
 /*
  * tomoyo_name_entry is a structure which is used for linking
@@ -315,6 +318,7 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
        struct tomoyo_free_memory_block_list *fmb;
        int len;
        char *cp;
+       struct list_head *head;
 
        if (!name)
                return NULL;
@@ -325,9 +329,10 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
                return NULL;
        }
        hash = full_name_hash((const unsigned char *) name, len - 1);
+       head = &tomoyo_name_list[hash_long(hash, TOMOYO_HASH_BITS)];
+
        mutex_lock(&lock);
-       list_for_each_entry(ptr, &tomoyo_name_list[hash % TOMOYO_MAX_HASH],
-                            list) {
+       list_for_each_entry(ptr, head, list) {
                if (hash == ptr->entry.hash && !strcmp(name, ptr->entry.name))
                        goto out;
        }
@@ -365,7 +370,7 @@ const struct tomoyo_path_info *tomoyo_save_name(const char *name)
        tomoyo_fill_path_info(&ptr->entry);
        fmb->ptr += len;
        fmb->len -= len;
-       list_add_tail(&ptr->list, &tomoyo_name_list[hash % TOMOYO_MAX_HASH]);
+       list_add_tail(&ptr->list, head);
        if (fmb->len == 0) {
                list_del(&fmb->list);
                kfree(fmb);