security: convert security hooks to use hlist

This changes security_hook_heads to use hlist_heads instead of
the circular doubly-linked list heads. This should cut down
the size of the struct by about half.

In addition, it allows mutation of the hooks at the tail of the
callback list without having to modify the head. The longer-term
purpose of this is to enable making the heads read only.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Reviewed-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index c4a345c..6d5bbd31 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -52,8 +52,8 @@ static const struct whitelist_entry whitelist[] = {
 	{ "net/unix/af_unix.c", "unix_skb_parms", "char" },
 	/* big_key payload.data struct splashing */
 	{ "security/keys/big_key.c", "path", "void *" },
-	/* walk struct security_hook_heads as an array of struct list_head */
-	{ "security/security.c", "list_head", "security_hook_heads" },
+	/* walk struct security_hook_heads as an array of struct hlist_head */
+	{ "security/security.c", "hlist_head", "security_hook_heads" },
 	{ }
 };