SELinux: ensure keys constant in hashtab_search

Makes the key argument passed into hashtab_search and all the functions
it calls constant. These functions include hash table function pointers
hash_value and keycmp. The only implementations of these currently
are symhash and symcmp, which do not modify the key. The key parameter
should never be changed by any of these, so it should be const. This
is necessary to allow calling these functions with keys found in kernel
object class and permission definitions.

Signed-off-by: Chad Sellers <csellers@tresys.com>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/selinux/ss/hashtab.c b/security/selinux/ss/hashtab.c
index 24e5ec9..77b530c 100644
--- a/security/selinux/ss/hashtab.c
+++ b/security/selinux/ss/hashtab.c
@@ -8,8 +8,8 @@
 #include <linux/errno.h>
 #include "hashtab.h"
 
-struct hashtab *hashtab_create(u32 (*hash_value)(struct hashtab *h, void *key),
-                               int (*keycmp)(struct hashtab *h, void *key1, void *key2),
+struct hashtab *hashtab_create(u32 (*hash_value)(struct hashtab *h, const void *key),
+                               int (*keycmp)(struct hashtab *h, const void *key1, const void *key2),
                                u32 size)
 {
 	struct hashtab *p;
@@ -71,7 +71,7 @@
 	return 0;
 }
 
-void *hashtab_search(struct hashtab *h, void *key)
+void *hashtab_search(struct hashtab *h, const void *key)
 {
 	u32 hvalue;
 	struct hashtab_node *cur;