ima: Simplify ima_lsm_copy_rule

Currently ima_lsm_copy_rule() set the arg_p field of the source rule to
NULL, so that the source rule could be freed afterward. It does not make
sense for this behavior to be inside a "copy" function. So move it
outside and let the caller handle this field.

ima_lsm_copy_rule() now produce a shallow copy of the original entry
including args_p field. Meaning only the lsm.rule and the rule itself
should be freed for the original rule. Thus, instead of calling
ima_lsm_free_rule() which frees lsm.rule as well as args_p field, free
the lsm.rule directly.
Signed-off-by: GUO Zihua <guozihua@huawei.com>
Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima_policy.c

@@ -398,12 +398,6 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
 
 		nentry->lsm[i].type = entry->lsm[i].type;
 		nentry->lsm[i].args_p = entry->lsm[i].args_p;
-		/*
-		 * Remove the reference from entry so that the associated
-		 * memory will not be freed during a later call to
-		 * ima_lsm_free_rule(entry).
-		 */
-		entry->lsm[i].args_p = NULL;
 
 		ima_filter_rule_init(nentry->lsm[i].type, Audit_equal,
 				     nentry->lsm[i].args_p,
@@ -417,6 +411,7 @@ static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
 
 static int ima_lsm_update_rule(struct ima_rule_entry *entry)
 {
+	int i;
 	struct ima_rule_entry *nentry;
 
 	nentry = ima_lsm_copy_rule(entry);
@@ -431,7 +426,8 @@ static int ima_lsm_update_rule(struct ima_rule_entry *entry)
 	 * references and the entry itself. All other memory references will now
 	 * be owned by nentry.
 	 */
-	ima_lsm_free_rule(entry);
+	for (i = 0; i < MAX_LSM_RULES; i++)
+		ima_filter_rule_free(entry->lsm[i].rule);
 	kfree(entry);
 
 	return 0;