audit: use union for audit_field values since they are mutually exclusive

Since only one of val, uid, gid and lsm* are used at any given time, combine
them to reduce the size of the struct audit_field.
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

include/linux/audit.h

@@ -66,12 +66,16 @@ struct audit_krule {
 
 struct audit_field {
 	u32				type;
-	u32				val;
-	kuid_t				uid;
-	kgid_t				gid;
+	union {
+		u32			val;
+		kuid_t			uid;
+		kgid_t			gid;
+		struct {
+			char		*lsm_str;
+			void		*lsm_rule;
+		};
+	};
 	u32				op;
-	char				*lsm_str;
-	void				*lsm_rule;
 };
 
 extern int is_audit_feature_set(int which);

kernel/auditfilter.c

@@ -71,6 +71,24 @@ static struct list_head audit_rules_list[AUDIT_NR_FILTERS] = {
 
 DEFINE_MUTEX(audit_filter_mutex);
 
+static void audit_free_lsm_field(struct audit_field *f)
+{
+	switch (f->type) {
+	case AUDIT_SUBJ_USER:
+	case AUDIT_SUBJ_ROLE:
+	case AUDIT_SUBJ_TYPE:
+	case AUDIT_SUBJ_SEN:
+	case AUDIT_SUBJ_CLR:
+	case AUDIT_OBJ_USER:
+	case AUDIT_OBJ_ROLE:
+	case AUDIT_OBJ_TYPE:
+	case AUDIT_OBJ_LEV_LOW:
+	case AUDIT_OBJ_LEV_HIGH:
+		kfree(f->lsm_str);
+		security_audit_rule_free(f->lsm_rule);
+	}
+}
+
 static inline void audit_free_rule(struct audit_entry *e)
 {
 	int i;
@@ -80,11 +98,8 @@ static inline void audit_free_rule(struct audit_entry *e)
 	if (erule->watch)
 		audit_put_watch(erule->watch);
 	if (erule->fields)
-		for (i = 0; i < erule->field_count; i++) {
-			struct audit_field *f = &erule->fields[i];
-			kfree(f->lsm_str);
-			security_audit_rule_free(f->lsm_rule);
-		}
+		for (i = 0; i < erule->field_count; i++)
+			audit_free_lsm_field(&erule->fields[i]);
 	kfree(erule->fields);
 	kfree(erule->filterkey);
 	kfree(e);
@@ -422,10 +437,6 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
 
 		f->type = data->fields[i];
 		f->val = data->values[i];
-		f->uid = INVALID_UID;
-		f->gid = INVALID_GID;
-		f->lsm_str = NULL;
-		f->lsm_rule = NULL;
 
 		/* Support legacy tests for a valid loginuid */
 		if ((f->type == AUDIT_LOGINUID) && (f->val == AUDIT_UID_UNSET)) {