netfilter: xt_IDLETIMER: fix sysfs callback function type

Use struct device_attribute instead of struct idletimer_tg_attr, and
the correct callback function type to avoid indirect call mismatches
with Control Flow Integrity checking.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_IDLETIMER.c

@@ -41,19 +41,13 @@
 #include <linux/workqueue.h>
 #include <linux/sysfs.h>
 
-struct idletimer_tg_attr {
-	struct attribute attr;
-	ssize_t	(*show)(struct kobject *kobj,
-			struct attribute *attr, char *buf);
-};
-
 struct idletimer_tg {
 	struct list_head entry;
 	struct timer_list timer;
 	struct work_struct work;
 
 	struct kobject *kobj;
-	struct idletimer_tg_attr attr;
+	struct device_attribute attr;
 
 	unsigned int refcnt;
 };
@@ -76,15 +70,15 @@ struct idletimer_tg *__idletimer_tg_find_by_label(const char *label)
 	return NULL;
 }
 
-static ssize_t idletimer_tg_show(struct kobject *kobj, struct attribute *attr,
-				 char *buf)
+static ssize_t idletimer_tg_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
 {
 	struct idletimer_tg *timer;
 	unsigned long expires = 0;
 
 	mutex_lock(&list_mutex);
 
-	timer =	__idletimer_tg_find_by_label(attr->name);
+	timer =	__idletimer_tg_find_by_label(attr->attr.name);
 	if (timer)
 		expires = timer->timer.expires;