nvmet: check sscanf value for subsys serial attr

For nvmet in configfs.c we check return values for all the sscanf()
calls. Add similar check into the nvmet_subsys_attr_serial_store().
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/target/configfs.c

@@ -849,10 +849,13 @@ static ssize_t nvmet_subsys_attr_serial_show(struct config_item *item,
 static ssize_t nvmet_subsys_attr_serial_store(struct config_item *item,
 					      const char *page, size_t count)
 {
-	struct nvmet_subsys *subsys = to_subsys(item);
+	u64 serial;
+
+	if (sscanf(page, "%llx\n", &serial) != 1)
+		return -EINVAL;
 
 	down_write(&nvmet_config_sem);
-	sscanf(page, "%llx\n", &subsys->serial);
+	to_subsys(item)->serial = serial;
 	up_write(&nvmet_config_sem);
 
 	return count;