nvmet: fix memory leak in nvmet_subsys_attr_model_store_locked

Since model_number is allocated before it needs to be freed before
kmemdump_nul.
Reviewed-by: Konstantin Shelekhin <k.shelekhin@yadro.com>
Reviewed-by: Dmitriy Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Aleksandr Miloserdov <a.miloserdov@yadro.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/configfs.c

@@ -1215,6 +1215,7 @@ static ssize_t nvmet_subsys_attr_model_store_locked(struct nvmet_subsys *subsys,
 		const char *page, size_t count)
 {
 	int pos = 0, len;
+	char *val;
 
 	if (subsys->subsys_discovered) {
 		pr_err("Can't set model number. %s is already assigned\n",
@@ -1237,9 +1238,11 @@ static ssize_t nvmet_subsys_attr_model_store_locked(struct nvmet_subsys *subsys,
 			return -EINVAL;
 	}
 
-	subsys->model_number = kmemdup_nul(page, len, GFP_KERNEL);
-	if (!subsys->model_number)
+	val = kmemdup_nul(page, len, GFP_KERNEL);
+	if (!val)
 		return -ENOMEM;
+	kfree(subsys->model_number);
+	subsys->model_number = val;
 	return count;
 }