UBI: improve mkvol request validation

Check that volume name is not shorter than 'name_len'.

No need to copy the trailing zero byte because whole array
was zeroed earlier.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/drivers/mtd/ubi/cdev.c b/drivers/mtd/ubi/cdev.c
index 3e3449e..4fb84e3 100644
--- a/drivers/mtd/ubi/cdev.c
+++ b/drivers/mtd/ubi/cdev.c
@@ -574,6 +574,10 @@
 		goto bad;
 	}
 
+	n = strnlen(req->name, req->name_len + 1);
+	if (n != req->name_len)
+		goto bad;
+
 	return 0;
 
 bad:
@@ -629,12 +633,11 @@
 			break;
 		}
 
+		req.name[req.name_len] = '\0';
 		err = verify_mkvol_req(ubi, &req);
 		if (err)
 			break;
 
-		req.name[req.name_len] = '\0';
-
 		mutex_lock(&ubi->volumes_mutex);
 		err = ubi_create_volume(ubi, &req);
 		mutex_unlock(&ubi->volumes_mutex);