ubi: Check for too small LEB size in VTBL code

If the LEB size is smaller than a volume table record we cannot
have volumes.
In this case abort attaching.

Cc: Chenyuan Yang <cy54@illinois.edu>
Cc: stable@vger.kernel.org
Fixes: 801c135c ("UBI: Unsorted Block Images")
Reported-by: Chenyuan Yang <cy54@illinois.edu>
Closes: https://lore.kernel.org/linux-mtd/1433EB7A-FC89-47D6-8F47-23BE41B263B3@illinois.edu/Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>

drivers/mtd/ubi/vtbl.c

@@ -791,6 +791,12 @@ int ubi_read_volume_table(struct ubi_device *ubi, struct ubi_attach_info *ai)
 	 * The number of supported volumes is limited by the eraseblock size
 	 * and by the UBI_MAX_VOLUMES constant.
 	 */
+
+	if (ubi->leb_size < UBI_VTBL_RECORD_SIZE) {
+		ubi_err(ubi, "LEB size too small for a volume record");
+		return -EINVAL;
+	}
+
 	ubi->vtbl_slots = ubi->leb_size / UBI_VTBL_RECORD_SIZE;
 	if (ubi->vtbl_slots > UBI_MAX_VOLUMES)
 		ubi->vtbl_slots = UBI_MAX_VOLUMES;