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 <[e-mail]>
Cc: [e-mail]
Fixes: 801c135ce73d ("UBI: Unsorted Block Images")
Reported-by: Chenyuan Yang <[e-mail]>
Closes: https://lore.kernel.org/linux-mtd/[e-mail]/
Signed-off-by: Richard Weinberger <[e-mail]>
Reviewed-by: Zhihao Cheng <[e-mail]>

drivers/mtd/ubi/vtbl.c

···
 	 * 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;