[PATCH 5.10 18/25] Revert "Revert "block: nbd: add sanity check for first_minor""

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Wen Yang <wenyang.linux@foxmail.com>

This reverts commit 0daa75bf750c400af0a0127fae37cd959d36dee7.

These problems such as:
https://lore.kernel.org/all/CACPK8XfUWoOHr-0RwRoYoskia4fbAbZ7DYf5wWBnv6qUnGq18w@mail.gmail.com/
It was introduced by introduced by commit b1a811633f73 ("block: nbd: add sanity check for first_minor")
and has been have been fixed by commit e4c4871a7394 ("nbd: fix max value for 'first_minor'").

Cc: Joel Stanley <joel@jms.id.au>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Pavel Skripkin <paskripkin@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sasha Levin <sashal@kernel.org>
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/block/nbd.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1771,7 +1771,17 @@ static int nbd_dev_add(int index)
 	refcount_set(&nbd->refs, 1);
 	INIT_LIST_HEAD(&nbd->list);
 	disk->major = NBD_MAJOR;
+
+	/* Too big first_minor can cause duplicate creation of
+	 * sysfs files/links, since first_minor will be truncated to
+	 * byte in __device_add_disk().
+	 */
 	disk->first_minor = index << part_shift;
+	if (disk->first_minor > 0xff) {
+		err = -EINVAL;
+		goto out_free_idr;
+	}
+
 	disk->fops = &nbd_fops;
 	disk->private_data = nbd;
 	sprintf(disk->disk_name, "nbd%d", index);