nbd: fix possible overflow for 'first_minor' in nbd_dev_add()

[ Upstream commit 940c264984fd1457918393c49674f6b39ee16506 ]

If 'part_shift' is not zero, then 'index << part_shift' might
overflow to a value that is not greater than '0xfffff', then sysfs
might complains about duplicate creation.

Fixes: b0d9111a2d53 ("nbd: use an idr to keep track of nbd devices")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20211102015237.2309763-3-yebin10@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 0d820c4..577c7db 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1749,11 +1749,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
        disk->major = NBD_MAJOR;
 
        /* Too big first_minor can cause duplicate creation of
-        * sysfs files/links, since MKDEV() expect that the max bits of
-        * first_minor is 20.
+        * sysfs files/links, since index << part_shift might overflow, or
+        * MKDEV() expect that the max bits of first_minor is 20.
         */
        disk->first_minor = index << part_shift;
-       if (disk->first_minor > MINORMASK) {
+       if (disk->first_minor < index || disk->first_minor > MINORMASK) {
                err = -EINVAL;
                goto out_free_idr;
        }