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    Subject[PATCH 5.14 718/849] nbd: fix possible overflow for first_minor in nbd_dev_add()
    Date
    From: Yu Kuai <yukuai3@huawei.com>

    [ 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>
    ---
    drivers/block/nbd.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index bdc6d656e785c..f72ff515ee51b 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -1777,11 +1777,11 @@ static int nbd_dev_add(int index)
    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;
    }
    --
    2.33.0


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