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    Subject[PATCH 5.10 099/103] block: fix use-after-free in disk_part_iter_next
    Date
    From: Ming Lei <ming.lei@redhat.com>

    commit aebf5db917055b38f4945ed6d621d9f07a44ff30 upstream.

    Make sure that bdgrab() is done on the 'block_device' instance before
    referring to it for avoiding use-after-free.

    Cc: <stable@vger.kernel.org>
    Reported-by: syzbot+825f0f9657d4e528046e@syzkaller.appspotmail.com
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    block/genhd.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    --- a/block/genhd.c
    +++ b/block/genhd.c
    @@ -256,14 +256,17 @@ struct hd_struct *disk_part_iter_next(st
    part = rcu_dereference(ptbl->part[piter->idx]);
    if (!part)
    continue;
    + get_device(part_to_dev(part));
    + piter->part = part;
    if (!part_nr_sects_read(part) &&
    !(piter->flags & DISK_PITER_INCL_EMPTY) &&
    !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
    - piter->idx == 0))
    + piter->idx == 0)) {
    + put_device(part_to_dev(part));
    + piter->part = NULL;
    continue;
    + }

    - get_device(part_to_dev(part));
    - piter->part = part;
    piter->idx += inc;
    break;
    }

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