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    Subject[PATCH 5.17 241/298] nbd: call genl_unregister_family() first in nbd_cleanup()
    Date
    From: Yu Kuai <yukuai3@huawei.com>

    [ Upstream commit 06c4da89c24e7023ea448cadf8e9daf06a0aae6e ]

    Otherwise there may be race between module removal and the handling of
    netlink command, which can lead to the oops as shown below:

    BUG: kernel NULL pointer dereference, address: 0000000000000098
    Oops: 0002 [#1] SMP PTI
    CPU: 1 PID: 31299 Comm: nbd-client Tainted: G E 5.14.0-rc4
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
    RIP: 0010:down_write+0x1a/0x50
    Call Trace:
    start_creating+0x89/0x130
    debugfs_create_dir+0x1b/0x130
    nbd_start_device+0x13d/0x390 [nbd]
    nbd_genl_connect+0x42f/0x748 [nbd]
    genl_family_rcv_msg_doit.isra.0+0xec/0x150
    genl_rcv_msg+0xe5/0x1e0
    netlink_rcv_skb+0x55/0x100
    genl_rcv+0x29/0x40
    netlink_unicast+0x1a8/0x250
    netlink_sendmsg+0x21b/0x430
    ____sys_sendmsg+0x2a4/0x2d0
    ___sys_sendmsg+0x81/0xc0
    __sys_sendmsg+0x62/0xb0
    __x64_sys_sendmsg+0x1f/0x30
    do_syscall_64+0x3b/0xc0
    entry_SYSCALL_64_after_hwframe+0x44/0xae
    Modules linked in: nbd(E-)

    Signed-off-by: Hou Tao <houtao1@huawei.com>
    Signed-off-by: Yu Kuai <yukuai3@huawei.com>
    Reviewed-by: Josef Bacik <josef@toxicpanda.com>
    Link: https://lore.kernel.org/r/20220521073749.3146892-2-yukuai3@huawei.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/block/nbd.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index ed678037ba6d..b4d309af27dd 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -2544,6 +2544,12 @@ static void __exit nbd_cleanup(void)
    struct nbd_device *nbd;
    LIST_HEAD(del_list);

    + /*
    + * Unregister netlink interface prior to waiting
    + * for the completion of netlink commands.
    + */
    + genl_unregister_family(&nbd_genl_family);
    +
    nbd_dbg_close();

    mutex_lock(&nbd_index_mutex);
    @@ -2562,7 +2568,6 @@ static void __exit nbd_cleanup(void)
    destroy_workqueue(nbd_del_wq);

    idr_destroy(&nbd_index_idr);
    - genl_unregister_family(&nbd_genl_family);
    unregister_blkdev(NBD_MAJOR, "nbd");
    }

    --
    2.35.1


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