Re: [PATCH -next v3 1/6] nbd: call genl_unregister_family() first in nbd_cleanup()

[Josef Bacik]

On Sat, May 21, 2022 at 03:37:44PM +0800, Yu Kuai wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>

Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>

Thanks,

Josef