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

Josef Bacik
2022-05-23T14:14:02Z

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@huawei.com>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef