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Subject: Re: [PATCH -next] nbd: get config_lock before sock_shutdown
To:     Zhong Jinghua <zhongjinghua@huaweicloud.com>, josef@toxicpanda.com,
        axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, nbd@other.debian.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230707062256.1271948-1-zhongjinghua@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <779966af-844a-3dba-93f8-9daabde8c85b@huaweicloud.com>
Date:   Fri, 28 Jul 2023 15:10:38 +0800
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?? 2023/07/07 14:22, Zhong Jinghua д??:
> Config->socks in sock_shutdown may trigger a UAF problem.
> The reason is that sock_shutdown does not hold the config_lock,
> so that nbd_ioctl can release config->socks at this time.
> 
> T0: NBD_SET_SOCK
> T1: NBD_DO_IT
> 
> T0						T1
> 
> nbd_ioctl
>    mutex_lock(&nbd->config_lock)
>    // get lock
>    __nbd_ioctl
>      nbd_start_device_ioctl
>        nbd_start_device
>         mutex_unlock(&nbd->config_lock)
>           // relase lock
>           wait_event_interruptible
>           (kill, enter sock_shutdown)
>           sock_shutdown
> 					nbd_ioctl
> 					  mutex_lock(&nbd->config_lock)
> 					  // get lock
> 					  __nbd_ioctl
> 					    nbd_add_socket
> 					      krealloc
> 						kfree(p)
> 					        //config->socks is NULL
>             nbd_sock *nsock = config->socks // error
> 
> Fix it by moving config_lock up before sock_shutdown.

LGTM
Reviewed-by: Yu Kuai <yukuai3@huawei.com>

> 
> Signed-off-by: Zhong Jinghua <zhongjinghua@huaweicloud.com>
> ---
>   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 c410cf29fb0c..accbe99ebb7e 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1428,13 +1428,18 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd)
>   	mutex_unlock(&nbd->config_lock);
>   	ret = wait_event_interruptible(config->recv_wq,
>   					 atomic_read(&config->recv_threads) == 0);
> +
> +	/*
> +	 * recv_work in flush_workqueue will not get this lock, because nbd_open
> +	 * will hold nbd->config_refs
> +	 */
> +	mutex_lock(&nbd->config_lock);
>   	if (ret) {
>   		sock_shutdown(nbd);
>   		nbd_clear_que(nbd);
>   	}
>   
>   	flush_workqueue(nbd->recv_workq);
> -	mutex_lock(&nbd->config_lock);
>   	nbd_bdev_reset(nbd);
>   	/* user requested, ignore socket errors */
>   	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
>