netdev - Re: [PATCH net] net/smc: fix panic smc_tcp_syn_recv

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Message-ID: <0902f55b-0d51-7f4d-0a9e-4b9423217fcf@linux.ibm.com>
Date: Fri, 22 Sep 2023 01:59:24 +0200
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com,
        jaka@...ux.ibm.com
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net] net/smc: fix panic smc_tcp_syn_recv_sock() while
 closing listen socket



On 20.09.23 14:08, D. Wythe wrote:
> From: "D. Wythe" <alibuda@...ux.alibaba.com>
> 
> Consider the following scenarios:
> 
> smc_release
> 	smc_close_active
> 		write_lock_bh(&smc->clcsock->sk->sk_callback_lock);
> 		smc->clcsock->sk->sk_user_data = NULL;
> 		write_unlock_bh(&smc->clcsock->sk->sk_callback_lock);
> 
> smc_tcp_syn_recv_sock
> 	smc = smc_clcsock_user_data(sk);
> 	/* now */
> 	/* smc == NULL */
> 
> Hence, we may read the a NULL value in smc_tcp_syn_recv_sock(). And
> since we only unset sk_user_data during smc_release, it's safe to
> drop the incoming tcp reqsock.
> 
> Fixes:  ("net/smc: net/smc: Limit backlog connections"
> Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> ---
>   net/smc/af_smc.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> index bacdd97..b4acf47 100644
> --- a/net/smc/af_smc.c
> +++ b/net/smc/af_smc.c
> @@ -125,6 +125,8 @@ static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk,
>   	struct sock *child;
>   
>   	smc = smc_clcsock_user_data(sk);
> +	if (unlikely(!smc))
> +		goto drop;
>   
>   	if (READ_ONCE(sk->sk_ack_backlog) + atomic_read(&smc->queued_smc_hs) >
>   				sk->sk_max_ack_backlog)

Hi D.Wythe,

this is unfortunately not sufficient for this fix. You have to make sure 
that is not a life-time problem. Even so, READ_ONCE() is also needed in 
this case.

Thanks,
Wenjia