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

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Message-ID: <20230921031956.GA92403@linux.alibaba.com>
Date: Thu, 21 Sep 2023 11:19:56 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com,
	wenjia@...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 Wed, Sep 20, 2023 at 08:08:34PM +0800, 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;

Is it possible smc != NULL here
> 
> 	if (READ_ONCE(sk->sk_ack_backlog) + atomic_read(&smc->queued_smc_hs) >
But later turns to NULL in 'atomic_read(&smc->queue_smc_hs)'
> 				sk->sk_max_ack_backlog)

Seems there is still a race ?

>-- 
>1.8.3.1