Subject: Re: [PATCH net] net/smc: fix panic smc_tcp_syn_recv_sock() while closing listen socket

From: Simon Horman <[email-masked]>
Date: Thu, 21 Sep 2023 22:43:25 +0100

On Wed, Sep 20, 2023 at 08:08:34PM +0800, D. Wythe wrote:
> From: "D. Wythe" <[email-masked]>
> 
> 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"

The tag above is malformed. The correct form is:

Fixes: 8270d9c21041 ("net/smc: Limit backlog connections")

> Signed-off-by: D. Wythe <[email-masked]>
> ---
>  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)
> -- 
> 1.8.3.1
> 
>