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

Wenjia Zhang
2023-09-21T23:59:38Z

On 20.09.23 14:08, D. Wythe wrote:
> From: "D. Wythe" <alibuda@linux.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@linux.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