From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2F7B8CE7A81 for ; Mon, 25 Sep 2023 08:30:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232827AbjIYIaI (ORCPT ); Mon, 25 Sep 2023 04:30:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232664AbjIYIaH (ORCPT ); Mon, 25 Sep 2023 04:30:07 -0400 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DFB58C4; Mon, 25 Sep 2023 01:29:59 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R121e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046060;MF=alibuda@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0VsoSBCa_1695630596; Received: from 30.221.144.144(mailfrom:alibuda@linux.alibaba.com fp:SMTPD_---0VsoSBCa_1695630596) by smtp.aliyun-inc.com; Mon, 25 Sep 2023 16:29:57 +0800 Message-ID: Date: Mon, 25 Sep 2023 16:29:53 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH net] net/smc: fix panic smc_tcp_syn_recv_sock() while closing listen socket Content-Language: en-US To: Wenjia Zhang , kgraul@linux.ibm.com, jaka@linux.ibm.com Cc: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org References: <1695211714-66958-1-git-send-email-alibuda@linux.alibaba.com> <0902f55b-0d51-7f4d-0a9e-4b9423217fcf@linux.ibm.com> From: "D. Wythe" In-Reply-To: <0902f55b-0d51-7f4d-0a9e-4b9423217fcf@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 9/22/23 7:59 AM, Wenjia Zhang wrote: > > > On 20.09.23 14:08, D. Wythe wrote: >> From: "D. Wythe" >> >> 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 >> --- >>   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 Wenjia, > > 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. > Life-time problem? If you means the smc will still be NULL in the future,  I don't really think so, smc is a local variable assigned by smc_clcsock_user_data. it's either NULL or a valid and unchanged value. And READ_ONCE() is needed indeed, considering not make too much change, maybe we can protected following smc = smc_clcsock_user_data(sk); with sk_callback_lock， which solves the same problem. What do you think? Best Wishes D. Wythe