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Wed, 5 Aug 2026 12:29:08 +0000 (GMT) Message-ID: <1f4251f0-0ab6-4f95-9658-d06ddedfae28@linux.ibm.com> Date: Wed, 5 Aug 2026 17:59:06 +0530 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net/smc: fix TOCTOU race between smc_listen_out() and listener close To: dust.li@linux.alibaba.com, Breno Leitao Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, alibuda@linux.alibaba.com, horms@kernel.org, mjambigi@linux.ibm.com, tonylu@linux.alibaba.com, guwen@linux.alibaba.com, hidayath@linux.ibm.com, pasic@linux.ibm.com, netdev@vger.kernel.org, linux-s390@vger.kernel.org References: <20260803070701.126339-1-sidraya@linux.ibm.com> <4157b86a-e2cb-470b-a526-137a650b9d5a@linux.ibm.com> Content-Language: en-US From: Sidraya Jayagond In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA1MDA5OSBTYWx0ZWRfX4lcO9a+C7+HM MPa18xmAeP7coRdVkrf8v6FYg+PxDw/4H0Z/W07IlAhlo7aUScElcIrijcCoNbt28qfg2PDjO7f hm5wVwS1zv4sCFPbdpYK505GE7jmk0+I++nfryWRZxadWW5zWvwzCHNRpcVxLzYcEMQRPcTkIWN Kps6HnjA1A35dVVRfJRxx9Ic6Qia9ahn/kI8ozY4niyrtmU7u5iIeoReFkwWyOo2RpQiW+7wwNK dglmIAmjUP7Vlu2WFsQKWUPBz3Ldmab/VQfT+zuRPN6XqctJAt8rq55EylrAUmk01Zts2ZnChp1 zkv413j828XviVteWJoQUCUXJt3zLFe33jXtXemAOkYejakv9FeH6dHgo3DCYXWQylSDz9OpWH2 KKmTn0Ky10b7gYWMBZT/VYgJOHtwqttVWbwfB5mwAKxVEod0Grbqm0FzSLkyTyWRyqTcqmZY0pM e7lCdpjH5uG70edj+Kg== X-Authority-Analysis: v=2.4 cv=WIFPmHsR c=1 sm=1 tr=0 ts=6a732ca0 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=SRrdq9N9AAAA:8 a=fLt5QA0OMVFA8XJhKYoA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: -HHs8ai1tsGuOp9XmR5DLjugnkI_PjwP X-Proofpoint-ORIG-GUID: 50nqUFLIcOp1fEIaBDb3SLlTb3d1CnF0 X-Proofpoint-Spam-Info: AW1haW4tMjYwODA1MDA5OSBTYWx0ZWRfX8wd60mi0Vfaq X48P0jcHh4PIgCrBiGQnhjtY+ohlc+Yc8VtJ/39YZoQCfRWwc4l9D4Jie3PrLKN4rwgTfamcOB4 XSFeCsFdUAQIutHsWvy7atBHf7AxCKE= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-05_04,2026-08-04_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 malwarescore=0 suspectscore=0 clxscore=1015 impostorscore=0 bulkscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608050099 On 05/08/26 12:51 pm, Dust Li wrote: > On 2026-08-04 12:52:12, Sidraya Jayagond wrote: >> >> >> On 03/08/26 6:24 pm, Breno Leitao wrote: >>>> @@ -1931,11 +1931,12 @@ static void smc_listen_out(struct smc_sock *new_smc) >>>> atomic_dec(&lsmc->queued_smc_hs); >>>> >>>> release_sock(newsmcsk); /* lock in smc_listen_work() */ >>>> + lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING); >>>> if (lsmc->sk.sk_state == SMC_LISTEN) { >>>> - lock_sock_nested(&lsmc->sk, SINGLE_DEPTH_NESTING); >>>> smc_accept_enqueue(&lsmc->sk, newsmcsk); >>>> release_sock(&lsmc->sk); >>>> } else { /* no longer listening */ >>>> + release_sock(&lsmc->sk); >>>> smc_close_non_accepted(newsmcsk); >>>> } >>> >>> Do you need to call smc_close_non_accepted() without the lock? otherwise >>> you can have the lock around the whole if/else clause. >> >> Yes, smc_close_non_accepted() calls __smc_release() in turn calls >> smc_close_active(), which in the SMC_ACTIVE case hits >> smc_close_stream_wait() a blocking wait that can sleep up to >> SMC_MAX_STREAM_WAIT_TIMEOUT (2 minutes). Holding the listener lock >> across that would stall any concurrent smc_accept(), smc_listen_out(), >> or smc_release() on the listener for the same duration. >> >> The release_sock() is intentionally placed before >> smc_close_non_accepted() to keep the critical section minimal: >> lock >> check state >> enqueue or not >> unlock >> then do the slow close work without the listener lock held. > > > That patch looks good to me. > > Reviewed-by: Dust Li > > > Two corrections to the justification though: > > 1. This newsmcsk sock have never been given to userspace, so > smc_close_stream_wait() should return immediately. I think the stronger > argument for keeping smc_close_non_accepted() outside the listener > lock is what follows in smc_close_active()/__smc_release(): > smc_close_final() can wait up to SMC_WR_TX_WAIT_FREE_SLOT_TIME (10s) > for a WR slot, and smc_clcsock_release() tears down the TCP > socket. > > 2. SMC_MAX_STREAM_WAIT_TIMEOUT is 2 * HZ, i.e. 2 seconds, not 2 minutes. > Thank you for the corrections,Dust. Both points are valid. > > Best regards, > Dust >