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Thu, 9 Jul 2026 14:47:18 +0000 (GMT) Received: from [9.224.68.161] (unknown [9.224.68.161]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 9 Jul 2026 14:47:18 +0000 (GMT) Message-ID: Date: Thu, 9 Jul 2026 16:47:18 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net] net/af_iucv: fix use-after-free of listen sock in iucv_callback_connreq() To: Hidayath Khan , aswin@linux.ibm.com, pasic@linux.ibm.com, nagamani@linux.ibm.com Cc: wenjia@linux.ibm.com, gbayer@linux.ibm.com, linux390-list@tuxmaker.boeblingen.de.ibm.com, mjambigi@linux.ibm.com, sidraya@linux.ibm.com, stable@vger.kernel.org References: <20260706084825.6231-1-hidayath@linux.ibm.com> Content-Language: en-US From: Alexandra Winter In-Reply-To: <20260706084825.6231-1-hidayath@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=KsJ9H2WN c=1 sm=1 tr=0 ts=6a4fb47c cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=ag1SF4gXAAAA:8 a=R2two0n6AAAA:8 a=VnNF1IyMAAAA:8 a=Gr6UgMjOUMMtFO0AKnQA:9 a=QEXdDO2ut3YA:10 a=Yupwre4RP9_Eg_Bd0iYG:22 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA5MDE0MSBTYWx0ZWRfX4BopwLO73ZHe /m8YudheP8H9Ct3VEMFY5KTN2mbGeKVN439wZ/waHLwLCmDV3E3CZFMux5BUWPUvR0fkF87i8Zh uKsZzZ1k9UoGyvn3aPGUR1/usbCj/Rs= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA5MDE0MSBTYWx0ZWRfX6BM+QdBabx0B +WGFSHgBjvI0N3WbTNQ4A5B3knQJoy9Ty6ZpW68ctwtVV+y5MxR3n3dCR2Ds5ezgfZWmr4fuc9S QbxsgX9XDyNwRGAeP9Zq9WcQnvoskpK1cK7krYQH5XI3b3ziVZP2sT6OnqLNcVnRAWhoqFvEOZv hw96wL0kj6lJb542WlSWSHpPNVp033x+bekXVaYiN3y+6gXz0qouWEGPKnpMrQtcO9fxRGbhMjp 36qiSC9zpdKvzCg4cuYHBk+kC1rl/UU47DTnpT1j54ZfETA1JW8uGfbBP93nxy5tnSbNg8vNE5Z jKzwwa1L4j4EWHnOG2gYew35z6kg7TGTu3lf4BzwV7AprRXJnVwf3t+dAfguev8ngGf2jf24A0j Pd7iie9vkrzsOageYrYnXkyjJreRhUubwub+/3xQNDS0Pr1Wi6KWuQpHPulDhQkniYJUfBoYlDZ MwgcLVtf6+8LUAX8I5A== X-Proofpoint-ORIG-GUID: z8mrOdc-1llC3_xGfI-CLi04ip2daOvM X-Proofpoint-GUID: z8mrOdc-1llC3_xGfI-CLi04ip2daOvM X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-09_03,2026-07-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 clxscore=1011 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607090141 On 06.07.26 10:48, Hidayath Khan wrote: > iucv_callback_connreq() looks up the listening socket in iucv_sk_list > under read_lock(&iucv_sk_list.lock), drops the lock, and only then > uses the socket (bh_lock_sock() and the following connection setup). > No reference is taken on the socket before the lock is released. > > The callback runs from the iucv tasklet. A concurrent close of the > listening socket does not synchronize with it. > Between read_unlock() and bh_lock_sock() a concurrent close on another > CPU can free the socket. > > Fixes: eac3731bd04c ("[S390]: Add AF_IUCV socket support") > Cc: stable@vger.kernel.org > Signed-off-by: Hidayath Khan > --- > net/iucv/af_iucv.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c > index fed240b453bd..890d9df5ae36 100644 > --- a/net/iucv/af_iucv.c > +++ b/net/iucv/af_iucv.c > @@ -1616,6 +1616,8 @@ static int iucv_callback_connreq(struct iucv_path *path, > iucv = iucv_sk(sk); > break; > } > + if (iucv) > + sock_hold(sk); > read_unlock(&iucv_sk_list.lock); > if (!iucv) > /* No socket found, not one of our paths. */ > @@ -1684,6 +1686,7 @@ static int iucv_callback_connreq(struct iucv_path *path, > err = 0; > fail: > bh_unlock_sock(sk); > + sock_put(sk); > return 0; > } > Instead of adding another refcount couldn't you simply move bh_lock_sock(sk) under iucv_sk_list.lock ? Like this: diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c index fed240b453bd..84a3f65b7c13 100644 --- a/net/iucv/af_iucv.c +++ b/net/iucv/af_iucv.c @@ -1614,6 +1614,7 @@ static int iucv_callback_connreq(struct iucv_path *path, * src_name == ipuser[0-7]. */ iucv = iucv_sk(sk); + bh_lock_sock(sk); break; } read_unlock(&iucv_sk_list.lock); @@ -1621,7 +1622,6 @@ static int iucv_callback_connreq(struct iucv_path *path, /* No socket found, not one of our paths. */ return -EINVAL; - bh_lock_sock(sk); /* Check if parent socket is listening */ low_nmcpy(user_data, iucv->src_name); But actually that doesn't completely close this gap, see my commit message for f558120cd709 ("net/iucv: fix use after free in iucv_sock_close()") Iiuc the socket locking in AF_IUCV is incomplete in general. Some links I stored for my reference (there may be better ones): https://lore.kernel.org/netdev/1280155406.2899.407.camel@edumazet-laptop/ https://wiki.linuxfoundation.org/networking/socket_locks https://medium.com/@c0ngwang/the-design-of-lock-sock-in-linux-kernel-69c3406e504b If you fix this correctly it should also fix the HS over IUCV recieve path.