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Wed, 30 Sep 2026 07:30:30 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav02.fra02v.mail.ibm.com (Postfix) with SMTP; Wed, 30 Sep 2026 07:30:30 +0000 (GMT) Received: by tuxmaker.boeblingen.de.ibm.com (Postfix, from userid 56341) id 58E0E160EDA; Wed, 30 Sep 2026 09:30:30 +0200 (CEST) From: Mahanta Jambigi To: andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, alibuda@linux.alibaba.com, dust.li@linux.alibaba.com, sidraya@linux.ibm.com Cc: hidayath@linux.ibm.com, pasic@linux.ibm.com, horms@kernel.org, tonylu@linux.alibaba.com, guwen@linux.alibaba.com, stable@vger.kernel.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org, Mahanta Jambigi Subject: [PATCH net v7] net/smc: fix lgr/lnk lifetime vs diag reader race Date: Wed, 30 Sep 2026 09:30:29 +0200 Message-ID: <20260930073029.1201202-1-mjambigi@linux.ibm.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: 6FrIHc7rLxznRgHT85d0WeZjsIen6YBA X-Proofpoint-GUID: 4dauCta61BZb04LyLFT10SSc8iw07Gp6 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTMwMDAyOCBTYWx0ZWRfX+MSlb48unLHU DQE5NvyGxxGxLzF2ZJRvwJgst2ZD0+QvjBEf9IV79e8Ej4AL5NXgdQ50vELX0YBh6l2CyfgC5yl IC58m9VaiievSMVoEXnYEGwGq6+KhF4= X-Authority-Analysis: v=2.4 cv=Vv62kO2n c=1 sm=1 tr=0 ts=6abcba9c cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=c4_d4hq89UDrnc4Je58A:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTMwMDAyOCBTYWx0ZWRfX58zB1jDbNLY4 SIWe3DdPvSgkAPSYPcdF+nRMhFe4xLSDUDzCGKwjSQpo/mNnQRI4K7jAPD+XHEjVMp0Fxedwbvn rPXTQ+AUuItGwJlK/0rHxFxYxmnxz8UWksZgzKQTeu8u9LnRWKFgTozIT79z5ZZ749cZR7vvPqp ZTs2yo6SGcUNqtx3EE72icZv8mSswKMFJodlQw+JIdoea5Jx9gbE5/qnmHmKp+J6clP27E2M07l fpOFpK9i/2NiWU4/GLUvOLNuuEjNjAwqxYunWPY/rzAPssE+5NxfpwALVimFOCUeejve6zKstWO aEr6MONHV/XdU4zCoGkTY6jSOH7ZdHBZXiKSUHbVfejtk6AwyLH7cXOXT+RxqrWqK2J83m0V3oK mDiAwyuklBi8P0jpdyZssywEn7/6vsEJQCX9EImaEBKedSnv5PIwk60jpbjO++GOXXtoD9AZUpB qhKCTYrhBhWvhyAv0yw== 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=2026-09-29_05,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 spamscore=0 phishscore=0 bulkscore=0 adultscore=0 priorityscore=1501 malwarescore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609300028 The diag dump walks the socket hash table under a read_lock and dereferen= ces conn->lgr and conn->lnk. Three paths expose a window where a hashed socke= t has freed or partially freed conn/lgr/lnk state. First, smc_conn_abort() calls smc_conn_free() during early handshake abor= ts while the socket is still hashed in SMC_INIT. On the smc_lgr_cleanup_earl= y() path this frees the lgr synchronously without holding the hash write_lock= . A concurrent diag reader can therefore load a non-NULL conn->lgr and derefe= rence lgr->is_smcd after the kfree. Guard the conn->lgr->is_smcd load in __smc_diag_dump() by skipping it when the socket is in SMC_INIT state. Th= e same guard also skips the CONNINFO/LGRINFO/DMBINFO blocks for SMC_CLOSED socke= ts, which may briefly remain hashed after smc_conn_free() when the fd is stil= l open; smcss already suppresses those attributes for closed sockets, so there is= no observability regression. Second, in smc_conn_kill() on SMC-D with dmb_nocopy, smcd_buf_detach() NU= LLs and frees conn->sndbuf_desc before the socket is unhashed. A concurrent diag = reader entering the CONNINFO block can dereference the freed descriptor. Unhash = the socket at the top of smc_conn_kill(), before smcd_buf_detach(). Third, in the terminal teardown branches of smc_close_active_abort() (PEERCLOSEWAIT and PROCESSABORT groups) and in smc_close_passive_work(), smc_conn_free() drops lgr and lnk references while the socket is still ha= shed. Unhash immediately before each smc_conn_free() call at those two sites. Fixes: f16a7dd5cf27 ("smc: netlink interface for SMC sockets") Fixes: 9dbe086c69b8 ("net/smc: fix invalid link access in dumping SMC-R c= onnections") Fixes: ae2be35cbed2 ("net/smc: {at|de}tach sndbuf to peer DMB if supporte= d") Cc: stable@vger.kernel.org Signed-off-by: Mahanta Jambigi --- Changes in v7: - no code changes; commit message only - document the SMC_CLOSED leg of the early-exit guard and the rationale that smcss already skips CLOSED sockets on the userspace side; add Fixes: ae2be35cbed2 for the smc_conn_kill() hunk since smcd_buf_detach() was introduced by that commit Changes in v6: - smc_diag.c: inline sk->sk_state !=3D SMC_INIT into the else-if conditio= n so conn->lgr->is_smcd is never loaded for SMC_INIT sockets; retain the SMC_INIT || SMC_CLOSED early-exit guard and out: label from v5 to defensively skip the CONNINFO/LGRINFO/DMBINFO blocks for sockets with no live connection - smc_close.c: remove the unconditional unhash from the top of smc_close_active_abort(); place it scoped immediately before each of the two smc_conn_free() calls in the PEERCLOSEWAIT and PROCESSABORT branches, and before smc_conn_free() in smc_close_passive_work(); this avoids prematurely hiding live SMC_ACTIVE/APPCLOSEWAIT sockets from smcss - smc_core.c: unhash at the top of smc_conn_kill(), before smcd_buf_detach(), so the socket is off the hash table before conn->sndbuf_desc is freed on the dmb_nocopy path Changes in v5: - guard conn/lgr/lnk blocks in __smc_diag_dump() with an (SMC_INIT || SMC_CLOSED) state check placed after the SMC_DIAG_FALLBACK nla_put; SMC_INIT can coexist with fallback (smc_sendmsg() MSG_FASTOPEN path), so the guard must not suppress the fallback reason Changes in v4: - dropped smc_conn_unhash() wrapper, conn->unhashed flag, and all changes to af_smc.c, smc.h, smc_core.c and smc_core.h; smc_unhash_sk() is already idempotent via sk_hashed(), so direct calls at the two teardown sites in smc_close.c are sufficient - dropped the __smc_release() hunk: it needs no change since the subsequent unhash there is already a safe no-op - fixed premature-unhash issue present in v3: smc_conn_free() must not unhash because smc_conn_abort() calls it before smc_switch_to_fallback() in both smc_listen_decline() and smc_connect_rdma() error paths; unhashing there would make live fallback sockets invisible to smcss - likewise, the ISM/RDMA retry loops (smc_find_ism_v2_device_serv(), smc_find_rdma_v2_device_serv()) call smc_conn_abort() on a failed attempt and then smc_conn_create() on the next device; unhashing in smc_conn_free() would permanently hide the established connection from smc_diag since smc_conn_create() does not re-hash the socket Changes in v3: - redesigned as a single patch; dropped the lgr_lnk_lock spinlock approach and the 2-patch split - fix is now at the socket hash layer: introduce smc_conn_unhash() with a per-connection unhashed flag; smc_conn_free() unhashes before dropping lgr/lnk refs, so any socket visible to the diag reader under the hash read_lock has valid conn->lgr and conn->lnk pointers - __smc_release() updated to call smc_conn_unhash() for non-fallback sockets so the flag is honoured when smc_conn_free() already ran first - smc_diag.c needs no changes; the hash read_lock invariant is sufficient without any per-connection lock in the dump path - dropped the clcsock/mutex_trylock fix as that will be addressed separately Changes in v2: - this is v2 of the 2-patch series; the earlier submission was mislabelled [PATCH v3] but was in fact the first version sent to the list - split into a 2-patch series; patch 1/2 adds per-connection lgr_lnk_lock infrastructure to smc_core, patch 2/2 fixes the diag dump path using it - dropped lock_sock()/release_sock() from __smc_diag_dump(); v1 held the socket lock across all lgr/lnk dereferences, requiring the hash read_lock to be dropped and re-acquired around each socket - dropped the restart-from-head loop in smc_diag_dump_proto(); the new design does not drop the hash read_lock mid-walk so the hlist truncation concern no longer applies - dropped refcount_inc_not_zero() socket pinning from the dump loop for the same reason: the hash read_lock is now held for the full walk - added per-connection lgr_lnk_lock spinlock to struct smc_connection; conn->lgr and conn->lnk are NULLed under this lock in smc_conn_free() before borrowed references are released, establishing the invariant: a non-NULL conn->lgr seen under lgr_lnk_lock guarantees the lgr is alive - added lgr_lnk_lock to smc_switch_link_and_count() to protect the conn->lnk pointer swap from concurrent diag readers - replaced mutex_lock() on clcsock_release_lock in smc_diag_msg_common_fill() with mutex_trylock(); mutex_lock() was valid in v1 because the hash spinlock had been dropped, but the new design holds the hash read_lock throughout so only a non-sleeping trylock is safe; a failed trylock leaves address fields zeroed, which is acceptable for a monitoring tool - all conn->lgr and conn->lnk accesses in __smc_diag_dump() use a snapshot-then-use pattern: fields are copied into local stack variables under lgr_lnk_lock and nla_put() is called after releasing the lock, avoiding any sleeping operation under the spinlock net/smc/smc_close.c | 3 +++ net/smc/smc_core.c | 1 + net/smc/smc_diag.c | 7 ++++++- 3 files changed, 10 insertions(+), 1 deletion(-) diff --git a/net/smc/smc_close.c b/net/smc/smc_close.c index bb0313ef5f7c..aa6363abdd74 100644 --- a/net/smc/smc_close.c +++ b/net/smc/smc_close.c @@ -154,6 +154,7 @@ void smc_close_active_abort(struct smc_sock *smc) if (sk->sk_state !=3D SMC_PEERABORTWAIT) break; sk->sk_state =3D SMC_CLOSED; + sk->sk_prot->unhash(sk); smc_conn_free(&smc->conn); release_clcsock =3D true; sock_put(sk); /* passive closing */ @@ -165,6 +166,7 @@ void smc_close_active_abort(struct smc_sock *smc) if (sk->sk_state !=3D SMC_PEERABORTWAIT) break; sk->sk_state =3D SMC_CLOSED; + sk->sk_prot->unhash(sk); smc_conn_free(&smc->conn); release_clcsock =3D true; break; @@ -433,6 +435,7 @@ static void smc_close_passive_work(struct work_struct= *work) sk->sk_state_change(sk); if ((sk->sk_state =3D=3D SMC_CLOSED) && (sock_flag(sk, SOCK_DEAD) || !sk->sk_socket)) { + sk->sk_prot->unhash(sk); smc_conn_free(conn); if (smc->clcsock) release_clcsock =3D true; diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c index 04aedd957543..d7bd6d7f428b 100644 --- a/net/smc/smc_core.c +++ b/net/smc/smc_core.c @@ -1517,6 +1517,7 @@ static void smc_conn_kill(struct smc_connection *co= nn, bool soft) { struct smc_sock *smc =3D container_of(conn, struct smc_sock, conn); + smc->sk.sk_prot->unhash(&smc->sk); if (conn->lgr->is_smcd && conn->lgr->peer_shutdown) conn->local_tx_ctrl.conn_state_flags.peer_conn_abort =3D 1; else diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c index bf0beaa23bdb..b29bd34acf7b 100644 --- a/net/smc/smc_diag.c +++ b/net/smc/smc_diag.c @@ -90,7 +90,8 @@ static int __smc_diag_dump(struct sock *sk, struct sk_b= uff *skb, r->diag_state =3D sk->sk_state; if (smc->use_fallback) r->diag_mode =3D SMC_DIAG_MODE_FALLBACK_TCP; - else if (smc_conn_lgr_valid(&smc->conn) && smc->conn.lgr->is_smcd) + else if (sk->sk_state !=3D SMC_INIT && + smc_conn_lgr_valid(&smc->conn) && smc->conn.lgr->is_smcd) r->diag_mode =3D SMC_DIAG_MODE_SMCD; else r->diag_mode =3D SMC_DIAG_MODE_SMCR; @@ -103,6 +104,9 @@ static int __smc_diag_dump(struct sock *sk, struct sk= _buff *skb, if (nla_put(skb, SMC_DIAG_FALLBACK, sizeof(fallback), &fallback) < 0) goto errout; + if (sk->sk_state =3D=3D SMC_INIT || sk->sk_state =3D=3D SMC_CLOSED) + goto out; + if ((req->diag_ext & (1 << (SMC_DIAG_CONNINFO - 1))) && smc->conn.alert_token_local) { struct smc_connection *conn =3D &smc->conn; @@ -185,6 +189,7 @@ static int __smc_diag_dump(struct sock *sk, struct sk= _buff *skb, goto errout; } +out: nlmsg_end(skb, nlh); return 0; --=20 2.50.1 (Apple Git-155)