From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1CB9A72630; Wed, 30 Sep 2026 00:51:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790729511; cv=none; b=i6bWs3EFT2l/L/bdKwUXvgzKR4WFsxekiFrlpTqEDigOcTlhLYT8JONnDSq/j2UVPts1Ex5ZnadeF3HgRrXhgXGkKcJS4AhgerNoPuMhou4dCvW/hqNie2FX/vKaAXfpBHOewWFtDM61TjP18CSPnFwEXexQ1USFPWW4Xkx92G8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790729511; c=relaxed/simple; bh=Y8Yv86j45dAUDm+HTINjd9b13trqoVz9QNDts84BzNI=; h=Subject:From:To:Cc:Date:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=Jt/tnchdrxFJL70DBlDopQMlpt0ERiKvyuMEpK6Zv2YBMdU7iP8nm69GiixWUIbJ1Bp/n3Tqt1edCQWejsiFNrIDf68jDiVp6J4fVOm6fJ9CF0JFiGq2zlx1uxnL7kqvyFl5EWXOiWVMSZMFgF9S5lsfHfIAjZSBDvF9TdnHY6E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b0ZHVNMr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b0ZHVNMr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B71A91F000FF; Wed, 30 Sep 2026 00:51:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790729509; bh=hIa8l3Wv1305+cLt2p2PWVQHZKo3oSVWoXD8VqI9hSY=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=b0ZHVNMr5sTipzrZOTLqNz5Szch/mQAHrFSQLLzVhYFMKGgcjG0CGISKNzao2HKqr PwvZIShFNv1oxI0DgScbUPx8V5ikIwzTyJ63eVQWKVQXiHPxw0by2ZdtY5aiK3nKcX qfNB8zNSUr3hhz26hhyUQ20kUF3lOUbm3YZntmnS6VSocpqma2Riil0dvAHwi82ZRm PvucIz7h749B2ByNDqwKLXJhb0jWrjuHKKJnE5RhyaalO1EcvpZ/nT2WNuCDlJqqSL 6j73XnoYlk0mw3hl4QpTZAtFrD/Q5t8jeire5gS34+02/TzQFepwr1ltUmbLCOfqGc Mz69MASmsFsIw== Subject: Re: [PATCH net v6] net/smc: fix lgr/lnk lifetime vs diag reader race From: netdev-bot+sashiko@kernel.org To: mjambigi@linux.ibm.com Cc: 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, 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 Date: Wed, 30 Sep 2026 00:51:48 +0000 Message-ID: <179072950825.434549.9827562031861482481@kernel.org> In-Reply-To: <20260926065023.1629497-1-mjambigi@linux.ibm.com> References: <20260926065023.1629497-1-mjambigi@linux.ibm.com> X-sashiko-severity: High Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider. Critical: 0 · High: 1 · Medium: 2 (1) · Low: 1 If you believe none of the issues are legitimate, please reply to each issue of Medium severity or higher and explain why the AI is wrong. If any of them are legitimate and you plan to respin, please let patchwork know by including "pw-bot: cr" as a separate line at the end of your reply (one such reply per series is enough). - [High] The patch leaves open another window of the class it says it closes ('a hashed socket has freed or partially freed conn/lgr/lnk… - [Medium] The new early exit in __smc_diag_dump() (net/smc/smc_diag.c:107-108, `if (sk->sk_state == SMC_INIT ||… - [Medium] For the smc_conn_abort() path, the patch's only protection against dereferencing a freed conn->lgr in __smc_diag_dump() is two… - [Low] The second race the patch fixes is smcd_buf_detach() freeing conn->sndbuf_desc in smc_conn_kill() while the socket is hashed and… Pre-existing issues: - [Medium] This problem wasn't introduced by this patch, but smc_diag_handler_dump() (net/smc/smc_diag.c:245-260) starts the dump… -- net/smc: fix lgr/lnk lifetime vs diag reader race This patch aims to close races between the SMC sock_diag dump and the teardown of conn/lgr/lnk state. It unhashes the socket before smc_conn_free() in the close paths and at the top of smc_conn_kill(). It also makes __smc_diag_dump() skip the lgr->is_smcd load, and all extension blocks, for SMC_INIT and SMC_CLOSED sockets. > diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c > index 9974149659c2f..663926465ba7f 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 *conn, bool soft) > { > struct smc_sock *smc = 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 = 1; > else [Severity: Low] Should this patch also have a Fixes: tag for ae2be35cbed2? The commit message says this hunk is needed because smcd_buf_detach() frees conn->sndbuf_desc in smc_conn_kill() on the dmb_nocopy path: smcd_buf_detach() { ... buf_desc = conn->sndbuf_desc; conn->sndbuf_desc = NULL; kfree(buf_desc); } That path was added by ae2be35cbed2 ("net/smc: {at|de}tach sndbuf to peer DMB if supported"). It was moved to its current place by 36cdf5d48ca1 ("net/smc: unregister the connection before draining the rx tasklet"), which itself has Fixes: ae2be35cbed2. Both tags in this patch, f16a7dd5cf27 and 9dbe086c69b8, are older than the dmb_nocopy detach code. Without a tag for ae2be35cbed2, stable trees that lack dmb_nocopy would get the unconditional unhash, but the stated reason for it would not apply there. > diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c > index bf0beaa23bdb6..b29bd34acf7b5 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_buff *skb, > r->diag_state = sk->sk_state; > if (smc->use_fallback) > r->diag_mode = SMC_DIAG_MODE_FALLBACK_TCP; > - else if (smc_conn_lgr_valid(&smc->conn) && smc->conn.lgr->is_smcd) > + else if (sk->sk_state != SMC_INIT && > + smc_conn_lgr_valid(&smc->conn) && smc->conn.lgr->is_smcd) > r->diag_mode = SMC_DIAG_MODE_SMCD; > else > r->diag_mode = SMC_DIAG_MODE_SMCR; [Severity: Medium] Is a plain read of sk->sk_state enough to stop this from reading a freed lgr? smc_conn_free() never clears conn->lgr. On the smc_conn_abort() path the writer does the following under lock_sock(), using only plain stores: smc_conn_abort() smc_conn_free() smc_lgr_unregister_conn() /* alert_token_local = 0 */ smc_lgr_cleanup_early(lgr) __smc_lgr_terminate() smc_lgr_free() /* lgrA freed, conn->lgr dangling */ One of two things follows: - smc_switch_to_fallback() and then sk_state = SMC_ACTIVE, for example in smc_connect_fallback(). - In the ISM/RDMA v2 server retry loops, smc_conn_create() sets conn->lgr = lgrB with a new token, and then newsmcsk->sk_state = SMC_ACTIVE. The reader here holds only the hash read_lock. There is no READ_ONCE(), and nothing orders the sk_state load before the later loads of conn->alert_token_local, conn->lgr and lgr->is_smcd. The control dependency on the sk_state test does not order those later loads. On weakly ordered CPUs such as arm64 or POWER, could this see SMC_ACTIVE with use_fallback still false, together with a stale token or the stale lgrA pointer, and then read lgrA->is_smcd after it was freed? This sk_state test and the second one below are separate reads, so within one dump they can return different values. KCSAN would likely report both as data races. > @@ -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 == SMC_INIT || sk->sk_state == SMC_CLOSED) > + goto out; > + [Severity: Medium] Does this drop CONNINFO, LGRINFO and DMBINFO for SMC_CLOSED sockets whose connection is still registered and valid? A hashed socket can reach SMC_CLOSED with its connection intact. For example, after shutdown(SHUT_WR) in SMC_APPCLOSEWAIT1 the socket is in SMC_APPCLOSEWAIT2, and then the peer aborts: smc_close_passive_work() smc_close_passive_abort_received() case SMC_APPCLOSEWAIT2: case SMC_PEERFINCLOSEWAIT: sk->sk_state = SMC_CLOSED; The fd is still open, so smc_close_passive_work() skips both the new unhash and smc_conn_free(): if ((sk->sk_state == SMC_CLOSED) && (sock_flag(sk, SOCK_DEAD) || !sk->sk_socket)) { sk->sk_prot->unhash(sk); smc_conn_free(conn); The socket therefore stays hashed with alert_token_local and conn->lgr still valid. With this patch, every caller of smc_conn_free() unhashes first: smc_close_active_abort(), smc_close_passive_work() and __smc_release(). It looks like any SMC_CLOSED socket still in the hash has valid connection state. If so, the SMC_CLOSED half of this check only hides valid data that smcss -D and smcss -R used to report when the matching diag_ext bits were set. The commit message describes only the narrower sk_state != SMC_INIT guard on the is_smcd load. This early exit appears only in the v5 and v6 changelog below the --- line, which is dropped when the patch is applied. Could the SMC_CLOSED part be removed, or described in the commit message if it is intended? > if ((req->diag_ext & (1 << (SMC_DIAG_CONNINFO - 1))) && > smc->conn.alert_token_local) { > struct smc_connection *conn = &smc->conn; [Severity: Medium] This is a pre-existing issue and was not introduced by this patch, but is req->diag_ext always inside the request payload here? smc_diag_handler_dump() starts the dump without checking the request length: if (h->nlmsg_type == SOCK_DIAG_BY_FAMILY && h->nlmsg_flags & NLM_F_DUMP) { { struct netlink_dump_control c = { .dump = smc_diag_dump, The generic check in __sock_diag_cmd() only compares against struct sock_diag_req (2 bytes), not struct smc_diag_req (52 bytes). inet_diag, unix_diag, packet_diag, netlink_diag, tipc_diag and vsock_diag all check nlmsg_len(h) against their own request size. With a 2-byte payload, diag_ext at offset 3 falls in skb tailroom that netlink_sendmsg() did not initialize. When a live SMC connection exists, whether CONNINFO, LGRINFO and DMBINFO appear in the reply would reveal bits of that uninitialized memory to an unprivileged local user. KMSAN would likely report this as an uninit-value use. Should smc_diag_handler_dump() reject requests where nlmsg_len(h) is less than sizeof(struct smc_diag_req)? [ ... ] > @@ -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; > [Severity: High] The commit message says the patch closes windows where "a hashed socket has freed or partially freed conn/lgr/lnk state". It also cites 9dbe086c69b8 ("net/smc: fix invalid link access in dumping SMC-R connections"). Is SMC-R link failover still exposed to the same race? The LGRINFO block above this label runs under only the hash read_lock: if (smc_conn_lgr_valid(&smc->conn) && !smc->conn.lgr->is_smcd && (req->diag_ext & (1 << (SMC_DIAG_LGRINFO - 1))) && !list_empty(&smc->conn.lgr->list)) { struct smc_link *link = smc->conn.lnk; ... memcpy(linfo.lnk[0].ibname, link->smcibdev->ibdev->name, sizeof(link->smcibdev->ibdev->name)); At the same time, smcr_link_down() or smc_llc_process_srv_delete_link() can run: smc_switch_conns() smc_switch_link_and_count() smcr_link_put(conn->lnk); conn->lnk = to_lnk; smcr_link_clear(lnk) __smcr_link_clear() memset(lnk, 0, sizeof(struct smc_link)); The link switch takes only conn->send_lock. The socket stays SMC_ACTIVE and hashed, and the lgr stays on its list. So neither the new SMC_INIT/SMC_CLOSED check nor the list_empty() check skips this block. If a reader has already loaded the old conn->lnk, could it dereference a NULL link->smcibdev? Could it instead report fields from a different link that has reused the lgr->lnk[] slot? The v2 posting protected the conn->lnk swap in smc_switch_link_and_count() with lgr_lnk_lock. v3 dropped that, and nothing has replaced it. -- Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260926065023.1629497-1-mjambigi%40linux.ibm.com