From patchwork Mon Jan 16 02:46:07 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jason Xing X-Patchwork-Id: 13102503 X-Patchwork-Delegate: kuba@kernel.org 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 E0492C3DA78 for ; Mon, 16 Jan 2023 02:47:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231680AbjAPCrb (ORCPT ); Sun, 15 Jan 2023 21:47:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51590 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231658AbjAPCrX (ORCPT ); Sun, 15 Jan 2023 21:47:23 -0500 Received: from mail-pj1-x1029.google.com (mail-pj1-x1029.google.com [IPv6:2607:f8b0:4864:20::1029]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B187E7286; Sun, 15 Jan 2023 18:47:21 -0800 (PST) Received: by mail-pj1-x1029.google.com with SMTP id w4-20020a17090ac98400b002186f5d7a4cso32580121pjt.0; Sun, 15 Jan 2023 18:47:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=abWfWv7dx4M21bFcNtuB4f9xzNG3ZWU0shwDajE0q7k=; b=TcpScGUIrGvJSXZgqAPxAiPea0EJwMAvQlVaPUDbDh0YoXF5dBbuCSkAongzzdFXdb +h1Op4dUg/W7Kn3+JuBps7B51HGtvh1pcwbSLSBh5dFrmFEBozuFGWycb8xKHHbzRlRs /Jn854qSvVwEGSTAOG+tjbMRLn8UliJV3K8OJxFtwmo0kHHorpdoR8WqTn/N/HgnRgVg dvoVEmn7j6wLKnKeLsU5128L/0qNtyBzK/yGiq+cG3bRbsPJxuMIzkyCFcqthOkugXEa MBUuF4AN+Zc32mqdbeB1Kx6AQMRydOIaiMV0UZwFXo5twKXgY1tVqXIf/sjzVvHX/yoO 9ywg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=abWfWv7dx4M21bFcNtuB4f9xzNG3ZWU0shwDajE0q7k=; b=lOPHbmTJ26EtwBeGnGtO02Ef1RWibycFhiwK7ourG+RNM9mrfzdW873aCjD754yNMq dQn45u6x4CjQM0PkCFyEieNbSKgpVbtrJsp80x8pM4VBr/gGw7hD1ESBGHUR5t6H2wpb PFJ+RLMKSTyC5SB95iibs9i8qOe1tQgjxv2DmclBjVZpSJgIwVz1GyE9FcmH1NJ9gEJq UkkgqL7u8iiY9iSkOzVrG5yqne+8WlV1/4gJgakkVeiKRb9PZXsNKlPy0VzLnKiiAJnd Jkq1tq9oiWPBkCwrLAWDXgMtkicjE76SBuMhbW+1ycdZG/WWcACy/twuG2z2rSVbdVZ2 BNwg== X-Gm-Message-State: AFqh2kppqMleaWFBTDm2XDe4HyrLg3hfgmobJEs02SS4Mgojse7DGTNz zwY+Wa8TW/L4vBTEP3RSPzU= X-Google-Smtp-Source: AMrXdXshFAWZ3CUECgS0/72Q4g8B4z2MmJltI2s8Aeo+GTLha1iEXGI5YktYAwT52bEgDu5d6vsEQQ== X-Received: by 2002:a17:902:e042:b0:194:9b4e:1c90 with SMTP id x2-20020a170902e04200b001949b4e1c90mr588179plx.57.1673837241165; Sun, 15 Jan 2023 18:47:21 -0800 (PST) Received: from KERNELXING-MB0.tencent.com ([103.7.29.31]) by smtp.gmail.com with ESMTPSA id c5-20020a170902d90500b001946119c22esm7091715plz.146.2023.01.15.18.47.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Jan 2023 18:47:20 -0800 (PST) From: Jason Xing To: edumazet@google.com, davem@davemloft.net, yoshfuji@linux-ipv6.org, dsahern@kernel.org, kuba@kernel.org, pabeni@redhat.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kerneljasonxing@gmail.com, Jason Xing Subject: [PATCH v3 net] tcp: avoid the lookup process failing to get sk in ehash table Date: Mon, 16 Jan 2023 10:46:07 +0800 Message-Id: <20230116024607.47164-1-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org From: Jason Xing While one cpu is working on looking up the right socket from ehash table, another cpu is done deleting the request socket and is about to add (or is adding) the big socket from the table. It means that we could miss both of them, even though it has little chance. Let me draw a call trace map of the server side. CPU 0 CPU 1 ----- ----- tcp_v4_rcv() syn_recv_sock() inet_ehash_insert() -> sk_nulls_del_node_init_rcu(osk) __inet_lookup_established() -> __sk_nulls_add_node_rcu(sk, list) Notice that the CPU 0 is receiving the data after the final ack during 3-way shakehands and CPU 1 is still handling the final ack. Why could this be a real problem? This case is happening only when the final ack and the first data receiving by different CPUs. Then the server receiving data with ACK flag tries to search one proper established socket from ehash table, but apparently it fails as my map shows above. After that, the server fetches a listener socket and then sends a RST because it finds a ACK flag in the skb (data), which obeys RST definition in RFC 793. Besides, Eric pointed out there's one more race condition where it handles tw socket hashdance. Only by adding to the tail of the list before deleting the old one can we avoid the race if the reader has already begun the bucket traversal and it would possibly miss the head. Many thanks to Eric for great help from beginning to end. Fixes: 5e0724d027f0 ("tcp/dccp: fix hashdance race for passive sessions") Suggested-by: Eric Dumazet Signed-off-by: Jason Xing Link: https://lore.kernel.org/lkml/20230112065336.41034-1-kerneljasonxing@gmail.com/ --- v3: 1) get rid of else-if statement. v2: 1) adding the sk node into the tail of list to prevent the race. 2) fix the race condition when handling time-wait socket hashdance. Signed-off-by: Jason Xing --- net/ipv4/inet_hashtables.c | 14 +++++++++++++- net/ipv4/inet_timewait_sock.c | 6 +++--- 2 files changed, 16 insertions(+), 4 deletions(-) diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 24a38b56fab9..28374f44e3d8 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -650,8 +650,19 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk) spin_lock(lock); if (osk) { WARN_ON_ONCE(sk->sk_hash != osk->sk_hash); + if (sk_hashed(osk)) { + /* Before deleting the node, we insert a new one to make + * sure that the look-up-sk process would not miss either + * of them and that at least one node would exist in ehash + * table all the time. Otherwise there's a tiny chance + * that lookup process could find nothing in ehash table. + */ + __sk_nulls_add_node_tail_rcu(sk, list); + } ret = sk_nulls_del_node_init_rcu(osk); - } else if (found_dup_sk) { + goto unlock; + } + if (found_dup_sk) { *found_dup_sk = inet_ehash_lookup_by_sk(sk, list); if (*found_dup_sk) ret = false; @@ -660,6 +671,7 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk) if (ret) __sk_nulls_add_node_rcu(sk, list); +unlock: spin_unlock(lock); return ret; diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 1d77d992e6e7..6d681ef52bb2 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -91,10 +91,10 @@ void inet_twsk_put(struct inet_timewait_sock *tw) } EXPORT_SYMBOL_GPL(inet_twsk_put); -static void inet_twsk_add_node_rcu(struct inet_timewait_sock *tw, +static void inet_twsk_add_node_tail_rcu(struct inet_timewait_sock *tw, struct hlist_nulls_head *list) { - hlist_nulls_add_head_rcu(&tw->tw_node, list); + hlist_nulls_add_tail_rcu(&tw->tw_node, list); } static void inet_twsk_add_bind_node(struct inet_timewait_sock *tw, @@ -147,7 +147,7 @@ void inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk, spin_lock(lock); - inet_twsk_add_node_rcu(tw, &ehead->chain); + inet_twsk_add_node_tail_rcu(tw, &ehead->chain); /* Step 3: Remove SK from hash chain */ if (__sk_nulls_del_node_init_rcu(sk))