From patchwork Mon Jan 16 07:38:13 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jason Xing X-Patchwork-Id: 13102698 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 1CB3EC54EBE for ; Mon, 16 Jan 2023 07:38:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231912AbjAPHi3 (ORCPT ); Mon, 16 Jan 2023 02:38:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51120 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231658AbjAPHi0 (ORCPT ); Mon, 16 Jan 2023 02:38:26 -0500 Received: from mail-pf1-x429.google.com (mail-pf1-x429.google.com [IPv6:2607:f8b0:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 271AAEC5A; Sun, 15 Jan 2023 23:38:26 -0800 (PST) Received: by mail-pf1-x429.google.com with SMTP id a184so20328616pfa.9; Sun, 15 Jan 2023 23:38:26 -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=wg2T7VbG1bTB43Zc6Xhxiu8pDGnHxwrmqsD8uohWqzI=; b=c/o2eejMpCEX9+LbXr0G3W+lLXEAq4aJO5DeAj/rq6nDlhFyWsdWwFMtsrqPALIkdZ tO+Y9ltQyunuUhqscifD/9mjbBvIyKUYr3Nvba6fJnXI7hNfRERcmUyB8r/a5skNHOg/ e3CDBO2QkkgI54Ta0X3Y4NgO5NkOw4i0ktxzKy1cVoiaUWeb0SuRwRQhSUsSyjlKoyOc sPtFlq0uLnvuFNqiakRog1fj1jI4fyuv0LE0x7Ub/b7tw0SqIDOFU/BgUo+wADZiAE5H ozJmFiDkd/KBJgNeqgD4jwFECBqETrj12WCr1W/ybTb7APyrK83CvkwBfjBCLfdP1pt8 qItQ== 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=wg2T7VbG1bTB43Zc6Xhxiu8pDGnHxwrmqsD8uohWqzI=; b=Dctd58H+AR8+tvfRIzR8c8jfuzyUkPH8CLggVd0PVOksYqTbDaPeIdZZEfyTcX8OzT QnfuD+mJGAOo3ylHQOlikWydI0+VN7T8uHjrigLrUR78PbPQQ9iyoesOT4aJYjmbUTcO URig7/iJKQ6yNKrLCOWfulHk+672o+SOKPRUbUFuv6XyDYB3KE5a0gcberpwg5s8DOcr eCzrbiJqzDUBqexTCRGS0qk+PN1xoAY+sFfiaQ9JoDCId6VMyXQErJHcwQ+EuhkpcCkA Kfda5CClJ0L9pnEQP7okhzp7dkKsvXPuszQ0XiBtJ2dY7Hg6/J+brzhA6Q7F/S5BEYoo L1tA== X-Gm-Message-State: AFqh2kqyHy/AXI8sxUrrd6heZ/FC3Jl12D9iM4Q8z+UErhXDW2YG7e5+ jYj1VCVT+jFJmJQXq+AqEQE= X-Google-Smtp-Source: AMrXdXuA1AF7GFtm9Vbyh7WL1RWa6Q2O0F8ZmIdRf8KnJWCmui4roXckeQ41N3CzYX+F7LLWJGPq9w== X-Received: by 2002:a05:6a00:bf5:b0:57c:2ab7:2c0b with SMTP id x53-20020a056a000bf500b0057c2ab72c0bmr12295617pfu.28.1673854705586; Sun, 15 Jan 2023 23:38:25 -0800 (PST) Received: from KERNELXING-MB0.tencent.com ([103.7.29.31]) by smtp.gmail.com with ESMTPSA id 65-20020a621844000000b005877d374069sm15020304pfy.10.2023.01.15.23.38.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Jan 2023 23:38:25 -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 v4 net] tcp: avoid the lookup process failing to get sk in ehash table Date: Mon, 16 Jan 2023 15:38:13 +0800 Message-Id: <20230116073813.24097-1-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/ --- v4: 1) adjust the code style and make it easier to read. 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. --- net/ipv4/inet_hashtables.c | 18 ++++++++++++++++-- net/ipv4/inet_timewait_sock.c | 6 +++--- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 24a38b56fab9..c64eec874b31 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -650,8 +650,21 @@ 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); - ret = sk_nulls_del_node_init_rcu(osk); - } else if (found_dup_sk) { + 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); + sk_nulls_del_node_init_rcu(osk); + } else { + ret = false; + } + goto unlock; + } + if (found_dup_sk) { *found_dup_sk = inet_ehash_lookup_by_sk(sk, list); if (*found_dup_sk) ret = false; @@ -660,6 +673,7 @@ 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))