From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E91DDC33CB3 for ; Tue, 14 Jan 2020 10:12:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C02A824692 for ; Tue, 14 Jan 2020 10:12:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578996737; bh=UoeNj3LierfqBK3dFQablLeSko3NlsPKQVgd4DF+MxY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=AP9PVE5OFj75DElp3LFF7d7KHibXRUMN9FT7o493AWnwqZQrOsI/ss3M5dBg3oLdk peBlg4xpjNFlVqiUPSXv9foD6SatBn/oJwKlm7yB9KMIpRCcpcorv2oGC67L78JdFC tKOuc9w9Facch4r3FxjjieaZ0rOo49M2R3G14zeE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731608AbgANKMR (ORCPT ); Tue, 14 Jan 2020 05:12:17 -0500 Received: from mail.kernel.org ([198.145.29.99]:48374 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731515AbgANKMQ (ORCPT ); Tue, 14 Jan 2020 05:12:16 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BF29024677; Tue, 14 Jan 2020 10:12:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578996735; bh=UoeNj3LierfqBK3dFQablLeSko3NlsPKQVgd4DF+MxY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Fa0wulJajRP2mhVKvGnnyKvwJEmJxiEbVmRYCApIBCHjCt6/4EDSw0+iHts/PlyuK ckSZrNfOcr3DqVRG4G+ZG4yWXaZiTp2vBKZdRJdHAlGRITwRYftG+SOB16wWA0IE9T e6jrNt4r/FLq9Ve2h9oddii9vIAoV0j0rLLSyodc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Markus Trippelsdorf , Eric Dumazet , Marcelo Ricardo Leitner , "David S. Miller" , Salvatore Bonaccorso Subject: [PATCH 4.9 05/31] tcp: minimize false-positives on TCP/GRO check Date: Tue, 14 Jan 2020 11:01:57 +0100 Message-Id: <20200114094340.570688818@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200114094334.725604663@linuxfoundation.org> References: <20200114094334.725604663@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Marcelo Ricardo Leitner commit 0b9aefea860063bb39e36bd7fe6c7087fed0ba87 upstream. Markus Trippelsdorf reported that after commit dcb17d22e1c2 ("tcp: warn on bogus MSS and try to amend it") the kernel started logging the warning for a NIC driver that doesn't even support GRO. It was diagnosed that it was possibly caused on connections that were using TCP Timestamps but some packets lacked the Timestamps option. As we reduce rcv_mss when timestamps are used, the lack of them would cause the packets to be bigger than expected, although this is a valid case. As this warning is more as a hint, getting a clean-cut on the threshold is probably not worth the execution time spent on it. This patch thus alleviates the false-positives with 2 quick checks: by accounting for the entire TCP option space and also checking against the interface MTU if it's available. These changes, specially the MTU one, might mask some real positives, though if they are really happening, it's possible that sooner or later it will be triggered anyway. Reported-by: Markus Trippelsdorf Cc: Eric Dumazet Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller Cc: Salvatore Bonaccorso Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_input.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -129,7 +129,8 @@ int sysctl_tcp_invalid_ratelimit __read_ #define REXMIT_LOST 1 /* retransmit packets marked lost */ #define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */ -static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb) +static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb, + unsigned int len) { static bool __once __read_mostly; @@ -140,8 +141,9 @@ static void tcp_gro_dev_warn(struct sock rcu_read_lock(); dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif); - pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n", - dev ? dev->name : "Unknown driver"); + if (!dev || len >= dev->mtu) + pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n", + dev ? dev->name : "Unknown driver"); rcu_read_unlock(); } } @@ -164,8 +166,10 @@ static void tcp_measure_rcv_mss(struct s if (len >= icsk->icsk_ack.rcv_mss) { icsk->icsk_ack.rcv_mss = min_t(unsigned int, len, tcp_sk(sk)->advmss); - if (unlikely(icsk->icsk_ack.rcv_mss != len)) - tcp_gro_dev_warn(sk, skb); + /* Account for possibly-removed options */ + if (unlikely(len > icsk->icsk_ack.rcv_mss + + MAX_TCP_OPTION_SPACE)) + tcp_gro_dev_warn(sk, skb, len); } else { /* Otherwise, we make more careful check taking into account, * that SACKs block is variable.