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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB72DC433EF for ; Wed, 27 Apr 2022 13:49:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236304AbiD0NwW (ORCPT ); Wed, 27 Apr 2022 09:52:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236554AbiD0NwT (ORCPT ); Wed, 27 Apr 2022 09:52:19 -0400 Received: from mail.netfilter.org (mail.netfilter.org [217.70.188.207]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 09061532FE for ; Wed, 27 Apr 2022 06:49:07 -0700 (PDT) Date: Wed, 27 Apr 2022 15:49:02 +0200 From: Pablo Neira Ayuso To: Florian Westphal Cc: netfilter-devel@vger.kernel.org, edumazet@google.com, ncardwell@google.com, Jaco Kroon , Jozsef Kadlecsik Subject: Re: [PATCH nf] netfilter: nf_conntrack_tcp: re-init for syn packets only Message-ID: References: <20220425094711.6255-1-fw@strlen.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220425094711.6255-1-fw@strlen.de> Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Mon, Apr 25, 2022 at 11:47:11AM +0200, Florian Westphal wrote: > Jaco Kroon reported tcp problems that Eric Dumazet and Neal Cardwell > pinpointed to nf_conntrack tcp_in_window() bug. > > tcp trace shows following sequence: > > I > R Flags [S], seq 3451342529, win 62580, options [.. tfo [|tcp]> > R > I Flags [S.], seq 2699962254, ack 3451342530, win 65535, options [..] > R > I Flags [P.], seq 1:89, ack 1, [..] > > Note 3rd ACK is from responder to initiator so following branch is taken: > } else if (((state->state == TCP_CONNTRACK_SYN_SENT > && dir == IP_CT_DIR_ORIGINAL) > || (state->state == TCP_CONNTRACK_SYN_RECV > && dir == IP_CT_DIR_REPLY)) > && after(end, sender->td_end)) { > > ... because state == TCP_CONNTRACK_SYN_RECV and dir is REPLY. > This causes the scaling factor to be reset to 0: window scale option > is only present in syn(ack) packets. This in turn makes nf_conntrack > mark valid packets as out-of-window. > > This was always broken, it exists even in original commit where > window tracking was added to ip_conntrack (nf_conntrack predecessor) > in 2.6.9-rc1 kernel. > > Restrict to 'tcph->syn', just like the 3rd condtional added in > commit 82b72cb94666 ("netfilter: conntrack: re-init state for retransmitted syn-ack"). > > Upon closer look, those conditionals/branches can be merged: > > Because earlier checks prevent syn-ack from showing up in > original direction, the 'dir' checks in the conditional quoted above are > redundant, remove them. Return early for pure syn retransmitted in reply > direction (simultaneous open). Applied, thanks