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 166C4C46467 for ; Wed, 11 Jan 2023 13:44:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229725AbjAKNoI (ORCPT ); Wed, 11 Jan 2023 08:44:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239211AbjAKNnK (ORCPT ); Wed, 11 Jan 2023 08:43:10 -0500 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:237:300::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 034CD2E4 for ; Wed, 11 Jan 2023 05:42:38 -0800 (PST) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1pFbNE-0003o3-Ff; Wed, 11 Jan 2023 14:42:36 +0100 From: Florian Westphal To: Subject: [PATCH nf] netfilter: conntrack: handle tcp challenge acks during connection reuse Date: Wed, 11 Jan 2023 14:42:32 +0100 Message-Id: <20230111134232.2631-1-fw@strlen.de> X-Mailer: git-send-email 2.38.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org When a connection is re-used, following can happen: [ connection starts to close, fin sent in either direction ] > syn # initator quickly reuses connection < ack # peer sends a challenge ack > rst # rst, sequence number == ack_seq of previous challenge ack > syn # this syn is expected to pass Problem is that the rst will fail window validation, so it gets tagged as invalid. If ruleset drops such packets, we get repeated syn-retransmits until initator gives up or peer starts responding with syn/ack. Before the commit indicated in the "Fixes" tag below this used to work: The challenge-ack made conntrack re-init state based on the challenge ack itself, so the following rst would pass window validation. Add challenge-ack support: If we get ack for syn, record the ack_seq, and then check if the rst sequence number matches the last ack number seen in reverse direction. Fixes: c7aab4f17021 ("netfilter: nf_conntrack_tcp: re-init for syn packets only") Reported-by: Michal Tesar Signed-off-by: Florian Westphal --- net/netfilter/nf_conntrack_proto_tcp.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index 656631083177..3ac1af6f59fc 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -1068,6 +1068,13 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct, ct->proto.tcp.last_flags |= IP_CT_EXP_CHALLENGE_ACK; } + + /* possible challenge ack reply to syn */ + if (old_state == TCP_CONNTRACK_SYN_SENT && + index == TCP_ACK_SET && + dir == IP_CT_DIR_REPLY) + ct->proto.tcp.last_ack = ntohl(th->ack_seq); + spin_unlock_bh(&ct->lock); nf_ct_l4proto_log_invalid(skb, ct, state, "packet (index %d) in dir %d ignored, state %s", @@ -1193,6 +1200,14 @@ int nf_conntrack_tcp_packet(struct nf_conn *ct, * segments we ignored. */ goto in_window; } + + /* Reset in response to a challenge-ack we let through earlier */ + if (old_state == TCP_CONNTRACK_SYN_SENT && + ct->proto.tcp.last_index == TCP_ACK_SET && + ct->proto.tcp.last_dir == IP_CT_DIR_REPLY && + ntohl(th->seq) == ct->proto.tcp.last_ack) + goto in_window; + break; default: /* Keep compilers happy. */ -- 2.38.2