From patchwork Thu Jul 18 10:33:56 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Matthieu Baerts (NGI0)" X-Patchwork-Id: 13736356 X-Patchwork-Delegate: kuba@kernel.org Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 39347132112; Thu, 18 Jul 2024 10:34:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721298862; cv=none; b=knIGQENIvhCM/jwruIIEmnjJBI9zb6q5PBAbpOMy7W0pXbiiV/yQSoyl+1cqhkg7MhryWOqlfO62lZ38AFAH0KMcDOj83sLF22U86noU4IJAL6ZeBTAw9wxIQCbvsjupqukz8Ex+sC10tH7iihIP+PJkRBXpXirk3bGIXVRH6kI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721298862; c=relaxed/simple; bh=piw2pOL8UZVssXmqpVfj53xjxXazAMpjHsH/ohQyXMg=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=PHO+x/JVOsKg1SYdlsTv3MPARO0p/dwm7T3x4FTuxocJMgtcNTa1C9UMYfnkujEkZzfA1RzCbyUxTs4ABlUgMm4LfL9F/qnZA6DjqGySB+QHwMQu5p+dgUzurRtr2oyjUuU4SE7PjN8qbQiDUB7Bn1Mskqln+bNWJ44gfRXhyrs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PU6YB/sZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PU6YB/sZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 860B8C4AF0F; Thu, 18 Jul 2024 10:34:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721298861; bh=piw2pOL8UZVssXmqpVfj53xjxXazAMpjHsH/ohQyXMg=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=PU6YB/sZpfcj8eEacdEbYfVj68jE9h+N33BDPYUPr5pxeGDG5Sylf2dvMnvvahrPk DwZeMRg+ms3WY3JJ32zNSNcwlZfPx/D1RFIE6dbVyg1LD4iUaRkBhMxj3jS9onMZE7 o92SkcHaQaXAnUsB2AwttxJPITyaNHczkXo/yJg3dcKSbQiOOmYTTFK8idBpmk2p0N PrBdo8pWeQvvzV3QZf98yHBTeoE2613QyRBnZHCXnRniyRrd3zV+WzKV9uqCgnasO2 aTgOAeIAoTX92Gv3TEvcFDDYmIZ5kcj080cVpEPBNfQui8IAUw0iHa0R8AYCYt+X5O HhxmbxAH0k/4g== From: "Matthieu Baerts (NGI0)" Date: Thu, 18 Jul 2024 12:33:56 +0200 Subject: [PATCH net v2 1/2] tcp: process the 3rd ACK with sk_socket for TFO/MPTCP Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-1-d653f85639f6@kernel.org> References: <20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-0-d653f85639f6@kernel.org> In-Reply-To: <20240718-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v2-0-d653f85639f6@kernel.org> To: Eric Dumazet , "David S. Miller" , David Ahern , Jakub Kicinski , Paolo Abeni , Kuniyuki Iwashima , Jerry Chu Cc: netdev@vger.kernel.org, mptcp@lists.linux.dev, linux-kernel@vger.kernel.org, "Matthieu Baerts (NGI0)" X-Mailer: b4 0.14.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5098; i=matttbe@kernel.org; h=from:subject:message-id; bh=piw2pOL8UZVssXmqpVfj53xjxXazAMpjHsH/ohQyXMg=; b=owEBbQKS/ZANAwAIAfa3gk9CaaBzAcsmYgBmmO+oD7vHXVzHiXzYqKPoJiLB4b8qzznq+oYMs XMkjqvvQOCJAjMEAAEIAB0WIQToy4X3aHcFem4n93r2t4JPQmmgcwUCZpjvqAAKCRD2t4JPQmmg c580D/91JMiUY/0yEXJzEHnrIX5gOmLt88L/ouI6Q77NwKDz7qtZF0NUJ+xS40c6C6aXq/WRnJB RuA9sJSWEC2kC/cZ6ZOUA2t4ELK7bGitEWwti46H/bmKZiqPYou7P38IlBXEFMnT3ZTOhmjrWGu +ZR3fLHnjTi+hVwNtRiGhIh6JZEXys9ltXWiMH2BTQeDlOS692fkUaVgxcWNo4GP9iz6CiHSjn7 AMdiSHMsN+8S5bxWBK8FD4KN7rNr3ATLzoWoX3NilvOwBswTHUlQgylvycolnHPsM4DcXoy/aDn jwpC9FrugB8QwSUA61M3mXTrOupNPQswjhvEgwymz/LD5fWixnXzq0soTKPM03Wgfwgrc+fD53D a2sNTGRjVgCtdOO0PLofF3/IoqNEoHm+eEENdGS4szd6wzo71mrYQXWdDjrJgIOtV5TgD40VYFX AlzZ8QBjRbs4dGqbMHtqWhGBjjxIONK1QcaoB6SJsucz2ItWIK8lqqOd7ezoLpffHXA00WAigWU pRBQn7L5fD0ZzXohs7lWhW1SjsaVu/FW3SYgFtfbLRUpxG4hH+zOyRiJQdukPAADsHbY9bmNdlL S98Rj0KGGH9xH66ozvqLwPelt0LJYIM7HHl9Mt0Wmtlii/8LULUdW2kuwbTjybA9gvvw2YIXBHC 6M6BRLKBjh0mJUg== X-Developer-Key: i=matttbe@kernel.org; a=openpgp; fpr=E8CB85F76877057A6E27F77AF6B7824F4269A073 X-Patchwork-Delegate: kuba@kernel.org The 'Fixes' commit recently changed the behaviour of TCP by skipping the processing of the 3rd ACK when a sk->sk_socket is set. The goal was to skip tcp_ack_snd_check() in tcp_rcv_state_process() not to send an unnecessary ACK in case of simultaneous connect(). Unfortunately, that had an impact on TFO and MPTCP. I started to look at the impact on MPTCP, because the MPTCP CI found some issues with the MPTCP Packetdrill tests [1]. Then Paolo suggested me to look at the impact on TFO with "plain" TCP. For MPTCP, when receiving the 3rd ACK of a request adding a new path (MP_JOIN), sk->sk_socket will be set, and point to the MPTCP sock that has been created when the MPTCP connection got established before with the first path. The newly added 'goto' will then skip the processing of the segment text (step 7) and not go through tcp_data_queue() where the MPTCP options are validated, and some actions are triggered, e.g. sending the MPJ 4th ACK [2] as demonstrated by the new errors when running a packetdrill test [3] establishing a second subflow. This doesn't fully break MPTCP, mainly the 4th MPJ ACK that will be delayed. Still, we don't want to have this behaviour as it delays the switch to the fully established mode, and invalid MPTCP options in this 3rd ACK will not be caught any more. This modification also affects the MPTCP + TFO feature as well, and being the reason why the selftests started to be unstable the last few days [4]. For TFO, the existing 'basic-cookie-not-reqd' test [5] was no longer passing: if the 3rd ACK contains data, and the connection is accept()ed before receiving them, these data would no longer be processed, and thus not ACKed. One last thing about MPTCP, in case of simultaneous connect(), a fallback to TCP will be done, which seems fine: `../common/defaults.sh` 0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_MPTCP) = 3 +0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress) +0 > S 0:0(0) +0 < S 0:0(0) win 1000 +0 > S. 0:0(0) ack 1 +0 < S. 0:0(0) ack 1 win 65535 +0 write(3, ..., 100) = 100 +0 > . 1:1(0) ack 1 +0 > P. 1:101(100) ack 1 Simultaneous SYN-data crossing is also not supported by TFO, see [6]. Link: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/9936227696 [1] Link: https://datatracker.ietf.org/doc/html/rfc8684#fig_tokens [2] Link: https://github.com/multipath-tcp/packetdrill/blob/mptcp-net-next/gtests/net/mptcp/syscalls/accept.pkt#L28 [3] Link: https://netdev.bots.linux.dev/contest.html?executor=vmksft-mptcp-dbg&test=mptcp-connect-sh [4] Link: https://github.com/google/packetdrill/blob/master/gtests/net/tcp/fastopen/server/basic-cookie-not-reqd.pkt#L21 [5] Link: https://github.com/google/packetdrill/blob/master/gtests/net/tcp/fastopen/client/simultaneous-fast-open.pkt [6] Fixes: 23e89e8ee7be ("tcp: Don't drop SYN+ACK for simultaneous connect().") Suggested-by: Paolo Abeni Suggested-by: Kuniyuki Iwashima Signed-off-by: Matthieu Baerts (NGI0) --- Notes: - We could also drop this 'goto consume', and send the unnecessary ACK in this simultaneous connect case, which doesn't seem to be a "real" case, more something for fuzzers. But that's not what the RFC 9293 recommends to do. - v2: - Check if the SYN bit is set instead of looking for TFO and MPTCP specific attributes, as suggested by Kuniyuki. - Updated the comment above - Please note that the v2 has been sent mainly to satisfy the CI (to be able to catch new bugs with MPTCP), and because the suggestion from Kuniyuki looks better. It has not been sent to urge TCP maintainers to review it quicker than it should, please take your time and enjoy netdev.conf :) --- net/ipv4/tcp_input.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index ff9ab3d01ced..bfe1bc69dc3e 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6820,7 +6820,12 @@ tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) if (sk->sk_shutdown & SEND_SHUTDOWN) tcp_shutdown(sk, SEND_SHUTDOWN); - if (sk->sk_socket) + /* For crossed SYN cases, not to send an unnecessary ACK. + * Note that sk->sk_socket can be assigned in other cases, e.g. + * with TFO (if accept()'ed before the 3rd ACK) and MPTCP (MPJ: + * sk_socket is the parent MPTCP sock). + */ + if (sk->sk_socket && th->syn) goto consume; break;