From mboxrd@z Thu Jan 1 00:00:00 1970 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 3CC4E41C7F for ; Tue, 16 Jul 2024 20:04:29 +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=1721160270; cv=none; b=Ijj/t+E4lYMCaEcjo9+F38NDi1D6H+ZFtaNGjbYnOVkC/IPMB7f7hZur/mP/ZdvMUq4A5nqEM1AY8wgDEP3Z88H2JAPfdNmNggUvkJmNoqr9iPBM345wmVDEj0TT7r2mZwk31/QBskHpQQczLbwUoXNRdYDppHmpUDPBWcxaD6E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721160270; c=relaxed/simple; bh=gIdLRVCS90Nj+b8n0UNHsFDi5yREho6pUPn/HqxpXEM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Jq1dnqKJy8irIQ+J8BAmot0cU2pnbLS7bwvGi+h4wMspuzpb5UamqdSUm/ctj6ITBsiDLTwbOib0p+3OthQszBosVWR2iHYlbgOVbILblRenMuvt73hbXhsYCorGEJKBXulca1P/n76kLSn5BAdBIujeBFydD8t656aslNKBqPg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ea7MVBHG; 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="ea7MVBHG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF80CC4AF0D; Tue, 16 Jul 2024 20:04:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721160269; bh=gIdLRVCS90Nj+b8n0UNHsFDi5yREho6pUPn/HqxpXEM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ea7MVBHGt1j4DMf1R172YSW8MgwTRVTeDd7RqNOfOX0LEyvYS7k+wrVMsnKrrlR5W xQCnRKxcN+hWzdRFD7aTr/H+LkGaiCWUEzjXHJjs3iO7nb6c9tNFQHyVywUAQEccWW fasf/KfOabrmLI51+nnqP+YOOmlGZQoRyGlYFyEVozJiB9zr0KB094+ZaUhduLWbyw WUKYv7VkoeaQLvE9QCXaGOzWp5lxR0Au6O6rGswiZcxPlcQSJVfwpEvhii6a9souAy Vh3vMeHbLbNa6T4FgjPC9ubkg2Qsih1UtHfeubswqDkuOr4fXhyVnvfTqzlKUOqtSJ aIKSi3BHDCFcw== Message-ID: <31eb13bf-7ea9-436f-92a9-a8745ed86f9e@kernel.org> Date: Tue, 16 Jul 2024 22:04:25 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH v3 net-next 1/2] tcp: Don't drop SYN+ACK for simultaneous connect(). Content-Language: en-GB To: Kuniyuki Iwashima Cc: davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, kuni1840@gmail.com, netdev@vger.kernel.org, pabeni@redhat.com References: <19b76438-2fc8-4f2f-a0ae-c988f5b17e9f@kernel.org> <20240716192320.54815-1-kuniyu@amazon.com> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; keydata= xsFNBFXj+ekBEADxVr99p2guPcqHFeI/JcFxls6KibzyZD5TQTyfuYlzEp7C7A9swoK5iCvf YBNdx5Xl74NLSgx6y/1NiMQGuKeu+2BmtnkiGxBNanfXcnl4L4Lzz+iXBvvbtCbynnnqDDqU c7SPFMpMesgpcu1xFt0F6bcxE+0ojRtSCZ5HDElKlHJNYtD1uwY4UYVGWUGCF/+cY1YLmtfb WdNb/SFo+Mp0HItfBC12qtDIXYvbfNUGVnA5jXeWMEyYhSNktLnpDL2gBUCsdbkov5VjiOX7 CRTkX0UgNWRjyFZwThaZADEvAOo12M5uSBk7h07yJ97gqvBtcx45IsJwfUJE4hy8qZqsA62A nTRflBvp647IXAiCcwWsEgE5AXKwA3aL6dcpVR17JXJ6nwHHnslVi8WesiqzUI9sbO/hXeXw TDSB+YhErbNOxvHqCzZEnGAAFf6ges26fRVyuU119AzO40sjdLV0l6LE7GshddyazWZf0iac nEhX9NKxGnuhMu5SXmo2poIQttJuYAvTVUNwQVEx/0yY5xmiuyqvXa+XT7NKJkOZSiAPlNt6 VffjgOP62S7M9wDShUghN3F7CPOrrRsOHWO/l6I/qJdUMW+MHSFYPfYiFXoLUZyPvNVCYSgs 3oQaFhHapq1f345XBtfG3fOYp1K2wTXd4ThFraTLl8PHxCn4ywARAQABzSRNYXR0aGlldSBC YWVydHMgPG1hdHR0YmVAa2VybmVsLm9yZz7CwZEEEwEIADsCGwMFCwkIBwIGFQoJCAsCBBYC AwECHgECF4AWIQToy4X3aHcFem4n93r2t4JPQmmgcwUCZUDpDAIZAQAKCRD2t4JPQmmgcz33 EACjROM3nj9FGclR5AlyPUbAq/txEX7E0EFQCDtdLPrjBcLAoaYJIQUV8IDCcPjZMJy2ADp7 /zSwYba2rE2C9vRgjXZJNt21mySvKnnkPbNQGkNRl3TZAinO1Ddq3fp2c/GmYaW1NWFSfOmw MvB5CJaN0UK5l0/drnaA6Hxsu62V5UnpvxWgexqDuo0wfpEeP1PEqMNzyiVPvJ8bJxgM8qoC cpXLp1Rq/jq7pbUycY8GeYw2j+FVZJHlhL0w0Zm9CFHThHxRAm1tsIPc+oTorx7haXP+nN0J iqBXVAxLK2KxrHtMygim50xk2QpUotWYfZpRRv8dMygEPIB3f1Vi5JMwP4M47NZNdpqVkHrm jvcNuLfDgf/vqUvuXs2eA2/BkIHcOuAAbsvreX1WX1rTHmx5ud3OhsWQQRVL2rt+0p1DpROI 3Ob8F78W5rKr4HYvjX2Inpy3WahAm7FzUY184OyfPO/2zadKCqg8n01mWA9PXxs84bFEV2mP VzC5j6K8U3RNA6cb9bpE5bzXut6T2gxj6j+7TsgMQFhbyH/tZgpDjWvAiPZHb3sV29t8XaOF BwzqiI2AEkiWMySiHwCCMsIH9WUH7r7vpwROko89Tk+InpEbiphPjd7qAkyJ+tNIEWd1+MlX ZPtOaFLVHhLQ3PLFLkrU3+Yi3tXqpvLE3gO3LM7BTQRV4/npARAA5+u/Sx1n9anIqcgHpA7l 5SUCP1e/qF7n5DK8LiM10gYglgY0XHOBi0S7vHppH8hrtpizx+7t5DBdPJgVtR6SilyK0/mp 9nWHDhc9rwU3KmHYgFFsnX58eEmZxz2qsIY8juFor5r7kpcM5dRR9aB+HjlOOJJgyDxcJTwM 1ey4L/79P72wuXRhMibN14SX6TZzf+/XIOrM6TsULVJEIv1+NdczQbs6pBTpEK/G2apME7vf mjTsZU26Ezn+LDMX16lHTmIJi7Hlh7eifCGGM+g/AlDV6aWKFS+sBbwy+YoS0Zc3Yz8zrdbi Kzn3kbKd+99//mysSVsHaekQYyVvO0KD2KPKBs1S/ImrBb6XecqxGy/y/3HWHdngGEY2v2IP Qox7mAPznyKyXEfG+0rrVseZSEssKmY01IsgwwbmN9ZcqUKYNhjv67WMX7tNwiVbSrGLZoqf Xlgw4aAdnIMQyTW8nE6hH/Iwqay4S2str4HZtWwyWLitk7N+e+vxuK5qto4AxtB7VdimvKUs x6kQO5F3YWcC3vCXCgPwyV8133+fIR2L81R1L1q3swaEuh95vWj6iskxeNWSTyFAVKYYVskG V+OTtB71P1XCnb6AJCW9cKpC25+zxQqD2Zy0dK3u2RuKErajKBa/YWzuSaKAOkneFxG3LJIv Hl7iqPF+JDCjB5sAEQEAAcLBXwQYAQIACQUCVeP56QIbDAAKCRD2t4JPQmmgc5VnD/9YgbCr HR1FbMbm7td54UrYvZV/i7m3dIQNXK2e+Cbv5PXf19ce3XluaE+wA8D+vnIW5mbAAiojt3Mb 6p0WJS3QzbObzHNgAp3zy/L4lXwc6WW5vnpWAzqXFHP8D9PTpqvBALbXqL06smP47JqbyQxj Xf7D2rrPeIqbYmVY9da1KzMOVf3gReazYa89zZSdVkMojfWsbq05zwYU+SCWS3NiyF6QghbW voxbFwX1i/0xRwJiX9NNbRj1huVKQuS4W7rbWA87TrVQPXUAdkyd7FRYICNW+0gddysIwPoa KrLfx3Ba6Rpx0JznbrVOtXlihjl4KV8mtOPjYDY9u+8x412xXnlGl6AC4HLu2F3ECkamY4G6 UxejX+E6vW6Xe4n7H+rEX5UFgPRdYkS1TA/X3nMen9bouxNsvIJv7C6adZmMHqu/2azX7S7I vrxxySzOw9GxjoVTuzWMKWpDGP8n71IFeOot8JuPZtJ8omz+DZel+WCNZMVdVNLPOd5frqOv mpz0VhFAlNTjU1Vy0CnuxX3AM51J8dpdNyG0S8rADh6C8AKCDOfUstpq28/6oTaQv7QZdge0 JY6dglzGKnCi/zsmp2+1w559frz4+IC7j/igvJGX4KDDKUs0mlld8J2u2sBXv7CGxdzQoHaz lzVbFe7fduHbABmYz9cefQpO7wDE/Q== Organization: NGI0 Core In-Reply-To: <20240716192320.54815-1-kuniyu@amazon.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Kuniyuki, Thank you for your reply! On 16/07/2024 21:23, Kuniyuki Iwashima wrote: > Hi Matthieu, > > From: Matthieu Baerts > Date: Mon, 15 Jul 2024 17:58:49 +0200 >> Hi Kuniyuki, >> >> On 10/07/2024 19:12, Kuniyuki Iwashima wrote: >>> RFC 9293 states that in the case of simultaneous connect(), the connection >>> gets established when SYN+ACK is received. [0] >>> >>> TCP Peer A TCP Peer B >>> >>> 1. CLOSED CLOSED >>> 2. SYN-SENT --> ... >>> 3. SYN-RECEIVED <-- <-- SYN-SENT >>> 4. ... --> SYN-RECEIVED >>> 5. SYN-RECEIVED --> ... >>> 6. ESTABLISHED <-- <-- SYN-RECEIVED >>> 7. ... --> ESTABLISHED >>> >>> However, since commit 0c24604b68fc ("tcp: implement RFC 5961 4.2"), such a >>> SYN+ACK is dropped in tcp_validate_incoming() and responded with Challenge >>> ACK. >>> >>> For example, the write() syscall in the following packetdrill script fails >>> with -EAGAIN, and wrong SNMP stats get incremented. >>> >>> 0 socket(..., SOCK_STREAM|SOCK_NONBLOCK, IPPROTO_TCP) = 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 1000 >>> >>> +0 write(3, ..., 100) = 100 >>> +0 > P. 1:101(100) ack 1 >>> >>> -- >>> >>> # packetdrill cross-synack.pkt >>> cross-synack.pkt:13: runtime error in write call: Expected result 100 but got -1 with errno 11 (Resource temporarily unavailable) >>> # nstat >>> ... >>> TcpExtTCPChallengeACK 1 0.0 >>> TcpExtTCPSYNChallenge 1 0.0 >>> >>> The problem is that bpf_skops_established() is triggered by the Challenge >>> ACK instead of SYN+ACK. This causes the bpf prog to miss the chance to >>> check if the peer supports a TCP option that is expected to be exchanged >>> in SYN and SYN+ACK. >>> >>> Let's accept a bare SYN+ACK for active-open TCP_SYN_RECV sockets to avoid >>> such a situation. >>> >>> Note that tcp_ack_snd_check() in tcp_rcv_state_process() is skipped not to >>> send an unnecessary ACK, but this could be a bit risky for net.git, so this >>> targets for net-next. >>> >>> Link: https://www.rfc-editor.org/rfc/rfc9293.html#section-3.5-7 [0] >>> Signed-off-by: Kuniyuki Iwashima >> >> Thank you for having worked on this patch! >> >>> --- >>> net/ipv4/tcp_input.c | 9 +++++++++ >>> 1 file changed, 9 insertions(+) >>> >>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c >>> index 47dacb575f74..1eddb6b9fb2a 100644 >>> --- a/net/ipv4/tcp_input.c >>> +++ b/net/ipv4/tcp_input.c >>> @@ -5989,6 +5989,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, >>> * RFC 5961 4.2 : Send a challenge ack >>> */ >>> if (th->syn) { >>> + if (sk->sk_state == TCP_SYN_RECV && sk->sk_socket && th->ack && >>> + TCP_SKB_CB(skb)->seq + 1 == TCP_SKB_CB(skb)->end_seq && >>> + TCP_SKB_CB(skb)->seq + 1 == tp->rcv_nxt && >>> + TCP_SKB_CB(skb)->ack_seq == tp->snd_nxt) >>> + goto pass; >>> syn_challenge: >>> if (syn_inerr) >>> TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); >>> @@ -5998,6 +6003,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, >>> goto discard; >>> } >>> >>> +pass: >>> bpf_skops_parse_hdr(sk, skb); >>> >>> return true; >>> @@ -6804,6 +6810,9 @@ tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) >>> tcp_fast_path_on(tp); >>> if (sk->sk_shutdown & SEND_SHUTDOWN) >>> tcp_shutdown(sk, SEND_SHUTDOWN); >>> + >>> + if (sk->sk_socket) >>> + goto consume; >> >> It looks like this modification changes the behaviour for MPTCP Join >> requests for listening sockets: 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 created >> before with the first path. > > Thanks for catching this! > > I completely missed how MPTCP sets sk->sk_socket before the 3rd ACK is > processed. No problem. That's a shame there was not a clear error in the selftests :) > I debugged a bit and confirmed mptcp_stream_accept() sets > the inflight subflow's sk->sk_socket with newsk->sk_socket. Yes, that's correct. >> This new 'goto' here will then skip the >> process 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 [1]. >> >> This doesn't fully break MPTCP, mainly the 4th MPJ ACK that will be >> delayed, > > Yes, the test failure depends on timing. I only reproduced it by running > the test many times on non-kvm qemu. Thank you for having checked! >> but it looks like it affects the MPTFO feature as well -- >> probably in case of retransmissions I suppose -- and being the reason >> why the selftests started to be unstable the last few days [2]. >> >> [1] https://datatracker.ietf.org/doc/html/rfc8684#fig_tokens >> [2] >> https://netdev.bots.linux.dev/contest.html?executor=vmksft-mptcp-dbg&test=mptcp-connect-sh >> >> >> Looking at what this patch here is trying to fix, I wonder if it would >> not be enough to apply this patch: >> >>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c >>> index ff9ab3d01ced..ff981d7776c3 100644 >>> --- a/net/ipv4/tcp_input.c >>> +++ b/net/ipv4/tcp_input.c >>> @@ -6820,7 +6820,7 @@ 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) >>> + if (sk->sk_socket && !sk_is_mptcp(sk)) >>> goto consume; >>> break; >>> >> >> But I still need to investigate how the issue that is being addressed by >> your patch can be translated to the MPTCP case. I guess we could add >> additional checks for MPTCP: new connection or additional path? etc. Or >> maybe that's not needed. > > My first intention was not to drop SYN+ACK in tcp_validate_incoming(), > and the goto is added in v2, which is rather to be more compliant with > RFC not to send an unnecessary ACK for simultaneous connect(). > > So, we could rewrite the condition as this, > > if (sk->sk_socket && !th->syn) (Just to be sure, do you mean the opposite with th->syn?) if (sk->sk_socket && th->syn) goto consume; That's a good idea! I sent my patch a couple of minutes ago [1], then I saw your suggestion here. It looks like it should work for the TFO case as well. Maybe your suggestion is more generic and will cover more cases? [1] https://lore.kernel.org/all/20240716-upstream-net-next-20240716-tcp-3rd-ack-consume-sk_socket-v1-1-4e61d0b79233@kernel.org/ > but I think your patch is better to give a hint that MPTCP has a > different logic. Because TFO has also a different logic, it might be good to have a clear comment about that. > Also, a similar check done before the goto, and this could be > improved ? > > if (sk->sk_socket) > sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); It is a bit late for me, but I think it can be kept as it is: for MPTCP, it will not wake up the userspace as the subflow is managed by the kernel. I would need to check if we could avoid that. Also, will this wakeup not be useful for TFO? Cheers, Matt -- Sponsored by the NGI0 Core fund.