From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 8126133936B for ; Fri, 14 Aug 2026 18:34:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786732458; cv=none; b=J1GsnNwPfvg/t5EHKlFdn7ET5fZAaNmpy89kjXnhri4zOwRHT/gi5JT6R/wQe9Hddg0LcKRqktgSS93W7c7jm1XxPe1a8AB661GTCfsTaEIbzKbMpx1deJRYdXTNQ0st4VZrB6O5wV9kzJedqeFnAAMfjmhYgktqNeaKyY9MX7g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786732458; c=relaxed/simple; bh=nDHhzb2vnOhpg4fn0MzsTczFv246b+Ig2DKDWwOI7kc=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=gAB/pVppTZ5Z8p+AH3h6H6HJ4c7Kev+bz0giSpsW9vMxXebWrQj68HNIF8CHRUzTZpoc33fnF4POPHPfa97qa+8r1RAWNMdVjaVhxTTzLQUbRoBSKKsnMgrBfqEhrDQSGx9K3R0uCImqLlsUyH2/9F3LC07HN5H8xUfMiBcfBlI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h45Xiew4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h45Xiew4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A4A01F000E9; Fri, 14 Aug 2026 18:34:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786732457; bh=lWVxGpl5ezAYCw3gkGwvab2BYOdY81Y2lBGi0jukFe8=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=h45Xiew4+aEISk1eqTRwK1OUFM2w23fAIcccIo2HSD8Ckq1S9wAKnRr5oxaQDloaF Wp4m4Pi52G7czXPq6vPOYGTqS73la6pBUtTAmXl94vr9r7v4D3yPgHpYcuddS0bezx gbmkelxDes0t5FhBlOruNQmAQNhMO2Eusm4/v/fi5GBb8eW8MN4KbV0ZM/QZtOJoDI WMPlJIlUsMgBhOSPCa0A8ehyBqdBHymxnGBeiO9HVbqWsPgK9vc3grSVKP9vU1gq99 axXW+wD0fChl/RIQZeMCAeJvSW/+HVlVf2YlHFae/s5Uu5YP+sbKy4UORZyCJvSkv1 sQT0z6GhYWSNw== Message-ID: <89cad67d-868c-4081-909f-84957d208ec4@kernel.org> Date: Fri, 14 Aug 2026 20:34:13 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH export v3 2/4] mptcp: reject joins after fallback in mptcp_is_fully_established Content-Language: fr From: Matthieu Baerts To: Paolo Abeni Cc: Chenguang Zhao , mptcp@lists.linux.dev, Chenguang Zhao References: <20260812054653.43799-1-chenguang.zhao@linux.dev> <20260812054653.43799-3-chenguang.zhao@linux.dev> <1d7c56b9-00c1-4550-a403-c3d704259267@redhat.com> <41078a8c-00c7-4cb1-8e57-237b4ea6c2f0@kernel.org> <643936d9-5da2-45cc-b108-f7c2e7785044@redhat.com> <8f69b636-57ff-4f1b-a562-826306ab23d3@redhat.com> <0146a9b7-f2aa-4412-8cc4-0cdbdd41a40e@kernel.org> Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 14/08/2026 18:49, Matthieu Baerts wrote: > Hi Paolo, > > On 14/08/2026 13:06, Paolo Abeni wrote: >> On 8/14/26 11:09 AM, Matthieu Baerts wrote: >>> 14 Aug 2026 10:43:41 Paolo Abeni : >>>> It's not clear to me what actually goes wrong and how. Do you have handy >>>> a event sequence or stack trace demonstrating the critical scenario? >>> >>> Indeed, better with packetdrill scripts: >>> >>> https://github.com/chrisocean716-star/packetdrill/blob/bf9be7a7bee3687500444b284a9db2a0009a5252/gtests/net/mptcp/dss/dss_drop_after_data_fallback_server.pkt >>> >>> => A fallback is done, a subflow can be initiated, then rejected. >>> >>> >>> https://github.com/chrisocean716-star/packetdrill/blob/fed57fab92c407eb433acdb8c8ce72bd8e3e2f37/gtests/net/mptcp/mp_join/mp_join_server_after_fallback.pkt >>> >>> => The MP_FAIL is partially ignored if received before being in fully >>> established state. >> >> Thanks! >> >> I'm pretty sure there is a miss-intepretation of the 2nd case. > > Thank you for having checked! > >> The problem is not with `msk->fully_established`. AFAICS >> msk->fully_established is true when the MP_FAIL is receive. >> >> The passive msk socket sets it at MPC ACK reception. > > Indeed, I should have checked the code instead of only reading the > comments from this test :) > >> The problem is that, at MP_FAIL reception, the infinite mapping is not >> sent immediately, but it's scheduled with the next xmit, and until such >> point the msk does not perform the fallback. >> >> I think a proper solution would be bounding MP_FAIL (reply) and infinite >> mapping in the same ack. >> >> As noted by Gang, it may require a new helper (build on top of the >> tcp_send_ack). > Sounds good to me! > > What about the 1st case (fallback)? > > Would it help to reset msk->fully_established in > __mptcp_try_fallback()?(while holding the data_lock? not even sure it is > needed at that stage) > But here, we will also need to update subflow_token_join_request() to > check mptcp_is_fully_established, or even mptcp_can_accept_new_subflow. > (I can send a quick RFC patch) Sent: https://lore.kernel.org/20260814-mptcp-reset-mpj-early-v1-0-3ca3260f9474@kernel.org > It would also benefit to the in-kernel PM and others places using > mptcp_is_fully_established(). subflow->fully_established doesn't need to > be reset. > > Cheers, > Matt Cheers, Matt -- Sponsored by the NGI0 Core fund.