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 74CFA3A9615 for ; Fri, 14 Aug 2026 16:49:14 +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=1786726155; cv=none; b=cAfL7piuGUD6EG7KC8Q6XFgdDfhe93MguHdnG5r/6pjP+sZHEzi2OtI4cwcs+S0c7rpBXLNR64dRT4HoPRlsRcm6dSOeUot7fbl+sAa9MTxU+b+73yCP8sYqhDLCGZ8VHaFcuDxyskfByde/f6FN6mBCK76Ltj5+fJ4T3Rm4YEc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786726155; c=relaxed/simple; bh=c31JOtt1SXGmmxjIkXrQF033r3l9GPEMDviNnxFfmRc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=m+ZEJ7rdEWbYuYvNzQAxui5u4HYXBCs9b3fBazED4Pkq/ZekgGw9zdoSm2fYI/eZbxzlOczVCsf2K/0KP18CYw2XBvpDkcVXHxz3JMAc01mRbxEaXAuRIvVR2fA2EpDGNXFu5qMQms0mA//jhxGeZbJ7+Gv9QtjSfkEm52w48uk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=g1lApEZD; 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="g1lApEZD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63C8C1F000E9; Fri, 14 Aug 2026 16:49:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786726154; bh=5i8pRqkQ4OS2Xbk6Fgv+lxQP+TJ49T/ALTZrxsznMHE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=g1lApEZDLNSUOfKzxvaLCDQaJKLRG1sNpcXtsa95GUnjBVQfhcf8znKvu7Qed7OGB F0cRuVJMDRUAO/HTHJywmiCblqR9Zi/8z9CHH/uJXRsGce/4Mw+uAm7De5vVKqxTgC M28LvVc6VD4/hnOsEEV9aiRTeZN1gykJGlHfFXJVRRx7p5YfEzdLLpDzWJ31Td1PEc YeWpAeFPlOnno3yg5sCBQzjRLrWtDjp2zOrToCfhmDnm8YWQN8Z6td0I5Oy495UMYD H8rDDIws8xJfOgxDylKfZvwHL1MWoWwBsEE7ubkITOoiNYTgiT0ys8u3vylZ1aLKer ngQYEUMHpmVwQ== Message-ID: <0146a9b7-f2aa-4412-8cc4-0cdbdd41a40e@kernel.org> Date: Fri, 14 Aug 2026 18:49:09 +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 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> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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) 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 -- Sponsored by the NGI0 Core fund.