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 ED5B730F549 for ; Mon, 1 Sep 2025 10:08:56 +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=1756721337; cv=none; b=nbdY8pqYP9TRokQvkcaeEkhSXc7Uq5Jq+iiT2bfPZxCD833kJLQAieCtqyQdpkwKsOanfEGzZ5XPmwCGh7MaGZmojlqF1pAbe0AnoGYm9no2OW70jmr/2ph23BPj4JAii1/zujzSRf61w1igVrOAXu6JgowYaIkdQB52jFAlDao= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756721337; c=relaxed/simple; bh=h3EFOgl7vbDyS9f3AHHoAGwDAr2s1fYv+Ej50/6X8Kw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ozSdENhy4EP6MHmfXECOO2nMiPIgWEieRbM7hAaY5me/lLLzYvqLkxoPhusmoMSbd7kOsfIe4E2SUALW0cKyyqnBdqeMVAaTROyTCOVxDUP/RuLEsDcwV7vLRO1HP7pMD0aTpRKyOMYnHOmymKO24iTSqdutk1ni9RKwhSHrhSg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CjcxogF/; 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="CjcxogF/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C213AC4CEF4; Mon, 1 Sep 2025 10:08:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756721336; bh=h3EFOgl7vbDyS9f3AHHoAGwDAr2s1fYv+Ej50/6X8Kw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=CjcxogF/cozEtKq7V02xCIypMBvnzQoRZhomDeHAROxLJONRRj5csoLicjd4r7SUN HUadUchDy+tEPJSxaZ/xsZkqHbgtK2n4O0t05+9LyP3zoeqGEJpSll+Rc1cI9rAvqX 6XVsXF/18So07zFOGuZA8P6ZY64osi1zi7VxN9LSvXd68k+GFkni/GX1qwfkBScRze rK/y7XlDJyy+NEIG+U7LQD9shDON0QGhXn00ZnjsMe/XrsmjJCgGPOHwNvsLsd1VaP Cl7+azV3C3HwuF0GUI2cl+oR+ABnxziXI7llvf0d4rVrTmiyE7m5/pMtWmYuwMyx8n 8213VS37z6DJA== Message-ID: <8d4ba38a-e19d-408b-b81d-a75362d170e2@kernel.org> Date: Mon, 1 Sep 2025 12:08:53 +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 mptcp-net 2/7] mptcp: pm: userspace: respect deny_join_id0 attr Content-Language: en-GB, fr-BE To: Mat Martineau , Christoph Paasch Cc: mptcp@lists.linux.dev References: <20250829-mptcp-pm-user-c-flag-v1-0-78b25dda7708@kernel.org> <20250829-mptcp-pm-user-c-flag-v1-2-78b25dda7708@kernel.org> <9de05bc0-fcf6-364f-b143-fb72cb8c4cae@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Christoph, Mat, On 30/08/2025 02:58, Mat Martineau wrote: > On Fri, 29 Aug 2025, Christoph Paasch wrote: > >> On Fri, Aug 29, 2025 at 1:33 PM Matthieu Baerts (NGI0) >> wrote: >>> >>> During the connection establishment, a peer can tell the other that it >>> cannot establish new subflows to the initial IP address and port by >>> setting the 'C' flag [1]. The RFC8684 is strict about that: >>> >>>   (...) therefore the receiver MUST NOT try to open any additional >>>   subflows toward this address and port. >>> >>> It is then important not to let the userspace PM establishing such >>> subflows, and return an error (ECONNREFUSED) if it tries to do so. >>> >>> Fixes: 702c2f646d42 ("mptcp: netlink: allow userspace-driven subflow >>> establishment") >>> Link: https://datatracker.ietf.org/doc/html/rfc8684\#section-3.1-20.6 >>> [1] >>> Signed-off-by: Matthieu Baerts (NGI0) >>> --- >>>  net/mptcp/pm_userspace.c | 6 ++++++ >>>  1 file changed, 6 insertions(+) >>> >>> diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c >>> index >>> 1911fe1799fa38a53381247a830a9a0daf1c4492..9968dc9a8b45112114953f66848ea22c971136d6 100644 >>> --- a/net/mptcp/pm_userspace.c >>> +++ b/net/mptcp/pm_userspace.c >>> @@ -391,6 +391,12 @@ int mptcp_pm_nl_subflow_create_doit(struct >>> sk_buff *skb, struct genl_info *info) >>>         if (err < 0) >>>                 goto create_err; >>> >>> +       if (READ_ONCE(msk->pm.remote_deny_join_id0) && addr_r.id == 0) { >> >> If userspace wants to, it could still work around that by still using >> the initial subflow's IP-address and just use a non-zero address-ID. Good point, I missed that! >> Is that really a concern ? Sure, the IETF-draft says "MUST NOT", and >> so, shouldn't we leave it up to the userspace PM to make that decision >> ? >> > > I concur with Christoph on this one, I think the PM (userspace or > kernel) is responsible for this aspect of the protocol so it doesn't > need to be double-checked here. Indeed, we could leave it up to the different PMs to make that decision. Initially, I didn't have this patch, and I had a simple patch setting the corresponding sysctl to 0 in userspace_pm.sh, just to check the event was correctly announced. But when writing the last patch's commit message ("mptcp: pm: nl: announce deny-join-id0 attribute"), I realised that the main missing feature was a way for the userspace daemon to know that the C flag was set. We cannot backport patch 7/7, but we can backport this one, and have a way to know this info on older kernels. I should have mentioned that in the commit message. In this case, I think we have a few options: - Keep this patch, but update the commit message to make it clearer what's its purpose, see [1] - Same, but revert it after patch 7/7 on net-next. - Keep it, but also check for the address and port. - Drop it. What would you prefer? Personally, I think we should keep it, at least for stable, but we don't need to check for the address and port: even if it is easy to check, it might be good to let a way for the userspace to still create such subflow. [1]: The last paragraph in this commit message would then be: > It is then important to let the userspace daemon know it is not allowed > to establish such subflows, and return an error (ECONNREFUSED) if it > tries to do so. Note that the userspace daemon will still be able to > establish subflows to the initial IP address and port, but by giving a > different remote ID: that's OK, that's its responsibility ; worst case, > the MP_JOIN is rejected by the other peer. Cheers, Matt -- Sponsored by the NGI0 Core fund.