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 BF293311592 for ; Tue, 2 Sep 2025 16:58:49 +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=1756832329; cv=none; b=N/MVbtZkwR4+TH/IbUzsI5fVWRaORaLeGJ8y+o5o41dabv/Sgmc/SkdsZ3UtIPT6Hjk4RRgp9gSZ0rmOiuL7s4R1xrttVElmbRLxnyfylBkENGWBR8RImow9ATuMovRl4lcOjSiGfK44FjGZgpH3Hq6rpvnsk/p3j4Q/64uGDGY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756832329; c=relaxed/simple; bh=mIan9e2oJqbCcamoVhxr5+tlYY7GgQ4fsbjxwWQnFGQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bdRnIRsUZm1GQtbqDmvOSlR2SL4clVlJSmXeCQoz22jXPprLG/qRzz4JBUewFX1+/GlEqr478ZnTYHw/pHF0PBka43hj39ZaoIiO+5EjG5DDXF9J5yUVdBmtv81qTNuUZd03TRrFmCQflXZuHrwbDlMXv77oGpHNcGRrybPnp+0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AEHP4jaZ; 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="AEHP4jaZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E32AC4CEED; Tue, 2 Sep 2025 16:58:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756832329; bh=mIan9e2oJqbCcamoVhxr5+tlYY7GgQ4fsbjxwWQnFGQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=AEHP4jaZbBVvG5kf6ktkkwlvp+jDbd4PiRZ5m6c2bgLCZr7HQDeKQGEWXrdaFlUTR 2NsOnwnxHcbffLi3Hfli7syk3WsoTAEJULRXYHZSBnHqfh9kPN5rstLdBpxq4OCCSK BPrYUI+iHGZoTPn/58GGDv2A9W4fIGc5G4rCjxOVNHzXAtkYmQ6sV7qrwB2eae66As n0dnqhSb0GIPKIuY7GGV5Ld24VJXl2vAAyodz8xURcVw4tk0acAX8BA/ooGTxcosE6 obdbkjseqOybBHrv6ewBmQflteGQi9OF9CswvJyDkCvkW9LSzgEmtNXm1Bt7MCYn6k NjTNbEePFmHvQ== Message-ID: <7602f5c9-7d36-4be4-89bf-2d113d4f13a8@kernel.org> Date: Tue, 2 Sep 2025 18:58:46 +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: Christoph Paasch Cc: Mat Martineau , 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> <8d4ba38a-e19d-408b-b81d-a75362d170e2@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 02/09/2025 18:43, Christoph Paasch wrote: > On Mon, Sep 1, 2025 at 3:08 AM Matthieu Baerts wrote: >> >> 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 > > Why not ? Yes, it is not typical to backport a new netlink message, > but I think it makes sense here. > It basically means that the fix involves not only the kernel but also > the userspace PMs. Yes, I guess we could backport it. I still don't know if we should use the (existing but not used) "flags" attribute, or a new dedicated one. >> , 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. > > The problem is that even this here is not complete, right ? A > userspace pm can still attempt to connect to the IP of the initial > subflow simply by using another address-ID. Yes, but that's not an issue for me: that's because the userspace PM didn't use the expected ID, so it is the userspace PM daemon responsibility :) Cheers, Matt -- Sponsored by the NGI0 Core fund.