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 AF73E1A6817 for ; Sat, 15 Aug 2026 17:33:58 +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=1786815239; cv=none; b=tiGOuOfiL8/C+7bSDjRxvJdeOCqPplgGZOz1GAl4gy/OnDd+hTHYj+k5FhnGVLtQpZK5LBS1+psOaLeAuh/i9rfF8E7UgMkVL59452avJWnPLYdR88TMus7BXvJ/pwhm86x0VCWzX9I1MSuOK1ni9HO1Yfg8NRzwEMelLMlo4TQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786815239; c=relaxed/simple; bh=qCIXgN/sz4+5BNl4tGyt7J9AkeQLtyZQKIVYgecELg0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fmSVJSxoUVmfxbF6CSUV7c3B/KqBz2kb4PEDJItm1ViT//bVytouBb8p9R3XtGzPHcIkONaXU/sU+lFw5eQs9527xa03Ap3gwKknKEjIhf1mdc402CiIKh2pIxCuRKY9Ml9QcX9kCFAU+Dq8zd7amz+gQbX3/nwbP1hOiH6KX7o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Jdjll0oD; 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="Jdjll0oD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B1B541F000E9; Sat, 15 Aug 2026 17:33:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786815238; bh=V+bIDFmk2Z4lg/IqhDPJxUuA2HyU0n9snpV86UU2hIk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Jdjll0oDdyaGlC7OC2vlMOfNVi328iYf7XZphrFXmBgw9FGoUtLbN/Tamps93uDTs G58uoR0IRMztV9SGasZyRZzSgpgs3Od7Ups1at4pXQbedrWDiQwTILWGBlEokZcj14 5dG8FsjBA0lF5oIpycC4smzgd84WkjoYP3m2uZU0GnT00eTEfJF1OIzYe8lRJP0BFj /Zdo5hJiiAC5yr7U5mbAQHu3kOryCaKSpXyA94CL2A79sGOYpPytkFnz8YrSHTmwOU ZgDT9zDf5WQXhEVk0bV0NO9IxCQexPYyWhLakJGKfuOrl6aBdjQZTaiGKmnagbGAC3 JG2+uZcKXPAnA== Message-ID: <29304df9-a7e7-4585-aecb-b3ae701ee5bb@kernel.org> Date: Sat, 15 Aug 2026 19:33:56 +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 v2] mptcp: options: handle MPC data + csum reqd + no csum Content-Language: fr To: Mat Martineau Cc: MPTCP Linux References: <20260805-mptcp-opt-mpc-csumreqd-no-csum-v2-1-dbb52e01a36d@kernel.org> <20f3ef05-aebd-84b0-55a6-8ed35c79d07b@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Mat, On 14/08/2026 03:48, Mat Martineau wrote: > On Wed, 5 Aug 2026, Matthieu Baerts (NGI0) wrote: > >> Before this modification, a remote peer could send an MP_CAPABLE with >> data, with the checksum flag set, but without adding the actual 2 bytes >> of checksum. As a result, uninitialised bytes could be used for the >> 'csum' field. >> >> That was not a critical issue, because this 'csum' field is only used to >> compare with the expected one, if previously negotiated in the 3WHS. >> Worst case, the checksum is likely wrong, a fallback is done without a >> reject if the negotiation was done earlier. That's OK. >> >> Yet, better to take the expected path with this case: only look at the >> checksum flag for MP_CAPABLEs not carrying a data-len. >> >> Such packet can be seen as a 3rd or 4th ACK. The RFC8684 mentions [1] >> that the 3rd packet should have the checksum flag set. When an MPC + ACK >> contains data, the checksum flag is redundant with the checksum field. >> It is not clear what should be done for the 4th ACK, nor if the flag has >> to be set if the checksum field is set. >> >> Therefore, it seems fine to only look at the presence of the checksum >> field, not to break the interaction with stacks that were not setting >> both. (...) > Yes, this looks like a good tradeoff between not breaking interaction > with other stacks while avoiding an invalid checksum. Thank you for the review! New patches for t/upstream-net and t/upstream: - aa590201e5a8: mptcp: options: handle MPC data + csum reqd + no csum - Results: 79d7297194ac..52bf6f574345 (export-net) - Results: 199ed983c1f7..55a0274d38e1 (export) Tests are now in progress: - export-net: https://github.com/multipath-tcp/mptcp_net-next/commit/f77d0f8990780a8dc74e236f213b46a0d9b72391/checks - export: https://github.com/multipath-tcp/mptcp_net-next/commit/84c282b44c231fa96cdec0e7f0fd99be9af9d82f/checks Cheers, Matt -- Sponsored by the NGI0 Core fund.