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 1A3B436167B for ; Mon, 28 Sep 2026 21:22:21 +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=1790630543; cv=none; b=LkZ4xhxG5jpcs8oLTp/f9YfelUUkbgWzT5Ru1Fpdgfzj3LadmmzKlRfrhePK30doltAyVKtCOnTEvzjguuK5gqrcc+ZMKm3UcoXY1gaMpc3tQMViyxMm4GtW9REOntYfyo1vyIjnLj6zqdoQ899XskVFObzXeRfHOmWr0BIa6qM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790630543; c=relaxed/simple; bh=GDHe/ZNII2u9uBOYyEpTM098IMhKl+iiiiaZOhmTo7c=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=eBpzk6QjL0g6y80c8gA48Q/UV9BtvicOtjH85ItDFW3X6Snf0U/CEdcej5+6uTNx21QKd8MKm3wK7jsxpF8f9XSqCS8KI83N2dEBRMvhbT6IJILhBE2AG3XvumxZVa0EiXXhFviT0J0bXHkw4AAMBfxTluOHiTfjOTTvo0bJ/SI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QbOm8kUz; 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="QbOm8kUz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BBCBC1F000FF; Mon, 28 Sep 2026 21:22:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790630541; bh=1U7xWDk3MlY9lhlKJIEMy+lziWUHnJnrtymTab+3o08=; h=Date:Subject:To:References:From:In-Reply-To; b=QbOm8kUzvh+4JacbpN6Wl7Imw6047c6iiwNgykMk+Tp8zzwGZqAqW6vvyfbWfXMPo ouR/sgpjc/ViQk983gPFlDdG9/Zgkd44zQMmAYd8s27+/KVccrMi228z2t4tSfQZro ji3+rM3mFF/WBl2xQ0x3U7m6mtbzzZioIdxRrp46BDxnMiv+yXni3DeouFHFLLbf+J Iqks/GVf2CMU5bqVS2pANu/ZuMOu3fL8Ch0Ap8CnYdSYiPhzGTCmtFVwS2bqZNdVOK NZy+7hNHeMY27b2p5wV4HHck1b1PBU5phpX4uR/OMYsFOFvEiZ5jcxflCnnHgYismc azwByKkE0JTMw== Message-ID: <6989a3c1-313c-4802-b78c-ceb3f2dbd3da@kernel.org> Date: Mon, 28 Sep 2026 23:22:19 +0200 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: Netfilter: match "tcp option" with the same type present multiple times Content-Language: fr To: Fernando Fernandez Mancera , Netfilter Devel , Netfilter Coreteam References: <0c08f9e6-123f-4514-a865-6f9e0f979167@suse.de> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Fernando, On 28/09/2026 23:17, Fernando Fernandez Mancera wrote: > On 9/28/26 10:54 PM, Fernando Fernandez Mancera wrote: >> On 9/28/26 2:13 PM, Matthieu Baerts wrote: >>> Hello Netfilter devs, >>> >>> First, thank you for maintaining Netfilter in the kernel and the >>> userspace tools. >>> >>> The MPTCP selftests are switching from IPTables to NFTables, and >>> Clashiko reported that this part of a rule wouldn't match anything: >>> >>>    tcp option mptcp subtype remove-addr drop >>> >>> When an MPTCP REMOVE_ADDR suboption (type 0x30, len >=4, subtype 0x4) is >>> added to the TCP options, it is added after an MPTCP DSS option (type >>> 0x30, len >= 8, subtype 0x2). In other words, there will be two MPTCP >>> (type 30) options in the TCP options. It looks like Netfilter doesn't >>> handle that, because it stops processing other TCP options when the >>> expected type is found: >>> >>> net/netfilter/nft_exthdr.c:nft_exthdr_tcp_eval() { >>>      ... >>>     for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) { >>>         optl = optlen(opt, i); >>> >>>         if (priv->type != opt[i]) >>>             continue; >>>         ... >>>         return;  // <== it will look at the first MPTCP option >>>     } >>>      ... >>> } >>> >>> It looks like it shouldn't stop if the wrong subtype is found, but the >>> subtype is not compared there if I'm not mistaken. Should there be a fix >>> to support this case? >>> >>> For more details about the Clashiko report: >>> >>> https://lore.kernel.org/179058242453.3145.1450534124183352369@kernel.org >>> >>> >>> BTW, I'm probably missing something, but adding the following doesn't >>> seem to have any effect on my side: >>> >>>    nft add table ip filter >>>    nft add chain ip filter OUTPUT \ >>>      { type filter hook output priority filter; policy accept; } >>>    nft insert rule ip filter OUTPUT tcp option mptcp exists counter drop >>> >>> Same with "mptcp subtype mp-capable", other subtypes or other types like >>> "timestamp". But if I use ... >>> >>>    nft insert rule ip filter OUTPUT meta l4proto tcp counter drop >>> >>> ... then the drop is effective. Any idea what I'm missing here? :) >>> >>> >>> (Also, it looks like the MPTCP suboptions are not documented in the nft >>> man page :) ) >>> >> >> Tomorrow there should be a patch in netfilter-devel adding it, we >> definitively should put more work into documentation. >> > > While at it, I will also document the existing limitation that was > discussed above too. Great, thank you for looking at all this :) Cheers, Matt -- Sponsored by the NGI0 Core fund.