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 5A1BD4D597C for ; Mon, 28 Sep 2026 20:26:41 +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=1790627202; cv=none; b=jj4v/NoKBn6on2tMqmTDNgMogEXYavGb+6VDRQ9Nf0+pa/KOUBzTg+rlK+bdsBBJiVQZORg/hDOAlHMJpWMs3beLjymrAXWR/exJhjZIC4LJe7P+mDsNC62iiNezwChhV+KBXpFpXOcbZd6SvEekdOQW4zZdmT7dEd2myKriiEI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790627202; c=relaxed/simple; bh=bQBIPk/RiSXlZQywiMTYskTnRMQnXaF3+U43YIPWmvQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=t0JzBO/9ExKhfnAsSiyBpgGPSxz2KVp4X3CnQaa1SZAPrZgVU1AytKPmxrvoLv7gSP8cwl0uIFB4SoUCS4vbAgKpt9X1aYiYiJaCQoCG85Gwt0htSfGXZ1jMhr64X0YLzSNGl0RxU1FewfSBzLfdGPnz3Xh81Tr9zAUSxyUWXQc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ehPFQ8CK; 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="ehPFQ8CK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 471001F000FF; Mon, 28 Sep 2026 20:26:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790627201; bh=6drJPILI7g/pSQbVyLAOTvuJCz16MkW+IIKcnrQMk9A=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ehPFQ8CKu8lCxqSD9fUZoCmPWongoI4kdz8Z7JhvjU5pjpAfw2ncVD7tx4nkhaI2a OcalCyf4/yXI4hLdSh56kU/lPzIaxZmKd1ZhKcQHF489wuExJ7hBPQKauOuuLSY/IL BdMWsPKF1RZrKppEH2/WZMWKkZucb5f66m3kG4PaHRr7LWsRiphyvCPDF76DivqFkZ ufTB6hlsXse7fkaPeMz57EXQy4SPnSBBP0OLO153nwkZ/HRlUwl97rL3HA/xjG8pAm KkRl5lNpTUVHAh4n7ld2cy57DmcPzhr0mA/XuvYqE2+Fs8PdGNbt/ZeALOKenVuxD8 HQG3avVyjxE8g== Message-ID: Date: Mon, 28 Sep 2026 22:26:37 +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: Florian Westphal Cc: Netfilter Devel , Netfilter Coreteam References: From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Florian, Thank you for your reply! On 28/09/2026 15:13, Florian Westphal wrote: > 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: > > Yes, this won't work. 'tcp option X' extracts the > option X. > > I don't see how this could be fixed within the limitations of the > architecture. That's what I was thinking too :-/ > Just use bpf. Yes, or with a raw payload expression with NFTables. >> 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? > > I don't know how, unless one would extend the kernel to make it aware of > mptcp, which also requires userspace to pass the suboption type to look > for in addition to 'mptcp option'. Should there be a note somewhere in the doc about this limitation? Because it looks like it will never be possible to match such subtype. There are other MPTCP suboptions that can be used with DSS, e.g. MP_PRIO and MP_FAIL. But also MP_RST that can be used with FAST_CLOSE. >> 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? :) > > No idea. > cd git/netfilter.org/nftables/tests/shell; ./run-tests.sh -k testcases/packetpath/tcp_options > > passes here. > Even tried adding 'tcp option timestamp exists...' to the test, also > passes. Arf, my bad, I still had debugging code, sorry... :/ Cheers, Matt -- Sponsored by the NGI0 Core fund.