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 30BDC50B414 for ; Tue, 29 Sep 2026 10:40:53 +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=1790678470; cv=none; b=XsgTRasypRxImmfq0Hus8TjG9ryotYRvFymcPC+1ZixYT8cILuph5uoNcMq84AupuSEPpJsKsuPSCof6BDiOsJ6UmcAYkaqo3/nvYk/mF7KlYcl4TjQhB5Y0HgZMGoa0DDQkGQBllgo9Hyd568UpZ28mXcNKo/6daCHFKLK0DS0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790678470; c=relaxed/simple; bh=AYMrAIYb6yG2/p0Nq+hffcF6ECkSli9XdXxr7qt39L0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oikB7fSYYrvQLuT1Y56onvtr2F14SDs5ppDthddUWTif8nvhtkHd09t1Xhzg8Xu2cAGxLe0nfELg6WhdDR2bS6sBknG300A0Llu15c0xSznDBzwx1v9f8bd4Grf3QC1VV7SXkKFyUDxa8twB/nQdWPZha+nfrXN4p/JtN4ipjHQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=I3ojvq15; 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="I3ojvq15" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8651F1F000FF; Tue, 29 Sep 2026 10:40:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790678450; bh=n+bsc8OIlrgDIuPs7zkaHvkF/hFUIV4YLC3+dC7RdAo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=I3ojvq15Zkij6A4rcqEqVEV82PploL9eypm+D6TRw5A2Dk1Kg+Q1SDbLMEOS/3nwm Jj9bx87/aptUdN0Y/k8whuofXdEnLmxgmAIt5249uFEY/zDUZsKgDAoeVFiEyCfitz ZaifxZ628dufQXzVPQ832VmuMSs+npaPtu/OCkRzrNrNY8/0TLymU+QFkxaTLIutQr n7QOKYrYsJYNA22wSVqeC+hFHbaOpnMlBceNOytogofnl6jJZQ34dlgU/Sb2Z+4TbL yw8KV4Izvtx0PNxx7W1sRpQ3LbdUq9SXNlKsez2yww3iSR7I8SjCAnNdb88Ir8B++x sYXeTTycOXBmQ== Message-ID: <4da35a94-af13-47de-adef-35b5671100b7@kernel.org> Date: Tue, 29 Sep 2026 12:40:47 +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: Pablo Neira Ayuso 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 On 29/09/2026 12:00, Pablo Neira Ayuso wrote: > On Tue, Sep 29, 2026 at 11:21:15AM +0200, Matthieu Baerts wrote: >> Hi Pablo, >> >> Thank you for your reply! >> >> On 28/09/2026 23:52, Pablo Neira Ayuso wrote: >>> Hi Mattieu, >>> >>> On Mon, Sep 28, 2026 at 02:13:16PM +0200, 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? >>> >>> Would it work for you if you can specify what TCP option you want to >>> match? ie. >>> >>> tcp option[2] mptcp subtype remove-addr drop >>> ^ >>> | >>> | >>> allow to specify a match at a given tcp option >> >> In my specific use-case, yes it would work. Some MPTCP sub-options will >> always be after another one... when the Linux stack is used. > > This would require a smaller patch. I understand. But I guess that still means adding a new option. In my case, it would work, but this might be confusing for people who want to use this filter: they need to know if a suboption can be used with another one. I guess they could have multiple rules to check the presence of a suboption in the first matched type, and in a second one, but that seems confusing. Or maybe not? >>> Or would this be too strict for your use-case and you would prefer >>> that you can match it anywhere? >> >> I think it would make more sense to match it anywhere. For example, an >> MP_RESET can be used alone, or after an MP_FASTCLOSE. Plus some stacks >> could reorder the options as there is no imposed order. > > I think this would require a MPTCP subtype parser, ie. make kernel > aware of MPTCP subtypes. In nft_exthdr_tcp_eval(), why can the comparison not be done there instead of copying the data in a register, and compare later on? If the comparison is done directly for a given type and is different, the code could continue and check for the same type. (Or store in multiple registers.) I don't know if you need something specific to MPTCP, maybe just a way to check all options with the same type. > I would support both of them eventually? Starting by the one above > that allows to match at a given position which looks simpler to > support to me. Then, look into adding a MPTCP subtype parser later? If the second one can be implemented in a simple way, perhaps the first one is not needed? If not, yes, good idea to start with the first one, which might be enough for most people. Cheers, Matt -- Sponsored by the NGI0 Core fund.