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charset=UTF-8 Content-Transfer-Encoding: 7bit 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. > 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. Cheers, Matt -- Sponsored by the NGI0 Core fund.