MSS clamping with XDP/eBPF
ValentÃn Gutierrez <[email protected]> Mon, 6 Nov 2023 10:57:22 +0100
| Newsgroups | org.kernel.vger.xdp-newbies |
|---|---|
| Message-ID | <CALQkE9a0VWPZs3cXmWCyd4TWp2uDzghfhd8-VAAAb2Gtc-5CgA@mail.gmail.com> |
Hi, I'm trying to perform some basic TCP MSS clamping with eBPF and it's being harder than expected: * Parsing TCP options can be challenging for the eBPF verifier as it's been shown in [1] by Christian Deacon. * bpf_store_hdr_opt() introduced in [2] doesn't seem to be useful here cause it refuses to overwrite an existing TCP option and MSS is already set when BPF_SOCK_OPS_WRITE_HDR_OPT_CB is triggered. * bpf_setsockopt() isn't able to set TCP_MAXSEG per [3]. Am I missing something? Thanks, Valentin Gutierrez [1] https://github.com/gamemann/XDP-TCP-Header-Options/ [2] https://lore.kernel.org/bpf/[email protected]/T/ [3] https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/net/core/filter.c#L5151