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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: "Toke Høiland-Jørgensen" <toke@toke.dk>
Cc: Daniel Golle <daniel@makrotopia.org>,
	Florent Daigniere <nextgens@freenetproject.org>,
	 WireGuard mailing list <wireguard@lists.zx2c4.com>
Subject: Re: passing-through TOS/DSCP marking
Date: Fri, 18 Jun 2021 14:24:29 +0200	[thread overview]
Message-ID: <CAHmME9qnqixzDKegMprkT8xNXHfbrhGZfwAROp6vjrQLJEo87g@mail.gmail.com> (raw)
In-Reply-To: <877disdre0.fsf@toke.dk>

Hey Toke,

On Fri, Jun 18, 2021 at 1:05 AM Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> > I think you can achieve something similar using BPF filters, by relying
> > on wireguard passing through the skb->hash value when encrypting.
> >
> > Simply attach a TC-BPF filter to the wireguard netdev, pull out the DSCP
> > value and store it in a map keyed on skb->hash. Then, run a second BPF
> > filter on the physical interface that shares that same map, lookup the
> > DSCP value based on the skb->hash value, and rewrite the outer IP
> > header.
> >
> > The read-side filter will need to use bpf_get_hash_recalc() to make sure
> > the hash is calculated before the packet gets handed to wireguard, and
> > it'll be subject to hash collisions, but I think it should generally
> > work fairly well (for anything that's flow-based of course). And it can
> > be done without patching wireguard itself :)
>
> Just for fun I implemented such a pair of eBPF filters, and tested that
> it does indeed work for preserving DSCP marks on a Wireguard tunnel. The
> PoC is here:
>
> https://github.com/xdp-project/bpf-examples/tree/master/preserve-dscp
>
> To try it out (you'll need a recent-ish kernel and clang version) run:
>
> git clone --recurse-submodules https://github.com/xdp-project/bpf-examples
> cd bpf-examples/preserve-dscp
> make
> ./preserve-dscp wg0 eth0
>
> (assuming wg0 and eth0 are the wireguard and physical interfaces in
> question, respectively).
>
> To actually deploy this it would probably need a few tweaks; in
> particular the second filter that rewrites packets should probably check
> that the packets are actually part of the Wireguard tunnel in question
> (by parsing the UDP header and checking the source port) before writing
> anything to the packet.
>
> -Toke

That is a super cool approach. Thanks for writing that! Sounds like a
good approach, and one pretty easy to deploy, without the need to
patch kernels and such.

Also, nice usage of BPF_MAP_TYPE_LRU_HASH for this.

Daniel -- can you let the list know if this works for your use case?

Jason

  reply	other threads:[~2021-06-18 12:24 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16 13:24 Daniel Golle
2021-06-16 16:28 ` Jason A. Donenfeld
2021-06-16 19:26   ` Daniel Golle
2021-06-16 23:33     ` Toke Høiland-Jørgensen
2021-06-17  7:55       ` Florent Daigniere
2021-06-17  9:41         ` Daniel Golle
2021-06-17 12:24           ` Toke Høiland-Jørgensen
     [not found]             ` <CAMaqUZ09KRtp01OK3u-Di52X_kH9eT4E-wmnPc6QzjSCd5dEiw@mail.gmail.com>
2021-06-17 20:54               ` Toke Høiland-Jørgensen
2021-06-17 23:04             ` Toke Høiland-Jørgensen
2021-06-18 12:24               ` Jason A. Donenfeld [this message]
2021-06-21 12:36                 ` Daniel Golle
2021-06-21 14:27                   ` Toke Høiland-Jørgensen
2021-06-30 17:23                     ` Daniel Golle
2021-06-30 20:55                       ` Toke Høiland-Jørgensen
2021-07-04 14:15                         ` Daniel Golle
2021-07-05 15:21                           ` Toke Høiland-Jørgensen
2021-07-05 16:05                             ` Daniel Golle
2021-07-05 16:59                               ` Toke Høiland-Jørgensen
2021-07-05 17:26                                 ` Daniel Golle
2021-07-05 21:20                                   ` Toke Høiland-Jørgensen
2021-07-06  7:00   ` Florent Daigniere
2021-07-06 20:08     ` Luiz Angelo Daros de Luca

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