[PATCH net v2] wireguard: use tunnel helpers for decapsulating ECN markings

[Jason A. Donenfeld]

On Mon, Apr 27, 2020 at 3:16 PM Toke Høiland-Jørgensen <toke at redhat.com> wrote:
>
> WireGuard currently only propagates ECN markings on tunnel decap according
> to the old RFC3168 specification. However, the spec has since been updated
> in RFC6040 to recommend slightly different decapsulation semantics. This
> was implemented in the kernel as a set of common helpers for ECN
> decapsulation, so let's just switch over WireGuard to using those, so it
> can benefit from this enhancement and any future tweaks.
>
> RFC6040 also recommends dropping packets on certain combinations of
> erroneous code points on the inner and outer packet headers which shouldn't
> appear in normal operation. The helper signals this by a return value > 1,
> so also add a handler for this case.

Thanks for the details in your other email and for this v2. I've
applied this to the wireguard tree and will send things up to net
later this week with a few other things brewing there.

By the way, the original code came out of a discussion I had with Dave
Taht while I was coding this on an airplane many years ago. I read
some old RFCs, made some changes, he tested them with cake, and told
me that the behavior looked correct. And that's about as far as I've
forayed into ECN land with WireGuard. It seems like it might be
helpful (at some point) to add something to the netns.sh test to make
sure that all this machinery is actually working and continues to work
properly as things change in the future.