[WireGuard] fq, ecn, etc with wireguard

[Jason A. Donenfeld]

Hi again,

So I implemented a first stab of this, which I intend to refine with
your feedback:

    https://git.zx2c4.com/WireGuard/commit/?id=a2dfc902e942cce8d5da4a42d6aa384413e7fc81


On the way out, the ECN is set to:

outgoing_skb->tos = encap_ecn(0, inner_skb->tos);

where encap_ecn is defined as:

u8 encap_ecn(u8 outer, u8 inner)
{
        outer &= ~INET_ECN_MASK;
        outer |= !INET_ECN_is_ce(inner) ? (inner & INET_ECN_MASK) :
                                          INET_ECN_ECT_0;
        return outer;
}

Since outer goes in as 0, this function can be reduced to simply:

outgoing_skb->tos = !INET_ECN_is_ce(inner_skb->tos) ? (inner_skb->tos
& INET_ECN_MASK) : INET_ECN_ECT_0;

QUESTION A: is 0 a good value to use here as outer? Or, in fact,
should I use the tos value that comes from the routing table for the
outer route?


On the way in, the ECN is set to:

if (INET_ECN_is_ce(outer_skb->tos))
        IP_ECN_set_ce(inner_skb->tos)

I do NOT compute the following:

        if (INET_ECN_is_not_ect(inner)) {
                switch (outer & INET_ECN_MASK) {
                case INET_ECN_NOT_ECT:
                        return EVERYTHING_IS_OKAY;
                case INET_ECN_ECT_0:
                case INET_ECN_ECT_1:
                        return BROKEN_SO_LOG_PACKET;
                case INET_ECN_CE:
                        return BROKEN_SO_DROP_PACKET;
                }
        }

QUESTION B: is it okay that I do not compute the above checks? Or is
this potentially very problematic?


I await your answer on questions A and B.

Thanks,
Jason