netdev - Re: [PATCH net v3] net: xdp: account for layer 3 packets in generic skb handler

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Date:   Mon, 27 Apr 2020 23:00:31 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>, netdev@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Adhipati Blambangan <adhipati@...a.io>,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH net v3] net: xdp: account for layer 3 packets in generic skb handler

"Jason A. Donenfeld" <Jason@...c4.com> writes:

> A user reported that packets from wireguard were possibly ignored by XDP
> [1]. Apparently, the generic skb xdp handler path seems to assume that
> packets will always have an ethernet header, which really isn't always
> the case for layer 3 packets, which are produced by multiple drivers.
> This patch fixes the oversight. If the mac_len is 0, then we assume
> that it's a layer 3 packet, and in that case prepend a pseudo ethhdr to
> the packet whose h_proto is copied from skb->protocol, which will have
> the appropriate v4 or v6 ethertype. This allows us to keep XDP programs'
> assumption correct about packets always having that ethernet header, so
> that existing code doesn't break, while still allowing layer 3 devices
> to use the generic XDP handler.
>
> [1] https://lore.kernel.org/wireguard/M5WzVK5--3-2@tuta.io/
>
> Reported-by: Adhipati Blambangan <adhipati@...a.io>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Toke Høiland-Jørgensen <toke@...hat.com>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>

Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>