netdev - Re: [PATCH net] af_packet: fix the tx skb protocol in raw sockets with ETH_P

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Message-ID: <CAF=yD-K74v6+hH1p0Fn6z7c9KH=4rqzOOaBxr+BqMj4Ydjxt_Q@mail.gmail.com>
Date:   Mon, 18 Mar 2019 10:49:56 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Yoshiki Komachi <komachi.yoshiki@....ntt.co.jp>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Yoshiki Komachi <ysk@...sfc.keio.ac.jp>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: Re: [PATCH net] af_packet: fix the tx skb protocol in raw sockets
 with ETH_P_ALL

On Mon, Mar 18, 2019 at 1:41 AM Yoshiki Komachi
<komachi.yoshiki@....ntt.co.jp> wrote:
>
> I am using "protocol ip" filters in TC to manipulate TC flower
> classifiers, which are only available with "protocol ip". However,
> I faced an issue that packets sent via raw sockets with ETH_P_ALL
> did not match the ip filters even if they did satisfy the condition
> (e.g., DHCP offer from dhcpd).
>
> I have determined that the behavior was caused by an unexpected
> value stored in skb->protocol, namely, ETH_P_ALL instead of ETH_P_IP,
> when packets were sent via raw sockets with ETH_P_ALL set.
>
> IMHO, storing ETH_P_ALL in skb->protocol is not appropriate for
> packets sent via raw sockets because ETH_P_ALL is not a real ether
> type used on wire, but a virtual one.
>
> This patch fixes the tx protocol selection in cases of transmission
> via raw sockets created with ETH_P_ALL so that it asks the driver to
> extract protocol from the Ethernet header.
>
> Signed-off-by: Yoshiki Komachi <komachi.yoshiki@....ntt.co.jp>

Acked-by: Willem de Bruijn <willemb@...gle.com>

The Fixes tag is missing. Calling sendmsg on a packet socket bound to
ETH_P_ALL goes back a long way. It is a user, not kernel, bug to do
so.

But no more than sending on a socket bound to ETH_P_NONE (0), which
was addressed in commit c72219b75fde ("packet: infer protocol from
ethernet header if unset").

Probing with packet_parse_headers is available only as of commit
75c65772c3 ("net/packet: Ask driver for protocol if not provided by
user") in v5.1-rc1. This fix does not need to go back further than
that, imho.