netdev - Re: [next] bonding: pass link-local packets to bonding master also.

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Message-ID: <m3d0qmfe0d.fsf@bernat.ch>
Date:   Fri, 30 Nov 2018 22:32:02 +0100
From:   Vincent Bernat <vincent@...nat.ch>
To:     Mahesh Bandewar <mahesh@...dewar.net>
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Veaceslav Falico <vfalico@...il.com>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, Michal Soltys <soltys@....info>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Chonggang Li <chonggangli@...gle.com>
Subject: Re: [next] bonding: pass link-local packets to bonding master also.

 ❦ 15 juillet 2018 19:12 -0700, Mahesh Bandewar <mahesh@...dewar.net>:

> Commit b89f04c61efe ("bonding: deliver link-local packets with
> skb->dev set to link that packets arrived on") changed the behavior
> of how link-local-multicast packets are processed. The change in
> the behavior broke some legacy use cases where these packets are
> expected to arrive on bonding master device also.

Unfortunately, this doesn't completely restore the previous
functionality as PACKET_ORIGDEV is broken for the copy: the original
interface is lost through the call to netif_rx(). A LLDP daemon
listening to the master interface won't get the original interface like
it was able to before 4.12.

I am a bit lost of what the original patch was trying to achieve. I am
using the following test program:

#v+
#!/usr/bin/env python3

import sys
import socket
import datetime

socket.SOL_PACKET = 263
socket.ETH_P_ALL = 3
socket.PACKET_ORIGDEV = 9

interface = sys.argv[1] if len(sys.argv) > 1 else 'lag1'

s = socket.socket(socket.AF_PACKET,
                  socket.SOCK_RAW,
                  socket.htons(socket.ETH_P_ALL))
s.bind((interface, 0))
s.setsockopt(socket.SOL_PACKET, socket.PACKET_ORIGDEV, 1)
while True:
    data, addrinfo = s.recvfrom(1500)
    if addrinfo[2] == socket.PACKET_OUTGOING:
        continue
    print(f"{datetime.datetime.now().isoformat()}: "
          f"Received {len(data)} bytes from {addrinfo}")
#v-

If I run it with a kernel compiled with the commit before b89f04c61efe
(plus a few more cherry-pick to make it work like ea8ffc0818d8 and
72ccc471e13b), I get:

#v+
2018-11-30T22:20:40.193378: Received 221 bytes from ('eth1', 35020, 2, 1, b'RT3\x00\x00\x02')
2018-11-30T22:20:40.194504: Received 221 bytes from ('eth0', 35020, 2, 1, b'RT3\x00\x00\x01')
#v-

If I send non link-local packets, I get:

#v+
2018-11-30T22:25:57.300965: Received 98 bytes from ('eth0', 2048, 0, 1, b'PT3\x00\x00\x02')
#v-

I am also able to correctly receive link-local packets directly on each
interface. So, it seems everything was working as expected before
b89f04c61efe.
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