netdev - Re: BUG?: receiving on a packet socket with .sll

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Message-ID: <CAF=yD-KsfvzAdd1jt9qEjy5kOghBrS=Oo3CVBm_QR9+=1zj7rQ@mail.gmail.com>
Date:   Mon, 7 May 2018 04:22:23 +0900
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Network Development <netdev@...r.kernel.org>
Subject: Re: BUG?: receiving on a packet socket with .sll_protocoll and bridging

>> > If now I add veth0 to a bridge (e.g.
>> >
>> >         ip link add br0 type bridge
>> >         ip link set dev veth0 master br0
>> >
>> > ) and continue to send on veth1 and receive on veth0 I don't receive
>> > the packets any more. The other direction (veth0 sending, veth1
>> > receiving) still works fine.
>> >
>> > Each of the following changes allow to
>> > receive again:
>> >
>> >  a) take veth0 out of the bridge
>> >  b) bind(2) the receiving socket to br0 instead of veth0
>> >  c) use .sll_protocol = htons(ETH_P_ALL) for bind(2)
>> >
>> > In the end only c) could be sensible (because I need to know the port
>> > the packet entered the stack and that might well be bridged), but I
>> > wonder why .sll_protocol = htons(ETH_P_MRP) seems to do the right thing
>> > for an unbridged device but not for a bridged one.
>> >
>> > Is this a bug or a feature I don't understand?
>>
>> Packets are redirected to the bridge device in __netif_receive_skb_core
>> at the rx_handler hook.
>
> OK, thanks for finding that place. It would have taken quite some of my
> time to find it.
>
>> This happens after packets are passed to packet types attached to
>> list ptype_all, which includes packet sockets with protocol ETH_P_ALL.
>> But before packets are passed to protocol specific packet types (and
>> sockets) attached to ptype_base[].
>
> Still I wonder if there is something to fix in the kernel or if this
> inconsistency is intended (or at least accepted).

It is established behavior.