netdev - Re: VETH & AF_PACKET problem

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Message-ID: <CAF=yD-KLrX4ak1GKb8UNWYw33f42nHGfOLsvBYa2=PqA+HZbTA@mail.gmail.com>
Date:   Tue, 13 Nov 2018 10:20:52 -0800
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     anandhkrishnan@...il.com
Cc:     Network Development <netdev@...r.kernel.org>
Subject: Re: VETH & AF_PACKET problem

On Sun, Nov 11, 2018 at 11:15 PM Anand H. Krishnan
<anandhkrishnan@...il.com> wrote:
>
> Hello,
>
> We are seeing a problem with AF_PACKET when used along with the
> veth interfaces. SCP complains that message authentication code is
> incorrect.
>
> I was browsing the code and I see that veth_xmit calls ____dev_forward_skb
> which does a skb_scrub_packet, which in turn calls the skb destructor function.

Where does it call this?

On the other hand, it is likely that skb_orphan() is called somewhere on the
receive path, which indeed will release the tx_ring slot.

> skb_orphan_frags, called by ____dev_forward_skb, seems to do the right thing,
> but it probably does not get called for packets from AF_PACKET socket, since the
> skb is not a zero copy skb (SKBTX_DEV_ZEROCOPY is not set).

Yes, an skb_copy_ubufs may be needed if the orphan is unavoidable.