netdev - VETH & AF_PACKET problem

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Message-ID: <CACeb84v7xj1PNGJj=Wbq_Nvq1QK32u6kD2=4oreUT0+VU2jbbQ@mail.gmail.com>
Date:   Mon, 12 Nov 2018 12:42:44 +0530
From:   "Anand H. Krishnan" <anandhkrishnan@...il.com>
To:     netdev@...r.kernel.org
Subject: VETH & AF_PACKET problem

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.

In the case of packets coming from the AF_PACKET socket, the destructor
function seems to set all the mmap-ed pages to be available for user space to
copy any new packet it wants. Isn't this a problem?

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).

Did I miss something basic here?

(Please cc me, since I am not part of this list)

Thanks,
Anand