netdev - Re: [PATCH net-next 2/2] tools: psock_tpacket: verify that packet was received on lo before counting it

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Date:   Wed, 4 Jan 2017 09:30:08 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     linux-kselftest@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>, shuah@...nel.org
Subject: Re: [PATCH net-next 2/2] tools: psock_tpacket: verify that packet was
 received on lo before counting it

On Tue, Jan 3, 2017 at 6:27 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> Packets from any/all interfaces may be queued up on the PF_PACKET socket
> before it is bound to the loopback interface by psock_tpacket, and
> when these are passed up by the kernel, they should not be counted
> toward the conditions needed to pass/fail the Rx tests.

The common and simpler solution to this problem is to open the socket
with protocol 0 to reject all packets, add the BPF filter and only then bind
with sll_ifindex set to lo. That way no false positives can arrive.