netdev - Re: [net-next,v2,1/5] vrf: add mac header for tunneled packets when sniffer is attached

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Date:   Fri, 13 Nov 2020 01:37:52 +0100
From:   Andrea Mayer <andrea.mayer@...roma2.it>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Shuah Khan <shuah@...nel.org>,
        Shrijeet Mukherjee <shrijeet@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Stefano Salsano <stefano.salsano@...roma2.it>,
        Paolo Lungaroni <paolo.lungaroni@...t.it>,
        Ahmed Abdelsalam <ahabdels.dev@...il.com>,
        Andrea Mayer <andrea.mayer@...roma2.it>
Subject: Re: [net-next,v2,1/5] vrf: add mac header for tunneled packets when
 sniffer is attached

Hi Jakub,

On Tue, 10 Nov 2020 14:50:45 -0800
Jakub Kicinski <kuba@...nel.org> wrote:

> On Sat,  7 Nov 2020 16:31:35 +0100 Andrea Mayer wrote:
> > Before this patch, a sniffer attached to a VRF used as the receiving
> > interface of L3 tunneled packets detects them as malformed packets and
> > it complains about that (i.e.: tcpdump shows bogus packets).
> > 
> > The reason is that a tunneled L3 packet does not carry any L2
> > information and when the VRF is set as the receiving interface of a
> > decapsulated L3 packet, no mac header is currently set or valid.
> > Therefore, the purpose of this patch consists of adding a MAC header to
> > any packet which is directly received on the VRF interface ONLY IF:
> > 
> >  i) a sniffer is attached on the VRF and ii) the mac header is not set.
> > 
> > In this case, the mac address of the VRF is copied in both the
> > destination and the source address of the ethernet header. The protocol
> > type is set either to IPv4 or IPv6, depending on which L3 packet is
> > received.
> > 
> > Signed-off-by: Andrea Mayer <andrea.mayer@...roma2.it>
> 
> Please keep David's review tag since you haven't changed the code.

I will keep David's review tag in v3.

Thanks,
Andrea