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

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Message-ID: <20201110145045.22dfd58e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 10 Nov 2020 14:50:45 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Andrea Mayer <andrea.mayer@...roma2.it>
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>
Subject: Re: [net-next,v2,1/5] vrf: add mac header for tunneled packets when
 sniffer is attached

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.