Re: [PATCH 2/2] net/dump: Correctly compute Ethernet packet offset

[Jason Wang]

On Fri, Jan 17, 2025 at 7:17 PM Laurent Vivier <lvivier@redhat.com> wrote:
>
> When a packet is sent with QEMU_NET_PACKET_FLAG_RAW by QEMU it
> never includes virtio-net header even if qemu_get_vnet_hdr_len()
> is not 0, and filter-dump is not managing this case.
>
> The only user of QEMU_NET_PACKET_FLAG_RAW is announce_self,
> we can show the problem using it and tcpddump:
>
> - QEMU parameters:
>
>   .. -monitor stdio \
>      -netdev bridge,id=netdev0,br=virbr0 \
>      -device virtio-net,mac=9a:2b:2c:2d:2e:2f,netdev=netdev0 \
>      -object filter-dump,netdev=netdev0,file=log.pcap,id=pcap0
>
> - HMP command:
>
>   (qemu) announce_self
>
> - TCP dump:
>
>   $ tcpdump -nxr log.pcap
>
>   without the fix:
>
>     08:00:06:04:00:03 > 2e:2f:80:35:00:01, ethertype Unknown (0x9a2b), length 
> 50:
>          0x0000:  2c2d 2e2f 0000 0000 9a2b 2c2d 2e2f 0000
>          0x0010:  0000 0000 0000 0000 0000 0000 0000 0000
>          0x0020:  0000 0000
>
>   with the fix:
>
>     ARP, Reverse Request who-is 9a:2b:2c:2d:2e:2f tell 9a:2b:2c:2d:2e:2f, 
> length 46
>          0x0000:  0001 0800 0604 0003 9a2b 2c2d 2e2f 0000
>          0x0010:  0000 9a2b 2c2d 2e2f 0000 0000 0000 0000
>          0x0020:  0000 0000 0000 0000 0000 0000 0000
>
> Fixes: 481c52320a26 ("net: Strip virtio-net header when dumping")
> Cc: akihiko.odaki@daynix.com
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks