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

[Akihiko Odaki <akihiko.odaki@gmail.com>]

On 2025/01/17 20:17, Laurent Vivier 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>

Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>