bug report: MAC src + protocol optiomization failing with 802.1Q frames

["Antoine C." <acalando@free.fr>]

Hello,

Following the mails I sent on the user mailing list, it seems that
there is a bug occurring with the first rule below (the second is
fine):

# nft list table netdev t
table netdev t {
        chain c {
              ether saddr aa:bb:cc:dd:00:38 ip saddr 192.168.140.56 \
log prefix "--tests 1&2 --"
              ip saddr 192.168.140.56 ether saddr aa:bb:cc:dd:00:38 \
log prefix "--tests 2&1 --"
        }
}

It is translated this way:
netdev t c
  [ meta load iiftype => reg 1 ]
  [ cmp eq reg 1 0x00000001 ]
  [ payload load 8b @ link header + 6 => reg 1 ]
  [ cmp eq reg 1 0xddccbbaa 0x00083800 ]
  [ payload load 4b @ network header + 12 => reg 1 ]
  [ cmp eq reg 1 0x388ca8c0 ]
  [ log prefix --tests 1&2 -- ]

The MAC source and the protocol are loaded at the same time
then checked... but with an 802.1Q packet, it is actually 
wrong: the ethertype will be 0x8100 and the protocol (here 
IPv4, 0x0800), will be 4 bytes further. And it that case,
the second test above will succeed because the protocol 
is loaded independently.

I just tested with latest versions of libmnl/libnftnl/nft 
and I get the same behavior.

The mail on the netfilter-user ML:
https://marc.info/?l=netfilter&m=176011821517829

Regards,
Antoine