Re: vlan missing with AF_PACKET and auxdata

[Michael Walle <michael@walle.cc>]

Am 2018-09-24 14:01, schrieb Michael Walle:
> Hi,
> 
> I'm using the AF_PACKET socket with setsockopt(PACKET_AUXDATA) to get
> the incoming VLAN tag. Correct me if I'm wrong, but as far as I see
> the first VLAN tag is always stripped - either in hardware or in
> net/core/dev.c in __netif_receive_skb_core() - and stored in
> skb->vlan_tci. Therefore, it won't be in the packet data anymore.
> 
> If I use the socket with ETH_P_ALL as protocol, everything works as
> expected. But if I'm using an actual protocol number, instead of the
> catch all, the tp_vlan_tci field inside the auxdata will be zero. I've
> traced this to commit d4b812dea4a236f729526facf97df1a9d18e191c (vlan:
> mask vlan prio bits):
> 
> +       if (unlikely(vlan_tx_tag_present(skb))) {
> +               if (vlan_tx_tag_get_id(skb))
> +                       skb->pkt_type = PACKET_OTHERHOST;
> +               /* Note: we might in the future use prio bits
> +                * and set skb->priority like in vlan_do_receive()
> +                * For the time being, just ignore Priority Code Point
> +                */
> +               skb->vlan_tci = 0;
> +       }
> 
> The ptype_all callbacks (which are working as expected) are before
> this code and the ptype_specific callbacks (which are not working) are
> after this piece of code. I don't know it this is a bug or not, I
> guess it is one, at least from the AF_PACKET socket point of view. If
> not, how I'm supposed to get the original VLAN tag with
> socket(AF_PACKET, my_protocol)?
> 
> I also don't understand the commit (message) as the subject suggesets
> only the prio bits should be masked, but with "skb->vlan_tci = 0"
> everything is masked. Therefore, I've put the original (hopefully the
> mail addresses are still valid) authors in CC.
> 

ping? :)

-michael