[nftables 0.9.2] NETDEV packet drop vs. packet capture visibility

[nftables 0.9.2] NETDEV packet drop vs. packet capture visibility

[ѽ҉ᶬḳ℠]

With

table netdev filter {
         chain input {
                 type filter hook ingress device "eth2" priority filter; 
policy accept;
                 ether type arp drop
                 ether type vlan drop
                 ether type 0x9000 drop
         }
}

in place those package types are visible (showing) during a packet 
capture (wirehshark ssh remote) on that interface. Is this to be 
expected as the packet is being captured prior being dropped by NFT or 
does indicate that the packages are not being dropped?

Re: [nftables 0.9.2] NETDEV packet drop vs. packet capture visibility

[Pablo Neira Ayuso]

On Thu, Mar 19, 2020 at 04:11:01PM +0000, ѽ҉ᶬḳ℠ wrote:
> With
> 
> table netdev filter {
>         chain input {
>                 type filter hook ingress device "eth2" priority filter;
> policy accept;
>                 ether type arp drop
>                 ether type vlan drop
>                 ether type 0x9000 drop
>         }
> }
> 
> in place those package types are visible (showing) during a packet capture
> (wirehshark ssh remote) on that interface. Is this to be expected as the
> packet is being captured prior being dropped by NFT or does indicate that
> the packages are not being dropped?

The ingress packet filtering happens right after the "taps", ie.
packet capture, e.g. wireshark.

The packet is captured before nft ingress drops them.

This is where the nf_ingress() hook is invoked:

https://elixir.bootlin.com/linux/v5.6-rc6/source/net/core/dev.c#L5056

Just a few lines before, you can see the routines for the packet
captures ("taps"):

https://elixir.bootlin.com/linux/v5.6-rc6/source/net/core/dev.c#L5043

Re: [nftables 0.9.2] NETDEV packet drop vs. packet capture visibility

[ѽ҉ᶬḳ℠]

On 19/03/2020 19:43, Pablo Neira Ayuso wrote:
> On Thu, Mar 19, 2020 at 04:11:01PM +0000, ѽ҉ᶬḳ℠ wrote:
>> With
>>
>> table netdev filter {
>>          chain input {
>>                  type filter hook ingress device "eth2" priority filter;
>> policy accept;
>>                  ether type arp drop
>>                  ether type vlan drop
>>                  ether type 0x9000 drop
>>          }
>> }
>>
>> in place those package types are visible (showing) during a packet capture
>> (wirehshark ssh remote) on that interface. Is this to be expected as the
>> packet is being captured prior being dropped by NFT or does indicate that
>> the packages are not being dropped?
> The ingress packet filtering happens right after the "taps", ie.
> packet capture, e.g. wireshark.
>
> The packet is captured before nft ingress drops them.
>
> This is where the nf_ingress() hook is invoked:
>
> https://elixir.bootlin.com/linux/v5.6-rc6/source/net/core/dev.c#L5056
>
> Just a few lines before, you can see the routines for the packet
> captures ("taps"):
>
> https://elixir.bootlin.com/linux/v5.6-rc6/source/net/core/dev.c#L5043

Thank you for the explanation/pointer.