Re: Issues with netdev egress hooks

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Daniel,

On Thu, Mar 07, 2024 at 02:34:38PM +0100, Daniel Mack wrote:
> On 3/6/24 19:17, Pablo Neira Ayuso wrote:
[...]
> > I guess you are running a kernel with
> > 
> > commit 0ae8e4cca78781401b17721bfb72718fdf7b4912
> > Author: Pablo Neira Ayuso <pablo@netfilter.org>
> > Date:   Thu Dec 14 11:50:12 2023 +0100
> > 
> >     netfilter: nf_tables: set transport offset from mac header for netdev/egress
> > 
> > so this is a different bug?
> 
> Interesting, I did in fact run a 6.4 production kernel when I tried
> this, and that didn't have that patch applied. Sorry for that oversight.
> 
> On 6.7, what I see is different but still broken:

I'm here with 6.8.0-rc6+:

> This rules does the right thing and patches the source MAC correctly:
> 
> table netdev dummy {
>   chain egress {
>     type filter hook egress device dummy priority 0;
>     ether saddr set 1:2:3:4:5:6 dup to eth0
>   }
> }
> 
> Whereas trying to patch the IP source addr leads to no packets being
> forwarded at all anymore:

My setup:

# ip link set up dev dummy
# ip a a 10.141.10.1/24 dev dummy
# ip ro del local 10.141.10.1 dev dummy table local proto kernel scope host src 10.141.10.1

testing with ping to 10.141.10.1

I need to remove the local route, otherwise packets go through
loopback interface.

> table netdev dummy {
>   chain egress {
>     type filter hook egress device dummy priority 0;
>     ip saddr set 1.1.1.1 dup to eth0
>   }
> }

1) tcpdump in dummy:

17:14:42.939483 f2:20:1a:4c:c4:a1 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 1.1.1.1 > 10.141.10.1: ICMP echo request, id 46403, seq 1, length 64

2) tcpdump in eth0:

17:15:21.006853 f2:20:1a:4c:c4:a1 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 1.1.1.1 > 10.141.10.1: ICMP echo request, id 1087, seq 1, length 64

> Interestingly, ether type filtering is also broken now, the following
> also doesn't match any packets:
> 
> table netdev dummy {
>   chain egress {
>     type filter hook egress device dummy priority 0;
>     ether type ip dup to eth0
>   }
> }

1) tcpdump in dummy

17:18:13.921128 f2:20:1a:4c:c4:a1 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 10.141.10.1 > 10.141.10.1: ICMP echo request, id 137, seq 1, length 64

2) tcpdump in eth0:

17:19:00.398882 f2:20:1a:4c:c4:a1 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 10.141.10.1 > 10.141.10.1: ICMP echo request, id 21186, seq 1, length 64

> I browsed through the patches since 6.7 and couldn't find anything that
> is related. Did I miss anything?

I tried again this first example you posted:

table netdev dummy {
  chain egress {
    type filter hook egress device "dummy" priority 0;
    ether type ip ether saddr set 01:02:03:04:05:06 ip saddr set 1.1.1.1 dup to "eth0"
  }
}

tcpdump dummy:

17:22:08.390312 01:02:03:04:05:06 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 1.1.1.1 > 10.141.10.1: ICMP echo request, id 47168, seq 1, length 64

tcpdump enps25:

17:20:28.298524 01:02:03:04:05:06 > f2:20:1a:4c:c4:a1, ethertype IPv4 (0x0800), length 98: 1.1.1.1 > 10.141.10.1: ICMP echo request, id 15435, seq 1, length 64

Maybe my setup is different?