Re: iptables-nft: Wrong payload merge of rule filter - "! --sport xx ! --dport xx"

[Sriram Rajagopalan <bglsriram@gmail.com>]

On Fri, Mar 8, 2024 at 5:00 PM Phil Sutter <phil@nwl.cc> wrote:
>
> Hi Sriram,
>
> On Fri, Mar 08, 2024 at 02:49:38PM +0530, Sriram Rajagopalan wrote:
> > iptables-nft based on nftables has an issue with the way the rule
> > filter - "! --sport xx ! --dport xx" is wrongly merged and rendered.
>
> I agree with your analysis and the patches look fine. Could you please
> submit them formally?
Sure, thanks!
>
> [...]
> > % export IPTABLES=/usr/local/sbin/iptables-legacy; sudo $IPTABLES -A
> > INPUT -p tcp ! --sport 22 ! --dport 22 -i vm2; echo -e "\n---- Before
> > data ----\n"; sudo $IPTABLES -L INPUT -vvvn; sudo python -c "from
> > scapy.all import *;
> > sendp(Ether(dst='9e:00:fa:a3:c9:48')/IP(src='1.1.1.1',
> > dst='2.2.2.2')/TCP(sport=23, dport=22), iface='vm1')"; echo -e "\n----
> > After data with either one of tcp sport/dport being 22 ----\n"; sudo
> > $IPTABLES -L INPUT -vn; sudo python -c "from scapy.all import *;
> > sendp(Ether(dst='9e:00:fa:a3:c9:48')/IP(src='1.1.1.1',
> > dst='2.2.2.2')/TCP(sport=23, dport=23), iface='vm1')"; echo -e "\n----
> > After data with neither one of tcp sport/dport being 22 ----\n"; sudo
> > $IPTABLES -L INPUT -vn; sudo $IPTABLES -D INPUT -p tcp ! --sport 22 !
> > --dport 22 -i vm2
> >
> >
> > ---- Before data ----
> >
> > ip filter INPUT 41
> >   [ meta load iifname => reg 1 ]
> >   [ cmp eq reg 1 0x00326d76 ]
> >   [ payload load 1b @ network header + 9 => reg 1 ]
> >   [ cmp eq reg 1 0x00000006 ]
> >   [ payload load 2b @ transport header + 0 => reg 1 ]
> >   [ cmp neq reg 1 0x00001600 ]
> >   [ payload load 2b @ transport header + 2 => reg 1 ]
> >   [ cmp neq reg 1 0x00001600 ]
> >   [ counter pkts 0 bytes 0 ]
>
> You're fibbing here: That netlink debug output can't come from
> iptables-legacy. I suspect it actually comes from your patched
> iptables-nft or nft too. :)
Oh.. yeah, probably yes. iptables-legacy would not use the VM instructions.
Sorry, for mixing up things.

>
> [...]
> > Author: Sriram Rajagopalan <bglsriram@gmail.com>
> > Date:   Fri Mar 07 20:09:38 2024 -0800
> >
> > iptables: Fixed the issue with combining the payload in case of invert
> > filter for tcp src and dst ports
> >
> > Signed-off-by: Sriram Rajagopalan <bglsriram@gmail.com>
> > Signed-off-by: Sriram Rajagopalan <sriramr@arista.com>
>
> Maybe avoid the double SoB? Apart from that:
>
> Acked-by: Phil Sutter <phil@nwl.cc>
>
> Thanks, Phil