Re: Redirect packet back to host stack after AF_XDP?

[Vincent Li <vincent.mc.li@gmail.com>]

On Tue, Jan 10, 2023 at 7:23 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Vincent Li <vincent.mc.li@gmail.com> writes:
>
> > On Mon, Jan 2, 2023 at 3:34 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >>
> >> Vincent Li <vincent.mc.li@gmail.com> writes:
> >>
> >> > On Wed, Dec 14, 2022 at 2:53 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >> >>
> >> >> Vincent Li <vincent.mc.li@gmail.com> writes:
> >> >>
> >> >> > Hi,
> >> >> >
> >> >> > If I have an user space stack like mTCP works on top of AF_XDP as tcp
> >> >> > stateful packet filter to drop tcp packet like tcp syn/rst/ack flood
> >> >> > or other tcp attack, and redirect good tcp packet back to linux host
> >> >> > stack after mTCP filtering, is that possible?
> >> >>
> >> >> Not really, no. You can inject it using regular userspace methods (say,
> >> >> a TUN device), or using AF_XDP on a veth device. But in both cases the
> >> >> packet will come in on a different interface, so it's not really
> >> >> transparent. And performance is not great either.
> >> >
> >> > I have thought about it more :) what about this scenario
> >> >
> >> >
> >> > good tcp rst/ack or bad flooding rst/ack -> NIC1 -> mTCP+AF_XDP ->NIC2
> >> >
> >> > NIC1 and NIC2 on the same host, drop flooding rst/ack by mTCP,
> >> > redirect good tcp rst/ack to NIC2, is that possible?
> >>
> >> You can do this if NIC2 is a veth device: you inject packets into the
> >> veth on the TX side, they come out on the other side and from the kernel
> >> PoV it looks like all packets come in on the peer veth. You'll need to
> >> redirect packets the other way as well.
> >>
> >> > any performance impact?
> >>
> >> Yes, obviously :)
> >>
> >> >> In general, if you want to filter traffic before passing it on to the
> >> >> kernel, the best bet is to implement your filtering in BPF and run it as
> >> >> an XDP program.
> >> >
> >> > I am thinking for scenario like tcp rst/ack flood DDOS attack to NIC1
> >> > above, I can't simply drop every rst/ack because there could be
> >> > legitimate rst/ack, in this case since mTCP can validate legitimate
> >> > stateful tcp connection, drop flooding rst/ack packet, redirect good
> >> > rst/ack to NIC2. I am not sure a BPF XDP program attached to NIC1 is
> >> > able to do stateful TCP packet filtering, does that make sense to you?
> >>
> >> It makes sense in the "it can probably be made to work" sense. Not in
> >> the "why would anyone want to do this" sense. If you're trying to
> >> protect against SYN flooding using XDP there are better solutions than
> >> proxying things through a user space TCP stack. See for instance Maxim's
> >> synproxy patches:
> >>
> >
> > SYN flooding is just one of the example, what I have in mind is an
> > user space TCP/IP stack runs on top of AF_XDP as middle box/proxy for
> > packet filtering or load balancing, like F5 BIG-IP runs an user space
> > TCP/IP stack on top of AF_XDP. I thought open source mTCP + AF_XDP
> > could be a similar use case as middle box.  user space TCP/IP stack +
> > AF_XDP as middle box/proxy,  the performance is not going to be good?
>
> Well, you can certainly build a proxy using AF_XDP by intercepting all
> the traffic and bridging it onto a veth device, say. I've certainly
> heard of people doing that. It'll have some non-trivial overhead,
> though; even if AF_XDP is fairly high performance, you're still making
> all traffic take an extra hop through userspace, and you'll lose
> features like hardware TSO, etc. Whether it can be done with "good"
> performance depends on your use case, I guess (i.e., how do you define
> "good performance"?).
>
> I guess I don't really see the utility in having a user-space TCP stack
> be a middlebox? If you're doing packet-level filtering, you could just
> do that in regular XDP (and the same for load balancing, see e.g.,
> Katran), and if you want to do application-level filtering (say, a WAF),
> you could just use the kernel TCP stack?
>

the reason I mention user-space TCP stack is user space stack appears
performs better than kernel TCP stack, and we see user-space stack +
DPDK for high speed packet processing applications out there, since
XDP/AF_XDP seems to be competing with DPDK, so I thought why not user
space stack + AF_XDP :)

> >> https://lore.kernel.org/r/20220615134847.3753567-1-maximmi@nvidia.com
> >
> > thanks,  it appears it requires iptables rules setup to work with the
> > synproxy if I recall correctly
>
> Might be; not familiar with the details of that...
>
> -Toke
>