Re: nft tproxy failed to redirect on one system

[Carl Lei <xecycle@gmail.com>]

On Tue, 22 Aug 2023 18:16:31 +0800
Carl Lei <me@xecycle.info> wrote:

> On Tue, 22 Aug 2023 12:05:01 +0200
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> 
> > On Mon, Aug 21, 2023 at 03:48:07PM +0800, Carl Lei wrote:
> > > Btw: sent to wrong address, re-sent to list...
> > > 
> > > On Fri, 11 Aug 2023 12:00:43 +0800
> > > Carl Lei <me@xecycle.info> wrote:
> > > 
> > > > Sorry for being incomplete, but I added nftrace before these
> > > > rules and saw packets went through the same chain of rules,
> > > > first hitting tproxy in mangle, then meta mark 42 counter
> > > > accept in input-new-isolated. But on one system it works for
> > > > local programs AND network-received packets, on another system
> > > > it works only for local programs.  On the bad system the
> > > > packets instead gets directed to whatever program originally
> > > > listening on the original port, or rejected; e.g. I have an
> > > > nginx listening on 0.0.0.0:80 but no programs on 443, then curl
> > > > http in a vm connected to vbr0 goes to my nginx, and curl https
> > > > gets rejected.  I expect them to go to that program listening
> > > > on 1081.  
> > > 
> > > Looked closer at the trace, I found that on the bad system, when
> > > the packet goes back to input rules, its trace id changed; on the
> > > good system it does not change.  Perhaps this explains it, but I
> > > don't know why it was changed?
> > 
> > Could you provide more detailed information on your setup? You refer
> > to a system where this works fine and another where this does not,
> > but you do not specify kernel and userspace versions?
> 
> Sorry I forgot that in my first email, indeed I replied to myself
> several times and already provided versions, but I did not realize I
> sent to a wrong address.  My used versions are (copying from my
> previous mails):
> 
> "they are both running Arch Linux, the good system running kernel
> 6.4.8-arch1-1, the bad system I tried both 6.4.4 and 6.4.9; nftables
> version both 1:1.0.7-2; the proxy program on 1081 is also identical,
> running identical config."
> 
> > Some simple script with 'ip netns' as a reproducer might also help
> > that might help people jump in a provide feedback.
> 
> I will try ASAP to make a reproducer.

Sorry for the delay, I finally figured out what is going on.

When I do `modprobe br_netfilter`, which automatically sets sysctl
net/bridge/bridge-nf-call-iptables=1, the rule breaks --- the packet
would change trace id when it comes back to INPUT chains.  After I set
that sysctl to 0, the rule works again.

And yes, the packet is coming from a container, having a veth connected
to a bridge on the host.