[tproxy] tproxy routing issue within processes in the same machine

[Balazs Scheidler]

Hi,

This may work, the point is that the TPROXY target will not reroute
packets, so if they originally were destined to the outgoing interface,
they will continue to be so and will never cause local sockets to be
looked up.

If the packet is already routed to localhost, then it can work.

On Tue, 2012-09-18 at 20:11 +0200, Karol Piłat wrote:
> Hello,
> 
> AFAIK it is possible.
> 1. You have to bind new (spoofed) connection's port in certain range 
> (e.g. 5000 - 10000, not ephemeral port range).
> 2. Setup rule to forward all outgoing TCP packets to ports in that range 
> to localhost
> 3. Make connections to physical, not loopback address.
> 
> I have it running on production for about 2 months now.
> 
> Iptables rules and routes:
>      ip rule add fwmark 1 lookup 100
>      ip route add local 0.0.0.0/0 dev lo table 100
> 
>      iptables -t mangle -N DIVERT
>      iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT
>      iptables -t mangle -A DIVERT -j MARK --set-mark 1
>      iptables -t mangle -A DIVERT -j ACCEPT
> 
>      iptables -t mangle -A OUTPUT -p tcp --dport 5000:9999 -j MARK 
> --set-mark 1
> 
> Example python code to create spoofed connection:
>      s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
>      s.setsockopt(socket.SOL_IP, 19, 1) # IP_TRANSPARENT, not available 
> in python's stdlib
>      s.bind(('1.2.3.4', 5001))
>      s.connect(('192.168.1.9', 1234)) # connection always to physical 
> interface address!
> 
> I do free port management by myself, but you can do bind() in a loop.
> 
> Best Regards,
> Karol Pilat
> 
> W dniu 18.09.2012 10:04, Balazs Scheidler pisze:
> > Hi,
> >
> > IIRC it doesn't work for local connections/sockets, as it can't reroute
> > outgoing packets to the local interface.
> >
> > On Sun, 2012-07-29 at 06:30 -0700, Ming-Ching Tiew wrote:
> >> tproxy has  problem working within 2 processes on the same machine,
> >> ie a client process using tproxy to spoof an IP,  has problem
> >> communicating  with the server process within the same machine.
> >>
> >> It seems tproxy attaches itself to mangle table PREROUTING
> >> chain, that is unable to hook to the in-machine process. I figured
> >> that for it to work, in this case, it needs to be able to attach itself
> >> to the INPUT chain. However that hook is not supported.
> >>
> >> Is there a way to get around this problem ?
> 
> 

-- 
Bazsi