[PATCH RFC v2 0/5] netfilter reverse path filter matches

[Florian Westphal <fw@strlen.de>]

Version 2 of the ipv4/v6 reverse path filter matches discussed during
nfws 2011.

The ipv4 match (ipt_rpfilter) tries to do exactly what the current
fib_validate_source does.  The main problem with this is that
we need to do an additional fib lookup to get the oif in the match.
[ delaying until FORWARD is invoked is not possible because by
  that point the stack might have already sent icmp errors ].

Patrick McHardy suggested to simply attach the result as the dst, so
ipv4 input path doesn't have to do it again.

This works, but does have a few side effects wrt. route-by-mark and
TPROXY, see patch changelog for details.

The ipv6 version does a pure 'reverse' lookup instead.  This makes
things a lot easier (e.g. when multiple route entries exist), but has
the caveat that a real reply packet might be handled differently due to
policy routing rules.

Userspace part is stored in my iptables repository on
http://git.breakpoint.cc/cgi-bin/gitweb.cgi?p=fw/iptables.git (branch 'rpfilter').

Kernel patches are located in the 'xt_rpfilter_5' branch on
http://git.breakpoint.cc/cgi-bin/gitweb.cgi?p=fw/nf-next.git
(patches will be sent as followup to this email).

[ in case you are wondering: the earlier xt_rpfilter version was
  removed -- causes too many module  dependency issues and most of the
  code cannot be shared anyway ].

Thanks,
Florian