On 06/04/2015 20:05, Kristof Provost wrote:
Author: kp
Date: Mon Apr 6 19:05:00 2015
New Revision: 281164
URL: https://svnweb.freebsd.org/changeset/base/281164
Log:
pf: Skip firewall for refragmented ip6 packets
In cases where we scrub (fragment reassemble) on both input and output
we risk ending up in infinite loops when forwarding packets.
Fragmented packets come in and get collected until we can defragment. At
that point the defragmented packet is handed back to the ip stack (at
the pfil point in ip6_input(). Normal processing continues.
Eventually we figure out that the packet has to be forwarded and we end
up at the pfil hook in ip6_forward(). After doing the inspection on the
defragmented packet we see that the packet has been defragmented and
because we're forwarding we have to refragment it.
In pf_refragment6() we split the packet up again and then ip6_forward()
the individual fragments. Those fragments hit the pfil hook on the way
out, so they're collected until we can reconstruct the full packet, at
which point we're right back where we left off and things continue until
we run out of stack.
Break that loop by marking the fragments generated by pf_refragment6()
as M_SKIP_FIREWALL. There's no point in processing those packets in the
firewall anyway. We've already filtered on the full packet.
Kristof,
Firstly, many thanks for working on this.
I was just wondering how this affects the case where we might have
if-bound rules?
Really basic example:
pass quick on $outside_if inet6 proto udp from any to $myhost
block drop quick on $inside_if inet6 proto udp from any to $myhost
port $secret_svc
pass quick on $inside_if inet6 proto udp from any to $myhost
If the fragments generated after processing occurs on the inbound
interface are then marked to be skipped then will they therefore not be
matched by the drop rule in the example above?
Regards,
Richard
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