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Hello,
On Sun, 20 Oct 2013, Hannes Frederic Sowa wrote:
> > Hm, maybe. I don't have too much insight into netfilter stack and
> > what are the differences between OUTPUT and FORWARD path but plan to
> > investigate. ;)
>
> It seems tables are processed with bh disabled, so no preemption while
> recursing. So I guess the use of tee_active is safe for breaking the
> tie here.
May be, I'll check it again, for now I see only
rcu_read_lock() in nf_hook_slow() which is preemptable.
Looking at rcu_preempt_note_context_switch, many levels of
RCU locks are preemptable too.
> The reason I exhaust stack space is that we can actually send out packets
> while looking up routes (rt6_probe). The nonreachability of the default
> gateway and the to-teed-to box does the rest.
In my test I used link route to local subnet,
--gateway to IP that is not present. I'll try other
variants.
> We need to change the route lookup of the duplicated packet in xt_tee to not
> cause ndisc probes to be generated.
>
> The more I review the patch the more I think it is ok. But we could actually
> try to just always return rt6i_gateway, as we should always be handed a cloned
> rt6_info where the gateway is already filled in, no?
Yes, this patch is ok and after spending the whole
saturday I'm preparing a new patch that will convert
rt6_nexthop() to return just rt6i_gateway, without daddr.
This can happen after filling rt6i_gateway in all places.
For your concern for loopback, I don't see problem,
local/anycast route will have rt6i_gateway=IP, they are
simple DST_HOST routes. I'm preparing now the patches and
will post them in following hours.
Regards
--
Julian Anastasov <ja@xxxxxx>
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