Marcelo Ricardo Leitner <marcelo.leit...@gmail.com> writes:
> On Mon, Nov 18, 2019 at 04:21:39PM -0500, Aaron Conole wrote:
>> Marcelo Ricardo Leitner <marcelo.leit...@gmail.com> writes:
>>
>> > On Fri, Nov 08, 2019 at 04:07:14PM -0500, Aaron Conole wrote:
>> >> The act_ct TC module shares a common conntrack and NAT infrastructure
>> >> exposed via netfilter. It's possible that a packet needs both SNAT and
>> >> DNAT manipulation, due to e.g. tuple collision. Netfilter can support
>> >> this because it runs through the NAT table twice - once on ingress and
>> >> again after egress. The act_ct action doesn't have such capability.
>> >>
>> >> Like netfilter hook infrastructure, we should run through NAT twice to
>> >> keep the symmetry.
>> >>
>> >> Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
>> >>
>> >> Signed-off-by: Aaron Conole <acon...@redhat.com>
>> >> ---
>> >> net/sched/act_ct.c | 13 ++++++++++++-
>> >> 1 file changed, 12 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
>> >> index fcc46025e790..f3232a00970f 100644
>> >> --- a/net/sched/act_ct.c
>> >> +++ b/net/sched/act_ct.c
>> >> @@ -329,6 +329,7 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
>> >> bool commit)
>> >> {
>> >> #if IS_ENABLED(CONFIG_NF_NAT)
>> >> + int err;
>> >> enum nf_nat_manip_type maniptype;
>> >>
>> >> if (!(ct_action & TCA_CT_ACT_NAT))
>> >> @@ -359,7 +360,17 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
>> >> return NF_ACCEPT;
>> >> }
>> >>
>> >> - return ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> >> + err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> >> + if (err == NF_ACCEPT &&
>> >> + ct->status & IPS_SRC_NAT && ct->status & IPS_DST_NAT) {
>> >> + if (maniptype == NF_NAT_MANIP_SRC)
>> >> + maniptype = NF_NAT_MANIP_DST;
>> >> + else
>> >> + maniptype = NF_NAT_MANIP_SRC;
>> >> +
>> >> + err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
>> >> + }
>> >
>> > I keep thinking about this and I'm not entirely convinced that this
>> > shouldn't be simpler. More like:
>> >
>> > if (DNAT)
>> > DNAT
>> > if (SNAT)
>> > SNAT
>> >
>> > So it always does DNAT before SNAT, similarly to what iptables would
>> > do on PRE/POSTROUTING chains.
>>
>> I can rewrite the whole function, but I wanted to start with the smaller
>> fix that worked. I also think it needs more testing then (since it's
>> something of a rewrite of the function).
>>
>> I guess it's not too important - do you think it gives any readability
>> to do it this way? If so, I can respin the patch changing it like you
>> describe.
>
> I didn't mean a rewrite, but just to never handle SNAT before DNAT. So
> the fix here would be like:
>
> - return ct_nat_execute(skb, ct, ctinfo, range, maniptype);
> + err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
> + if (err == NF_ACCEPT && maniptype == NF_NAT_MANIP_DST &&
> + ct->status & IPS_SRC_NAT && ct->status & IPS_DST_NAT) {
> + maniptype = NF_NAT_MANIP_SRC;
> + err = ct_nat_execute(skb, ct, ctinfo, range, maniptype);
> + }
> + return err;
But the maniptype of the first call could be NAT_MANIP_SRC. In fact,
that's what I see if the packet is reply direction && !related.
So, we need the block to invert the manipulation type. Otherwise, we
miss the DNAT manipulation.
So I don't think I can use that block.
>> >> + return err;
>> >> #else
>> >> return NF_ACCEPT;
>> >> #endif
>> >> --
>> >> 2.21.0
>> >>
>>
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