Re: [PATCH net 2/2] act_ct: support asymmetric conntrack

[Paul Blakey]

On 11/14/2019 4:22 PM, Roi Dayan wrote:
>
> On 2019-11-08 11:07 PM, 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 <aconole@xxxxxxxxxx>
>> ---
>>   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);
>> +	}
>> +	return err;
>>   #else
>>   	return NF_ACCEPT;
>>   #endif
>>
> +paul

Hi Aaron,

I think I understand the issue and this looks good,

Can you describe the scenario to reproduce this?


Thanks,

Paul.