Subject: Re: [PATCH] netfilter: xtables: userspace notification target

From: Patrick McHardy <[email-masked]>
Date: Wed, 14 Jul 2010 13:48:04 +0200

On 13.07.2010 18:38, Pablo Neira Ayuso wrote:
> On 13/07/10 12:23, Luciano Coelho wrote:
>> On Tue, 2010-07-13 at 10:50 +0200, ext Pablo Neira Ayuso wrote:
>>> On 13/07/10 08:18, Changli Gao wrote:
>>>> On Tue, Jul 13, 2010 at 8:11 AM, Samuel
>>>> Ortiz<[email-masked]>  wrote:
>>>>>
>>>>> The userspace notification Xtables target sends a netlink notification
>>>>> whenever a packet hits the target. Notifications have a label
>>>>> attribute
>>>>> for userspace to match it against a previously set rule. The rules
>>>>> also
>>>>> take a --all option to switch between sending a notification for all
>>>>> packets or for the first one only.
>>>>> Userspace can also send a netlink message to toggle this switch
>>>>> while the
>>>>> target is in place. This target uses the nefilter netlink framework.
>>>>>
>>>>> This target combined with various matches (quota, rateest, etc..)
>>>>> allows
>>>>> userspace to make decisions on interfaces handling. One could for
>>>>> example
>>>>> decide to switch between power saving modes depending on estimated
>>>>> rate
>>>>> thresholds.
>>>>>
>>>>
>>>> It much like the following iptables rules.
>>>>
>>>> iptables -N log_and_drop
>>>> iptables -A log_and_drop -j NFLOG --nflog-group 1 --nflog-prefix
>>>> "log_and_drop"
>>>> iptables -A log_and_drop -j DROP
>>>>
>>>> ...
>>>> iptables ... -m quota --quota-bytes 20000 -j log_and_drop
>>>> ...
>>>
>>> Indeed, this looks to me like something that you can do with NFLOG and
>>> some combination of matches.
>>
>> Is it possible to have the NFLOG send only one notification to the
>> userspace?
> 
> Not possible, but you could easily extend NFLOG to implement this
> feature if it's not possible to do what you need with the existing
> matches/targets. This NOTIF infrastructure is redundant and it looks
> like a subset of NFLOG.

If you're using connection tracking, you can use conntrack marks
to avoid sending more than a single message:

iptables ... -m connmark --mark 0x1/0x1 -j RETURN
iptables ... -j NFLOG ...
iptables ... -j CONNMARK --set-mark 0x1/0x1