Re: [PATCH 1/1] netfilter: xtables: add quota support to nfacct

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Mon, Dec 30, 2013 at 04:14:21PM -0700, Mathieu Poirier wrote:
> On 30 December 2013 15:17, Mathieu Poirier <mathieu.poirier@linaro.org> wrote:
> > Hey Florian - I think that is an acceptable compromise.  The LOG chain
> > and rules are extra but it is setup only once and as such scale well.
> >
> > Thank you for that,
> > Mathieu
> >
> > On 30 December 2013 14:46, Florian Westphal <fw@strlen.de> wrote:
> >> Mathieu Poirier <mathieu.poirier@linaro.org> wrote:
> >>> Upon reaching the limit of 10000 byte of http traffic, any outgoing
> >>> http packets will be dropped and a single broadcast message will be
> >>> sent to user space.  That is because the match explicitly takes care
> >>> of sending the notification.
> >>>
> >>> With your proposal:
> >>>
> >>> iptables -I OUTPUT -p http \
> >>>          -m nfacct --nfacct-name http-limit --quota 10000 --match-once \
> >>>          -j NFLOG --nflog-prefix "http: " --nflog-group 34
> >>>
> >>> will log the quota reached event but won't prevent further http
> >>> traffic from going out.  One could instinctively add another rule
> >>> right after the above one, something like:
> >>>
> >>> iptables -I OUTPUT -p http \
> >>>          -m nfacct --nfacct-name http-limit --quota 10000 \
> >>>          -j REJECT
> >>>
> >>> but that won't work either because the packet/byte could will be
> >>> incremented twice.
> >>
> >> The usual workaround is to create custom chains to deal with this,
> >> i.e.
> >> iptables -N LOG_DROP_HTTP
> >> iptables -A LOG_DROP_HTTP -j NFLOG --nflog-prefix "http: " --nflog-group 34
> >> iptables -A LOG_DROP_HTTP -j REJECT
> >> iptables -I OUTPUT -p http -m nfacct ... -j LOG_DROP_HTTP
> 
> I may have spoken too quickly.  With this solution a log message is
> sent every time a packet over quota is received, something we
> definitely want to avoid.  I was able to cover that case when sending
> a notification from the match function.

Then, keep your code to send netlink notifications, I don't find any
better solution at this moment.