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

[Florian Westphal <fw@strlen.de>]

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