netdev - Re: [PATCH net-next] bridge: ebtables: Avoid resetting limit rule state

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Date:   Tue, 28 Nov 2017 00:30:08 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Linus Lüssing <linus.luessing@...3.blue>
Cc:     netfilter-devel@...r.kernel.org,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "David S . Miller" <davem@...emloft.net>, coreteam@...filter.org,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] bridge: ebtables: Avoid resetting limit rule
 state

Hi Linus,

On Sat, Nov 25, 2017 at 08:44:18AM +0100, Linus Lüssing wrote:
> So far any changes with ebtables will reset the state of limit rules,
> leading to spikes in traffic. This is especially noticeable if changes
> are done frequently, for instance via a daemon.
> 
> This patch fixes this by bailing out from (re)setting if the limit
> rule was initialized before.
> 
> When sending packets every 250ms for 600s, with a
> "--limit 1/sec --limit-burst 50" rule and a command like this
> in the background:
> 
> $ ebtables -N VOIDCHAIN
> $ while true; do ebtables -F VOIDCHAIN; sleep 30; done
> 
> The results are:
> 
> Before: ~1600 packets
> After: 650 packets
> 
> Signed-off-by: Linus Lüssing <linus.luessing@...3.blue>
> ---
>  net/bridge/netfilter/ebt_limit.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/bridge/netfilter/ebt_limit.c b/net/bridge/netfilter/ebt_limit.c
> index 61a9f1be1263..f74b48633feb 100644
> --- a/net/bridge/netfilter/ebt_limit.c
> +++ b/net/bridge/netfilter/ebt_limit.c
> @@ -69,6 +69,10 @@ static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
>  {
>  	struct ebt_limit_info *info = par->matchinfo;
>  
> +	/* Do not reset state on unrelated table changes */
> +	if (info->prev)
> +		return 0;

What kernel version are you using? I suspect you don't have this
applied?

commit ec23189049651b16dc2ffab35a4371dc1f491aca
Author: Willem de Bruijn <willemb@...gle.com>
Date:   Mon Jan 2 17:19:46 2017 -0500

    xtables: extend matches and targets with .usersize