linux-kernel - Re: xt_recent broken in kernel 3.19.0 + PATCH

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Date:	Wed, 11 Feb 2015 19:15:29 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Chris Vine <chris@...ne.freeserve.co.uk>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netfilter-devel@...r.kernel.org,
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: xt_recent broken in kernel 3.19.0 + PATCH

(Cc'ing netdev and netfilter-devel lists)

On Wed, Feb 11, 2015 at 10:31 AM, Chris Vine
<chris@...ne.freeserve.co.uk> wrote:
> On Wed, 11 Feb 2015 09:28:34 +0000
> Chris Vine <chris@...ne.freeserve.co.uk> wrote:
>> With kernel 3.19.0, the following iptables rule, where SSH_TRIES is
>> set to 4:
>>
>>   iptables -D SSH_CHAIN -m conntrack --ctstate NEW \
>>     -m recent --update --seconds $SSH_LOGIN_PERIOD --hitcount
>> $SSH_TRIES -j DROP
>>
>> generates this error message in syslog:
>>
>>   kernel: xt_recent: hitcount (4) is larger than packets to be
>>   remembered (4) for table DEFAULT
>>
>> and the rule fails to install in the table.  No error is generated
>> with kernel 3.18.6.
>
> The rule provoking this should of course have been the one appending
> the rule, which is:
>
>   iptables -A SSH_CHAIN -m conntrack --ctstate NEW \
>     -m recent --update --seconds $SSH_LOGIN_PERIOD --hitcount $SSH_TRIES -j DROP
>
> On looking at the code, the changes in the 3.19 kernel seem not to have
> been tested and there is an off-by-one error.  The patch below restores
> behaviour to be identical to that found in the 3.18 kernel.
>
> Chris
>
> --- linux-3.19.0/net/netfilter/xt_recent.c~     2015-02-10 09:18:44.657376355 +0000
> +++ linux-3.19.0/net/netfilter/xt_recent.c      2015-02-11 17:58:33.311608835 +0000
> @@ -378,7 +378,7 @@
>         mutex_lock(&recent_mutex);
>         t = recent_table_lookup(recent_net, info->name);
>         if (t != NULL) {
> -               if (info->hit_count > t->nstamps_max_mask) {
> +               if (info->hit_count > t->nstamps_max_mask + 1) {
>                         pr_info("hitcount (%u) is larger than packets to be remembered (%u) for table %s\n",
>                                 info->hit_count, t->nstamps_max_mask + 1,
>                                 info->name);
> --
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