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Message-ID: <565319EB.2090909@iogearbox.net>
Date: Mon, 23 Nov 2015 14:51:39 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Florian Westphal <fw@...len.de>, Tejun Heo <tj@...nel.org>
CC: davem@...emloft.net, pablo@...filter.org, kaber@...sh.net,
kadlec@...ckhole.kfki.hu, daniel.wagner@...-carit.de,
nhorman@...driver.co, lizefan@...wei.com, hannes@...xchg.org,
netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...com, ninasc@...com,
Neil Horman <nhorman@...driver.com>,
Jan Engelhardt <jengelh@...i.de>
Subject: Re: [PATCH 9/9] netfilter: implement xt_cgroup cgroup2 path match
On 11/23/2015 02:43 PM, Daniel Borkmann wrote:
> On 11/21/2015 07:54 PM, Florian Westphal wrote:
>> Tejun Heo <tj@...nel.org> wrote:
>>> On Sat, Nov 21, 2015 at 05:56:06PM +0100, Florian Westphal wrote:
>>>>> +struct xt_cgroup_info_v1 {
>>>>> + __u8 has_path;
>>>>> + __u8 has_classid;
>>>>> + __u8 invert_path;
>>>>> + __u8 invert_classid;
>>>>> + char path[PATH_MAX];
>>>>> + __u32 classid;
>>>>> +
>>>>> + /* kernel internal data */
>>>>> + void *priv __attribute__((aligned(8)));
>>>>> +};
>>>>
>>>> Ahem. Am I reading this right? This struct is > 4k in size?
>>>> If so -- Ugh. Does sizeof(path) really have to be PATH_MAX?
>>>
>>> Hmmm... yeap but would this be an acutual problem?
>>
>> Since rule blob can be allocated via vmalloc i guess "no", its not
>> really a problem unless someone needs realy insane amount of such rules.
>>
>> I don't have any better suggestion, so I guess its necessary evil.
>>
>> The only other question I have is wheter PATH_MAX might be a possible
>> ABI breaker in future. It would have to be guaranteed that this is the
>> same size forever, else you'd get strange errors on rule insertion if
>> the sizes of the kernel and userspace version differs.
>
> Haven't looked deeply into kernfs, but if it's possible to get the object
> from the struct file eventually, you could let iptables frontend open that
> path and just pass the fd down. Would be sizeof(int) vs PATH_MAX then, i.e.
> when you have a large number of rules to load.
( ... but with the downside that things like save/restore wouldn't work. )
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