netdev - Re: [PATCH net-next 1/2] net: netfilter: export xt_policy match_policy_in() as xt_policy_match_policy

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Message-ID: <CAHsH6GsRAKeEfASu2DiTK0kQwORZXkDBvDFFnMuzKMXTqQj0Lg@mail.gmail.com>
Date:   Mon, 15 Jan 2018 13:48:41 +0200
From:   Eyal Birger <eyal.birger@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, netdev@...r.kernel.org,
        coreteam@...filter.org, shmulik@...anetworks.com,
        Eyal Birger <eyal@...anetworks.com>
Subject: Re: [PATCH net-next 1/2] net: netfilter: export xt_policy
 match_policy_in() as xt_policy_match_policy_in()

On Mon, Jan 15, 2018 at 12:57 PM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
> On Sun, Jan 14, 2018 at 02:47:46PM +0200, Eyal Birger wrote:
>> On Fri, Jan 12, 2018 at 4:00 PM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
>> > On Fri, Jan 12, 2018 at 03:56:21PM +0200, Eyal Birger wrote:
>> >> On Fri, Jan 12, 2018 at 3:41 PM, Pablo Neira Ayuso <pablo@...filter.org> wrote:
>> >> > On Fri, Jan 12, 2018 at 02:57:24PM +0200, Eyal Birger wrote:
>> >> >> @@ -51,9 +52,9 @@ match_xfrm_state(const struct xfrm_state *x, const struct xt_policy_elem *e,
>> >> >>              MATCH(reqid, x->props.reqid);
>> >> >>  }
>> >> >>
>> >> >> -static int
>> >> >> -match_policy_in(const struct sk_buff *skb, const struct xt_policy_info *info,
>> >> >> -             unsigned short family)
>> >> >> +int xt_policy_match_policy_in(const struct sk_buff *skb,
>> >> >> +                           const struct xt_policy_info *info,
>> >> >> +                           unsigned short family)
>> >> >>  {
>> >> >>       const struct xt_policy_elem *e;
>> >> >>       const struct sec_path *sp = skb->sp;
>> >> >> @@ -80,10 +81,11 @@ match_policy_in(const struct sk_buff *skb, const struct xt_policy_info *info,
>> >> >>
>> >> >>       return strict ? 1 : 0;
>> >> >>  }
>> >> >> +EXPORT_SYMBOL_GPL(xt_policy_match_policy_in);
>> >> >
>> >> > If you just want to call xt_policy_match from tc, then you could use
>> >> > tc ipt infrastructure instead.
>> >>
>> >> Thanks for the suggestion -
>> >> Are you referring to act_ipt? it looks like it allows calling targets;
>> >> I couldn't find a classifier calling a netfilter matcher.
>> >
>> > Then, I'd suggest you extend that infrastructure to alllow to call
>> > matches, so we reduce the number of interdepencies between different
>> > subsystems.
>>
>> This appears very versatile. though in this case the use of the xtables code and
>> structures was done in order to avoid introducing new uapi structures
>> and supporting
>> match code, not necessarily to expose the full capabilities of extended matches,
>> similar in spirit to what was done in the em_ipset ematch.
>>
>> Perhaps in order to avoid the direct export of xt_policy code, I could call
>> xt_request_find_match() from the em_policy module, requesting the
>> xt_policy match?
>> this way api exposure is minimized while not overly complicating the
>> scope of this feature.
>>
>> What do you think?
>
> That would look better indeed.
>
> But once you call xt_request_find_match() from there, how far is to
> allow any arbitrary match? I think you only have to specify the match
> name, family and the binary layout structure that represents
> xt_policy, right?
>

I don't think that should be a problem. I'd need to pass the protocol onto
the ematches .change() callbacks and get the appropriate match from there.

> I'm telling this, because I think it would be fair enough to me if you
> add the generic infrastructure to the kernel to allow arbitrary load
> of xt matches, and then from userspace you just add the code to
> support this which is what you need.
>
> Probably someone else - not you - may follow up later on to generalize
> the userspace codebase to support other matches, by when that happens,
> the right bits will be in the kernel already.

I'm fine with submitting the more generic infrastructure.
Will follow up with a new series.

Thanks again!
Eyal.