netdev - Re: [RFC] SPD basic actions per netdev

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Message-ID: <20100401003352.GA19147@gondor.apana.org.au>
Date:	Thu, 1 Apr 2010 08:33:52 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	jamal <hadi@...erus.ca>
Cc:	Timo Teras <timo.teras@....fi>,
	"David S. Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Subject: Re: [RFC] SPD basic actions per netdev

On Wed, Mar 31, 2010 at 12:37:58PM -0400, jamal wrote:
> 
> This may be oversight in current implementation and possibly
> nobody has needed it before - hence it is not functional.
> 
> I want to have a drop-all policy on a per-interface level
> for incoming packets and add exceptions as i need them.
> [using the flow table is cheap if you have xfrm built in].
> i.e something along the lines of:
> 
> #eth0, wild-card drop all
> ip xfrm policy add src 0.0.0.0/0 dst 0.0.0.0/0 dev eth0 \
>        dir in ptype main action block priority $SOME-HIGH-value
> #eth0, exception
> ip xfrm policy add blah blah dev eth0 \
> dir in ptype main action allow priority $SOME-small-value
> #eth1, wild-card drop all
> ip xfrm policy add src 0.0.0.0/0 dst 0.0.0.0/0 dev eth1 \
>        dir in ptype main action block priority $SOME-HIGH-value
> #eth1 exception ...
> 
> The problem is this works as long as i dont specify an interface.
> i.e, this would work in the in-direction:
> 
> ip xfrm policy add src 0.0.0.0/0 dst 0.0.0.0/0 \
>         dir in ptype main action block priority $SOME-HIGH-value
> 
> This would not work:
> ip xfrm policy add src 0.0.0.0/0 dst 0.0.0.0/0 dev eth0 \
>        dir in ptype main action block priority $SOME-HIGH-value
> 
> 
> The checks in the selector matching is the culprit, example for v4:
> 
> __xfrm4_selector_match(struct xfrm_selector *sel, struct flowi *fl)
> {
>         return  .... &&
>                 .... &&
>                 (fl->oif == sel->ifindex || !sel->ifindex);
> }
> 
> i.e in the second case i have a non-zero sel->ifindex but
> a zero fl->oif; so it wont match.
> 
> One approach to fix this is to pass the direction then i can do
> in the function call, then i can do something along the lines of
> matching if:
> (fl_dir == FLOW_DIR_IN && (fl->iif == sel->ifindex || !sel->ifindex) ||
> (fl->oif == sel->ifindex || !sel->ifindex);
> 
> Is there any reason the selector matching only assumes fl->oif?
> Are there any unforeseen issues/breakages if i added a check for the
> above.

If we're going to change this then we should just add a second
interface field to the selector, rather than trying to overload
the existing one.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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