linux-kernel - Re: [RFC PATCH] xfrm: fix handling of XFRM policies mark and mask.

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Message-Id: <5D4F2414-B869-46AA-B684-01F9EA88AD03@telecom-bretagne.eu>
Date:	Wed, 6 Feb 2013 15:39:34 +0100
From:	Emmanuel Thierry <emmanuel.thierry@...ecom-bretagne.eu>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Steffen Klassert <steffen.klassert@...unet.com>,
	Romain KUNTZ <r.kuntz@...lavors.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	herbert@...dor.apana.org.au,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jamal Hadi Salim <hadi@...erus.ca>
Subject: Re: [RFC PATCH] xfrm: fix handling of XFRM policies mark and mask.


Le 6 févr. 2013 à 15:30, Jamal Hadi Salim a écrit :

> On 13-02-06 08:53 AM, Emmanuel Thierry wrote:
>> Actually, we didn't think about this problem since we work with priorities, putting the default policy (without a mark) at a minor priority than the marked one.
> 
> I think priorities are the way to go in cases of ambiguity.
> 
>> Your remark makes clearer the ideas behind the design of XFRM, but this leads to an interesting concern. If on policy insertion, the policy were inserted depending on the accuracy of the mark (the more the mask is specific, the more the mark must be put at the beginning of the list), how would we decide which is the more specific between these ones ?
>> 
>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000005
>> 
>> ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir out mark 0x00000001 mask 0x00000003
> 
> They look different to me, no? i.e i dont see a conflict - one has mark=5 and the other
> has mark=3.

I think you misread the example !
Marks are both 1, masks are different.

This case is more complex than a policy with no mark (so mark=0 and mask=0) versus a policy with an exact mark (so mark=1 and mask=0xffffffff), and i wanted to know if the algorithm would take these kind of cases into account.

Best regards
Emmanuel Thierry

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