linux-kernel - Re: [PATCH net-next] xfrm: policy: Remove obsolete WARN while xfrm policy inserting

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Date:   Wed, 15 Apr 2020 09:14:43 +0200
From:   Steffen Klassert <steffen.klassert@...unet.com>
To:     Yuehaibing <yuehaibing@...wei.com>
CC:     <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
        <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] xfrm: policy: Remove obsolete WARN while xfrm
 policy inserting

On Thu, Apr 09, 2020 at 04:19:37PM +0800, Yuehaibing wrote:
> 
> 
> On 2020/4/6 17:03, Steffen Klassert wrote:
> > On Mon, Mar 30, 2020 at 10:05:32PM +0800, Yuehaibing wrote:
> >> On 2020/3/28 19:23, Steffen Klassert wrote:
> >>> On Fri, Mar 27, 2020 at 08:34:43PM +0800, YueHaibing wrote:
> >>>> Since commit 7cb8a93968e3 ("xfrm: Allow inserting policies with matching
> >>>> mark and different priorities"), we allow duplicate policies with
> >>>> different priority, this WARN is not needed any more.
> >>>
> >>> Can you please describe a bit more detailed why this warning
> >>> can't trigger anymore?
> >>
> >> No, this warning is triggered while detect a duplicate entry in the policy list
> >>
> >> regardless of the priority. If we insert policy like this:
> >>
> >> policy A (mark.v = 3475289, mark.m = 0, priority = 1)	//A is inserted
> >> policy B (mark.v = 0, mark.m = 0, priority = 0) 	//B is inserted
> >> policy C (mark.v = 3475289, mark.m = 0, priority = 0)	//C is inserted and B is deleted
> > 
> > The codepath that replaces a policy by another should just trigger
> > on policy updates (XFRM_MSG_UPDPOLICY). Is that the case in your
> > test?
> 
> Yes, this is triggered by XFRM_MSG_UPDPOLICY
> 
> > 
> > It should not be possible to add policy C with XFRM_MSG_NEWPOLICY
> > as long as you have policy B inserted.
> > 
> > The update replaces an old policy by a new one, the lookup keys of
> > the old policy must match the lookup keys of the new one. But policy
> > B has not the same lookup keys as C, the mark is different. So B should
> > not be replaced with C.
> 
> 1436 static bool xfrm_policy_mark_match(struct xfrm_policy *policy,
> 1437                                    struct xfrm_policy *pol)
> 1438 {
> 1439         u32 mark = policy->mark.v & policy->mark.m;
> 1440
> 1441         if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
> 1442                 return true;
> 1443
> 1444         if ((mark & pol->mark.m) == pol->mark.v &&    //policy is C, pol is B, so mark is 0, pol->mark.m is 0, pol->mark.v is 0
> 1445             policy->priority == pol->priority)	   //priority is same zero, so return true, B is replaced with C
> 1446                 return true;
> 1447
> 1448         return false;
> 1449 }
> 
> Should xfrm_policy_mark_match be fixed？

Yes, xfrm_policy_mark_match should only replace if the found
policy has the same lookup keys.