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

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Date:   Thu, 9 Apr 2020 16:19:37 +0800
From:   Yuehaibing <yuehaibing@...wei.com>
To:     Steffen Klassert <steffen.klassert@...unet.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 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？

> 
>> policy D (mark.v = 3475289, mark.m = 0, priority = 1)	
>>
>> while finding delpol in xfrm_policy_insert_list,
>> first round delpol is matched C, whose priority is less than D, so contiue the loop,
>> then A is matched， WARN_ON is triggered.  It seems the WARN is useless.
> 
> Looks like the warning is usefull, it found a bug.
> 
> 
> .
>