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Subject: Re: [PATCH] xfrm: policy: Only use mark as policy lookup key
To:     Xin Long <lucien.xin@gmail.com>
References: <20200421143149.45108-1-yuehaibing@huawei.com>
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CC:     Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        davem <davem@davemloft.net>, <kuba@kernel.org>,
        network dev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jamal Hadi Salim <hadi@cyberus.ca>
From:   Yuehaibing <yuehaibing@huawei.com>
Message-ID: <cb82c789-8eb5-e7bf-4f5a-4a8ec0672648@huawei.com>
Date:   Fri, 24 Apr 2020 11:48:24 +0800
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On 2020/4/23 17:43, Xin Long wrote:
> On Thu, Apr 23, 2020 at 4:41 PM Yuehaibing <yuehaibing@huawei.com> wrote:
>>
>> On 2020/4/23 14:37, Xin Long wrote:
>>> On Thu, Apr 23, 2020 at 10:26 AM Yuehaibing <yuehaibing@huawei.com> wrote:
>>>>
>>>> On 2020/4/22 23:41, Xin Long wrote:
>>>>> On Wed, Apr 22, 2020 at 8:18 PM Yuehaibing <yuehaibing@huawei.com> wrote:
>>>>>>
>>>>>> On 2020/4/22 17:33, Steffen Klassert wrote:
>>>>>>> On Tue, Apr 21, 2020 at 10:31:49PM +0800, YueHaibing wrote:
>>>>>>>> While update xfrm policy as follow:
>>>>>>>>
>>>>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
>>>>>>>>  priority 1 mark 0 mask 0x10
>>>>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
>>>>>>>>  priority 2 mark 0 mask 0x00
>>>>>>>> ip -6 xfrm policy update src fd00::1/128 dst fd00::2/128 dir in \
>>>>>>>>  priority 2 mark 0 mask 0x10
>>>>>>>>
>>>>>>>> We get this warning:
>>>>>>>>
>>>>>>>> WARNING: CPU: 0 PID: 4808 at net/xfrm/xfrm_policy.c:1548
>>>>>>>> Kernel panic - not syncing: panic_on_warn set ...
>>>>>>>> CPU: 0 PID: 4808 Comm: ip Not tainted 5.7.0-rc1+ #151
>>>>>>>> Call Trace:
>>>>>>>> RIP: 0010:xfrm_policy_insert_list+0x153/0x1e0
>>>>>>>>  xfrm_policy_inexact_insert+0x70/0x330
>>>>>>>>  xfrm_policy_insert+0x1df/0x250
>>>>>>>>  xfrm_add_policy+0xcc/0x190 [xfrm_user]
>>>>>>>>  xfrm_user_rcv_msg+0x1d1/0x1f0 [xfrm_user]
>>>>>>>>  netlink_rcv_skb+0x4c/0x120
>>>>>>>>  xfrm_netlink_rcv+0x32/0x40 [xfrm_user]
>>>>>>>>  netlink_unicast+0x1b3/0x270
>>>>>>>>  netlink_sendmsg+0x350/0x470
>>>>>>>>  sock_sendmsg+0x4f/0x60
>>>>>>>>
>>>>>>>> Policy C and policy A has the same mark.v and mark.m, so policy A is
>>>>>>>> matched in first round lookup while updating C. However policy C and
>>>>>>>> policy B has same mark and priority, which also leads to matched. So
>>>>>>>> the WARN_ON is triggered.
>>>>>>>>
>>>>>>>> xfrm policy lookup should only be matched when the found policy has the
>>>>>>>> same lookup keys (mark.v & mark.m) no matter priority.
>>>>>>>>
>>>>>>>> Fixes: 7cb8a93968e3 ("xfrm: Allow inserting policies with matching mark and different priorities")
>>>>>>>> Signed-off-by: YueHaibing <yuehaibing@huawei.com>
>>>>>>>> ---
>>>>>>>>  net/xfrm/xfrm_policy.c | 16 +++++-----------
>>>>>>>>  1 file changed, 5 insertions(+), 11 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
>>>>>>>> index 297b2fd..67d0469 100644
>>>>>>>> --- a/net/xfrm/xfrm_policy.c
>>>>>>>> +++ b/net/xfrm/xfrm_policy.c
>>>>>>>> @@ -1436,13 +1436,7 @@ static void xfrm_policy_requeue(struct xfrm_policy *old,
>>>>>>>>  static bool xfrm_policy_mark_match(struct xfrm_policy *policy,
>>>>>>>>                                 struct xfrm_policy *pol)
>>>>>>>>  {
>>>>>>>> -    u32 mark = policy->mark.v & policy->mark.m;
>>>>>>>> -
>>>>>>>> -    if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
>>>>>>>> -            return true;
>>>>>>>> -
>>>>>>>> -    if ((mark & pol->mark.m) == pol->mark.v &&
>>>>>>>> -        policy->priority == pol->priority)
>>>>>>>
>>>>>>> If you remove the priority check, you can't insert policies with matching
>>>>>>> mark and different priorities anymore. This brings us back the old bug.
>>>>>>
>>>>>> Yes, this is true.
>>>>>>
>>>>>>>
>>>>>>> I plan to apply the patch from Xin Long, this seems to be the right way
>>>>>>> to address this problem.
>>>>>>
>>>>>> That still brings an issue, update like this:
>>>>>>
>>>>>> policy A (mark.v = 1, mark.m = 0, priority = 1)
>>>>>> policy B (mark.v = 1, mark.m = 0, priority = 1)
>>>>>>
>>>>>> A and B will all in the list.
>>>>> I think this is another issue even before:
>>>>> 7cb8a93968e3 ("xfrm: Allow inserting policies with matching mark and
>>>>> different priorities")
>>>>>
>>>>>>
>>>>>> So should do this:
>>>>>>
>>>>>>  static bool xfrm_policy_mark_match(struct xfrm_policy *policy,
>>>>>>                                    struct xfrm_policy *pol)
>>>>>>  {
>>>>>> -       u32 mark = policy->mark.v & policy->mark.m;
>>>>>> -
>>>>>> -       if (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m)
>>>>>> -               return true;
>>>>>> -
>>>>>> -       if ((mark & pol->mark.m) == pol->mark.v &&
>>>>>> +       if ((policy->mark.v & policy->mark.m) == (pol->mark.v & pol->mark.m) &&
>>>>>>             policy->priority == pol->priority)
>>>>>>                 return true;
>>>>> "mark.v & mark.m" looks weird to me, it should be:
>>>>> ((something & mark.m) == mark.v)
>>>>>
>>>>> So why should we just do this here?:
>>>>> (policy->mark.v == pol->mark.v && policy->mark.m == pol->mark.m &&
>>>>>  policy->priority == pol->priority)
>>>>
>>>>
>>>> This leads to this issue:
>>>>
>>>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir in mark 0x00000001 mask 0x00000005
>>>>  ip -6 xfrm policy add src fd00::1/128 dst fd00::2/128 dir in mark 0x00000001 mask 0x00000003
>>>>
>>>> the two policies will be in list, which should not be allowed.
>>> I think these are two different policies.
>>> For instance:
>>> mark = 0x1234567b will match the 1st one only.
>>> mark = 0x1234567d will match the 2st one only
>>>
>>> So these should have been allowed, no?
>>
>> If mark = 0x12345671, it may match different policy depends on the order of inserting,
>>
>> ip xfrm policy update src 172.16.2.0/24 dst 172.16.1.0/24 dir in ptype main \
>> tmpl src 192.168.2.10 dst 192.168.1.20 proto esp mode tunnel mark 0x00000001 mask 0x00000005
>>
>> ip xfrm policy update src 172.16.2.0/24 dst 172.16.1.0/24 dir in ptype main \
>> tmpl src 192.168.2.100 dst 192.168.1.100 proto esp mode beet mark 0x00000001 mask 0x00000003
>>
>> In fact, your case should use different priority to match.
> Sorry, but it does match your above policies now, like in xfrm_policy_match(),
> when fl->flowi_mark == 0x1234567b:
> 
> (fl->flowi_mark & pol->mark.m) != pol->mark.v
> 0x1234567b & 0x00000005 == 0x00000001
> 
> and when fl->flowi_mark ==  0x1234567d:
> 0x1234567d & 0x00000003 ==  0x00000001
> 
> am I missing something?

when fl->flowi_mark == 0x12345671

0x12345671 & 0x00000005 == 0x00000001
0x12345671 & 0x00000003 == 0x00000001

This will match different policy depends on the order of policy inserting, it is not expected.

> 
> 
>>
>>>
>>> I'm actually confused now.
>>> does the mask work against its own value, or the other value?
>>> as 'A == (mark.v&mark.m)' and '(A & mark.m) == mark.v' are different things.
>>>
>>> This can date back to Jamal's xfrm by MARK:
>>>
>>> https://lwn.net/Articles/375829/
>>>
>>> where it does 'm->v & m->m' in xfrm_mark_get() and
>>> 'policy->mark.v & policy->mark.m' in xfrm_policy_insert() while
>>> it does '(A & pol->mark.m) == pol->mark.v' in other places.
>>>
>>> Now I'm thinking 'm->v & m->m' is meaningless, by which if we get
>>> a value != m->v, it means this mark can never be matched by any.
>>>
>>>   policy A (mark.v = 1, mark.m = 0, priority = 1)
>>>   policy B (mark.v = 1, mark.m = 0, priority = 1)
>>>
>>> So probably we should avoid this case by check m->v == (m->v & m->m)
>>> when adding a new policy.
>>>
>>> wdyt?
>>>
>>
> 
> .
>