Re: [PATCH] xfrm: policy: Only use mark as policy lookup key

From: Yuehaibing
Date: Thu Apr 30 2020 - 02:30:35 EST

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On 2020/4/24 11:48, Yuehaibing wrote:
> On 2020/4/23 17:43, Xin Long wrote:
>> On Thu, Apr 23, 2020 at 4:41 PM Yuehaibing <yuehaibing@xxxxxxxxxx> wrote:
>>>
>>> On 2020/4/23 14:37, Xin Long wrote:
>>>> On Thu, Apr 23, 2020 at 10:26 AM Yuehaibing <yuehaibing@xxxxxxxxxx> wrote:
>>>>>
>>>>> On 2020/4/22 23:41, Xin Long wrote:
>>>>>> On Wed, Apr 22, 2020 at 8:18 PM Yuehaibing <yuehaibing@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>>>>>>> ---
>>>>>>>>> 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.
>

Steffen, any futher comment ?

>>
>>
>>>
>>>>
>>>> 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?
>>>>
>>>
>>
>> .
>>
>
>
> .
>

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