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

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Date:   Thu, 23 Apr 2020 10:25:58 +0800
From:   Yuehaibing <yuehaibing@...wei.com>
To:     Xin Long <lucien.xin@...il.com>
CC:     Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        davem <davem@...emloft.net>, <kuba@...nel.org>,
        network dev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xfrm: policy: Only use mark as policy lookup key

On 2020/4/22 23:41, Xin Long wrote:
> On Wed, Apr 22, 2020 at 8:18 PM Yuehaibing <yuehaibing@...wei.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@...wei.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.

> 
>>
>>
>>
>>>
>>> .
>>>
>>
> 
> .
>