linux-kernel - Re: [PATCH v3 3/3] IB/core: Obtain subnet

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Message-ID: <427FB96F-2550-4106-B8AD-EC589C1FD82B@oracle.com>
Date:   Tue, 15 Jun 2021 16:13:14 +0000
From:   Haakon Bugge <haakon.bugge@...cle.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Anand Khoje <anand.a.khoje@...cle.com>,
        OFED mailing list <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "jgg@...pe.ca" <jgg@...pe.ca>
Subject: Re: [PATCH v3 3/3] IB/core: Obtain subnet_prefix from cache in IB
 devices.



> On 15 Jun 2021, at 07:08, Leon Romanovsky <leon@...nel.org> wrote:
> 
> On Mon, Jun 14, 2021 at 04:29:09PM +0000, Haakon Bugge wrote:
>> 
>> 
>>> On 14 Jun 2021, at 09:25, Leon Romanovsky <leon@...nel.org> wrote:
>>> 
>>> On Mon, Jun 14, 2021 at 03:32:39AM +0000, Haakon Bugge wrote:
>>>> 
>>>> 
>>>>> On 9 Jun 2021, at 12:40, Leon Romanovsky <leon@...nel.org> wrote:
>>>>> 
>>>>> On Wed, Jun 09, 2021 at 09:26:03AM +0000, Anand Khoje wrote:
>>>>>> Hi Leon,
>>>>> 
>>>>> Please don't do top-posting.
>>>>> 
>>>>> 
>>>>>> 
>>>>>> The set_bit()/clear_bit() and enum ib_port_data_flags  has been added as a device that can be used for future enhancements. 
>>>>>> Also, usage of set_bit()/clear_bit() ensures the operations on this bit is atomic.
>>>>> 
>>>>> The bitfield variables are better suit this use case.
>>>>> Let's don't overcomplicate code without the reason.
>>>> 
>>>> The problem is always that people tend to build on what's in there. For example, look at the bitfields in rdma_id_private, tos_set,  timeout_set, and min_rnr_timer_set.
>>>> 
>>>> What do you think will happen when, let's say, rdma_set_service_type() and rdma_set_ack_timeout() are called in close proximity in time? There is no locking, and the RMW will fail intermittently.
>>> 
>>> We are talking about device initialization flow that shouldn't be
>>> performed in parallel to another initialization of same device, so the
>>> comparison to rdma-cm is not valid here.
>> 
>> I can agree to that. And it is probably not worthwhile to fix the bit-fields in rdma_id_private?
> 
> Before this article [1], I would say no, we don't need to fix.
> Now, I'm not sure about that.
> 
> "He also notes that even though the design flaws are difficult to exploit
> on their own, they can be combined with the other flaws found to make for
> a much more serious problem."
> 
> and 
> 
> "In other words, people did notice this vulnerability and a defense was standardized,
> but in practice the defense was never adopted. This is a good example that security
> defenses must be adopted before attacks become practical."

Let me send you a commit tomorrow. The last sentence you quoted above is ambiguous as far as I can understand. But the intention is clear though :-)


Thxs, Håkon