linux-kernel - Re: [PATCH v3] RDMA/core: Fix race when resolving IP address

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Date:   Mon, 8 Jul 2019 22:11:29 +0200
From:   Dag Moxnes <dag.moxnes@...cle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>, Mark Bloch <markb@...lanox.com>
Cc:     "dledford@...hat.com" <dledford@...hat.com>,
        "leon@...nel.org" <leon@...nel.org>,
        Parav Pandit <parav@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] RDMA/core: Fix race when resolving IP address



Den 08.07.2019 21:38, skrev Jason Gunthorpe:
> On Mon, Jul 08, 2019 at 07:22:45PM +0000, Mark Bloch wrote:
>>
>> On 7/8/19 11:47 AM, Dag Moxnes wrote:
>>> Thanks Jason,
>>>
>>> Regards,
>>> Dag
>>>
>>> Den 08.07.2019 19:50, skrev Jason Gunthorpe:
>>>> On Mon, Jul 08, 2019 at 01:16:24PM +0200, Dag Moxnes wrote:
>>>>> Use neighbour lock when copying MAC address from neighbour data struct
>>>>> in dst_fetch_ha.
>>>>>
>>>>> When not using the lock, it is possible for the function to race with
>>>>> neigh_update, causing it to copy an invalid MAC address.
>>>>>
>>>>> It is possible to provoke this error by calling rdma_resolve_addr in a
>>>>> tight loop, while deleting the corresponding ARP entry in another tight
>>>>> loop.
>>>>>
>>>>> This will cause the race shown it the following sample trace:
>>>>>
>>>>> rdma_resolve_addr()
>>>>>     rdma_resolve_ip()
>>>>>       addr_resolve()
>>>>>         addr_resolve_neigh()
>>>>>           fetch_ha()
>>>>>             dst_fetch_ha()
>>>>>               n->nud_state == NUD_VALID
>>>> It isn't nud_state that is the problem here, it is the parallel
>>>> memcpy's onto ha. I fixed the commit message
>>>>
>>>> This could also have been solved by using the ha_lock, but I don't
>>>> think we have a reason to particularly over-optimize this.
>> Sorry I'm late to the party, but why not just use: neigh_ha_snapshot()?
> Yes, that is much better, please respin this
OK, will do!
Can I still post it as a v4? Or should I do it differently as you 
already applied it?

Regards,
-Dag
>
> Thanks,
> Jason