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

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Date:   Mon, 8 Jul 2019 19:22:45 +0000
From:   Mark Bloch <markb@...lanox.com>
To:     Dag Moxnes <dag.moxnes@...cle.com>, Jason Gunthorpe <jgg@...pe.ca>
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



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()?

>>
>>>   drivers/infiniband/core/addr.c | 9 ++++++---
>>>   1 file changed, 6 insertions(+), 3 deletions(-)
>> Applied to for-next, thanks
>>
>> Jason
> 

Mark