Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v3] RDMA/core: Fix race when resolving IP address
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     dledford@redhat.com, leon@kernel.org, parav@mellanox.com,
        linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1562584584-13132-1-git-send-email-dag.moxnes@oracle.com>
 <20190708175025.GA6976@ziepe.ca>
From:   Dag Moxnes <dag.moxnes@oracle.com>
Message-ID: <4b9ae7b8-310c-e0b6-7a8e-33e6d5bef83d@oracle.com>
Date:   Mon, 8 Jul 2019 20:47:38 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.7.0
MIME-Version: 1.0
In-Reply-To: <20190708175025.GA6976@ziepe.ca>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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