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

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Message-ID: <20190708193814.GF23996@ziepe.ca>
Date:   Mon, 8 Jul 2019 16:38:14 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Mark Bloch <markb@...lanox.com>
Cc:     Dag Moxnes <dag.moxnes@...cle.com>,
        "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 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

Thanks,
Jason