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

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Message-ID: <20190708230525.GI23996@ziepe.ca>
Date:   Mon, 8 Jul 2019 20:05:25 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dag Moxnes <dag.moxnes@...cle.com>
Cc:     Mark Bloch <markb@...lanox.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 10:11:29PM +0200, Dag Moxnes wrote:
> 
> 
> 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?

post a v4

Jason