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

[Jason Gunthorpe <jgg@ziepe.ca>]

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