Re: [PATCH v2] RDMA/core: Fix race when resolving IP address

[Parav Pandit]

On Fri, Jun 28, 2019 at 2:20 PM Dag Moxnes <dag.moxnes@xxxxxxxxxx> 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.
>
> Signed-off-by: Dag Moxnes <dag.moxnes@xxxxxxxxxx>
> Signed-off-by: HÃkon Bugge <haakon.bugge@xxxxxxxxxx>
>
> ---
> v1 -> v2:
>    * Modified implementation to improve readability
> ---
>  drivers/infiniband/core/addr.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
> index 2f7d141598..51323ffbc5 100644
> --- a/drivers/infiniband/core/addr.c
> +++ b/drivers/infiniband/core/addr.c
> @@ -333,11 +333,14 @@ static int dst_fetch_ha(const struct dst_entry *dst,
>         if (!n)
>                 return -ENODATA;
>
> -       if (!(n->nud_state & NUD_VALID)) {
> +       read_lock_bh(&n->lock);
> +       if (n->nud_state & NUD_VALID) {
> +               memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
> +               read_unlock_bh(&n->lock);
> +       } else {
> +               read_unlock_bh(&n->lock);
>                 neigh_event_send(n, NULL);
>                 ret = -ENODATA;
> -       } else {
> -               memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
>         }
>
>         neigh_release(n);
> --
> 2.20.1
>
Reviewed-by: Parav Pandit <parav@xxxxxxxxxxxx>

A sample trace such as below in commit message would be good to have.
Or the similar one that you noticed with ARP delete sequence.

neigh_changeaddr()
  neigh_flush_dev()
   n->nud_state = NUD_NOARP;

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