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SubjectRe: [PATCH] RDMA/core: Fix race when resolving IP address
On Fri, Jun 21, 2019 at 04:09:16PM +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.
>
> Signed-off-by: Dag Moxnes <dag.moxnes@oracle.com>
> Change-Id: I3c5f982b304457f0a83ea7def2fac70315ed38b4
> drivers/infiniband/core/addr.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
> index 2f7d141598..e4945fd1bb 100644
> +++ b/drivers/infiniband/core/addr.c
> @@ -333,12 +333,16 @@ static int dst_fetch_ha(const struct dst_entry *dst,
> if (!n)
> return -ENODATA;
>
> + read_lock_bh(&n->lock)
> if (!(n->nud_state & NUD_VALID)) {
> - neigh_event_send(n, NULL);
> ret = -ENODATA;
> } else {
> memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
> }
> + read_unlock_bh(&n->lock);
> +
> + if (ret)
> + neigh_event_send(n, NULL);
>
> neigh_release(n);

Can we write this with less spaghetti please, maybe:

static int dst_fetch_ha(const struct dst_entry *dst,
struct rdma_dev_addr *dev_addr,
const void *daddr)
{
struct neighbour *n;
int ret = 0;

n = dst_neigh_lookup(dst, daddr);
if (!n)
return -ENODATA;

read_lock_bh(&n->lock);
if (!(n->nud_state & NUD_VALID)) {
read_unlock_bh(&n->lock);
goto out_send;
}
memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
read_unlock_bh(&n->lock);

goto out_release;

out_send:
neigh_event_send(n, NULL);
ret = -ENODATA;
out_release:
neigh_release(n);

return ret;
}

Also, Parav should look at it.

Thanks,
Jason

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