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

[Dag Moxnes]

Hi Jason,


Thanks for the review.


On 6/21/19 4:56 PM, Jason Gunthorpe wrote:
> 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@xxxxxxxxxx>
> > 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)
Miising semicolon at end of statement. Sorry about that.
> >   	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;
> }

Personally I find it more readable when the unlock is done in one place,

but sure, I can rewrite it the way you suggest if the reviewers agree that

that way is preferable.

Regards,

-Dag


> Also, Parav should look at it.
>
> Thanks,
> Jason