Re: [net-next PATCH] net: ptr_ring: otherwise safe empty checks can overrun array bounds

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jan 02, 2018 at 11:52:19AM -0500, David Miller wrote:
> From: John Fastabend <john.fastabend@gmail.com>
> Date: Wed, 27 Dec 2017 19:50:25 -0800
> 
> > When running consumer and/or producer operations and empty checks in
> > parallel its possible to have the empty check run past the end of the
> > array. The scenario occurs when an empty check is run while
> > __ptr_ring_discard_one() is in progress. Specifically after the
> > consumer_head is incremented but before (consumer_head >= ring_size)
> > check is made and the consumer head is zeroe'd.
> > 
> > To resolve this, without having to rework how consumer/producer ops
> > work on the array, simply add an extra dummy slot to the end of the
> > array. Even if we did a rework to avoid the extra slot it looks
> > like the normal case checks would suffer some so best to just
> > allocate an extra pointer.
> > 
> > Reported-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> > Fixes: c5ad119fb6c09 ("net: sched: pfifo_fast use skb_array")
> > Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> 
> Applied, thanks John.

I think that patch is wrong. I'd rather it got reverted.