RE: [dpdk-dev] [PATCH v2] ring: fix use after free in ring release

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> -----Original Message-----
> From: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>
> Sent: Monday, May 1, 2023 7:32 AM
> To: wangyunjian@huawei.com
> Cc: dev@dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; konstantin.v.ananyev@yandex.ru;
> luyicai@huawei.com; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] ring: fix use after free in ring release
> 
> 
> 
> > After the memzone is freed, it is not removed from the 'rte_ring_tailq'.
> > If rte_ring_lookup is called at this time, it will cause a
> > use-after-free problem. This change prevents that from happening.
> >
> > Fixes: 4e32101f9b01 ("ring: support freeing")
> > Cc: stable@dpdk.org
> >
> > Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> > ---
> > v2: update code suggested by Honnappa Nagarahalli
> > ---
> >  lib/ring/rte_ring.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/lib/ring/rte_ring.c b/lib/ring/rte_ring.c index
> > 8ed455043d..2755323b8a 100644
> > --- a/lib/ring/rte_ring.c
> > +++ b/lib/ring/rte_ring.c
> > @@ -333,11 +333,6 @@ rte_ring_free(struct rte_ring *r)
> >  		return;
> >  	}
> >
> > -	if (rte_memzone_free(r->memzone) != 0) {
> > -		RTE_LOG(ERR, RING, "Cannot free memory\n");
> > -		return;
> > -	}
> > -
> >  	ring_list = RTE_TAILQ_CAST(rte_ring_tailq.head, rte_ring_list);
> >  	rte_mcfg_tailq_write_lock();
> >
> > @@ -354,6 +349,9 @@ rte_ring_free(struct rte_ring *r)
> >
> >  	TAILQ_REMOVE(ring_list, te, next);
> >
> > +	if (rte_memzone_free(r->memzone) != 0)
> > +		RTE_LOG(ERR, RING, "Cannot free memory\n");
> > +
> 
> I nit: I think it is a bit better to first release the lock and then free the
> memzone.
I think both of our suggestions are contradictory. Any reason why you want to free outside the locked region?

I thought, since it belongs to the ring being freed, it makes sense to free it while holding the lock to avoid any race conditions (though, I have not checked what those are).

> Apart from that, LGTM.
> Acked-by: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>
> 
> >  	rte_mcfg_tailq_write_unlock();
> >
> >  	rte_free(te);
> > --
> > 2.33.0
>