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

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

<snip>

> >
> >>>>
> >>>>
> >>>>
> >>>>> 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?
> >>
> >>
> >> Don't know what you mean by 'both suggestions' here.
> > I wrote 'both of our suggestions'. Essentially, in v1, freeing the memzone
> was outside of the lock. I suggested to move it inside and you are suggesting
> to move it inside.
> 
> 
> Ah ok, I missed v1 and your comments for it.
> As I said before, I don't think that we need to hold qlock here while calling
> mmezone_free().
> Though I don't see any harm with it either.
> I'd personally would move memzone_free() after releasing qlock, but if you
> guys prefer to keep it as it is - I wouldn't insist.
I looked at other libraries, stack library is the closest. Stack library frees the memzone outside the lock. I think we should keep it consistent.
I am fine to move the free outside the lock.

> 
> >
> >> I think I gave only one - move memzone_free() after tailq_write_unlock().
> >> To be more precise:
> >> 1) rte_mcfg_tailq_write_lock();
> >> ...
> >> 2) TAILQ_REMOVE(...);
> >> 3) rte_mcfg_tailq_write_unlock();
> >> 4) rte_memzone_free(r->memzone);
> >>
> >> As I remember, memzones are protected by their own lock (mlock), so
> >> we don't need to hold qlock to free a memzone, after ring was already
> >> removed from the ring_list.
> >>
> >>>
> >>> 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).
> >>
> >>
> >> As I understand, it is ok with current design to grab mlock while holding
> qlock.
> >> So, there is nothing wrong with current patch, I just think that in
> >> that case it is excessive, and can be safely avoided.
> >>
> >>>
> >>>> Apart from that, LGTM.
> >>>> Acked-by: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>
> >>>>
> >>>>>    	rte_mcfg_tailq_write_unlock();
> >>>>>
> >>>>>    	rte_free(te);
> >>>>> --
> >>>>> 2.33.0
> >>>>
> >>>
> >