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

[wangyunjian <wangyunjian@huawei.com>]

> -----Original Message-----
> From: Honnappa Nagarahalli [mailto:Honnappa.Nagarahalli@arm.com]
> Sent: Thursday, May 4, 2023 7:46 AM
> To: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>; wangyunjian
> <wangyunjian@huawei.com>
> Cc: dev@dpdk.org; luyicai <luyicai@huawei.com>; stable@dpdk.org; nd
> <nd@arm.com>; nd <nd@arm.com>
> Subject: RE: [dpdk-dev] [PATCH v2] ring: fix use after free in ring release
> 
> <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.

Thanks, Konstantin Ananyev and Honnappa Nagarahalli.
I will update the patch in v3 and 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
> > >>>>
> > >>>
> > >