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

[Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>]

03/05/2023 06:44, Honnappa Nagarahalli пишет:
> <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 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
>>>>
>>>
>