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

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

> -----Original Message-----
> From: Yunjian Wang <wangyunjian@huawei.com>
> Sent: Monday, April 17, 2023 8:12 AM
> To: dev@dpdk.org
> Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>;
> konstantin.v.ananyev@yandex.ru; luyicai@huawei.com; Yunjian Wang
> <wangyunjian@huawei.com>; stable@dpdk.org
> Subject: [dpdk-dev] [PATCH] ring: fix use after free in ring release
> 
> When using the ring to find out tailq entry, however it had been freed by
> rte_memzone_free function. This change prevents that from happening.
I am unable to follow the problem you are describing.
After the memzone for the ring is released, the contents of the memzone are not being used. I understand that the variable 'r' is being used, but that should not cause any issues.

> 
> Fixes: 4e32101f9b01 ("ring: support freeing")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> ---
>  lib/ring/rte_ring.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/ring/rte_ring.c b/lib/ring/rte_ring.c index
> 8ed455043d..17d2d7f8a8 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;
> -	}
Why do we need to free the memzone later?

> -
>  	ring_list = RTE_TAILQ_CAST(rte_ring_tailq.head, rte_ring_list);
>  	rte_mcfg_tailq_write_lock();
> 
> @@ -349,7 +344,7 @@ rte_ring_free(struct rte_ring *r)
> 
>  	if (te == NULL) {
>  		rte_mcfg_tailq_write_unlock();
> -		return;
> +		goto free_memzone;
>  	}
> 
>  	TAILQ_REMOVE(ring_list, te, next);
> @@ -357,6 +352,10 @@ rte_ring_free(struct rte_ring *r)
>  	rte_mcfg_tailq_write_unlock();
> 
>  	rte_free(te);
> +
> +free_memzone:
> +	if (rte_memzone_free(r->memzone) != 0)
> +		RTE_LOG(ERR, RING, "Cannot free memory\n");
>  }
> 
>  /* dump the status of the ring on the console */
> --
> 2.33.0