ring: fix use after free

[ upstream commit ce4bd6e14aa693c80c5218f7d896c98b3b85b54a ]

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: 4e32101 ("ring: support freeing")

Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

lib/librte_ring/rte_ring.c

@@ -341,11 +341,6 @@ 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();
 
@@ -364,6 +359,9 @@ rte_ring_free(struct rte_ring *r)
 
 	rte_mcfg_tailq_write_unlock();
 
+	if (rte_memzone_free(r->memzone) != 0)
+		RTE_LOG(ERR, RING, "Cannot free memory\n");
+
 	rte_free(te);
 }