vhost: validate index in available entries API

This patch validates the queue index parameter, in order
to ensure neither out-of-bound accesses nor NULL pointer
dereferencing happen.

Fixes: a67f286a65 ("vhost: export queue free entries")
Cc: stable@dpdk.org

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>

lib/librte_vhost/vhost.c

@@ -1260,7 +1260,12 @@ rte_vhost_avail_entries(int vid, uint16_t queue_id)
 	if (!dev)
 		return 0;
 
+	if (queue_id >= VHOST_MAX_VRING)
+		return 0;
+
 	vq = dev->virtqueue[queue_id];
+	if (!vq)
+		return 0;
 
 	rte_spinlock_lock(&vq->access_lock);