vhost: fix virtqueues metadata allocation

The Vhost-user backend implementation assumes there will be
no holes in the device's array of virtqueues metadata
pointers.

It can happen though, and would cause segmentation faults,
memory leaks or undefined behaviour.

This patch keep the assumption that there is no holes in this
array, and allocate all uninitialized virtqueues metadata up
to requested index.

Fixes: 160cbc8 ("vhost: remove a hack on queue allocation")
Cc: stable@dpdk.org

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

lib/librte_vhost/vhost.c

@@ -579,22 +579,29 @@ int
 alloc_vring_queue(struct virtio_net *dev, uint32_t vring_idx)
 {
 	struct vhost_virtqueue *vq;
+	uint32_t i;
 
-	vq = rte_malloc(NULL, sizeof(struct vhost_virtqueue), 0);
-	if (vq == NULL) {
-		VHOST_LOG_CONFIG(ERR,
-			"Failed to allocate memory for vring:%u.\n", vring_idx);
-		return -1;
-	}
+	/* Also allocate holes, if any, up to requested vring index. */
+	for (i = 0; i <= vring_idx; i++) {
+		if (dev->virtqueue[i])
+			continue;
 
-	dev->virtqueue[vring_idx] = vq;
-	init_vring_queue(dev, vring_idx);
-	rte_spinlock_init(&vq->access_lock);
-	vq->avail_wrap_counter = 1;
-	vq->used_wrap_counter = 1;
-	vq->signalled_used_valid = false;
+		vq = rte_malloc(NULL, sizeof(struct vhost_virtqueue), 0);
+		if (vq == NULL) {
+			VHOST_LOG_CONFIG(ERR,
+				"Failed to allocate memory for vring:%u.\n", i);
+			return -1;
+		}
+
+		dev->virtqueue[i] = vq;
+		init_vring_queue(dev, vring_idx);
+		rte_spinlock_init(&vq->access_lock);
+		vq->avail_wrap_counter = 1;
+		vq->used_wrap_counter = 1;
+		vq->signalled_used_valid = false;
+	}
 
-	dev->nr_vring += 1;
+	dev->nr_vring = RTE_MAX(dev->nr_vring, vring_idx + 1);
 
 	return 0;
 }