[dpdk-stable] [PATCH] vhost: fix potential buffer overflow

[Marvin Liu <yong.liu@intel.com>]

In vhost datapath, descriptor's length are mostly used in two coherent
operations. First step is used for address translation, second step is
used for memory transaction from guest to host. But the iterval between
two steps will give a window for malicious guest, in which can change
descriptor length after vhost calcuated buffer size. Thus may lead to
buffer overflow in vhost side. This potential risk can be eliminated by
accessing the descriptor length once.

Fixes: 1be4ebb1c464 ("vhost: support indirect descriptor in mergeable Rx")
Fixes: 2f3225a7d69b ("vhost: add vector filling support for packed ring")
Fixes: 75ed51697820 ("vhost: add packed ring batch dequeue")

Signed-off-by: Marvin Liu <yong.liu@intel.com>
Cc: stable@dpdk.org

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 583bf379c6..0a7d008a91 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -548,10 +548,11 @@ fill_vec_buf_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			return -1;
 		}
 
-		len += descs[idx].len;
+		dlen = descs[idx].len;
+		len += dlen;
 
 		if (unlikely(map_one_desc(dev, vq, buf_vec, &vec_id,
-						descs[idx].addr, descs[idx].len,
+						descs[idx].addr, dlen,
 						perm))) {
 			free_ind_table(idesc);
 			return -1;
@@ -668,9 +669,10 @@ fill_vec_buf_packed_indirect(struct virtio_net *dev,
 			return -1;
 		}
 
-		*len += descs[i].len;
+		dlen = descs[i].len;
+		*len += dlen;
 		if (unlikely(map_one_desc(dev, vq, buf_vec, &vec_id,
-						descs[i].addr, descs[i].len,
+						descs[i].addr, dlen,
 						perm)))
 			return -1;
 	}
@@ -691,6 +693,7 @@ fill_vec_buf_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	bool wrap_counter = vq->avail_wrap_counter;
 	struct vring_packed_desc *descs = vq->desc_packed;
 	uint16_t vec_id = *vec_idx;
+	uint64_t dlen;
 
 	if (avail_idx < vq->last_avail_idx)
 		wrap_counter ^= 1;
@@ -723,11 +726,12 @@ fill_vec_buf_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 							len, perm) < 0))
 				return -1;
 		} else {
-			*len += descs[avail_idx].len;
+			dlen = descs[avail_idx].len;
+			*len += dlen;
 
 			if (unlikely(map_one_desc(dev, vq, buf_vec, &vec_id,
 							descs[avail_idx].addr,
-							descs[avail_idx].len,
+							dlen,
 							perm)))
 				return -1;
 		}
@@ -2314,7 +2318,7 @@ vhost_reserve_avail_batch_packed(struct virtio_net *dev,
 	}
 
 	vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
-		pkts[i]->pkt_len = descs[avail_idx + i].len - buf_offset;
+		pkts[i]->pkt_len = lens[i] - buf_offset;
 		pkts[i]->data_len = pkts[i]->pkt_len;
 		ids[i] = descs[avail_idx + i].id;
 	}
-- 
2.17.1