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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Marvin,

On 2/26/21 8:33 AM, Marvin Liu wrote:
> 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")

As the offending commits have been introduced in different LTS, I would
prefer the patch to be split. It will make is easier for backporting later.

> 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;
>  	}
> 

Other than that, the patch looks valid to me.
With the split done:

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime