Re: [dpdk-dev] [PATCH] vhost: avoid buffer overflow in update_secure_len

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> Sent: Wednesday, November 18, 2015 10:57 AM
> To: Rich Lane <rich.lane@bigswitch.com>
> Cc: dev@dpdk.org; Xie, Huawei <huawei.xie@intel.com>; Wang, Zhihong
> <zhihong.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
> Subject: Re: [PATCH] vhost: avoid buffer overflow in update_secure_len
> 
> On Tue, Nov 17, 2015 at 08:39:30AM -0800, Rich Lane wrote:
> >
> > I don't think that adding a SIGINT handler is the right solution,
> > though. The guest app could be killed with another signal (SIGKILL).
> 
> Good point.
> 
> > Worse, a malicious or
> > buggy guest could write to just that field. vhost should not crash no
> > matter what the guest writes into the virtqueues.
> 
> Yeah, I agree with you: though we could fix this issue in the source side, we also
> should do some defend here.
> 

Exactly, DPDK should be able to take care of both ends:
# Provide interface for resource cleanup
# Be prepared if the app doesn't shutdown properly

> How about following patch then?
> 
> Note that the vec_id overflow check should be done before referencing it, but
> not after. Hence I moved it ahead.
> 
> 	--yliu
> 
> ---
> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c index
> 9322ce6..08f5942 100644
> --- a/lib/librte_vhost/vhost_rxtx.c
> +++ b/lib/librte_vhost/vhost_rxtx.c
> @@ -132,6 +132,8 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
> 
>  		/* Get descriptor from available ring */
>  		desc = &vq->desc[head[packet_success]];
> +		if (desc->len == 0)
> +			break;
> 
>  		buff = pkts[packet_success];
> 
> @@ -153,6 +155,8 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t queue_id,
>  			/* Buffer address translation. */
>  			buff_addr = gpa_to_vva(dev, desc->addr);
>  		} else {
> +			if (desc->len < vq->vhost_hlen)
> +				break;
>  			vb_offset += vq->vhost_hlen;
>  			hdr = 1;
>  		}
> @@ -446,6 +450,9 @@ update_secure_len(struct vhost_virtqueue *vq, uint32_t
> id,
>  	uint32_t vec_id = *vec_idx;
> 
>  	do {
> +		if (vec_id >= BUF_VECTOR_MAX)
> +			break;
> +
>  		next_desc = 0;
>  		len += vq->desc[idx].len;
>  		vq->buf_vec[vec_id].buf_addr = vq->desc[idx].addr; @@ -519,6
> +526,8 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
>  					goto merge_rx_exit;
>  				} else {
>  					update_secure_len(vq, res_cur_idx, &secure_len,
> &vec_idx);
> +					if (secure_len == 0)
> +						goto merge_rx_exit;
>  					res_cur_idx++;
>  				}
>  			} while (pkt_len > secure_len);
> @@ -631,6 +640,8 @@ rte_vhost_dequeue_burst(struct virtio_net *dev,
> uint16_t queue_id,
>  		uint8_t alloc_err = 0;
> 
>  		desc = &vq->desc[head[entry_success]];
> +		if (desc->len == 0)
> +			break;
> 
>  		/* Discard first buffer as it is the virtio header */
>  		if (desc->flags & VRING_DESC_F_NEXT) { @@ -638,6 +649,8 @@
> rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
>  			vb_offset = 0;
>  			vb_avail = desc->len;
>  		} else {
> +			if (desc->len < vq->vhost_hlen)
> +				break;
>  			vb_offset = vq->vhost_hlen;
>  			vb_avail = desc->len - vb_offset;
>  		}