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

["Xie, Huawei" <huawei.xie@intel.com>]

On 11/18/2015 10:56 AM, Yuanhan Liu wrote:
> 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.
>
> 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;
Why do we exit when secure_len is 0 rather than 1? :). Malicious guest
could easily forge the desc len so that secure_len never reach pkt_len
even it is not zero so that host enters into dead loop here.
Generally speaking, we shouldn't fix for a specific issue, and the
security checks should be as few as possible. We need to consider
refactor the code here for the generic fix.

>  					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;
>  		}
>