Re: [dpdk-dev] [PATCH v2] vhost: fix segfault on bad descriptor address

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Thu, Jul 14, 2016 at 11:18:39AM +0300, Ilya Maximets wrote:
> In current implementation vhost will crash with segmentation fault
> if malicious or buggy virtio application breaks addresses of descriptors.
> 
> Before commit 0823c1cb0a73 this crash was reproducible even with
> normal DPDK application that tries to change number of virtqueues
> dynamically inside VM.
> 
> Fix that by checking addresses of descriptors before using.
> 
> Also fixed return value on error for 'copy_mbuf_to_desc_mergeable()'
> from '-1' to '0' because it returns unsigned value and it means
> number of used descriptors.

Yeah, that's a good fix. Thanks.

Maybe you'd better make it a standalone patch.

> Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
> ---
> Version 2:
> 	* Rebased on top of current master.
> 	* host's address now checked in meargeable case,
> 	  because needed refactoring already done.
> 	* Commit-message changed because old issue with
> 	  virtio reload accidentially fixed by commit
> 	  0823c1cb0a73.
> 
>  lib/librte_vhost/vhost_rxtx.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> index 15ca956..31e8b58 100644
> --- a/lib/librte_vhost/vhost_rxtx.c
> +++ b/lib/librte_vhost/vhost_rxtx.c
> @@ -147,10 +147,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
>  
>  	desc = &vq->desc[desc_idx];
> -	if (unlikely(desc->len < dev->vhost_hlen))
> +	desc_addr = gpa_to_vva(dev, desc->addr);
> +	if (unlikely(desc->len < dev->vhost_hlen || !desc_addr))
>  		return -1;

So, you discards the workaround from Rich?

>  
> -	desc_addr = gpa_to_vva(dev, desc->addr);
>  	rte_prefetch0((void *)(uintptr_t)desc_addr);
>  
>  	virtio_enqueue_offload(m, &virtio_hdr.hdr);
> @@ -182,7 +182,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  				return -1;
>  
>  			desc = &vq->desc[desc->next];
> -			desc_addr   = gpa_to_vva(dev, desc->addr);
> +			desc_addr = gpa_to_vva(dev, desc->addr);
> +			if (unlikely(!desc_addr))
> +				return -1;
> +
>  			desc_offset = 0;
>  			desc_avail  = desc->len;
>  		}
> @@ -387,10 +390,10 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	LOG_DEBUG(VHOST_DATA, "(%d) current index %d | end index %d\n",
>  		dev->vid, cur_idx, end_idx);
>  
> -	if (buf_vec[vec_idx].buf_len < dev->vhost_hlen)
> -		return -1;
> -
>  	desc_addr = gpa_to_vva(dev, buf_vec[vec_idx].buf_addr);
> +	if (buf_vec[vec_idx].buf_len < dev->vhost_hlen || !desc_addr)
> +		return 0;
> +
>  	rte_prefetch0((void *)(uintptr_t)desc_addr);
>  
>  	virtio_hdr.num_buffers = end_idx - start_idx;
> @@ -425,6 +428,8 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  
>  			vec_idx++;
>  			desc_addr = gpa_to_vva(dev, buf_vec[vec_idx].buf_addr);
> +			if (unlikely(!desc_addr))
> +				return 0;
>  
>  			/* Prefetch buffer address. */
>  			rte_prefetch0((void *)(uintptr_t)desc_addr);
> @@ -507,7 +512,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
>  		*(volatile uint16_t *)&vq->used->idx += nr_used;
>  		vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
>  			sizeof(vq->used->idx));
> -		vq->last_used_idx = end;
> +		vq->last_used_idx += nr_used;

Ditto, this may deserve another patch, too.

	--yliu