Re: [PATCH] vhost/vdpa: reject VRING_NUM larger than device max

[Michael S. Tsirkin]

On Sat, Aug 08, 2026 at 06:34:15PM +0800, Jia Jia wrote:
> vhost_vring_set_num() only requires a non-zero power-of-two that fits
> in 16 bits. vhost-vdpa then hands that value to the backend through
> set_vq_num() without comparing it to get_vq_num_max().
> 
> A local process with access to /dev/vhost-vdpa-* can therefore set a
> queue size larger than the device advertises. On the vdpa_sim backend,
> the worker then walks descriptors beyond the mapped descriptor ring.
> KASAN reports a 16-byte out-of-bounds read, corresponding to one
> vring_desc, in the vringh IOTLB path:
> 
>   BUG: KASAN: out-of-bounds in _copy_from_iter
>   Read of size 16
>   copy_from_iotlb
>   copydesc_iotlb
>   vringh_getdesc_iotlb
>   vdpasim_net_work
> 
> Check the requested size against get_vq_num_max() in
> vhost_vdpa_vring_ioctl() before calling vhost_vring_ioctl(), and return
> -EINVAL when the request is too large.
> 
> Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")

sign off missing

> ---
>  drivers/vhost/vdpa.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ac55275fa0d0..b2083e1ef150 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -716,6 +716,13 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  				vhost_vdpa_unsetup_vq_irq(v, idx);
>  		}
>  		break;
> +	case VHOST_SET_VRING_NUM:
> +		/* Reject sizes above the max reported by the device. */
> +		if (copy_from_user(&s, argp, sizeof(s)))
> +			return -EFAULT;
> +		if (s.num > ops->get_vq_num_max(vdpa))
> +			return -EINVAL;
> +		break;
>  	}
>  
>  	r = vhost_vring_ioctl(&v->vdev, cmd, argp);
> -- 
> 2.34.1