Virtualization - Feb 2021 - [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get_config()

It's legal to have 'offset + len' equal to
sizeof(struct virtio_net_config), since 'ndev->config' is a
'struct virtio_net_config', so we can safely copy its content under
this condition.

Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5
devices")
Cc: stable at vger.kernel.org
Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index dc88559a8d49..10e9b09932eb 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -1820,7 +1820,7 @@ static void mlx5_vdpa_get_config(struct vdpa_device *vdev,
unsigned int offset,
 	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
 	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
 
-	if (offset + len < sizeof(struct virtio_net_config))
+	if (offset + len <= sizeof(struct virtio_net_config))
 		memcpy(buf, (u8 *)&ndev->config + offset, len);
 }
 
-- 
2.29.2

On Mon, Feb 08, 2021 at 05:17:41PM +0100, Stefano Garzarella
wrote:
> It's legal to have 'offset + len' equal to
> sizeof(struct virtio_net_config), since 'ndev->config' is a
> 'struct virtio_net_config', so we can safely copy its content under
> this condition.
> 
> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5
devices")
> Cc: stable at vger.kernel.org
> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>
> ---
>  drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index dc88559a8d49..10e9b09932eb 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -1820,7 +1820,7 @@ static void mlx5_vdpa_get_config(struct vdpa_device
*vdev, unsigned int offset,
>  	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>  	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>  
> -	if (offset + len < sizeof(struct virtio_net_config))
> +	if (offset + len <= sizeof(struct virtio_net_config))
>  		memcpy(buf, (u8 *)&ndev->config + offset, len);
>  }
Actually first I am not sure we need these checks at all.
vhost_vdpa_config_validate already validates the values, right?

Second, what will happen when we extend the struct and then
run new userspace on an old kernel? Looks like it will just
fail right? So what is the plan? I think we should
allow a bigger size, and return the copied config size to userspace.

> -- 
> 2.29.2

On 2021/2/9 ??12:17, Stefano Garzarella wrote:
> It's legal to have 'offset + len' equal to
> sizeof(struct virtio_net_config), since 'ndev->config' is a
> 'struct virtio_net_config', so we can safely copy its content under
> this condition.
>
> Fixes: 1a86b377aa21 ("vdpa/mlx5: Add VDPA driver for supported mlx5
devices")
> Cc: stable at vger.kernel.org
> Signed-off-by: Stefano Garzarella <sgarzare at redhat.com>

Acked-by: Jason Wang <jasowang at redhat.com>

> ---
>   drivers/vdpa/mlx5/net/mlx5_vnet.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c
b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index dc88559a8d49..10e9b09932eb 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -1820,7 +1820,7 @@ static void mlx5_vdpa_get_config(struct vdpa_device
*vdev, unsigned int offset,
>   	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
>   	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>   
> -	if (offset + len < sizeof(struct virtio_net_config))
> +	if (offset + len <= sizeof(struct virtio_net_config))
>   		memcpy(buf, (u8 *)&ndev->config + offset, len);
>   }
>