linux-kernel - Re: [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get

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Date:   Tue, 9 Feb 2021 09:58:45 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        Parav Pandit <parav@...dia.com>, Eli Cohen <elic@...dia.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get_config()

On Tue, Feb 09, 2021 at 11:24:03AM +0800, Jason Wang wrote:
>
>On 2021/2/9 上午2:38, Michael S. Tsirkin wrote:
>>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@...r.kernel.org
>>>Signed-off-by: Stefano Garzarella <sgarzare@...hat.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?
>
>
>I think they're working at different levels. There's no guarantee that 
>vhost-vdpa is the driver for this vdpa device.
>

Maybe we can do these checks in the vdpa_get_config() helper and we can 
also add a vdpa_set_config() to do the same.

Thanks,
Stefano

>
>>
>>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?
>
>
>In this case, get_config() should match the spec behaviour. That is to 
>say the size of config space depends on the feature negotiated.
>
>Thanks
>
>
>>  I think we should
>>allow a bigger size, and return the copied config size to userspace.
>>
>>
>>>-- 
>>>2.29.2
>