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Subject: Re: [PATCH] vdpa/mlx5: fix param validation in mlx5_vdpa_get_config()
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>
Cc:     virtualization@lists.linux-foundation.org,
        Parav Pandit <parav@nvidia.com>, Eli Cohen <elic@nvidia.com>,
        linux-kernel@vger.kernel.org
References: <20210208161741.104939-1-sgarzare@redhat.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <fc523fbe-b742-0ebe-84d1-2b7e5529f00b@redhat.com>
Date:   Tue, 9 Feb 2021 11:24:03 +0800
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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@vger.kernel.org
>> Signed-off-by: Stefano Garzarella <sgarzare@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?


I think they're working at different levels. There's no guarantee that 
vhost-vdpa is the driver for this vdpa device.


>
> 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