linux-kernel - Re: [PATCH v3 09/13] vhost/vdpa: remove vhost_vdpa_config

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Date:   Fri, 5 Feb 2021 11:27:32 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     Xie Yongji <xieyongji@...edance.com>, kvm@...r.kernel.org,
        Laurent Vivier <lvivier@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        linux-kernel@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3 09/13] vhost/vdpa: remove vhost_vdpa_config_validate()


On 2021/2/5 上午1:22, Stefano Garzarella wrote:
> get_config() and set_config() callbacks in the 'struct vdpa_config_ops'
> usually already validated the inputs. Also now they can return an error,
> so we don't need to validate them here anymore.
>
> Let's use the return value of these callbacks and return it in case of
> error in vhost_vdpa_get_config() and vhost_vdpa_set_config().
>
> Originally-by: Xie Yongji <xieyongji@...edance.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>   drivers/vhost/vdpa.c | 41 +++++++++++++----------------------------
>   1 file changed, 13 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ef688c8c0e0e..d61e779000a8 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -185,51 +185,35 @@ static long vhost_vdpa_set_status(struct vhost_vdpa *v, u8 __user *statusp)
>   	return 0;
>   }
>   
> -static int vhost_vdpa_config_validate(struct vhost_vdpa *v,
> -				      struct vhost_vdpa_config *c)
> -{
> -	long size = 0;
> -
> -	switch (v->virtio_id) {
> -	case VIRTIO_ID_NET:
> -		size = sizeof(struct virtio_net_config);
> -		break;
> -	}
> -
> -	if (c->len == 0)
> -		return -EINVAL;
> -
> -	if (c->len > size - c->off)
> -		return -E2BIG;
> -
> -	return 0;
> -}
> -
>   static long vhost_vdpa_get_config(struct vhost_vdpa *v,
>   				  struct vhost_vdpa_config __user *c)
>   {
>   	struct vdpa_device *vdpa = v->vdpa;
>   	struct vhost_vdpa_config config;
>   	unsigned long size = offsetof(struct vhost_vdpa_config, buf);
> +	long ret;
>   	u8 *buf;
>   
>   	if (copy_from_user(&config, c, size))
>   		return -EFAULT;
> -	if (vhost_vdpa_config_validate(v, &config))
> +	if (config.len == 0)
>   		return -EINVAL;
>   	buf = kvzalloc(config.len, GFP_KERNEL);


Then it means usersapce can allocate a very large memory.

Rethink about this, we should limit the size here (e.g PAGE_SIZE) or 
fetch the config size first (either through a config ops as you 
suggested or a variable in the vdpa device that is initialized during 
device creation).

Thanks

>   	if (!buf)
>   		return -ENOMEM;
>   
> -	vdpa_get_config(vdpa, config.off, buf, config.len);
> +	ret = vdpa_get_config(vdpa, config.off, buf, config.len);
> +	if (ret)
> +		goto out;
>   
>   	if (copy_to_user(c->buf, buf, config.len)) {
> -		kvfree(buf);
> -		return -EFAULT;
> +		ret = -EFAULT;
> +		goto out;
>   	}
>   
> +out:
>   	kvfree(buf);
> -	return 0;
> +	return ret;
>   }
>   
>   static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> @@ -239,21 +223,22 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
>   	const struct vdpa_config_ops *ops = vdpa->config;
>   	struct vhost_vdpa_config config;
>   	unsigned long size = offsetof(struct vhost_vdpa_config, buf);
> +	long ret;
>   	u8 *buf;
>   
>   	if (copy_from_user(&config, c, size))
>   		return -EFAULT;
> -	if (vhost_vdpa_config_validate(v, &config))
> +	if (config.len == 0)
>   		return -EINVAL;
>   
>   	buf = vmemdup_user(c->buf, config.len);
>   	if (IS_ERR(buf))
>   		return PTR_ERR(buf);
>   
> -	ops->set_config(vdpa, config.off, buf, config.len);
> +	ret = ops->set_config(vdpa, config.off, buf, config.len);
>   
>   	kvfree(buf);
> -	return 0;
> +	return ret;
>   }
>   
>   static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)