Re: [PATCH v3 09/13] vhost/vdpa: remove vhost_vdpa_config_validate()

[Stefano Garzarella]

On Fri, Feb 05, 2021 at 08:32:37AM -0500, Michael S. Tsirkin wrote:
> On Fri, Feb 05, 2021 at 10:16:51AM +0100, Stefano Garzarella wrote:
> > On Fri, Feb 05, 2021 at 11:27:32AM +0800, Jason Wang wrote:
> > >
> > > 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@xxxxxxxxxxxxx>
> > > > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > > > ---
> > > >  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.
> >
> > Good point.
> >
> > >
> > > 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).
> >
> > Maybe PAGE_SIZE is okay as a limit.
> >
> > If instead we want to fetch the config size, then better a config ops in my
> > opinion, to avoid adding a new parameter to __vdpa_alloc_device().
> >
> > I vote for PAGE_SIZE, but it isn't a strong opinion.
> >
> > What do you and @Michael suggest?
> >
> > Thanks,
> > Stefano
>
> Devices know what the config size is. Just have them provide it.

Okay, I'll add get_config_size() callback in vdpa_config_ops and I'll 
leave vhost_vdpa_config_validate() that will use that callback instead 
of 'virtio_id' to get the config size from the device.

At this point I think I can remove the "vdpa: add return value to 
get_config/set_config callbacks" patch and leave void return to 
get_config/set_config callbacks.

Does this make sense?

Thanks,
Stefano