Re: [PATCH V3 6/6] ublk_drv: add mechanism for supporting unprivileged ublk device

[Ming Lei <ming.lei@redhat.com>]

Hi Jonathan,

On Tue, Jan 03, 2023 at 01:35:14PM -0700, Jonathan Corbet wrote:
> I have one quick question...
> 
> Ming Lei <ming.lei@redhat.com> writes:
> 
> > In case of UBLK_F_UNPRIVILEGED_DEV:
> >
> > 1) for command UBLK_CMD_ADD_DEV, it is always allowed, and user needs
> > to provide owner's uid/gid in this command, so that udev can set correct
> > ownership for the created ublk device, since the device owner uid/gid
> > can be queried via command of UBLK_CMD_GET_DEV_INFO.
> 
> Why do you have the user provide the uid/gid rather than just using the
> user's credentials directly?  It seems a bit strange to me to let
> unprivileged users create devices with arbitrary ownership.  What am I
> missing here?

It is one good question.

The original idea is to allow user A to create device for another user
B, and it still depends on user A's capability, such as, if the created
daemon can open the created device which is owned by user B actually.

The above behavior may be extended in future if there is such
requirement. I will switch to just allow to create device for the
current user in V4, then we can start with this easy/simple model.

BTW, that is exactly the current userspace implementation, only the
current uid/gid is passed.

	https://github.com/ming1/ubdsrv/tree/unprivileged-ublk


Thanks,
Ming