[PATCH v2] nvme: remove unprivileged passthrough support

[Christoph Hellwig]

On Mon, Oct 23, 2023 at 09:18:36AM -0600, Keith Busch wrote:
> On Mon, Oct 23, 2023 at 07:44:56AM +0200, Christoph Hellwig wrote:
> > Yes, you need someone with root access to change the device node
> > persmissions.  But we allowed that under the assumption it is safe
> > to do so, which it turns out it is not.
> 
> Okay, iiuc, while we have to opt-in to allow this hole, we need another
> option for users to set to allow this usage because it's not safe.
> 
> Here are two options I have considered for unpriveledged access, please
> let me know if you have others or thoughts.
> 
>   Restrict access for processes with CAP_SYS_RAWIO, which can be granted
>   to non-root users. This cap is already used in scsi subsystem, too.

Well, that's sensible in general.

>   A per nvme-generic namespace sysfs attribute that only root can toggle
>   that would override any caps and just rely on access permissions.

And that I'm not confident about as long as we can only use the broken
PRP scheme on NVMe.