Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path()

[Matthew Wilcox]

On Thu, Jul 25, 2019 at 12:05:29PM -0700, Sagi Grimberg wrote:
> 
> > > > NVMe-OF is configured using configfs. The target is specified by the
> > > > user writing a path to a configfs attribute. This is the way it works
> > > > today but with blkdev_get_by_path()[1]. For the passthru code, we need
> > > > to get a nvme_ctrl instead of a block_device, but the principal is the same.
> > > 
> > > Why isn't a fd being passed in there instead of a random string?
> > 
> > I suppose we could echo a string of the file descriptor number there,
> > and look up the fd in the process' file descriptor table ...
> 
> Assuming that there is a open handle somewhere out there...

Well, that's how we'd know that the application echoing /dev/nvme3 into
configfs actually has permission to access /dev/nvme3.  Think about
containers, for example.  It's not exactly safe to mount configfs in a
non-root container since it can access any NVMe device in the system,
not just ones which it's been given permission to access.  Right?