Re: [PATCH V31 25/25] debugfs: Disable open() when kernel is locked down

[Greg KH]

On Tue, Mar 26, 2019 at 12:20:24PM -0700, Andy Lutomirski wrote:
> On Tue, Mar 26, 2019 at 11:28 AM Matthew Garrett
> <matthewgarrett@xxxxxxxxxx> wrote:
> >
> > From: Matthew Garrett <mjg59@xxxxxxxxxx>
> >
> > debugfs has not been meaningfully audited in terms of ensuring that
> > userland cannot trample over the kernel. At Greg's request, disable
> > access to it entirely when the kernel is locked down. This is done at
> > open() time rather than init time as the kernel lockdown status may be
> > made stricter at runtime.
> 
> Ugh.  Some of those files are very useful.  Could this perhaps still
> allow O_RDONLY if we're in INTEGRITY mode?

Useful for what?  Debugging, sure, but for "normal operation", no kernel
functionality should ever require debugfs.  If it does, that's a bug and
should be fixed.

thanks,

greg k-h