On Wed, Apr 11, 2018 at 07:54:12PM -0700, Andy Lutomirski wrote:

On Wed, Apr 11, 2018 at 1:33 PM, Greg KH [off-list ref] wrote:

quoted

On Wed, Apr 11, 2018 at 09:09:16PM +0100, David Howells wrote:

quoted

Greg KH [off-list ref] wrote:

quoted

Why not just disable debugfs entirely?  This half-hearted way to sorta
lock it down is odd, it is meant to not be there at all, nothing in your
normal system should ever depend on it.

So again just don't allow it to be mounted at all, much simpler and more
obvious as to what is going on.

Yeah, I agree - and then I got complaints because it seems that it's been
abused to allow drivers and userspace components to communicate.

With in-kernel code?  Please let me know and I'll go fix it up to not
allow that, as that is not ok.

I do know of some bad examples of out-of-tree code abusing debugfs to do
crazy things (battery level monitoring?), but that's their own fault...

debugfs is for DEBUGGING!  For anything you all feel should be "secure",
then just disable it entirely.

Debugfs is very, very useful for, ahem, debugging.  I really think
this is an example of why we should split lockdown into the read and
write varieties and allow mounting and reading debugfs when only write
is locked down.

Ok, but be sure that there are no "secrets" in those debugging files if
you really buy into the whole "lock down" mess...

Really, it's easier to just disable the whole thing.

greg k-h