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SubjectRe: [PATCH 25/27] debugfs: Restrict debugfs when the kernel is locked down
On Mon, Mar 25, 2019 at 03:09:52PM -0700, Matthew Garrett wrote:
> From: David Howells <dhowells@redhat.com>
>
> Disallow opening of debugfs files that might be used to muck around when
> the kernel is locked down as various drivers give raw access to hardware
> through debugfs. Given the effort of auditing all 2000 or so files and
> manually fixing each one as necessary, I've chosen to apply a heuristic
> instead. The following changes are made:
>
> (1) chmod and chown are disallowed on debugfs objects (though the root dir
> can be modified by mount and remount, but I'm not worried about that).
>
> (2) When the kernel is locked down, only files with the following criteria
> are permitted to be opened:
>
> - The file must have mode 00444
> - The file must not have ioctl methods
> - The file must not have mmap
>
> (3) When the kernel is locked down, files may only be opened for reading.
>
> Normal device interaction should be done through configfs, sysfs or a
> miscdev, not debugfs.

Then why not just not allow debugfs at all if it is such a "big
problem"?

Actually, it is a big problem, and I am pushing for systems to not mount
debugfs at all these days, but that's a different story...

Just "disabling" it entirely for this crazy dream of a "locked down"
kernel is fine for me.

thanks,

greg k-h

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