linux-kernel - Re: [PATCH 24/24] debugfs: Restrict debugfs when the kernel is locked down

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Message-ID: <20180413202241.GB4484@amd>
Date:   Fri, 13 Apr 2018 22:22:41 +0200
From:   Pavel Machek <pavel@....cz>
To:     David Howells <dhowells@...hat.com>
Cc:     torvalds@...ux-foundation.org, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, jmorris@...ei.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 24/24] debugfs: Restrict debugfs when the kernel is
 locked down

On Wed 2018-04-11 17:27:16, David Howells wrote:
> 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).

This has nothing to do with the lockdown goals, right? I find chown of
such files quite nice, to allow debugging without doing sudo all the time.

>  (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

Dunno. Would not it be nicer to go through the debugfs files and split
them into safe/unsafe varieties?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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