From: Vasiliy Kulikov <segoon@openwall.com>
To: Greg KH <gregkh@suse.de>
Cc: linux-kernel@vger.kernel.org, Kees Cook <kees.cook@canonical.com>,
Eugene Teo <eugeneteo@gmail.com>
Subject: Re: [RFC] add mount options to sysfs
Date: Wed, 18 May 2011 21:05:45 +0400 [thread overview]
Message-ID: <20110518170545.GA4435@albatros> (raw)
In-Reply-To: <20110518163951.GA24143@suse.de>
On Wed, May 18, 2011 at 09:39 -0700, Greg KH wrote:
> On Wed, May 18, 2011 at 08:31:44PM +0400, Vasiliy Kulikov wrote:
> > Currently there is no good way to effectively globally restrict an
> > access to sysfs files. It's possible only to chmod the sysfs'
> > root/directories to fully deny access to sysfs (sub-)tree to some users
> > or chmod files after they are created. The latter approach is racy,
> > however.
>
> Why do you want to do this? What is in sysfs files that is not
> gloabally ok to access? That should be fixed first, if at all, instead
> of wanting to modify the whole sysfs tree, right?
I don't hide the goal (I didn't find any other weird permissions, if
you mean this). It is primary about additional global controlable
layer of defining permission:
1) *IF* another sensitive file with weird permissions is found, mount
option is IMO the best temporary workaround.
2) Somebody might be worried about information leaks via world readable
files - not strict bugs, but leaks in sense of local policy. See numerous
discussions about hiding kernel addresses - there is no unified opinion
about it. Some admins would be happy with denying access to almost all
system information except some white list.
> > The patch introduces sysfs mount options parsing and adds 4 new options:
> > uid, gid, mode and umask. uid, gid, and umask are classical options,
> > mode is a global restricting mode mask that defined the most relaxed
> > possible file mode. E.g. if mode=0750 then "chmod 0664" changes file's
> > permissions to 0640.
>
> What is going to break if you do this? Have you tested it? I'd be very
> worried about this.
I've tested it on my laptop (I'm writing booted with this kernel). By
default nothing has changed (umask=0000, mode=0777). Mounting sysfs
with mode=0770 leads to the predictable state - no sysfs information is
available to nonroot, e.g. no ACPI battery state. umask is tested with
pluging a USB flash.
mode has one advantage over umask. It is temporary - "mount -o
remount,mode=0777" restores the initial state.
I'd want to implement similar options for debugfs.
Thanks,
--
Vasiliy
next prev parent reply other threads:[~2011-05-18 17:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-18 16:31 [RFC] add mount options to sysfs Vasiliy Kulikov
2011-05-18 16:39 ` Greg KH
2011-05-18 17:05 ` Vasiliy Kulikov [this message]
2011-05-18 19:17 ` Greg KH
2011-05-19 6:26 ` Vasiliy Kulikov
2011-05-19 17:12 ` Greg KH
2011-05-20 9:59 ` Vasiliy Kulikov
2011-05-20 13:30 ` Greg KH
2011-05-20 13:34 ` Vasiliy Kulikov
2011-05-20 13:36 ` Vasiliy Kulikov
2011-05-20 13:54 ` Greg KH
2011-05-20 15:17 ` Kees Cook
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