linux-kernel - Re: [RFC] add mount options to sysfs

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Date:	Fri, 20 May 2011 13:59:20 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, Kees Cook <kees.cook@...onical.com>,
	Eugene Teo <eugeneteo@...il.com>
Subject: Re: [RFC] add mount options to sysfs

On Thu, May 19, 2011 at 10:12 -0700, Greg KH wrote:
> On Thu, May 19, 2011 at 10:26:23AM +0400, Vasiliy Kulikov wrote:
> > On Wed, May 18, 2011 at 12:17 -0700, Greg KH wrote:
> > > Maybe, but fixing the file would be the obvious solution.
> > 
> > I mean for a sysadmin, not for a developer.
> 
> And I mean for the developer.
> 
> We have checks in place now to prevent this type of thing from happening
> again in the future.  If it does, and it might, we will fix it, it's
> that simple.

Simple indeed.  But not as fast as simple:

https://lkml.org/lkml/2011/2/4/74
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=49d50fb1c28738ef6bad0c2b87d5355a1653fed5

More than 40 days from the report to the actual commit.  Sometimes it
needs some workaround.

> > What do you mean by "breaking system"?  Root is able to chmod
> > and chown sysfs files already, he may do "chmod -R" or similar.
> > I suggest sane, race free way to globally restrict permissions *IF* root
> > wants it.
> 
> If root wants it, they can do this today with a simple 1 line bash
> command, so I don't see the issue.

The issue is a race condition between the file creation and chmod'ing.

> > Here https://lkml.org/lkml/2011/2/25/300 you, not aware of usefull
> > applications of world-writable debugfs file, agreeded to statically
> > restrict permissions of all files.  I suggest more flexible and
> > configurable in runtime solution.  It doesn't break anything - default
> > behaviour doesn't differ from current one.  What has changed in your
> > mind since 2/25?
> 
> That's debugfs, not sysfs, which we are talking about here, right?

Correct.  So, if I understood you, you are OK with adding mount options
for debugfs, but not sysfs, right?  What is the difference between them
in sense of permissions?


Thanks,

-- 
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments
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