linux-kernel - Re: [PATCH v2 resend] vfs: new O

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Date:	Mon, 9 Nov 2009 09:58:03 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk, dhowells@...hat.com, hch@...radead.org,
	adilger@....com, mtk.manpages@...il.com,
	torvalds@...ux-foundation.org, drepper@...il.com,
	jamie@...reable.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 resend] vfs: new O_NODE open flag

On Fri 2009-11-06 12:55:33, Eric W. Biederman wrote:
> Pavel Machek <pavel@....cz> writes:
> 
> > On Thu 2009-11-05 15:27:06, Miklos Szeredi wrote:
> >> On Thu, 5 Nov 2009, Alan Cox wrote:
> >> > >  - re-opening normally after checking file type (there's a debate
> >> > >    whether this would have security issues, but currently we do allow
> >> > >    re-opening with increased permissions thorugh /proc/*/fd)
> >> > 
> >> > Which has already been demonstrated to be an (unfixed) security hole.
> >> 
> >> No it hasn't :)  Jamie theorized that there *might* be a real world
> >> situation where the application writer didn't anticipate this
> >> behavior.  But as to actual demonstration, we have not seen one yet, I
> >> think.
> >
> > See bugtraq, or lkml thread about symlinks with permissions. There's
> > demo script there.
> 
> Exactly a theoretical discussion, that demonstrates user space
> applications with security holes can be written if they make
> assumptions about the world that are not true.
> 
> So far no one who believes this to be a security hole has found it
> worth their while to look at nd->intent.open in proc_pid_follow_link
> and write a patch.    Pavel you started out asking for help on how
> to do that and I think I have answered the original question.


> I am tired of the whining.  If no one who is persuaded the kernel is
> wrong can be bothered to write a possibly buggy 5 line patch this is
> clearly not a security hole.

"I did not get a patch so it can't be security hole". Interesting.

I still hope to write it one day, but as I do not have untrusted users
on my systems, it is not particulary urgent. (And I still hope distro
security people do they job.)
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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