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

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Message-ID: <20091106141742.GA1428@ucw.cz>
Date:	Fri, 6 Nov 2009 15:17:42 +0100
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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 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.

> And as for reopening O_NODE files with increased permission: that's
> feature people actually expressed interest in, so it's hardly a
> security hole, is it?

Just because people want it does not mean it is not a security hole.

Consider passing /etc/shadow filedesciptor to (legacy) suid root
program. Maybe it now prints /etc/shadow content, because it assumes
that if you have fd you are allowed to read the file?

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