linux-kernel - Re: [PATCH 01/11] fs: add O_BENEATH

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Message-ID: <20140630154928.GB10375@google.com>
Date:	Mon, 30 Jun 2014 16:49:28 +0100
From:	David Drysdale <drysdale@...gle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	LSM List <linux-security-module@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Meredydd Luff <meredydd@...atehouse.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)

On Mon, Jun 30, 2014 at 07:49:41AM -0700, Andy Lutomirski wrote:
> On Jun 30, 2014 3:36 AM, "David Drysdale" <drysdale@...gle.com> wrote:
> >
> > Add a new O_BENEATH_ONLY flag for openat(2) which restricts the
> > provided path, rejecting (with -EACCES) paths that are not beneath
> > the provided dfd.  In particular, reject:
> >  - paths that contain .. components
> >  - paths that begin with /
> >  - symlinks that have paths as above.
> 
> I like this a lot.  However, I think I'd like it even better if it
> were AT_BENEATH_ONLY so that it could be added to the rest of the *at
> family.
> 
> --Andy

Wouldn't it need to be both O_BENEATH_ONLY (for openat()) and 
AT_BENEATH_ONLY (for other *at() functions), like O_NOFOLLOW and
AT_SYMLINK_NOFOLLOW?  (I.e. aren't the AT_* flags in a different
numbering space than O_* flags?)

Or am I misunderstanding?

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