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

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Date:	Tue, 8 Jul 2014 17:54:24 +0100
From:	David Drysdale <drysdale@...gle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	LSM List <linux-security-module@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Meredydd Luff <meredydd@...atehouse.org>,
	Kees Cook <keescook@...omium.org>,
	James Morris <james.l.morris@...cle.com>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)

On Tue, Jul 8, 2014 at 1:03 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Jun 30, 2014 at 11:28:01AM +0100, David Drysdale 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.
>
>
> How is this implemented in FreeBSD?  I can't find any references to
> O_BENEATH_ONLY except for your patchset.

FreeBSD have the relative-only behaviour for openat() relative to a
Capsicum capability dfd [1], and for a process in capability-mode [2],
but they don't have the O_BENEATH_ONLY as a separately-accessible
openat() flag.  However, it seemed like a more widely useful idea so
separating it out was suggested.

[1] http://fxr.watson.org/fxr/source/kern/vfs_lookup.c?v=FREEBSD10#L238
[2] http://fxr.watson.org/fxr/source/kern/vfs_lookup.c?v=FREEBSD10#L171
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