linux-kernel - Re: [PATCH 2/7] Overlayfs: Use copy-up security hooks

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Message-ID: <3253042.xfZ6VF8OvX@sifl>
Date:	Mon, 10 Nov 2014 10:45:37 -0500
From:	Paul Moore <paul@...l-moore.com>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-unionfs@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] Overlayfs: Use copy-up security hooks

On Friday, November 07, 2014 10:05:40 PM David Howells wrote:
> Paul Moore <paul@...l-moore.com> wrote:
> > So the LSM must modify the xattr in place?  I suppose that since the
> > @value is allocated to the max size it shouldn't be a problem.  Just
> > checking ...
> 
> ... And the caller must provide a maximally sized buffer (which it likely
> has to allocate anyway).
> 
> I'm not sure I really need to provide the modification thing.  I suspect a
> binary keep or discard decision is sufficient.

The docker use case we've been talking about in this thread doesn't really 
care about the on-disk file labels (xattrs) because the docker folks want to 
use context= mounts; however if someone did care about on-disk file labels for 
the upper layer in the overlayfs then they might want to modify the xattr.

-- 
paul moore
www.paul-moore.com

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