linux-kernel - Re: [PATCH 3/7] SELinux: Stub in copy-up handling

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Date:	Mon, 10 Nov 2014 10:47:59 -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 3/7] SELinux: Stub in copy-up handling

On Friday, November 07, 2014 10:08:48 PM David Howells wrote:
> Paul Moore <paul@...l-moore.com> wrote:
> > > +static int selinux_inode_copy_up_xattr(struct dentry *src, struct
> > > dentry
> > > ...*dst,
> > > +				       const char *name, void *value, size_t *size)
> > > +{
> > > +	if (strcmp(name, XATTR_NAME_SELINUX) == 0)
> > > +		return 1; /* Discard */
> > 
> > I understand that this is just a stub, but I we need to discuss this at
> > some point and I figure better in this patch than elsewhere where it
> > might get lost.
> > 
> > For the docker, context= mount use case (similar to SELinux/sVirt)
> > dropping
> > the SELinux xattr is probably an okay behavior.  However, I would expect
> > that ultimately this is something we would want to control by policy
> > and/or the presence of a context= label.
> 
> The problem is that the label you actually want has already been set and you
> have to be careful not to overwrite it.
> 
> The other hook (->inode_copy_up) is called first to label the destination
> inode - and that has access to the source file also so it can label the
> destination with consideration of the attributes on the source.  Normally,
> the attributes on the source will be in memory attached to the source
> inode, I would imagine.

Hmmm, I guess I need to take a closer look at how overlayfs creates files 
during a copy on write.

-- 
paul moore
www.paul-moore.com

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