From mboxrd@z Thu Jan  1 00:00:00 1970
From: Valerie Aurora <vaurora@redhat.com>
Subject: Re: [RFC PATCH] Show data flow for file copyup in unions
Date: Wed, 17 Mar 2010 20:53:58 -0400
Message-ID: <20100318005358.GA24348@shell>
References: <20100316181711.GB24819@shell> <20335.1268779891@jrobl>
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Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Dmitry Monakhov <dmonakhov@openvz.org>,
	Jeff Layton <jlayton@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
To: "J. R. Okajima" <hooanon05@yahoo.co.jp>
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On Wed, Mar 17, 2010 at 07:51:31AM +0900, J. R. Okajima wrote:
> 
> Valerie Aurora:
> > 1. Don't copyup if the operation would fail (e.g., open(O_WRONLY) on a
> > file with mode 444).  It's inefficient and a possible security hole to
> > copy up a file if no write (or maybe even read) can occur anyway.
> 
> Just a question.
> How about this case?
> When the file is writable (0644 or something) but its parent directory
> is readonly (0555), do you think the file should be copied-up?

This problem comes up with readdir() too, since we copy up all the
directory entries from the lower layer on what is ostensibly a
read-only access.

I think what people will expect is that we copy up in that case.  I
can think of ways this can go wrong, but perhaps that should be an
explicit requirement on the top-layer file system, that it can handle
create/unlink() in a directory without write permission.

-VAL