linux-kernel - Re: [RFC PATCH] Show data flow for file copyup in unions

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Message-ID: <20100318005358.GA24348@shell>
Date:	Wed, 17 Mar 2010 20:53:58 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	"J. R. Okajima" <hooanon05@...oo.co.jp>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	Jeff Layton <jlayton@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Show data flow for file copyup in unions

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
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