linux-kernel - Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

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Date:	Sun, 20 Dec 2009 21:04:04 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Pavel Machek <pavel@....cz>
Cc:	Jeff Layton <jlayton@...hat.com>,
	Jamie Lokier <jamie@...reable.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	miklos@...redi.hu
Subject: Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks
	and file bind mounts (try #5)

On Sun, Dec 20, 2009 at 08:59:03PM +0100, Pavel Machek wrote:
> > WTF not?  It's convenient and doesn't lose any real security.  If your
> > code relies on inaccessibility of <path> since some component of that
> > path is inaccessible, you are *already* fscked.  Consider e.g. fchdir()
> > and its implications - if you have an opened descriptor for parent,
> > having no exec permissions on grandparent won't stop you at all.  Already.
> > On all Unices, regardless of openat(), etc.
> 
> Consider FD passing over unix socket. Passing R/O file descriptor to
> the other task, then having the task write to the file is certainly bad.

You've omitted the "R/O file descriptor of a file that is writable for
that other task" part...
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