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

Al Viro
2009-12-20T21:04:18Z

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...