O_NOFOLLOW

[Thomas Bushnell, BSG]

   Date: Sat, 24 Oct 1998 05:35:50 -0400
   From: Roland McGrath <roland@frob.com>

   > This was AFAIK implemented to guard against creating, e.g. forcing
   > root to create a file (core) that is symlinked to /etc/passwd.

   ? What's wrong with O_CREAT|O_EXCL?

The point is apparently for opening files which might legitimately
already exist, but which must not be symlinks; it's a reasonable
solution to a long-standing category of security weaknesses.  

We can implement it in the Hurd purely in the library; if it's set
then enable O_NOFOLLOW, followed by io_stat and then an error if we
got a symlink.

Thomas