On Sun, Sep 23, 2012 at 07:30:38AM +0100, Al Viro wrote:
> On Sat, Sep 22, 2012 at 10:59:04PM -0700, Eric W. Biederman wrote:
> 
> > The test:
> > >> +	if (filp->f_vfsmnt->mnt_root == filp->f_dentry)
> > kicks in and no redirection is performed.
> 
> Umm...  OK, after the first round of recursion.  Unless you bind /something/pts
> on /something.

Other way round, of course...  E.g.
mount --bind /dev /dev/pts
mount --bind /dev /dev/pts/pts
etc. enough times to overflow the kernel stack on recursion.