[CFR] [PATCH] jail mount/unmount patch

[Kostik Belousov]

On Thu, Jul 28, 2011 at 07:38:11PM +0200, Pawel Jakub Dawidek wrote:
> On Thu, Jul 28, 2011 at 08:25:39PM +0300, Kostik Belousov wrote:
> > On Thu, Jul 28, 2011 at 06:07:52PM +0200, Pawel Jakub Dawidek wrote:
> > > In you patch you depend on fact that full path to mount directory is
> > > passed to the nmount(2) system call. This doesn't have to be true.
> > > I changed mount(8) to call realpath(3) in mount directory, but I see no
> > > reason someone calling nmount(2) directly with "./foo" mount dir.
> > > 
> > > I think the proper way is to build full path from within the kernel
> > > using vn_fullpath_global().
> > 
> > It indeed may work if the supplied vnode is a directory, since it
> > will fall back to the dotdot lookup loop if the namecache is purged.
> 
> Exactly. Mount directory by definition is always a directory, so it
> should be reliable.

It is so on FreeBSD, but is not true for a random Unix in existence.
E.g., Solaris does allow to mount over the file, and it is useful.
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