Re: [PATCH] private mounts

[Jamie Lokier <jamie@shareable.org>]

Miklos Szeredi wrote:
> > But you don't need a new system call to bind an fd.
> > 
> > "mount --bind /proc/self/fd/N mount_point" works, try it.
> 
> Ahh, yes :)
> 
> Still proc_check_root() has to be relaxed, to allow dereferencing link
> under a different namespace.

Not necessary.

Why not have the FUSE daemon keep open a file descriptor for the
directory it's mounted on, and have it sent that to new would-be
mounters of the same directory using a unix domain socket (rather as
Pavel suggested)?

> Maybe the check should be skipped for
> capable(CAP_SYS_ADMIN) or similar.

No.  The check is to prevent processes in chroot jails from accessing
directories outside their jail.  Even CAP_SYS_ADMIN processes must be
forbidden from doing that.

But proc_check_root is unnecessarily strict, in that it prevents a
process from traversing into a "child" namespace.

IMHO, a better security restriction anyway would be for processes in
chroot jails to not be able to see processes outside the jail in /proc
- only processes inside the jail should be visible.  I think everyone
agrees that would be best.

If that were implemented, then proc_check_root would be redundant and
could be removed entirely.

-- Jamie