Re: [patch 0/8] mount ownership and unprivileged mount syscall (v4)

Serge E. Hallyn
2007-04-20T12:42:53Z

Quoting Miklos Szeredi (miklos@szeredi.hu):
> This patchset has now been bared to the "lowest common denominator"
> that everybody can agree on. Or at least there weren't any objections
> to this proposal.
>
> Andrew, please consider it for -mm.
>
> Thanks,
> Miklos
> ----
>
> v3 -> v4:
>
> - simplify interface as much as possible, now only a single option
> ("user=UID") is used to control everything
> - no longer allow/deny mounting based on file/directory permissions,
> that approach does not always make sense
>
> ----
> This patchset adds support for keeping mount ownership information in
> the kernel, and allow unprivileged mount(2) and umount(2) in certain
> cases.
>
> The mount owner has the following privileges:
>
> - unmount the owned mount
> - create a submount under the owned mount
>
> The sysadmin can set the owner explicitly on mount and remount. When
> an unprivileged user creates a mount, then the owner is automatically
> set to the user.
>
> The following use cases are envisioned:
>
> 1) Private namespace, with selected mounts owned by user.
> E.g. /home/$USER is a good candidate for allowing unpriv mounts and
> unmounts within.
>
> 2) Private namespace, with all mounts owned by user and having the
> "nosuid" flag. User can mount and umount anywhere within the
> namespace, but suid programs will not work.
>
> 3) Global namespace, with a designated directory, which is a mount
> owned by the user. E.g. /mnt/users/$USER is set up so that it is
> bind mounted onto itself, and set to be owned by $USER. The user
> can add/remove mounts only under this directory.
>
> The following extra security measures are taken for unprivileged
> mounts:
>
> - usermounts are limited by a sysctl tunable
> - force "nosuid,nodev" mount options on the created mount

Very nice. I like these semantics.

I'll try to rework my laptop in the next few days to use this patchset
as a test.

thanks,
-serge