Securely sharing directories between jails

[Roland Smith]

On Wed, Feb 01, 2012 at 08:30:31AM +0100, Stas Verberkt wrote:
> L.S.,
> 
> I want to set up my system in a way where applications are clustered
> over jails, e.g. a httpd, smbd and dbmsd jail. However, in most cases I
> need to share data over the jails, which is stored on the host.
> Often, nullfs and mounting ro is suitable, but I need write access in
> some cases. As nullfs rw over multiple jails can be considered insecure,
> I was wondering what would be a secure way.

You could use a combination of nullfs and unionfs. Below is is what I do to
share /usr/ports on the host with a jail, but keep the jail from writing in
the host's tree.

    host# cd /usr/local/var/jails/192.168.0.100/usr
    host# mkdir tmp/foo
    host# mount_nullfs /usr/ports/ ports/
    host# mount_unionfs -o noatime tmp/foo ports/

With this, the jail sees the hosts' /usr/ports tree, but when it wants to
write there, the written files end up under tmp/foo in the jails' tree.

Roland
-- 
R.F.Smith                                   http://www.xs4all.nl/~rsmith/
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