[uml-user] chroot'ing an UML - /proc/mm

[Erik de B. - L. <Erik@LowVoice.nl>]

Hi List,

To create an extra barrier between the host and guest OS we wanted to chroot
a UML system. We created a chrooted environment to run an non-writable but
executable linux kernel while the user the UML runs as only has writable
filesystems and a read-ony hostfs. This way, even with a compromised or
exploitable kernel you couldn't write binary executable files onto the host
filesystem. This is essential to get tools for further exploiting bugs on
the host. We think this very much solves many security issue we could think
off.
We've bind mounted just the /dev/net to the inside of chroot so it can use
tun/tap networking, but no other things of /dev are reachable. We've also
been trying to do the same with /proc/mm but this is a file, so it's only
possible to bind the whole /proc. It's a lot safer than not chrooting at
all, but would because it's safer than a non chrooted environment anyway,
but it would very much remove a lot of risks that still exist. We think that
changing the location of /proc/mm to /proc/mm/mm would make deeper security
measures possible.

Erik