Instead of mounting a new filesystem, revert to doing a `rw` bind.
However do not make `/` `rshared`, just `/var` as that is where we expect
filesystems to be mounted for persistence. Also only make the actual
container rootfs writeable, not the whole directory.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Based on kernel_config{,.debug} from commit
724561bf69
Enable Landlock and userland sandbox example:
* CONFIG_SECURITY_LANDLOCK=y
* CONFIG_SAMPLES=y
Signed-off-by: Mickaël Salaün <mic@digikod.net>
