Stephen Smalley <stephen.smalley.work@xxxxxxxxx> writes: > On Fri, Aug 2, 2024 at 4:27 AM Dominick Grift > <dominick.grift@xxxxxxxxxxx> wrote: >> >> >> I think this question was already asked but I could not find the >> discussion. >> >> What would be the challenges to support a monolitic policy on a volatile >> root? >> >> In a volatile root scenario there is only a non-volatile readonly >> /usr. Would it be possible to teach libselinux that if there is a >> /usr/selinux and not a /etc/selinux and/or /var/lib/selinux that it would >> use that instead? >> >> The challenge I am currently facing with systemd.volatile=yes is that >> when the policy is loaded from initramfs that systemd-tmpfiles (and >> systemd-sysusers) cannot properly populate root from /usr/share/factory >> (or created) because they rely on libselinux,get/setfilecon and thus on >> /etc/selinux/contexts/files. There is a slight chicken and egg situation there. >> >> Often times its not a probable because one can do with automatic type >> transitions but some of these files get created atomically (/etc/passwd >> and /etc/shadow for example) and not to mention that these libselinux >> linked components might get confused and noisy if selinux is enabled and >> enforcing but there is no /etc/selinux. >> >> Duplicating policy in initramfs and /etc, /var/lib would invite >> inconsistencies and is not feasible but if the policy is readonly and >> thus monolitic then this might be feasible if it is not too >> ugly. Actually in such a scenario we would probably not need a policy in >> initramfs at all since systemd would just load it from /usr instead of /etc. > > I've seen a similar concern raised previously even for modular/managed policy. > It's all just software so I don't think it would be hard to modify > libselinux to fall back to /usr/selinux if there is no file in > /etc/selinux; it just requires someone to write a patch for it. May > have policy implications (i.e. anything that currently accesses > /etc/selinux now also may need search access to usr_t) but that's > pretty common anyway. Using /usr for factory policy files has been on my todo list for a long time. Files from /usr/etc/selinux and /usr/lib/selinux would be used as default but they would be overridden by files in /etc/selinux resp /var/lib/selinux. i.e. libselinux would first look into /etc/selinux and if a file does not exist, look into /usr/etc/selinux. likewise for libsemanage. It would also use modules from /usr/lib/selinux but these modules would be overridden by modules from /var/lib/selinux Policy rebuild (`semodule -R`) would install new policy and modules into /etc and /var as it's now.
