Re: [Libguestfs] [COMMON PATCH 0/1] mlcustomize: skip SELinux relabeling if it's disabled
On Fri, Apr 21, 2023 at 09:01:40PM +0300, Andrey Drobyshev wrote:
This patch effectively limits the number of cases when we would want
to
do a complete SELinux relabeling on Linux guest conversion.
This was brought to my attention as we've recently had a support case
when the conversion was taking too much time mostly because of
relabeling performed with "setfiles -F".
Although this patch might be worthy of taking as it is, I'd also like to
clarify, do we really need relabeling of the entire file system during
conversion? What exactly might go wrong here if we don't do that?
Since this process might take hours on VMs big enough, it would be
beneficial to be able to limit number of such cases even further, if
possible. Unfortunately I couldn't find any hints in the libguestfs commit
history as the relabeling code goes back to 0131d6f666 ("New tool: virt-v2v.").
Relabelling is generally needed because we may have modified or
created files during the conversion. These will not be labelled
correctly by the libguestfs appliance (as would happen when the guest
runs normally) because whatever SELinux mechanism that does this isn't
running.
If SELinux is enforcing this can and will stop services from starting
up at boot (you will see permission errors), and can even prevent a
guest from booting at all.
Note we don't even have a list of possible files affected because we
run stuff like dracut & rpm.
We should probably only need to relabel over "system directories"
(whatever that means), but we currently relabel over everything
mounted (basically everything mentioned in /etc/fstab) because that's
easier. The alternate path if setfiles doesn't work touches
/.autorelabel, but that just moves the same work to boot time.
I don't think we've seen a case of labelling taking a long time, but
it could happen.
The patch you posted is fine because if SELinux is disabled then file
labels naturally get out of synch over time, as they won't be set on
newly created files. This is why setting SELinux to disabled isn't
really a "reversible" operation. You cannot reenable SELinux
afterwards without first doing a full filesystem relabel and reboot.
(Permissive doesn't have this problem.)
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines. Boot with a
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http://libguestfs.org/virt-v2v