Re: Question regarding restorecon and btrfs read-only snapshots

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On Wed, Mar 19, 2025 at 8:25 AM Stephen Smalley
<stephen.smalley.work@xxxxxxxxx> wrote:
>
> On Wed, Mar 19, 2025 at 9:16 AM Stephen Smalley
> <stephen.smalley.work@xxxxxxxxx> wrote:
> >
> > On Tue, Mar 18, 2025 at 9:11 AM Petr Lautrbach <lautrbach@xxxxxxxxxx> wrote:
> > >
> > > Stephen Smalley <stephen.smalley.work@xxxxxxxxx> writes:
> > >
> > > > On Mon, Mar 17, 2025 at 1:32 PM Petr Lautrbach <lautrbach@xxxxxxxxxx> wrote:
> > > >>
> > > >> Cathy Hu <cahu@xxxxxxx> writes:
> > > >>
> > > >> > On 17.03.25 15:29, Petr Lautrbach wrote:
> > > >> >>
> > > >> >> You could use `-e <directory>` to exclude read only subdirectories.
> > > >> >>
> > > >> >
> > > >> > Yes that is possible, but also requires a manual change by the user to set
> > > >> > this up together with the snapshot (same as telling them to add <<none>>),
> > > >> > which we would like to avoid.
> > > >>
> > > >> Your -relabel.service's are generated and so can be restorecon options
> > > >> there.
> > > >>
> > > >> Fedora uses fixfiles -
> > > >> https://github.com/SELinuxProject/selinux/blob/main/policycoreutils/scripts/fixfiles
> > > >> - which detects ro filesystems and skip them.
> > > >
> > > > We already have logic in libselinux/src/selinux_restorecon.c to
> > > > exclude filesystems that lack seclabel support; should we augment this
> > > > to also exclude read-only filesystems to avoid the need to work around
> > > > this in all callers?
> > > >
> > >
> > > https://github.com/SELinuxProject/selinux/blob/main/libselinux/src/selinux_restorecon.c#L238
> > >
> > > You're right, I didn't know about that.
> > >
> > > I think it would make sense to exclude also `ro` mount points.
> >
> > I think the tricky part is the case where the caller deliberately
> > passed those mount points to restorecon/setfiles. The current
> > exclusion logic IIRC won't exclude any explicitly passed directories
> > to avoid silently failing. But skipping read-only mounts on a
> > traversal of a subdirectory would make sense IMHO.
>
> Actually, maybe not. Scenario: Read-only mount on a higher level
> directory with read-write mount of a lower level directory (e.g.
> read-only / with a writable /var), and restorecon or setfiles invoked
> on /.
> Maybe it is best to just defer this to the callers.

You beat me to this, I had a draft sitting in my inbox. My suggestion
was to report that it occured, but not
fail and keep going if the return code is for read only failure.

>
> >
> > >
> > > >>
> > > >>
> > > >>
> > > >> > Is there a reason why these r-o subvolumes are not skipped by default?
> > > >> > Could they be skipped without a problem and it is just missing the implementation?
> > > >> >
> > > >> > Thanks :)
> > > >> >
> > > >> > Kind regards,
> > > >> > Cathy
> > > >> >
> > >
>





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