Filesystem extended attributes support

[Shawn Webb]

On Sat, Jul 04, 2020 at 10:11:00PM +0200, Baptiste Daroussin wrote:
> On Sat, Jul 04, 2020 at 10:13:45AM -0400, Shawn Webb wrote:
> > Hey FreeBSD pkg(8) developers,
> > 
> > Attached is a patch that implements filesystem extended attributes
> > support. Only the system namespace is supported. In case the patch
> > gets scrubbed from this email, I've posted it here:
> > https://gist.github.com/d0b4653bc5942dbcdcd1db877d37c2dc
> > 
> > Anyone who wants to write unit tests is welcomed to do so.
> > 
> > This patch to pkg does depend on a separate patch to libarchive:
> > https://github.com/libarchive/libarchive/pull/1409
> > 
> > HardenedBSD has a separate patch to tmpfs that enables incredibly
> > basic extended attribute support. The tmpfs patch is only needed for
> > those who use tmpfs with poudriere.
> > 
> > And finally, another patch to the jails subsystem that allows a
> > privileged user within a jail to set system namespace filesystem
> > extended attributes (disabled by default) is needed for poudriere
> > users.
> > 
> > The patch to tmpfs and jails is not included here as they are
> > tangential.
> 
> Thank you for the patch at quick glance it looks fine to me. I would have
> obviously to wait for libarchive to merge the patch first to be able to test it
> and do a proper review at the time.
> 
> Don't hesitate to ping me again if you see no progress with libarchive has
> merged the said patch.
> 
> I would have to rework it a bit probably:
> - Add a configure detection of the fact libarchive does or not have the
>   necessary support
> - Add regression tests to ensure I don't break this in the future.
> - Maybe add an option to enable/disable it via pkg.conf (not sure yet about
> that ;))

Sounds good. Thanks for the positive response. I might try to upstream
the tmpfs patch as well, but I'm not sure I've got the locking right,
yet. It's my first time working on a filesystem of any sort, and I'm
not confident I got it right on the first try. Time will tell.

With extended attribute support, pkg could also store a hash of the
file as an extended attribute. One could use that as a method to
determine whether changes have been made. Think: application integrity
enforcement.

So filesystem extended attribute support may have virtues outside of
HardenedBSD's exploit mitigation toggling use case.

Thanks,

-- 
Shawn Webb
Cofounder / Security Engineer
HardenedBSD

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