[Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7)
Dr. David Alan Gilbert
dgilbert at redhat.com
Fri Jun 19 08:39:53 UTC 2020
* Chirantan Ekbote (chirantan at chromium.org) wrote:
> On Fri, Jun 19, 2020 at 4:27 AM Vivek Goyal <vgoyal at redhat.com> wrote:
> >
> > On Thu, Jun 18, 2020 at 08:16:55PM +0100, Dr. David Alan Gilbert wrote:
> > > * Vivek Goyal (vgoyal at redhat.com) wrote:
> > > > On Thu, Apr 16, 2020 at 05:49:05PM +0100, Stefan Hajnoczi wrote:
> > > > > virtiofsd doesn't need of all Linux capabilities(7) available to root. Keep a
> > > > > whitelisted set of capabilities that we require. This improves security in
> > > > > case virtiofsd is compromised by making it hard for an attacker to gain further
> > > > > access to the system.
> > > >
> > > > Hi Stefan,
> > > >
> > > > I just noticed that this patch set breaks overlayfs on top of virtiofs.
> > > >
> > > > overlayfs sets "trusted.overlay.*" and xattrs in trusted domain
> > > > need CAP_SYS_ADMIN.
> > > >
>
> Not just that but it needs CAP_SYS_ADMIN in the init namespace[1]. We
> have the same problem. Our virtiofs process has CAP_SYS_ADMIN in a
> user namespace and it cannot set any trusted or security xattrs. The
> security xattrs check is at least namespace aware so you only need
> CAP_SYS_ADMIN in the namespace that mounted the fs but that doesn't
> help us much.
It would have been good if you'd mentioned that; it would have saved
Vivek some confusion!
> We ended up working around it by prefixing "user.virtiofs." to the
> xattr name[2], which has its own problems but there was pretty much no
> chance that we would be able to give the fs device CAP_SYS_ADMIN in
> the init namespace.
What problems did you hit with that? We should standardise the renaming
so we make an on-disc format that's compatible.
Dave
>
> [1]: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/+/5e857ce6eae7ca21b2055cca4885545e29228fe2/fs/xattr.c#116
> [2]: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2243111
>
--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK
More information about the Virtio-fs
mailing list