Re: [Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7)

[Vivek Goyal]

On Fri, Jun 19, 2020 at 01:46:20PM +0900, Chirantan Ekbote wrote:
> On Fri, Jun 19, 2020 at 4:27 AM Vivek Goyal <vgoyal@redhat.com> wrote:
> >
> > On Thu, Jun 18, 2020 at 08:16:55PM +0100, Dr. David Alan Gilbert wrote:
> > > * Vivek Goyal (vgoyal@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.
> 
> 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.

Chirantan, 

So you ended up renaming all "trusted", "security" and "system" xattrs?
Only "user" xattrs are complete passthrough?

IOW, security.selinux will be renamed to user.virtiofs.security.selinux
on host?

Thanks
Vivek