Re: [PATCH for-5.1 2/3] virtiofsd: add container-friendly -o chroot sandboxing option

[Stefan Hajnoczi]

On Wed, Jul 22, 2020 at 05:58:11PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jul 22, 2020 at 02:02:05PM +0100, Stefan Hajnoczi wrote:
> > virtiofsd cannot run in an unprivileged container because CAP_SYS_ADMIN
> > is required to create namespaces.
> > 
> > Introduce a weaker sandbox that is sufficient in container environments
> > because the container runtime already sets up namespaces. Use chroot to
> > restrict path traversal to the shared directory.
> > 
> > virtiofsd loses the following:
> > 
> > 1. Mount namespace. The process chroots to the shared directory but
> >    leaves the mounts in place. Seccomp rejects mount(2)/umount(2)
> >    syscalls.
> > 
> > 2. Pid namespace. This should be fine because virtiofsd is the only
> >    process running in the container.
> > 
> > 3. Network namespace. This should be fine because seccomp already
> >    rejects the connect(2) syscall, but an additional layer of security
> >    is lost. Container runtime-specific network security policies can be
> >    used drop network traffic (except for the vhost-user UNIX domain
> >    socket).
> 
> IIUC this relies on the fact that the container will still have 
> CAP_SYS_CHROOT IOW, we still don't have a solution for running
> virtiofsd as an unprivileged user.

Yes, this still requires root in the container.

Stefan

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