Re: [PATCH] virtiofsd: Use clone() and not unshare(), support non-root

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Tue, Jun 02, 2020 at 09:53:18PM -0400, Colin Walters wrote:
> On Tue, Jun 2, 2020, at 5:55 AM, Stefan Hajnoczi wrote:
> > Ping Colin. It would be great if you have time to share your thoughts on
> > this discussion and explain how you are using this patch.
> 
> Yeah sorry about not replying in this thread earlier, this was just a quick Friday side project for me and the thread obviously exploded =)
> 
> Thinking about this more, probably what would be good enough for now is an option to just disable internal containerization/sandboxing.  In fact per the discussion our production pipeline runs inside OpenShift 4 and because Kubernetes doesn't support user namespaces yet it also doesn't support recursive containerization, so we need an option to turn off the internal containerization.
> 
> Our use case is somewhat specialized - for what we're doing we generally trust the guest.  We use VMs for operating system testing and development of content we trust, as opposed to e.g. something like kata.
> 
> It's fine for us to run virtiofs as the same user/security context as qemu.
> 
> So...something like this?  (Only compile tested)
...
> @@ -2775,6 +2775,8 @@ static void setup_capabilities(void)
>  static void setup_sandbox(struct lo_data *lo, struct fuse_session *se,
>                            bool enable_syslog)
>  {
> +    if (se->no_namespaces)
> +        return;
>      setup_namespaces(lo, se);
>      setup_mounts(lo->source);
>      setup_seccomp(enable_syslog);

Something along these lines should work. Hopefully seccomp can be
retained. It would also be necessary to check how not having the shared
directory as / in the mount namespace affects functionality. For one,
I'm pretty sure symlink escapes and similar path traversals outside the
shared directory will be possible since virtiofsd normally relies on /
as protection.

Stefan

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