Re: [vserver] Network isolation and VServer

Daniel Risacher wrote:
> My apologies in advance if this is re-opening old wounds.
>
> I recently set up VServer (mainly so I could run Zimbra w/ less pain)
> and I found that the network isolation did not work the way I
> (perhaps naively?) expected it to. (Mainly re: binding to TCP ports
> and IPADDR_ANY.)
>
> I write this message to (1) determine whether my understanding of
> VServer's functionality is correct, and possibly (2) suggest potential
> improvements for discussion.
>
> How I think it DOES work
> ------------------------
>
> * Host processes that bind to IPADDR_ANY can recieve connections to any
> host or guest address
>
> * Guest processes that bund to IPADDR_ANY show as having been bound to
> the guest primary IP address, but can receive connections to the
> localhost address that come from the same guest.

This is just an optimization that kicks in if your guest only has one
address, it significantly speeds up the lookups.

> * Bind attempts to IPADDR_ANY from the host will fail if a guest is
> already listening on that port
>
> * Bind attempts to IPADDR_ANY from a guest will fail if the host is
> already listening to IPADDR_ANY on that port
>
> * Connection attempts to "localhost" from a guest can be answered by
> the host.
>
> How I think it SHOULD work
> --------------------------
>
> I start from the general assumption that a virtual machine should seem
> like an isolated, independent machine as much as possible. It seems
> to be a desirable goal to minimize the amount of application-level
> configuration tomfoolery that is required. Based on this...

You only have to configure the host, which shouldn't really be running
any services in the first place.

> * Bind attempts to IPADDR_ANY should not fail based on something
> happening in a different security context. I.e. Bind attempts to
> IPADDR_ANY from the host should be able to succeed, even if a guest
> is already listening on that port, and likewise bind attempts to
> IPADDR_ANY from a guest should be able to succeed, even if the host
> is already listening to IPADDR_ANY

So when someone connects to it, where should they be directed? You can't
have multiple listeners on the same IP:port pairs, when the contexts
overlap.

> * Processes listening on IPADDR_ANY should receive connections to any
> IP address that are set up for that virtual machine (be it the host
> or a guest).

The host does not have a context. How would you expect that to work?

> Questions
> ---------
> So, given the above discussion, here are my questions:
>
> Do I mis-understand or mis-state how VServer functions today?
>
> Is my proposed alternative functionality "better", or is there some
> reason why today's behaviour is "better"?

It just goes against the general Linux-VServer paradigm. As far as
possible, we do isolation by limiting the guest to a subset of the
host's resources. As such, limiting the host's ability to use the IP
addresses it wants is just not something that fits in.

> How could we implement a more robust version of network isolation?
> Has any work been done in this area previously?

I don't get what robust means in this context.

> How do the other virtualization environments handle this sort of
> thing?

OpenVZ and the containers people use virtualized network stacks for the
guests, which I consider to be too much overhead (both performance and
configuration wise).

> Thanks for the consideration,
> Dan Risacher

-- 
Daniel Hokka Zakrisson