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Re: [Libguestfs] [PATCH nbdkit 0/4] Reflection plugin, peer name.

On Sun, Sep 15, 2019 at 03:55:41PM +0100, Richard W.M. Jones wrote:
This series is based on my blog posting here:

It depends on the fix for realloc:

This series adds a fun plugin, and also an semi-related feature I've
long thought to be desirable.  You can consider patches 1 & 4, and
patches 2 & 3 as forming standalone patch series (but they do depend
on each other).

The fun plugin is a reflection plugin which "reflects" client
information back to the client.  We have a few fun plugins like this
(hello there, nbdkit-full-plugin) and normally I would push these
without review, but in this particular case there's a specific danger
that sending back data under control of the client might lead to a
security problem.  I _believe_ I have avoided that pitfall, but my
belief isn't as good as having experts review it :-)

Even though I am not part of that group you mentioned I had a look at it and I
could not find any issue with that; you are keeping the size returned by the
base64 decoder and other than that it is all data which should be safe as far as
I understand it.

The new feature is nbdkit_peer_name() which returns the sockaddr of
the peer.  It's essentially a wrapper around getpeername(2).  This

It's a pity there is no information for UNIX sockets.  Would it make sense to at
least try to get the PID (or even a command name) using at least:

 getsockopt(..., SOL_SOCKET, SO_PEERCRED, ...)

at least where SO_PEERCRED is defined?

It looks good to me.

would allow several features to be implemented in future:

- Plugins could accept or reject connections based on IP address.

- Plugins could change content based on client.  (The fourth patch in
  the series is a PoC of this implemented in the new reflection
  plugin.)  Be cautious about combining this feature with multi-conn
  as it's not obviously always safe to do.

- Some filters could usefully modify their behaviour based on client
  address: The TODO file currently notes that the rate filter could
  be changed to limit traffic based on client IP.


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