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Re: [Libguestfs] [PATCH nbdkit 4/4] reflection: Enhance plugin to support client address mode.



On 9/15/19 9:55 AM, Richard W.M. Jones wrote:
> ---

Short commit message; at a minimum, I'd probably at least mention that
we thought about potential security issues, and didn't see how it could
be abused.

>  .../reflection/nbdkit-reflection-plugin.pod   | 23 ++++-
>  plugins/reflection/reflection.c               | 88 +++++++++++++++++++
>  tests/Makefile.am                             |  2 +
>  tests/test-reflection-address.sh              | 63 +++++++++++++
>  4 files changed, 174 insertions(+), 2 deletions(-)
> 
> diff --git a/plugins/reflection/nbdkit-reflection-plugin.pod b/plugins/reflection/nbdkit-reflection-plugin.pod
> index 1b260b6..7f52c58 100644
> --- a/plugins/reflection/nbdkit-reflection-plugin.pod
> +++ b/plugins/reflection/nbdkit-reflection-plugin.pod
> @@ -1,10 +1,10 @@
>  =head1 NAME
>  
> -nbdkit-reflection-plugin - reflect export name back to the client
> +nbdkit-reflection-plugin - reflect client info back to the client

Could perhaps squash this hunk into patch 1, but it's also fine here.

> +Another use for the reflection plugin is to send back the client's IP
> +address:
> +
> + $ nbdkit reflection mode=address
> + $ nbdsh -u 'nbd://localhost' -c 'print(h.pread(h.get_size(), 0))'
> +
> +which will print something like:
> +
> + b'[::1]:58912'

Do we want a mode that attempts to do DNS lookup to convert an address
back to a name, so that this could result in b'localhost:58912'?


> +
> +  case AF_UNIX:
> +    /* We don't want to expose the socket path because it's a host
> +     * filesystem name.  The client might not really be running on the
> +     * same machine (eg. it using a proxy).  However it doesn't even

missing 'is'


> +++ b/tests/test-reflection-address.sh
> @@ -0,0 +1,63 @@

> +# Test the relection plugin with mode=address.

reflection (hmm, I missed that typo in patch 1, where this was copied from)

> +# Run nbdkit.
> +start_nbdkit -P reflection-address.pid -U $sock \
> +       reflection mode=address

Is it worth also trying to test a TCP socket (although we have to worry
about finding a free port for the server, as well as heavily filtering
the result as it might be [::1] or 127.0.0.1, and most certainly will
have a different client port number per test run.

But overall, I think this is a useful thing to add to the plugin, and
I'm not seeing any security holes in letting the client know the
client's IP address as seen by the server.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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