[Libguestfs] [nbdkit PATCH 4/4] nbd: Add TLS client support
Eric Blake
eblake at redhat.com
Thu May 30 03:13:38 UTC 2019
Well, really add parameters to pass on to libnbd which does all the
heavy lifting :)
I'd love to also add a uri=... parameter, but until I fix configure.ac
to permit a newer API than libnbd 0.1 that is not possible.
Signed-off-by: Eric Blake <eblake at redhat.com>
---
RFC: Compiled, but I have not heavily tested it yet. Ideally, I
should enhance or copy test-tls{,-psk}.sh to show nbdkit as the
encryption client forwarding on to a plaintext qemu-io Unix socket.
---
plugins/nbd/nbdkit-nbd-plugin.pod | 77 +++++++++++++++++++++++++------
plugins/nbd/nbd.c | 72 +++++++++++++++++++++++++++--
TODO | 13 +-----
3 files changed, 132 insertions(+), 30 deletions(-)
diff --git a/plugins/nbd/nbdkit-nbd-plugin.pod b/plugins/nbd/nbdkit-nbd-plugin.pod
index 7baff98..77f34d3 100644
--- a/plugins/nbd/nbdkit-nbd-plugin.pod
+++ b/plugins/nbd/nbdkit-nbd-plugin.pod
@@ -5,7 +5,8 @@ nbdkit-nbd-plugin - nbdkit nbd plugin
=head1 SYNOPSIS
nbdkit nbd { socket=SOCKNAME | hostname=HOST [port=PORT] } [export=NAME]
- [retry=N] [shared=BOOL]
+ [retry=N] [shared=BOOL] [tls=MODE] [tls-certificates=DIR] [tls-verify=BOOL]
+ [tls-username=NAME] [tls-psk=FILE]
=head1 DESCRIPTION
@@ -20,13 +21,11 @@ original server lacks it). Use of this plugin along with nbdkit
filters (adding I<--filter> to the nbdkit command line) makes it
possible to apply any nbdkit filter to any other NBD server.
-For now, this is limited to connecting to another NBD server over an
-unencrypted connection; if the data is sensitive, it is better to
-stick to a Unix socket rather than transmitting plaintext over TCP. It
-is feasible that future additions will support encryption.
-
=head1 PARAMETERS
+The following parameters are available whether or not the plugin was
+compiled against libnbd:
+
=over 4
=item B<socket=>SOCKNAME
@@ -69,6 +68,46 @@ nbdkit will share that single connection.
=back
+The following parameters are only available if the plugin was compiled
+against libnbd:
+
+=over 4
+
+=item B<tls=>MODE
+
+Selects which TLS mode to use with the server. If no other tls option
+is present, this defaults to C<off>, where the client does not attempt
+encryption (and may be rejected by a server that requires it). If
+omitted but another tls option is present, this defaults to C<on>,
+where the client opportunistically attempts a TLS handshake, but will
+continue running unencrypted if the server does not support
+encryption. If set to C<require>, this requires an encrypted
+connection to the server.
+
+=item B<tls-certificates=>DIR
+
+This specifies the directory containing X.509 client certificates to
+present to the server.
+
+=item B<tls-verify=>BOOL
+
+Setting this to true disables server name verification, which opens
+you to potential Man-in-the-Middle (MITM) attacks, but allows for a
+simpler setup for distributing certificates.
+
+=item B<tls-username=>NAME
+
+If provided, this overrides the user name to present to the server
+alongside the certificate.
+
+=item B<tls-psk=>FILE
+
+If provided, this is the filename containing the Pre-Shared Keys (PSK)
+to present to the server. While this is easier to set up than X.509,
+it requires that the PSK file be transmitted over a secure channel.
+
+=back
+
=head1 EXAMPLES
Expose the contents of an export served by an old style server over a
@@ -80,9 +119,9 @@ that the old server exits.
nbdkit --exit-with-parent --tls=require nbd socket=$sock &
exec /path/to/oldserver --socket=$sock )
- ┌────────────┐ ┌────────┐ ┌────────────┐
- │ new client │ ────────▶│ nbdkit │ ────────▶│ old server │
- └────────────┘ TCP └────────┘ Unix └────────────┘
+ ┌────────────┐ TLS ┌────────┐ plaintext ┌────────────┐
+ │ new client │ ────────▶│ nbdkit │ ───────────▶│ old server │
+ └────────────┘ TCP └────────┘ Unix └────────────┘
Combine nbdkit's partition filter with qemu-nbd's ability to visit
qcow2 files (nbdkit does not have a native qcow2 plugin), performing
@@ -97,16 +136,23 @@ utilize a 5-second retry to give qemu-nbd time to create the socket:
exec qemu-nbd -k $sock -f qcow2 /path/to/image.qcow2 )
Conversely, expose the contents of export I<foo> from a new style
-server with unencrypted data to a client that can only consume
+server with encrypted data to a client that can only consume
unencrypted old style. Use I<--run> to clean up nbdkit at the time the
-client exits.
+client exits. In general, note that it is best to keep the plaintext
+connection limited to a Unix socket on the local machine.
- nbdkit -U - -o nbd hostname=example.com export=foo \
+ nbdkit -U - -o nbd hostname=example.com export=foo tls=require \
--run '/path/to/oldclient --socket=$unixsocket'
- ┌────────────┐ ┌────────┐ ┌────────────┐
- │ old client │ ────────▶│ nbdkit │ ────────▶│ new server │
- └────────────┘ Unix └────────┘ TCP └────────────┘
+ ┌────────────┐ plaintext ┌────────┐ TLS ┌────────────┐
+ │ old client │ ───────────▶│ nbdkit │ ────────▶│ new server │
+ └────────────┘ Unix └────────┘ TCP └────────────┘
+
+Look for the C<libnbd_version> line to learn if the nbd plugin was
+compiled against libnbd for TLS support (required for the previous
+example):
+
+ nbdkit --dump-plugin nbd
=head1 SEE ALSO
@@ -115,6 +161,7 @@ L<nbdkit-captive(1)>,
L<nbdkit-filter(3)>,
L<nbdkit-tls(1)>,
L<nbdkit-plugin(3)>,
+L<libnbd(3)>,
L<qemu-nbd(1)>.
=head1 AUTHORS
diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c
index b1e978a..dbf9096 100644
--- a/plugins/nbd/nbd.c
+++ b/plugins/nbd/nbd.c
@@ -87,6 +87,9 @@ static char *sockname;
static const char *hostname;
static const char *port;
+/* XXX Need libnbd 0.1.1 to connect via URI */
+/* static const char *uri; */
+
/* Human-readable server description */
static char *servname;
@@ -100,6 +103,13 @@ static unsigned long retry;
static bool shared;
static struct handle *shared_handle;
+/* Control TLS settings */
+static int tls = -1;
+static const char *tls_certificates;
+static int tls_verify = -1;
+static const char *tls_username;
+static const char *tls_psk;
+
static struct handle *nbdplug_open_handle (int readonly);
static void nbdplug_close_handle (struct handle *h);
@@ -113,9 +123,10 @@ nbdplug_unload (void)
}
/* Called for each key=value passed on the command line. This plugin
- * accepts socket=<sockname> or hostname=<hostname>/port=<port>
- * (exactly one connection required), and optional parameters
- * export=<name>, retry=<n>.
+ * accepts socket=<sockname>, hostname=<hostname>/port=<port>, or
+ * uri=<uri> (exactly one connection required), and optional
+ * parameters export=<name>, retry=<n>, shared=<bool>, and various tls
+ * settings.
*/
static int
nbdplug_config (const char *key, const char *value)
@@ -134,6 +145,11 @@ nbdplug_config (const char *key, const char *value)
hostname = value;
else if (strcmp (key, "port") == 0)
port = value;
+ else if (strcmp (key, "uri") == 0) {
+ /* XXX Implement once we build against newer libnbd */
+ nbdkit_error ("libnbd too old for uri support");
+ return -1;
+ }
else if (strcmp (key, "export") == 0)
export = value;
else if (strcmp (key, "retry") == 0) {
@@ -150,6 +166,29 @@ nbdplug_config (const char *key, const char *value)
return -1;
shared = r;
}
+ else if (strcmp (key, "tls") == 0) {
+ if (strcasecmp (optarg, "require") == 0 ||
+ strcasecmp (optarg, "required") == 0 ||
+ strcasecmp (optarg, "force") == 0)
+ tls = 2;
+ else {
+ tls = nbdkit_parse_bool (optarg);
+ if (tls == -1)
+ exit (EXIT_FAILURE);
+ }
+ }
+ else if (strcmp (key, "tls-certificates") == 0)
+ tls_certificates = value;
+ else if (strcmp (key, "tls-verify") == 0) {
+ r = nbdkit_parse_bool (value);
+ if (r == -1)
+ return -1;
+ tls_verify = r;
+ }
+ else if (strcmp (key, "tls-username") == 0)
+ tls_username = value;
+ else if (strcmp (key, "tls-psk") == 0)
+ tls_psk = value;
else {
nbdkit_error ("unknown parameter '%s'", key);
return -1;
@@ -197,6 +236,9 @@ nbdplug_config_complete (void)
if (!export)
export = "";
+ if (tls == -1)
+ tls = tls_certificates || tls_verify >= 0 || tls_username || tls_psk;
+
if (shared && (shared_handle = nbdplug_open_handle (false)) == NULL)
return -1;
return 0;
@@ -207,6 +249,18 @@ nbdplug_config_complete (void)
"hostname=<HOST> The hostname for the TCP socket to connect to.\n" \
"port=<PORT> TCP port or service name to use (default 10809).\n" \
"export=<NAME> Export name to connect to (default \"\").\n" \
+ "tls=<MODE> How to use TLS; one of 'off', 'on', or 'require'.\n" \
+ "tls-certificates=<DIR> Directory containing files for X.509 certificates.\n" \
+ "tls-verify=<BOOL> True (default for X.509) to validate server.\n" \
+ "tls-username=<NAME> Override username presented in X.509 TLS.\n" \
+ "tls-psk=<FILE> File containing Pre-Shared Key for TLS.\n" \
+
+static void
+nbdplug_dump_plugin (void)
+{
+ /* XXX libnbd 0.1 doesn't expose a version in libnbd.h */
+ printf ("libnbd_version=%s\n", "0.1");
+}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
@@ -398,6 +452,17 @@ nbdplug_open_handle (int readonly)
goto err;
if (nbd_request_meta_context (h->nbd, "base:allocation") == -1)
goto err;
+ if (nbd_set_tls (h->nbd, tls) == -1)
+ goto err;
+ if (tls_certificates &&
+ nbd_set_tls_certificates (h->nbd, tls_certificates) == -1)
+ goto err;
+ if (tls_verify >= 0 && nbd_set_tls_verify_peer (h->nbd, tls_verify) == -1)
+ goto err;
+ if (tls_username && nbd_set_tls_username (h->nbd, tls_username) == -1)
+ goto err;
+ if (tls_psk && nbd_set_tls_psk_file (h->nbd, tls_psk) == -1)
+ goto err;
if (sockname)
r = nbd_connect_unix (h->nbd, sockname);
else
@@ -749,6 +814,7 @@ static struct nbdkit_plugin plugin = {
.config = nbdplug_config,
.config_complete = nbdplug_config_complete,
.config_help = nbdplug_config_help,
+ .dump_plugin = nbdplug_dump_plugin,
.open = nbdplug_open,
.close = nbdplug_close,
.get_size = nbdplug_get_size,
diff --git a/TODO b/TODO
index b9ddb1e..332400b 100644
--- a/TODO
+++ b/TODO
@@ -90,13 +90,6 @@ qemu-nbd for these use cases.
https://lists.gnu.org/archive/html/qemu-devel/2017-11/msg02971.html
is a partial solution but it needs cleaning up.
-nbdkit-nbd-plugin could use enhancements:
-
-* Enable client-side TLS (right now, the nbd plugin allows us to
- support an encrypted client connecting to a plain server; but we
- would need TLS to support a plain client connecting to an encrypted
- server).
-
nbdkit-floppy-plugin:
* Add boot sector support. In theory this is easy (eg. using
@@ -159,11 +152,7 @@ Filters allow certain types of composition, but others would not be
possible, for example RAIDing over multiple nbd sources. Because the
plugin API limits us to loading a single plugin to the server, the
best way to do this (and the most robust) is to compose multiple
-nbdkit processes.
-
-The nbd plugin (plugins/nbd) already contains an NBD client, so we
-could factor this client out and make it available to other plugins to
-use.
+nbdkit processes. Perhaps libnbd will prove useful for this purpose.
Build-related
-------------
--
2.20.1
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