[Libguestfs] [nbdkit PATCH v2 5/5] nbd: Add TLS client support

Well, really add parameters to pass on to libnbd which does all the heavy lifting :) Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- plugins/nbd/nbdkit-nbd-plugin.pod | 91 ++++++++++++++++++++++--------- plugins/nbd/nbd.c | 52 +++++++++++++++++- TODO | 13 +---- 3 files changed, 117 insertions(+), 39 deletions(-) diff --git a/plugins/nbd/nbdkit-nbd-plugin.pod b/plugins/nbd/nbdkit-nbd-plugin.pod index c78fdca..38688a3 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] | [uri=]URI } - [export=NAME] [retry=N] [shared=BOOL] + [export=NAME] [retry=N] [shared=BOOL] [tls=MODE] [tls-certificates=DIR] + [tls-verify=BOOL] [tls-username=NAME] [tls-psk=FILE] =head1 DESCRIPTION @@ -20,11 +21,6 @@ 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 One of B<socket>, B<hostname> or B<uri> must be provided to designate @@ -32,6 +28,9 @@ the server. The server can speak either new or old style protocol. C<uri=> is a magic config key and may be omitted in most cases. See L<nbdkit(1)/Magic parameters>. +The following parameters are available whether or not the plugin was +compiled against libnbd: + =over 4 =item B<socket=>SOCKNAME @@ -47,16 +46,6 @@ Connect to the NBD server at the given remote C<HOST> using a TCP socket. When B<hostname> is supplied, use B<PORT> instead of the default port 10809. -=item B<uri=>URI - -When B<uri> is supplied, decode B<URI> to determine the address to -connect to. A URI can specify a TCP connection (such as -C<nbd://localhost:10809>) or a Unix socket (such as -C<nbd+unix:///?socket=/path/to/sock>). The B<uri> parameter is only -available when the plugin was compiled against libnbd, although -whether it works also depends on whether libnbd was compiled against -libxml2. - =item B<export=>NAME If this parameter is given, and the server speaks new style protocol, @@ -82,6 +71,55 @@ nbdkit will share that single connection. =back +The following parameters are only available if the plugin was compiled +against libnbd: + +=over 4 + +=item B<uri=>URI + +When B<uri> is supplied, decode B<URI> to determine the address to +connect to. A URI can specify a TCP connection (such as +C<nbd://localhost:10809>) or a Unix socket (such as +C<nbd+unix:///?socket=/path/to/sock>). However, whether the B<uri> +parameter works depends on whether libnbd was compiled against +libxml2. + +=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 @@ -93,9 +131,9 @@ 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 @@ -110,19 +148,20 @@ 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 C<uri> support: +compiled against libnbd for C<uri> and TLS support: nbdkit --dump-plugin nbd diff --git a/plugins/nbd/nbd.c b/plugins/nbd/nbd.c index 2268bd0..02cc86d 100644 --- a/plugins/nbd/nbd.c +++ b/plugins/nbd/nbd.c @@ -100,6 +100,13 @@ 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); @@ -114,7 +121,8 @@ nbdplug_unload (void) /* Called for each key=value passed on the command line. This plugin * accepts socket=<sockname>, hostname=<hostname>/port=<port>, or * [uri=]<uri> (exactly one connection required), and optional - * parameters export=<name>, retry=<n> and shared=<bool>. + * parameters export=<name>, retry=<n>, shared=<bool> and various + * tls settings. */ static int nbdplug_config (const char *key, const char *value) @@ -151,6 +159,29 @@ 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; @@ -195,6 +226,9 @@ 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; @@ -209,6 +243,11 @@ nbdplug_config_complete (void) "retry=<N> Retry connection up to N seconds (default 0).\n" \ "shared=<BOOL> True to share one server connection among all clients,\n" \ " rather than a connection per client (default false).\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) @@ -409,6 +448,17 @@ nbdplug_open_handle (int readonly) goto err; if (nbd_add_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 (uri) r = nbd_connect_uri (h->nbd, uri); else if (sockname) 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