nbd: enable use of TLS with qemu-nbd server

This modifies the qemu-nbd program so that it is possible to
request the use of TLS with the server. It simply adds a new
command line option --tls-creds which is used to provide the
ID of a QCryptoTLSCreds object previously created via the
--object command line option.

For example

  qemu-nbd --object tls-creds-x509,id=tls0,endpoint=server,\
                    dir=/home/berrange/security/qemutls \
           --tls-creds tls0 \
           --exportname default

TLS requires the new style NBD protocol, so if no export name
is set (via --export-name), then we use the default NBD protocol
export name ""

TLS is only supported when using an IPv4/IPv6 socket listener.
It is not possible to use with UNIX sockets, which includes
when connecting the NBD server to a host device.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1455129674-17255-16-git-send-email-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-nbd.c

@@ -42,6 +42,7 @@
 #define QEMU_NBD_OPT_DISCARD       3
 #define QEMU_NBD_OPT_DETECT_ZEROES 4
 #define QEMU_NBD_OPT_OBJECT        5
+#define QEMU_NBD_OPT_TLSCREDS      6
 
 static NBDExport *exp;
 static bool newproto;
@@ -54,6 +55,7 @@ static int shared = 1;
 static int nb_fds;
 static QIOChannelSocket *server_ioc;
 static int server_watch = -1;
+static QCryptoTLSCreds *tlscreds;
 
 static void usage(const char *name)
 {
@@ -342,7 +344,7 @@ static gboolean nbd_accept(QIOChannel *ioc, GIOCondition cond, gpointer opaque)
     nb_fds++;
     nbd_update_server_watch();
     nbd_client_new(newproto ? NULL : exp, cioc,
-                   NULL, NULL, nbd_client_closed);
+                   tlscreds, NULL, nbd_client_closed);
     object_unref(OBJECT(cioc));
 
     return TRUE;
@@ -402,6 +404,37 @@ static QemuOptsList qemu_object_opts = {
 };
 
 
+
+static QCryptoTLSCreds *nbd_get_tls_creds(const char *id, Error **errp)
+{
+    Object *obj;
+    QCryptoTLSCreds *creds;
+
+    obj = object_resolve_path_component(
+        object_get_objects_root(), id);
+    if (!obj) {
+        error_setg(errp, "No TLS credentials with id '%s'",
+                   id);
+        return NULL;
+    }
+    creds = (QCryptoTLSCreds *)
+        object_dynamic_cast(obj, TYPE_QCRYPTO_TLS_CREDS);
+    if (!creds) {
+        error_setg(errp, "Object with id '%s' is not TLS credentials",
+                   id);
+        return NULL;
+    }
+
+    if (creds->endpoint != QCRYPTO_TLS_CREDS_ENDPOINT_SERVER) {
+        error_setg(errp,
+                   "Expecting TLS credentials with a server endpoint");
+        return NULL;
+    }
+    object_ref(obj);
+    return creds;
+}
+
+
 int main(int argc, char **argv)
 {
     BlockBackend *blk;
@@ -441,6 +474,7 @@ int main(int argc, char **argv)
         { "verbose", 0, NULL, 'v' },
         { "object", 1, NULL, QEMU_NBD_OPT_OBJECT },
         { "export-name", 1, NULL, 'x' },
+        { "tls-creds", 1, NULL, QEMU_NBD_OPT_TLSCREDS },
         { NULL, 0, NULL, 0 }
     };
     int ch;
@@ -458,6 +492,7 @@ int main(int argc, char **argv)
     BlockdevDetectZeroesOptions detect_zeroes = BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF;
     QDict *options = NULL;
     const char *export_name = NULL;
+    const char *tlscredsid = NULL;
 
     /* The client thread uses SIGTERM to interrupt the server.  A signal
      * handler ensures that "qemu-nbd -v -c" exits with a nice status code.
@@ -634,6 +669,9 @@ int main(int argc, char **argv)
                 exit(EXIT_FAILURE);
             }
         }   break;
+        case QEMU_NBD_OPT_TLSCREDS:
+            tlscredsid = optarg;
+            break;
         }
     }
 
@@ -650,6 +688,28 @@ int main(int argc, char **argv)
         exit(EXIT_FAILURE);
     }
 
+    if (tlscredsid) {
+        if (sockpath) {
+            error_report("TLS is only supported with IPv4/IPv6");
+            exit(EXIT_FAILURE);
+        }
+        if (device) {
+            error_report("TLS is not supported with a host device");
+            exit(EXIT_FAILURE);
+        }
+        if (!export_name) {
+            /* Set the default NBD protocol export name, since
+             * we *must* use new style protocol for TLS */
+            export_name = "";
+        }
+        tlscreds = nbd_get_tls_creds(tlscredsid, &local_err);
+        if (local_err) {
+            error_report("Failed to get TLS creds %s",
+                         error_get_pretty(local_err));
+            exit(EXIT_FAILURE);
+        }
+    }
+
     if (disconnect) {
         int nbdfd = open(argv[optind], O_RDWR);
         if (nbdfd < 0) {

qemu-nbd.texi

@@ -21,9 +21,10 @@ Export a QEMU disk image using the NBD protocol.
 @item --object type,id=@var{id},...props...
 Define a new instance of the @var{type} object class identified by @var{id}.
 See the @code{qemu(1)} manual page for full details of the properties
-supported. The common object type that it makes sense to define is the
+supported. The common object types that it makes sense to define are the
 @code{secret} object, which is used to supply passwords and/or encryption
-keys.
+keys, and the @code{tls-creds} object, which is used to supply TLS
+credentials for the qemu-nbd server.
 @item -p, --port=@var{port}
 The TCP port to listen on (default @samp{10809})
 @item -o, --offset=@var{offset}
@@ -76,6 +77,10 @@ Don't exit on the last connection
 @item -x NAME, --export-name=NAME
 Set the NBD volume export name. This switches the server to use
 the new style NBD protocol negotiation
+@item --tls-creds=ID
+Enable mandatory TLS encryption for the server by setting the ID
+of the TLS credentials object previously created with the --object
+option.
 @item -v, --verbose
 Display extra debugging information
 @item -h, --help