[Qemu-devel] [PATCH v2 14/15] nbd: enable use of TLS with qemu-nbd server

["Daniel P. Berrange" <berrange@redhat.com>]

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

Note that it is mandatory to supply the --exportname argument
when requesting TLS, since it requires use of the new style
NBD protocol where the client requests a volume name explicitly.

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>
---
 qemu-nbd.c    | 57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 qemu-nbd.texi |  4 ++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 53b22d7..b85a4c8 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -45,6 +45,7 @@
 #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;
@@ -57,6 +58,7 @@ 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)
 {
@@ -344,7 +346,7 @@ static gboolean nbd_accept(QIOChannel *ioc, GIOCondition cond, gpointer opaque)
     }
 
     if (nbd_client_new(newproto ? NULL : exp, cioc,
-                       NULL, NULL, nbd_client_closed)) {
+                       tlscreds, NULL, nbd_client_closed)) {
         nb_fds++;
         nbd_update_server_watch();
     }
@@ -426,6 +428,37 @@ static int object_create(void *opaque, QemuOpts *opts, Error **errp)
     return 0;
 }
 
+
+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;
@@ -465,6 +498,7 @@ int main(int argc, char **argv)
         { "verbose", 0, NULL, 'v' },
         { "object", 1, NULL, QEMU_NBD_OPT_OBJECT },
         { "exportname", 1, NULL, 'x' },
+        { "tls-creds", 1, NULL, QEMU_NBD_OPT_TLSCREDS },
         { NULL, 0, NULL, 0 }
     };
     int ch;
@@ -483,6 +517,7 @@ int main(int argc, char **argv)
     QDict *options = NULL;
     QemuOpts *opts;
     const char *exportname = 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.
@@ -639,6 +674,9 @@ int main(int argc, char **argv)
                 exit(1);
             }
             break;
+        case QEMU_NBD_OPT_TLSCREDS:
+            tlscredsid = optarg;
+            break;
         case '?':
             errx(EXIT_FAILURE, "Try `%s --help' for more information.",
                  argv[0]);
@@ -657,6 +695,23 @@ int main(int argc, char **argv)
         exit(1);
     }
 
+    if (tlscredsid) {
+        if (!exportname) {
+            errx(EXIT_FAILURE, "Export name is required when using TLS");
+        }
+        if (sockpath) {
+            errx(EXIT_FAILURE, "TLS is only supported with IPv4/IPv6");
+        }
+        if (device) {
+            errx(EXIT_FAILURE, "TLS is not supported with a host device");
+        }
+        tlscreds = nbd_get_tls_creds(tlscredsid, &local_err);
+        if (local_err) {
+            errx(EXIT_FAILURE, "Failed to get TLS creds %s",
+                 error_get_pretty(local_err));
+        }
+    }
+
     if (disconnect) {
         int nbdfd = open(argv[optind], O_RDWR);
         if (nbdfd < 0) {
diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 22d6b5a..34e59a1 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -66,6 +66,10 @@ Export QEMU disk image using NBD protocol.
 @item -x NAME, --exportname=NAME
   set the NDB 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
-- 
2.5.0