nbd_set_tls - Man Page

enable or require TLS (authentication and encryption)

Synopsis

 #include <libnbd.h>

 int nbd_set_tls (struct nbd_handle *h, int tls);

Description

Enable or require TLS (authenticated and encrypted connections) to the NBD server.  The possible settings are:

LIBNBD_TLS_DISABLE

Disable TLS.  (The default setting, unless using nbd_connect_uri(3) with a URI that requires TLS)

LIBNBD_TLS_ALLOW

Enable TLS if possible.

This option is insecure (or best effort) in that in some cases it will fall back to an unencrypted and/or unauthenticated connection if TLS could not be established.  Use LIBNBD_TLS_REQUIRE below if the connection must be encrypted.

Some servers will drop the connection if TLS fails so fallback may not be possible.

LIBNBD_TLS_REQUIRE

Require an encrypted and authenticated TLS connection. Always fail to connect if the connection is not encrypted and authenticated.

As well as calling this you may also need to supply the path to the certificates directory (nbd_set_tls_certificates(3)), the username (nbd_set_tls_username(3)) and/or the Pre-Shared Keys (PSK) file (nbd_set_tls_psk_file(3)).  For now, when using nbd_connect_uri(3), any URI query parameters related to TLS are not handled automatically.  Setting the level higher than zero will fail if libnbd was not compiled against gnutls; you can test whether this is the case with nbd_supports_tls(3).

Return Value

If the call is successful the function returns 0.

Errors

On error -1 is returned.

Refer to “ERROR HANDLING” in libnbd(3) for how to get further details of the error.

Handle State

The handle must be newly created, otherwise this call will return an error.

Version

This function first appeared in libnbd 1.0.

If you need to test if this function is available at compile time check if the following macro is defined:

 #define LIBNBD_HAVE_NBD_SET_TLS 1

Example

This example is also available as examples/encryption.c in the libnbd source code.

 /* An example showing how to connect to a server which is
  * using TLS encryption.
  *
  * This requires nbdkit, and psktool from gnutls.
  *
  * Both libnbd and nbdkit support TLS-PSK which is a
  * simpler-to-deploy form of encryption.  (Of course
  * certificate-based encryption is also supported, but
  * it’s harder to make a self-contained example).
  */
 
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
 #include <libnbd.h>
 
 #define TMPDIR "/tmp/XXXXXX"
 #define KEYS "keys.psk"
 #define USERNAME "alice"
 
 static char dir[] = TMPDIR;
 static char keys[] = TMPDIR "/" KEYS;
 static char cmd[] =
   "psktool -u " USERNAME " -p " TMPDIR "/" KEYS;
 
 /* Remove the temporary keys file when the program
  * exits.
  */
 static void
 cleanup_keys (void)
 {
   unlink (keys);
   rmdir (dir);
 }
 
 /* Create the temporary keys file to share with the
  * server.
  */
 static void
 create_keys (void)
 {
   size_t i;
 
   if (mkdtemp (dir) == NULL) {
     perror ("mkdtemp");
     exit (EXIT_FAILURE);
   }
   i = strlen (cmd) - strlen (TMPDIR) - strlen (KEYS) - 1;
   memcpy (&cmd[i], dir, strlen (TMPDIR));
   memcpy (keys, dir, strlen (TMPDIR));
 
   if (system (cmd) != 0) {
     fprintf (stderr, "psktool command failed\n");
     exit (EXIT_FAILURE);
   }
 
   atexit (cleanup_keys);
 }
 
 int
 main (int argc, char *argv[])
 {
   struct nbd_handle *nbd;
   char buf[512];
 
   create_keys ();
 
   /* Create the libnbd handle. */
   nbd = nbd_create ();
   if (nbd == NULL) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Enable TLS in the client. */
   if (nbd_set_tls (nbd, LIBNBD_TLS_REQUIRE) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Enable TLS-PSK and pass the keys filename. */
   if (nbd_set_tls_psk_file (nbd, keys) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Set the local username for authentication. */
   if (nbd_set_tls_username (nbd, USERNAME) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Run nbdkit as a subprocess, enabling and requiring
    * TLS-PSK encryption.
    */
   char *args[] = {
     "nbdkit", "-s", "--exit-with-parent",
     "--tls", "require", "--tls-psk", keys,
     "pattern", "size=1M", NULL
   };
   if (nbd_connect_command (nbd, args) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Read the first sector. */
   if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* TLS connections must be shut down. */
   if (nbd_shutdown (nbd, 0) == -1) {
     fprintf (stderr, "%s\n", nbd_get_error ());
     exit (EXIT_FAILURE);
   }
 
   /* Close the libnbd handle. */
   nbd_close (nbd);
 
   exit (EXIT_SUCCESS);
 }

See Also

nbd_connect_uri(3), nbd_create(3), nbd_get_tls(3), nbd_get_tls_negotiated(3), nbd_set_tls_certificates(3), nbd_set_tls_psk_file(3), nbd_set_tls_username(3), nbd_supports_tls(3), “ENCRYPTION AND AUTHENTICATION” in libnbd(3), libnbd(3).

Authors

Eric Blake

Richard W.M. Jones

License

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

Referenced By

libnbd(3), nbd_connect_uri(3), nbd_get_tls(3), nbd_get_tls_negotiated(3), nbd_set_tls_certificates(3), nbd_set_tls_psk_file(3), nbd_set_tls_username(3), nbd_set_tls_verify_peer(3), nbd_supports_tls(3).

2020-05-26 libnbd-1.3.7