nbd_set_tls(3)

1nbd_set_tls(3)                      LIBNBD                      nbd_set_tls(3)
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NAME

6       nbd_set_tls - enable or require TLS (authentication and encryption)
7

SYNOPSIS

9        #include <libnbd.h>
10
11        int nbd_set_tls (struct nbd_handle *h, int tls);
12

DESCRIPTION

14       Enable or require TLS (authenticated and encrypted connections) to the
15       NBD server.  The possible settings are:
16
17       "LIBNBD_TLS_DISABLE"
18           Disable TLS.  (The default setting, unless using nbd_connect_uri(3)
19           with a URI that requires TLS)
20
21       "LIBNBD_TLS_ALLOW"
22           Enable TLS if possible.
23
24           This option is insecure (or best effort) in that in some cases it
25           will fall back to an unencrypted and/or unauthenticated connection
26           if TLS could not be established.  Use "LIBNBD_TLS_REQUIRE" below if
27           the connection must be encrypted.
28
29           Some servers will drop the connection if TLS fails so fallback may
30           not be possible.
31
32       "LIBNBD_TLS_REQUIRE"
33           Require an encrypted and authenticated TLS connection.  Always fail
34           to connect if the connection is not encrypted and authenticated.
35
36       As well as calling this you may also need to supply the path to the
37       certificates directory (nbd_set_tls_certificates(3)), the username
38       (nbd_set_tls_username(3)) and/or the Pre-Shared Keys (PSK) file
39       (nbd_set_tls_psk_file(3)).  For now, when using nbd_connect_uri(3), any
40       URI query parameters related to TLS are not handled automatically.
41       Setting the level higher than zero will fail if libnbd was not compiled
42       against gnutls; you can test whether this is the case with
43       nbd_supports_tls(3).
44

RETURN VALUE

46       If the call is successful the function returns 0.
47

ERRORS

49       On error "-1" is returned.
50
51       Refer to "ERROR HANDLING" in libnbd(3) for how to get further details
52       of the error.
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HANDLE STATE

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

59       This function first appeared in libnbd 1.0.
60
61       If you need to test if this function is available at compile time check
62       if the following macro is defined:
63
64        #define LIBNBD_HAVE_NBD_SET_TLS 1
65

EXAMPLE

67       This example is also available as examples/encryption.c in the libnbd
68       source code.
69
70        /* An example showing how to connect to a server which is
71         * using TLS encryption.
72         *
73         * This requires nbdkit, and psktool from gnutls.
74         *
75         * Both libnbd and nbdkit support TLS-PSK which is a
76         * simpler-to-deploy form of encryption.  (Of course
77         * certificate-based encryption is also supported, but
78         * it’s harder to make a self-contained example).
79         */
80
81        #include <stdio.h>
82        #include <stdlib.h>
83        #include <string.h>
84        #include <unistd.h>
85
86        #include <libnbd.h>
87
88        #define TMPDIR "/tmp/XXXXXX"
89        #define KEYS "keys.psk"
90        #define USERNAME "alice"
91
92        static char dir[] = TMPDIR;
93        static char keys[] = TMPDIR "/" KEYS;
94        static char cmd[] =
95          "psktool -u " USERNAME " -p " TMPDIR "/" KEYS;
96
97        /* Remove the temporary keys file when the program
98         * exits.
99         */
100        static void
101        cleanup_keys (void)
102        {
103          unlink (keys);
104          rmdir (dir);
105        }
106
107        /* Create the temporary keys file to share with the
108         * server.
109         */
110        static void
111        create_keys (void)
112        {
113          size_t i;
114
115          if (mkdtemp (dir) == NULL) {
116            perror ("mkdtemp");
117            exit (EXIT_FAILURE);
118          }
119          i = strlen (cmd) - strlen (TMPDIR) - strlen (KEYS) - 1;
120          memcpy (&cmd[i], dir, strlen (TMPDIR));
121          memcpy (keys, dir, strlen (TMPDIR));
122
123          if (system (cmd) != 0) {
124            fprintf (stderr, "psktool command failed\n");
125            exit (EXIT_FAILURE);
126          }
127
128          atexit (cleanup_keys);
129        }
130
131        int
132        main (int argc, char *argv[])
133        {
134          struct nbd_handle *nbd;
135          char buf[512];
136
137          create_keys ();
138
139          /* Create the libnbd handle. */
140          nbd = nbd_create ();
141          if (nbd == NULL) {
142            fprintf (stderr, "%s\n", nbd_get_error ());
143            exit (EXIT_FAILURE);
144          }
145
146          /* Enable TLS in the client. */
147          if (nbd_set_tls (nbd, LIBNBD_TLS_REQUIRE) == -1) {
148            fprintf (stderr, "%s\n", nbd_get_error ());
149            exit (EXIT_FAILURE);
150          }
151
152          /* Enable TLS-PSK and pass the keys filename. */
153          if (nbd_set_tls_psk_file (nbd, keys) == -1) {
154            fprintf (stderr, "%s\n", nbd_get_error ());
155            exit (EXIT_FAILURE);
156          }
157
158          /* Set the local username for authentication. */
159          if (nbd_set_tls_username (nbd, USERNAME) == -1) {
160            fprintf (stderr, "%s\n", nbd_get_error ());
161            exit (EXIT_FAILURE);
162          }
163
164          /* Run nbdkit as a subprocess, enabling and requiring
165           * TLS-PSK encryption.
166           */
167          char *args[] = {
168            "nbdkit", "-s", "--exit-with-parent",
169            "--tls", "require", "--tls-psk", keys,
170            "pattern", "size=1M", NULL
171          };
172          if (nbd_connect_command (nbd, args) == -1) {
173            fprintf (stderr, "%s\n", nbd_get_error ());
174            exit (EXIT_FAILURE);
175          }
176
177          /* Read the first sector. */
178          if (nbd_pread (nbd, buf, sizeof buf, 0, 0) == -1) {
179            fprintf (stderr, "%s\n", nbd_get_error ());
180            exit (EXIT_FAILURE);
181          }
182
183          /* TLS connections must be shut down. */
184          if (nbd_shutdown (nbd, 0) == -1) {
185            fprintf (stderr, "%s\n", nbd_get_error ());
186            exit (EXIT_FAILURE);
187          }
188
189          /* Close the libnbd handle. */
190          nbd_close (nbd);
191
192          exit (EXIT_SUCCESS);
193        }
194

AUTHORS

202       Eric Blake
203
204       Richard W.M. Jones
205

COPYRIGHT

207       Copyright (C) 2019-2020 Red Hat Inc.
208

LICENSE

210       This library is free software; you can redistribute it and/or modify it
211       under the terms of the GNU Lesser General Public License as published
212       by the Free Software Foundation; either version 2 of the License, or
213       (at your option) any later version.
214
215       This library is distributed in the hope that it will be useful, but
216       WITHOUT ANY WARRANTY; without even the implied warranty of
217       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
218       Lesser General Public License for more details.
219
220       You should have received a copy of the GNU Lesser General Public
221       License along with this library; if not, write to the Free Software
222       Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
223       02110-1301 USA
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227libnbd-1.6.2                      2021-03-02                    nbd_set_tls(3)