server/crypto.c

   1 /* nbdkit
   2  * Copyright (C) 2017 Red Hat Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdarg.h>
  38 #include <stdint.h>
  39 #include <stdbool.h>
  40 #include <inttypes.h>
  41 #include <string.h>
  42 #include <unistd.h>
  43 #include <fcntl.h>
  44 #include <limits.h>
  45 #include <errno.h>
  46 #include <sys/types.h>
  47 #include <assert.h>
  48
  49 #include "internal.h"
  50
  51 #ifdef HAVE_GNUTLS
  52
  53 #include <gnutls/gnutls.h>
  54
  55 static int crypto_auth;
  56 #define CRYPTO_AUTH_CERTIFICATES 1
  57 #define CRYPTO_AUTH_PSK 2
  58
  59 static gnutls_certificate_credentials_t x509_creds;
  60 static gnutls_psk_server_credentials_t psk_creds;
  61
  62 static void print_gnutls_error (int err, const char *fs, ...)
  63   __attribute__((format (printf, 2, 3)));
  64
  65 static void
  66 print_gnutls_error (int err, const char *fs, ...)
  67 {
  68   va_list args;
  69
  70   fprintf (stderr, "%s: GnuTLS error: ", program_name);
  71
  72   va_start (args, fs);
  73   vfprintf (stderr, fs, args);
  74   va_end (args);
  75
  76   fprintf (stderr, ": %s\n", gnutls_strerror (err));
  77 }
  78
  79 /* Try to load certificates from 'path'.  Returns true if successful.
  80  * If it's not a certicate directory it returns false.  Exits on
  81  * other errors.
  82  */
  83 static int
  84 load_certificates (const char *path)
  85 {
  86   CLEANUP_FREE char *ca_cert_filename = NULL;
  87   CLEANUP_FREE char *server_cert_filename = NULL;
  88   CLEANUP_FREE char *server_key_filename = NULL;
  89   CLEANUP_FREE char *ca_crl_filename = NULL;
  90   int err;
  91
  92   if (asprintf (&ca_cert_filename, "%s/ca-cert.pem", path) == -1) {
  93     perror ("asprintf");
  94     exit (EXIT_FAILURE);
  95   }
  96   if (asprintf (&server_cert_filename, "%s/server-cert.pem", path) == -1) {
  97     perror ("asprintf");
  98     exit (EXIT_FAILURE);
  99   }
 100   if (asprintf (&server_key_filename, "%s/server-key.pem", path) == -1) {
 101     perror ("asprintf");
 102     exit (EXIT_FAILURE);
 103   }
 104   if (asprintf (&ca_crl_filename, "%s/ca-crl.pem", path) == -1) {
 105     perror ("asprintf");
 106     exit (EXIT_FAILURE);
 107   }
 108
 109   /* Our test for a certificate directory is that ca-cert.pem,
 110    * server-cert.pem and server-key.pem must all exist in the path.
 111    */
 112   if (access (ca_cert_filename, R_OK) == -1)
 113     return 0;
 114   if (access (server_cert_filename, R_OK) == -1)
 115     return 0;
 116   if (access (server_key_filename, R_OK) == -1)
 117     return 0;
 118
 119   /* Any problem past here is a hard error. */
 120
 121   err = gnutls_certificate_allocate_credentials (&x509_creds);
 122   if (err < 0) {
 123     print_gnutls_error (err, "allocating credentials");
 124     exit (EXIT_FAILURE);
 125   }
 126   err = gnutls_certificate_set_x509_trust_file (x509_creds, ca_cert_filename,
 127                                                 GNUTLS_X509_FMT_PEM);
 128   if (err < 0) {
 129     print_gnutls_error (err, "loading %s", ca_cert_filename);
 130     exit (EXIT_FAILURE);
 131   }
 132
 133   if (access (ca_crl_filename, R_OK) == 0) {
 134     err = gnutls_certificate_set_x509_crl_file (x509_creds, ca_crl_filename,
 135                                                 GNUTLS_X509_FMT_PEM);
 136     if (err < 0) {
 137       print_gnutls_error (err, "loading %s", ca_crl_filename);
 138       exit (EXIT_FAILURE);
 139     }
 140   }
 141
 142   err = gnutls_certificate_set_x509_key_file (x509_creds,
 143                                               server_cert_filename,
 144                                               server_key_filename,
 145                                               GNUTLS_X509_FMT_PEM);
 146   if (err < 0) {
 147     print_gnutls_error (err, "loading server certificate and key (%s, %s)",
 148                         server_cert_filename, server_key_filename);
 149     exit (EXIT_FAILURE);
 150   }
 151
 152   debug ("successfully loaded TLS certificates from %s", path);
 153   return 1;
 154 }
 155
 156 static int
 157 start_certificates (void)
 158 {
 159   /* Try to locate the certificates directory and load them. */
 160   if (tls_certificates_dir == NULL) {
 161     const char *home;
 162     CLEANUP_FREE char *path = NULL;
 163
 164     if (geteuid () != 0) {
 165       home = getenv ("HOME");
 166       if (home) {
 167         if (asprintf (&path, "%s/.pki/%s", home, PACKAGE_NAME) == -1) {
 168           perror ("asprintf");
 169           exit (EXIT_FAILURE);
 170         }
 171         if (load_certificates (path))
 172           goto found_certificates;
 173         free (path);
 174         if (asprintf (&path, "%s/.config/pki/%s", home, PACKAGE_NAME) == -1) {
 175           perror ("asprintf");
 176           exit (EXIT_FAILURE);
 177         }
 178         if (load_certificates (path))
 179           goto found_certificates;
 180       }
 181     }
 182     else { /* geteuid () == 0 */
 183       if (load_certificates (root_tls_certificates_dir))
 184         goto found_certificates;
 185     }
 186   }
 187   else {
 188     if (load_certificates (tls_certificates_dir))
 189       goto found_certificates;
 190   }
 191   return -1;
 192
 193  found_certificates:
 194 #ifdef HAVE_GNUTLS_CERTIFICATE_SET_KNOWN_DH_PARAMS
 195   gnutls_certificate_set_known_dh_params (x509_creds, GNUTLS_SEC_PARAM_MEDIUM);
 196 #endif
 197   return 0;
 198 }
 199
 200 static int
 201 start_psk (void)
 202 {
 203   int err;
 204   CLEANUP_FREE char *abs_psk_file = NULL;
 205
 206   /* Make sure the path to the PSK file is absolute. */
 207   abs_psk_file = realpath (tls_psk, NULL);
 208   if (abs_psk_file == NULL) {
 209     perror (tls_psk);
 210     exit (EXIT_FAILURE);
 211   }
 212
 213   err = gnutls_psk_allocate_server_credentials (&psk_creds);
 214   if (err < 0) {
 215     print_gnutls_error (err, "allocating PSK credentials");
 216     exit (EXIT_FAILURE);
 217   }
 218
 219   /* Note that this function makes a copy of the string.
 220    * CLEANUP_FREE macro above will free abs_psk_file when
 221    * we return, but this is safe.
 222    */
 223   gnutls_psk_set_server_credentials_file (psk_creds, abs_psk_file);
 224
 225   return 0;
 226 }
 227
 228 /* Initialize crypto.  This also handles the command line parameters
 229  * and loading the server certificate.
 230  */
 231 void
 232 crypto_init (bool tls_set_on_cli)
 233 {
 234   int err, r;
 235   const char *what;
 236
 237   err = gnutls_global_init ();
 238   if (err < 0) {
 239     print_gnutls_error (err, "initializing GnuTLS");
 240     exit (EXIT_FAILURE);
 241   }
 242
 243   if (tls == 0)                 /* --tls=off */
 244     return;
 245
 246   /* --tls-psk overrides certificates. */
 247   if (tls_psk != NULL) {
 248     what = "Pre-Shared Keys (PSK)";
 249     r = start_psk ();
 250     if (r == 0)
 251       crypto_auth = CRYPTO_AUTH_PSK;
 252   }
 253   else {
 254     what = "X.509 certificates";
 255     r = start_certificates ();
 256     if (r == 0)
 257       crypto_auth = CRYPTO_AUTH_CERTIFICATES;
 258   }
 259
 260   if (r == 0) {
 261     debug ("TLS enabled using: %s", what);
 262     return;
 263   }
 264
 265   /* If we get here, we didn't manage to load the PSK file /
 266    * certificates.  If --tls=require was given on the command line
 267    * then that's a problem.
 268    */
 269   if (tls == 2) {               /* --tls=require */
 270     fprintf (stderr,
 271              "%s: --tls=require but could not load TLS certificates.\n"
 272              "Try setting ‘--tls-certificates=/path/to/certificates’ or read\n"
 273              "the \"TLS\" section in nbdkit(1).\n",
 274              program_name);
 275     exit (EXIT_FAILURE);
 276   }
 277
 278   /* If --tls=on was given on the command line, warn before we turn
 279    * TLS off.
 280    */
 281   if (tls == 1 && tls_set_on_cli) { /* explicit --tls=on */
 282     fprintf (stderr,
 283              "%s: warning: --tls=on but could not load TLS certificates.\n"
 284              "TLS will be disabled and TLS connections will be rejected.\n"
 285              "Try setting ‘--tls-certificates=/path/to/certificates’ or read\n"
 286              "the \"TLS\" section in nbdkit(1).\n",
 287              program_name);
 288   }
 289
 290   tls = 0;
 291   debug ("TLS disabled: could not load TLS certificates");
 292 }
 293
 294 void
 295 crypto_free (void)
 296 {
 297   if (tls > 0) {
 298     switch (crypto_auth) {
 299     case CRYPTO_AUTH_CERTIFICATES:
 300       gnutls_certificate_free_credentials (x509_creds);
 301       break;
 302     case CRYPTO_AUTH_PSK:
 303       gnutls_psk_free_server_credentials (psk_creds);
 304       break;
 305     }
 306   }
 307
 308   gnutls_global_deinit ();
 309 }
 310
 311 /* Read buffer from GnuTLS and either succeed completely
 312  * (returns > 0), read an EOF (returns 0), or fail (returns -1).
 313  */
 314 static int
 315 crypto_recv (struct connection *conn, void *vbuf, size_t len)
 316 {
 317   gnutls_session_t session = conn->crypto_session;
 318   char *buf = vbuf;
 319   ssize_t r;
 320   bool first_read = true;
 321
 322   assert (session != NULL);
 323
 324   while (len > 0) {
 325     r = gnutls_record_recv (session, buf, len);
 326     if (r < 0) {
 327       if (r == GNUTLS_E_INTERRUPTED || r == GNUTLS_E_AGAIN)
 328         continue;
 329       nbdkit_error ("gnutls_record_recv: %s", gnutls_strerror (r));
 330       errno = EIO;
 331       return -1;
 332     }
 333     if (r == 0) {
 334       if (first_read)
 335         return 0;
 336       /* Partial record read.  This is an error. */
 337       errno = EBADMSG;
 338       return -1;
 339     }
 340     first_read = false;
 341     buf += r;
 342     len -= r;
 343   }
 344
 345   return 1;
 346 }
 347
 348 /* If this send()'s length is so large that it is going to require
 349  * multiple TCP segments anyway, there's no need to try and merge it
 350  * with any corked data from a previous send that used SEND_MORE.
 351  */
 352 #define MAX_SEND_MORE_LEN (64 * 1024)
 353
 354 /* Write buffer to GnuTLS and either succeed completely
 355  * (returns 0) or fail (returns -1). flags is ignored for now.
 356  */
 357 static int
 358 crypto_send (struct connection *conn, const void *vbuf, size_t len, int flags)
 359 {
 360   gnutls_session_t session = conn->crypto_session;
 361   const char *buf = vbuf;
 362   ssize_t r;
 363
 364   assert (session != NULL);
 365
 366   if (len + gnutls_record_check_corked (session) > MAX_SEND_MORE_LEN) {
 367     if (gnutls_record_uncork (session, GNUTLS_RECORD_WAIT) < 0)
 368       return -1;
 369   }
 370   else if (flags & SEND_MORE)
 371     gnutls_record_cork (session);
 372
 373   while (len > 0) {
 374     r = gnutls_record_send (session, buf, len);
 375     if (r < 0) {
 376       if (r == GNUTLS_E_INTERRUPTED || r == GNUTLS_E_AGAIN)
 377         continue;
 378       return -1;
 379     }
 380     buf += r;
 381     len -= r;
 382   }
 383
 384   if (!(flags & SEND_MORE) &&
 385       gnutls_record_uncork (session, GNUTLS_RECORD_WAIT) < 0)
 386     return -1;
 387
 388   return 0;
 389 }
 390
 391 /* There's no place in the NBD protocol to send back errors from
 392  * close, so this function ignores errors.
 393  */
 394 static void
 395 crypto_close (struct connection *conn)
 396 {
 397   gnutls_session_t session = conn->crypto_session;
 398   int sockin, sockout;
 399
 400   assert (session != NULL);
 401
 402   gnutls_transport_get_int2 (session, &sockin, &sockout);
 403
 404   gnutls_bye (session, GNUTLS_SHUT_RDWR);
 405
 406   if (sockin >= 0)
 407     close (sockin);
 408   if (sockout >= 0 && sockin != sockout)
 409     close (sockout);
 410
 411   gnutls_deinit (session);
 412   conn->crypto_session = NULL;
 413 }
 414
 415 /* Upgrade an existing connection to TLS.  Also this should do access
 416  * control if enabled.  The protocol code ensures this function can
 417  * only be called once per connection.
 418  */
 419 int
 420 crypto_negotiate_tls (struct connection *conn, int sockin, int sockout)
 421 {
 422   gnutls_session_t session;
 423   CLEANUP_FREE char *priority = NULL;
 424   int err;
 425
 426   /* Create the GnuTLS session. */
 427   err = gnutls_init (&session, GNUTLS_SERVER);
 428   if (err < 0) {
 429     nbdkit_error ("gnutls_init: %s", gnutls_strerror (err));
 430     free (session);
 431     return -1;
 432   }
 433
 434   switch (crypto_auth) {
 435   case CRYPTO_AUTH_CERTIFICATES:
 436     /* Associate the session with the server credentials (key, cert). */
 437     err = gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE,
 438                                   x509_creds);
 439     if (err < 0) {
 440       nbdkit_error ("gnutls_credentials_set: %s", gnutls_strerror (err));
 441       goto error;
 442     }
 443
 444     /* If verify peer is enabled, tell GnuTLS to request the client
 445      * certificates.  (Note the default is to not request or verify
 446      * certificates).
 447      */
 448     if (tls_verify_peer) {
 449 #ifdef HAVE_GNUTLS_SESSION_SET_VERIFY_CERT
 450       gnutls_certificate_server_set_request (session, GNUTLS_CERT_REQUEST);
 451       gnutls_session_set_verify_cert (session, NULL, 0);
 452 #else
 453       nbdkit_error ("--tls-verify-peer: "
 454                     "GnuTLS >= 3.4.6 is required for this feature");
 455       goto error;
 456 #endif
 457     }
 458
 459     priority = strdup (TLS_PRIORITY);
 460     if (priority == NULL) {
 461       nbdkit_error ("strdup: %m");
 462       goto error;
 463     }
 464     break;
 465
 466   case CRYPTO_AUTH_PSK:
 467     /* Associate the session with the server PSK credentials. */
 468     err = gnutls_credentials_set (session, GNUTLS_CRD_PSK, psk_creds);
 469     if (err < 0) {
 470       nbdkit_error ("gnutls_credentials_set: %s", gnutls_strerror (err));
 471       goto error;
 472     }
 473
 474     if (asprintf (&priority,
 475                   "%s:+ECDHE-PSK:+DHE-PSK:+PSK", TLS_PRIORITY) == -1) {
 476       nbdkit_error ("asprintf: %m");
 477       goto error;
 478     }
 479     break;
 480
 481   default:
 482     abort ();
 483   }
 484
 485   assert (priority != NULL);
 486   err = gnutls_priority_set_direct (session, priority, NULL);
 487   if (err < 0) {
 488     nbdkit_error ("failed to set TLS session priority to %s: %s",
 489                   priority, gnutls_strerror (err));
 490     goto error;
 491   }
 492
 493   /* Set up GnuTLS so it reads and writes on the raw sockets. */
 494   gnutls_transport_set_int2 (session, sockin, sockout);
 495
 496   /* Perform the handshake. */
 497   debug ("starting TLS handshake");
 498   gnutls_handshake_set_timeout (session,
 499                                 GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);
 500
 501   do {
 502     err = gnutls_handshake (session);
 503   } while (err < 0 && gnutls_error_is_fatal (err) == 0);
 504   if (err < 0) {
 505     gnutls_handshake_description_t in, out;
 506
 507     /* Get some additional debug information about where in the
 508      * handshake protocol it failed.  You have to look up these codes in
 509      * <gnutls/gnutls.h>.
 510      */
 511     in = gnutls_handshake_get_last_in (session);
 512     out = gnutls_handshake_get_last_out (session);
 513     nbdkit_error ("gnutls_handshake: %s (%d/%d)",
 514                   gnutls_strerror (err), (int) in, (int) out);
 515     goto error;
 516   }
 517   debug ("TLS handshake completed");
 518
 519   /* Set up the connection recv/send/close functions so they call
 520    * GnuTLS wrappers instead.
 521    */
 522   conn->crypto_session = session;
 523   conn->recv = crypto_recv;
 524   conn->send = crypto_send;
 525   conn->close = crypto_close;
 526   return 0;
 527
 528  error:
 529   gnutls_deinit (session);
 530   return -1;
 531 }
 532
 533 #else /* !HAVE_GNUTLS */
 534
 535 /* GnuTLS was not available at compile time.  These are stub versions
 536  * of the above functions which either do nothing or report errors as
 537  * appropriate.
 538  */
 539
 540 void
 541 crypto_init (bool tls_set_on_cli)
 542 {
 543   if (tls > 0) {
 544     fprintf (stderr,
 545              "%s: TLS cannot be enabled because "
 546              "this binary was compiled without GnuTLS.\n",
 547              program_name);
 548     exit (EXIT_FAILURE);
 549   }
 550
 551   tls = 0;
 552   debug ("TLS disabled: nbdkit was not compiled with GnuTLS support");
 553 }
 554
 555 void
 556 crypto_free (void)
 557 {
 558   /* nothing */
 559 }
 560
 561 int
 562 crypto_negotiate_tls (struct connection *conn, int sockin, int sockout)
 563 {
 564   /* Should never be called because tls == 0. */
 565   abort ();
 566 }
 567
 568 #endif /* !HAVE_GNUTLS */