auth-pam.c

   1 /*
   2  * Copyright (c) 2000 Damien Miller.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24
  25 #include "includes.h"
  26
  27 #ifdef USE_PAM
  28 #include "xmalloc.h"
  29 #include "log.h"
  30 #include "auth.h"
  31 #include "auth-options.h"
  32 #include "auth-pam.h"
  33 #include "servconf.h"
  34 #include "canohost.h"
  35 #include "readpass.h"
  36
  37 extern char *__progname;
  38
  39 extern int use_privsep;
  40
  41 RCSID("$Id$");
  42
  43 #define NEW_AUTHTOK_MSG \
  44         "Warning: Your password has expired, please change it now."
  45 #define NEW_AUTHTOK_MSG_PRIVSEP \
  46         "Your password has expired, the session cannot proceed."
  47
  48 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  49         struct pam_response **resp, void *appdata_ptr);
  50
  51 /* module-local variables */
  52 static struct pam_conv conv = {
  53         (int (*)())do_pam_conversation,
  54         NULL
  55 };
  56 static char *__pam_msg = NULL;
  57 static pam_handle_t *__pamh = NULL;
  58 static const char *__pampasswd = NULL;
  59
  60 /* states for do_pam_conversation() */
  61 enum { INITIAL_LOGIN, OTHER } pamstate = INITIAL_LOGIN;
  62 /* remember whether pam_acct_mgmt() returned PAM_NEW_AUTHTOK_REQD */
  63 static int password_change_required = 0;
  64 /* remember whether the last pam_authenticate() succeeded or not */
  65 static int was_authenticated = 0;
  66
  67 /* Remember what has been initialised */
  68 static int session_opened = 0;
  69 static int creds_set = 0;
  70
  71 /* accessor which allows us to switch conversation structs according to
  72  * the authentication method being used */
  73 void do_pam_set_conv(struct pam_conv *conv)
  74 {
  75         pam_set_item(__pamh, PAM_CONV, conv);
  76 }
  77
  78 /* start an authentication run */
  79 int do_pam_authenticate(int flags)
  80 {
  81         int retval = pam_authenticate(__pamh, flags);
  82         was_authenticated = (retval == PAM_SUCCESS);
  83         return retval;
  84 }
  85
  86 /*
  87  * PAM conversation function.
  88  * There are two states this can run in.
  89  *
  90  * INITIAL_LOGIN mode simply feeds the password from the client into
  91  * PAM in response to PAM_PROMPT_ECHO_OFF, and collects output
  92  * messages with into __pam_msg.  This is used during initial
  93  * authentication to bypass the normal PAM password prompt.
  94  *
  95  * OTHER mode handles PAM_PROMPT_ECHO_OFF with read_passphrase()
  96  * and outputs messages to stderr. This mode is used if pam_chauthtok()
  97  * is called to update expired passwords.
  98  */
  99 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
 100         struct pam_response **resp, void *appdata_ptr)
 101 {
 102         struct pam_response *reply;
 103         int count;
 104         char buf[1024];
 105
 106         /* PAM will free this later */
 107         reply = xmalloc(num_msg * sizeof(*reply));
 108
 109         for (count = 0; count < num_msg; count++) {
 110                 if (pamstate == INITIAL_LOGIN) {
 111                         /*
 112                          * We can't use stdio yet, queue messages for
 113                          * printing later
 114                          */
 115                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 116                         case PAM_PROMPT_ECHO_ON:
 117                                 xfree(reply);
 118                                 return PAM_CONV_ERR;
 119                         case PAM_PROMPT_ECHO_OFF:
 120                                 if (__pampasswd == NULL) {
 121                                         xfree(reply);
 122                                         return PAM_CONV_ERR;
 123                                 }
 124                                 reply[count].resp = xstrdup(__pampasswd);
 125                                 reply[count].resp_retcode = PAM_SUCCESS;
 126                                 break;
 127                         case PAM_ERROR_MSG:
 128                         case PAM_TEXT_INFO:
 129                                 if (PAM_MSG_MEMBER(msg, count, msg) != NULL) {
 130                                         message_cat(&__pam_msg,
 131                                             PAM_MSG_MEMBER(msg, count, msg));
 132                                 }
 133                                 reply[count].resp = xstrdup("");
 134                                 reply[count].resp_retcode = PAM_SUCCESS;
 135                                 break;
 136                         default:
 137                                 xfree(reply);
 138                                 return PAM_CONV_ERR;
 139                         }
 140                 } else {
 141                         /*
 142                          * stdio is connected, so interact directly
 143                          */
 144                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 145                         case PAM_PROMPT_ECHO_ON:
 146                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 147                                 fgets(buf, sizeof(buf), stdin);
 148                                 reply[count].resp = xstrdup(buf);
 149                                 reply[count].resp_retcode = PAM_SUCCESS;
 150                                 break;
 151                         case PAM_PROMPT_ECHO_OFF:
 152                                 reply[count].resp =
 153                                     read_passphrase(PAM_MSG_MEMBER(msg, count,
 154                                         msg), RP_ALLOW_STDIN);
 155                                 reply[count].resp_retcode = PAM_SUCCESS;
 156                                 break;
 157                         case PAM_ERROR_MSG:
 158                         case PAM_TEXT_INFO:
 159                                 if ((*msg)[count].msg != NULL)
 160                                         fprintf(stderr, "%s\n",
 161                                             PAM_MSG_MEMBER(msg, count, msg));
 162                                 reply[count].resp = xstrdup("");
 163                                 reply[count].resp_retcode = PAM_SUCCESS;
 164                                 break;
 165                         default:
 166                                 xfree(reply);
 167                                 return PAM_CONV_ERR;
 168                         }
 169                 }
 170         }
 171
 172         *resp = reply;
 173
 174         return PAM_SUCCESS;
 175 }
 176
 177 /* Called at exit to cleanly shutdown PAM */
 178 void do_pam_cleanup_proc(void *context)
 179 {
 180         int pam_retval = PAM_SUCCESS;
 181
 182         if (__pamh && session_opened) {
 183                 pam_retval = pam_close_session(__pamh, 0);
 184                 if (pam_retval != PAM_SUCCESS)
 185                         log("Cannot close PAM session[%d]: %.200s",
 186                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 187         }
 188
 189         if (__pamh && creds_set) {
 190                 pam_retval = pam_setcred(__pamh, PAM_DELETE_CRED);
 191                 if (pam_retval != PAM_SUCCESS)
 192                         debug("Cannot delete credentials[%d]: %.200s",
 193                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 194         }
 195
 196         if (__pamh) {
 197                 pam_retval = pam_end(__pamh, pam_retval);
 198                 if (pam_retval != PAM_SUCCESS)
 199                         log("Cannot release PAM authentication[%d]: %.200s",
 200                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 201         }
 202 }
 203
 204 /* Attempt password authentation using PAM */
 205 int auth_pam_password(Authctxt *authctxt, const char *password)
 206 {
 207         extern ServerOptions options;
 208         int pam_retval;
 209         struct passwd *pw = authctxt->pw;
 210
 211         do_pam_set_conv(&conv);
 212
 213         /* deny if no user. */
 214         if (pw == NULL)
 215                 return 0;
 216         if (pw->pw_uid == 0 && options.permit_root_login == PERMIT_NO_PASSWD)
 217                 return 0;
 218         if (*password == '\0' && options.permit_empty_passwd == 0)
 219                 return 0;
 220
 221         __pampasswd = password;
 222
 223         pamstate = INITIAL_LOGIN;
 224         pam_retval = do_pam_authenticate(
 225             options.permit_empty_passwd == 0 ? PAM_DISALLOW_NULL_AUTHTOK : 0);
 226         if (pam_retval == PAM_SUCCESS) {
 227                 debug("PAM Password authentication accepted for "
 228                     "user \"%.100s\"", pw->pw_name);
 229                 return 1;
 230         } else {
 231                 debug("PAM Password authentication for \"%.100s\" "
 232                     "failed[%d]: %s", pw->pw_name, pam_retval,
 233                     PAM_STRERROR(__pamh, pam_retval));
 234                 return 0;
 235         }
 236 }
 237
 238 /* Do account management using PAM */
 239 int do_pam_account(char *username, char *remote_user)
 240 {
 241         int pam_retval;
 242
 243         do_pam_set_conv(&conv);
 244
 245         if (remote_user) {
 246                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 247                 pam_retval = pam_set_item(__pamh, PAM_RUSER, remote_user);
 248                 if (pam_retval != PAM_SUCCESS)
 249                         fatal("PAM set ruser failed[%d]: %.200s", pam_retval,
 250                             PAM_STRERROR(__pamh, pam_retval));
 251         }
 252
 253         pam_retval = pam_acct_mgmt(__pamh, 0);
 254         debug2("pam_acct_mgmt() = %d", pam_retval);
 255         switch (pam_retval) {
 256                 case PAM_SUCCESS:
 257                         /* This is what we want */
 258                         break;
 259 #if 0
 260                 case PAM_NEW_AUTHTOK_REQD:
 261                         message_cat(&__pam_msg, use_privsep ?
 262                             NEW_AUTHTOK_MSG_PRIVSEP : NEW_AUTHTOK_MSG);
 263                         /* flag that password change is necessary */
 264                         password_change_required = 1;
 265                         /* disallow other functionality for now */
 266                         no_port_forwarding_flag |= 2;
 267                         no_agent_forwarding_flag |= 2;
 268                         no_x11_forwarding_flag |= 2;
 269                         break;
 270 #endif
 271                 default:
 272                         log("PAM rejected by account configuration[%d]: "
 273                             "%.200s", pam_retval, PAM_STRERROR(__pamh,
 274                             pam_retval));
 275                         return(0);
 276         }
 277
 278         return(1);
 279 }
 280
 281 /* Do PAM-specific session initialisation */
 282 void do_pam_session(char *username, const char *ttyname)
 283 {
 284         int pam_retval;
 285
 286         do_pam_set_conv(&conv);
 287
 288         if (ttyname != NULL) {
 289                 debug("PAM setting tty to \"%.200s\"", ttyname);
 290                 pam_retval = pam_set_item(__pamh, PAM_TTY, ttyname);
 291                 if (pam_retval != PAM_SUCCESS)
 292                         fatal("PAM set tty failed[%d]: %.200s",
 293                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 294         }
 295
 296         pam_retval = pam_open_session(__pamh, 0);
 297         if (pam_retval != PAM_SUCCESS)
 298                 fatal("PAM session setup failed[%d]: %.200s",
 299                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 300
 301         session_opened = 1;
 302 }
 303
 304 /* Set PAM credentials */
 305 void do_pam_setcred(int init)
 306 {
 307         int pam_retval;
 308
 309         if (__pamh == NULL)
 310                 return;
 311
 312         do_pam_set_conv(&conv);
 313
 314         debug("PAM establishing creds");
 315         pam_retval = pam_setcred(__pamh,
 316             init ? PAM_ESTABLISH_CRED : PAM_REINITIALIZE_CRED);
 317         if (pam_retval != PAM_SUCCESS) {
 318                 if (was_authenticated)
 319                         fatal("PAM setcred failed[%d]: %.200s",
 320                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 321                 else
 322                         debug("PAM setcred failed[%d]: %.200s",
 323                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 324         } else
 325                 creds_set = 1;
 326 }
 327
 328 /* accessor function for file scope static variable */
 329 int is_pam_password_change_required(void)
 330 {
 331         return password_change_required;
 332 }
 333
 334 /*
 335  * Have user change authentication token if pam_acct_mgmt() indicated
 336  * it was expired.  This needs to be called after an interactive
 337  * session is established and the user's pty is connected to
 338  * stdin/stdout/stderr.
 339  */
 340 void do_pam_chauthtok(void)
 341 {
 342         int pam_retval;
 343
 344         do_pam_set_conv(&conv);
 345
 346         if (password_change_required) {
 347                 if (use_privsep)
 348                         fatal("Password changing is currently unsupported"
 349                             " with privilege separation");
 350                 pamstate = OTHER;
 351                 pam_retval = pam_chauthtok(__pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 352                 if (pam_retval != PAM_SUCCESS)
 353                         fatal("PAM pam_chauthtok failed[%d]: %.200s",
 354                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 355 #if 0
 356                 /* XXX: This would need to be done in the parent process,
 357                  * but there's currently no way to pass such request. */
 358                 no_port_forwarding_flag &= ~2;
 359                 no_agent_forwarding_flag &= ~2;
 360                 no_x11_forwarding_flag &= ~2;
 361                 if (!no_port_forwarding_flag && options.allow_tcp_forwarding)
 362                         channel_permit_all_opens();
 363 #endif
 364         }
 365 }
 366
 367 /* Cleanly shutdown PAM */
 368 void finish_pam(void)
 369 {
 370         do_pam_cleanup_proc(NULL);
 371         fatal_remove_cleanup(&do_pam_cleanup_proc, NULL);
 372 }
 373
 374 /* Start PAM authentication for specified account */
 375 void start_pam(const char *user)
 376 {
 377         int pam_retval;
 378         extern ServerOptions options;
 379         extern u_int utmp_len;
 380         const char *rhost;
 381
 382         debug("Starting up PAM with username \"%.200s\"", user);
 383
 384         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &__pamh);
 385
 386         if (pam_retval != PAM_SUCCESS)
 387                 fatal("PAM initialisation failed[%d]: %.200s",
 388                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 389
 390         rhost = get_remote_name_or_ip(utmp_len, options.verify_reverse_mapping);
 391         debug("PAM setting rhost to \"%.200s\"", rhost);
 392
 393         pam_retval = pam_set_item(__pamh, PAM_RHOST, rhost);
 394         if (pam_retval != PAM_SUCCESS)
 395                 fatal("PAM set rhost failed[%d]: %.200s", pam_retval,
 396                     PAM_STRERROR(__pamh, pam_retval));
 397 #ifdef PAM_TTY_KLUDGE
 398         /*
 399          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 400          * and will fail in various stupid ways if they don't get one.
 401          * sshd doesn't set the tty until too late in the auth process and may
 402          * not even need one (for tty-less connections)
 403          * Kludge: Set a fake PAM_TTY
 404          */
 405         pam_retval = pam_set_item(__pamh, PAM_TTY, "NODEVssh");
 406         if (pam_retval != PAM_SUCCESS)
 407                 fatal("PAM set tty failed[%d]: %.200s",
 408                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 409 #endif /* PAM_TTY_KLUDGE */
 410
 411         fatal_add_cleanup(&do_pam_cleanup_proc, NULL);
 412 }
 413
 414 /* Return list of PAM environment strings */
 415 char **fetch_pam_environment(void)
 416 {
 417 #ifdef HAVE_PAM_GETENVLIST
 418         return(pam_getenvlist(__pamh));
 419 #else /* HAVE_PAM_GETENVLIST */
 420         return(NULL);
 421 #endif /* HAVE_PAM_GETENVLIST */
 422 }
 423
 424 void free_pam_environment(char **env)
 425 {
 426         int i;
 427
 428         if (env != NULL) {
 429                 for (i = 0; env[i] != NULL; i++)
 430                         xfree(env[i]);
 431         }
 432 }
 433
 434 /* Print any messages that have been generated during authentication */
 435 /* or account checking to stderr */
 436 void print_pam_messages(void)
 437 {
 438         if (__pam_msg != NULL)
 439                 fputs(__pam_msg, stderr);
 440 }
 441
 442 /* Append a message to buffer */
 443 void message_cat(char **p, const char *a)
 444 {
 445         char *cp;
 446         size_t new_len;
 447
 448         new_len = strlen(a);
 449
 450         if (*p) {
 451                 size_t len = strlen(*p);
 452
 453                 *p = xrealloc(*p, new_len + len + 2);
 454                 cp = *p + len;
 455         } else
 456                 *p = cp = xmalloc(new_len + 2);
 457
 458         memcpy(cp, a, new_len);
 459         cp[new_len] = '\n';
 460         cp[new_len + 1] = '\0';
 461 }
 462
 463 #endif /* USE_PAM */