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 "ssh.h"
  29 #include "xmalloc.h"
  30 #include "log.h"
  31 #include "auth.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 RCSID("$Id$");
  40
  41 #define NEW_AUTHTOK_MSG \
  42         "Warning: Your password has expired, please change it now"
  43
  44 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  45         struct pam_response **resp, void *appdata_ptr);
  46
  47 /* module-local variables */
  48 static struct pam_conv conv = {
  49         do_pam_conversation,
  50         NULL
  51 };
  52 static char *__pam_msg = NULL;
  53 static pam_handle_t *__pamh = NULL;
  54 static const char *__pampasswd = NULL;
  55
  56 /* states for do_pam_conversation() */
  57 enum { INITIAL_LOGIN, OTHER } pamstate = INITIAL_LOGIN;
  58 /* remember whether pam_acct_mgmt() returned PAM_NEWAUTHTOK_REQD */
  59 static int password_change_required = 0;
  60 /* remember whether the last pam_authenticate() succeeded or not */
  61 static int was_authenticated = 0;
  62
  63 /* Remember what has been initialised */
  64 static int session_opened = 0;
  65 static int creds_set = 0;
  66
  67 /* accessor which allows us to switch conversation structs according to
  68  * the authentication method being used */
  69 void do_pam_set_conv(struct pam_conv *conv)
  70 {
  71         pam_set_item(__pamh, PAM_CONV, conv);
  72 }
  73
  74 /* start an authentication run */
  75 int do_pam_authenticate(int flags)
  76 {
  77         int retval = pam_authenticate(__pamh, flags);
  78         was_authenticated = (retval == PAM_SUCCESS);
  79         return retval;
  80 }
  81
  82 /*
  83  * PAM conversation function.
  84  * There are two states this can run in.
  85  *
  86  * INITIAL_LOGIN mode simply feeds the password from the client into
  87  * PAM in response to PAM_PROMPT_ECHO_OFF, and collects output
  88  * messages with into __pam_msg.  This is used during initial
  89  * authentication to bypass the normal PAM password prompt.
  90  *
  91  * OTHER mode handles PAM_PROMPT_ECHO_OFF with read_passphrase()
  92  * and outputs messages to stderr. This mode is used if pam_chauthtok()
  93  * is called to update expired passwords.
  94  */
  95 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  96         struct pam_response **resp, void *appdata_ptr)
  97 {
  98         struct pam_response *reply;
  99         int count;
 100         char buf[1024];
 101
 102         /* PAM will free this later */
 103         reply = malloc(num_msg * sizeof(*reply));
 104         if (reply == NULL)
 105                 return PAM_CONV_ERR;
 106
 107         for (count = 0; count < num_msg; count++) {
 108                 if (pamstate == INITIAL_LOGIN) {
 109                         /*
 110                          * We can't use stdio yet, queue messages for
 111                          * printing later
 112                          */
 113                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 114                         case PAM_PROMPT_ECHO_ON:
 115                                 free(reply);
 116                                 return PAM_CONV_ERR;
 117                         case PAM_PROMPT_ECHO_OFF:
 118                                 if (__pampasswd == NULL) {
 119                                         free(reply);
 120                                         return PAM_CONV_ERR;
 121                                 }
 122                                 reply[count].resp = xstrdup(__pampasswd);
 123                                 reply[count].resp_retcode = PAM_SUCCESS;
 124                                 break;
 125                         case PAM_ERROR_MSG:
 126                         case PAM_TEXT_INFO:
 127                                 if ((*msg)[count].msg != NULL) {
 128                                         message_cat(&__pam_msg,
 129                                             PAM_MSG_MEMBER(msg, count, msg));
 130                                 }
 131                                 reply[count].resp = xstrdup("");
 132                                 reply[count].resp_retcode = PAM_SUCCESS;
 133                                 break;
 134                         default:
 135                                 free(reply);
 136                                 return PAM_CONV_ERR;
 137                         }
 138                 } else {
 139                         /*
 140                          * stdio is connected, so interact directly
 141                          */
 142                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 143                         case PAM_PROMPT_ECHO_ON:
 144                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 145                                 fgets(buf, sizeof(buf), stdin);
 146                                 reply[count].resp = xstrdup(buf);
 147                                 reply[count].resp_retcode = PAM_SUCCESS;
 148                                 break;
 149                         case PAM_PROMPT_ECHO_OFF:
 150                                 reply[count].resp =
 151                                     read_passphrase(PAM_MSG_MEMBER(msg, count,
 152                                         msg), RP_ALLOW_STDIN);
 153                                 reply[count].resp_retcode = PAM_SUCCESS;
 154                                 break;
 155                         case PAM_ERROR_MSG:
 156                         case PAM_TEXT_INFO:
 157                                 if ((*msg)[count].msg != NULL)
 158                                         fprintf(stderr, "%s\n",
 159                                             PAM_MSG_MEMBER(msg, count, msg));
 160                                 reply[count].resp = xstrdup("");
 161                                 reply[count].resp_retcode = PAM_SUCCESS;
 162                                 break;
 163                         default:
 164                                 free(reply);
 165                                 return PAM_CONV_ERR;
 166                         }
 167                 }
 168         }
 169
 170         *resp = reply;
 171
 172         return PAM_SUCCESS;
 173 }
 174
 175 /* Called at exit to cleanly shutdown PAM */
 176 void do_pam_cleanup_proc(void *context)
 177 {
 178         int pam_retval = PAM_SUCCESS;
 179
 180         if (__pamh && session_opened) {
 181                 pam_retval = pam_close_session(__pamh, 0);
 182                 if (pam_retval != PAM_SUCCESS)
 183                         log("Cannot close PAM session[%d]: %.200s",
 184                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 185         }
 186
 187         if (__pamh && creds_set) {
 188                 pam_retval = pam_setcred(__pamh, PAM_DELETE_CRED);
 189                 if (pam_retval != PAM_SUCCESS)
 190                         debug("Cannot delete credentials[%d]: %.200s",
 191                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 192         }
 193
 194         if (__pamh) {
 195                 pam_retval = pam_end(__pamh, pam_retval);
 196                 if (pam_retval != PAM_SUCCESS)
 197                         log("Cannot release PAM authentication[%d]: %.200s",
 198                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 199         }
 200 }
 201
 202 /* Attempt password authentation using PAM */
 203 int auth_pam_password(Authctxt *authctxt, const char *password)
 204 {
 205         extern ServerOptions options;
 206         int pam_retval;
 207         struct passwd *pw = authctxt->pw;
 208
 209         do_pam_set_conv(&conv);
 210
 211         /* deny if no user. */
 212         if (pw == NULL)
 213                 return 0;
 214         if (pw->pw_uid == 0 && options.permit_root_login == PERMIT_NO_PASSWD)
 215                 return 0;
 216         if (*password == '\0' && options.permit_empty_passwd == 0)
 217                 return 0;
 218
 219         __pampasswd = password;
 220
 221         pamstate = INITIAL_LOGIN;
 222         pam_retval = do_pam_authenticate(
 223             options.permit_empty_passwd == 0 ? PAM_DISALLOW_NULL_AUTHTOK : 0);
 224         if (pam_retval == PAM_SUCCESS) {
 225                 debug("PAM Password authentication accepted for "
 226                     "user \"%.100s\"", pw->pw_name);
 227                 return 1;
 228         } else {
 229                 debug("PAM Password authentication for \"%.100s\" "
 230                     "failed[%d]: %s", pw->pw_name, pam_retval,
 231                     PAM_STRERROR(__pamh, pam_retval));
 232                 return 0;
 233         }
 234 }
 235
 236 /* Do account management using PAM */
 237 int do_pam_account(char *username, char *remote_user)
 238 {
 239         int pam_retval;
 240
 241         do_pam_set_conv(&conv);
 242
 243         if (remote_user) {
 244                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 245                 pam_retval = pam_set_item(__pamh, PAM_RUSER, remote_user);
 246                 if (pam_retval != PAM_SUCCESS)
 247                         fatal("PAM set ruser failed[%d]: %.200s", pam_retval,
 248                             PAM_STRERROR(__pamh, pam_retval));
 249         }
 250
 251         pam_retval = pam_acct_mgmt(__pamh, 0);
 252         switch (pam_retval) {
 253                 case PAM_SUCCESS:
 254                         /* This is what we want */
 255                         break;
 256                 case PAM_NEW_AUTHTOK_REQD:
 257                         message_cat(&__pam_msg, NEW_AUTHTOK_MSG);
 258                         /* flag that password change is necessary */
 259                         password_change_required = 1;
 260                         break;
 261                 default:
 262                         log("PAM rejected by account configuration[%d]: "
 263                             "%.200s", pam_retval, PAM_STRERROR(__pamh,
 264                             pam_retval));
 265                         return(0);
 266         }
 267
 268         return(1);
 269 }
 270
 271 /* Do PAM-specific session initialisation */
 272 void do_pam_session(char *username, const char *ttyname)
 273 {
 274         int pam_retval;
 275
 276         do_pam_set_conv(&conv);
 277
 278         if (ttyname != NULL) {
 279                 debug("PAM setting tty to \"%.200s\"", ttyname);
 280                 pam_retval = pam_set_item(__pamh, PAM_TTY, ttyname);
 281                 if (pam_retval != PAM_SUCCESS)
 282                         fatal("PAM set tty failed[%d]: %.200s",
 283                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 284         }
 285
 286         pam_retval = pam_open_session(__pamh, 0);
 287         if (pam_retval != PAM_SUCCESS)
 288                 fatal("PAM session setup failed[%d]: %.200s",
 289                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 290
 291         session_opened = 1;
 292 }
 293
 294 /* Set PAM credentials */
 295 void do_pam_setcred(int init)
 296 {
 297         int pam_retval;
 298
 299         do_pam_set_conv(&conv);
 300
 301         debug("PAM establishing creds");
 302         pam_retval = pam_setcred(__pamh,
 303             init ? PAM_ESTABLISH_CRED : PAM_REINITIALIZE_CRED);
 304         if (pam_retval != PAM_SUCCESS) {
 305                 if (was_authenticated)
 306                         fatal("PAM setcred failed[%d]: %.200s",
 307                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 308                 else
 309                         debug("PAM setcred failed[%d]: %.200s",
 310                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 311         } else
 312                 creds_set = 1;
 313 }
 314
 315 /* accessor function for file scope static variable */
 316 int is_pam_password_change_required(void)
 317 {
 318         return password_change_required;
 319 }
 320
 321 /*
 322  * Have user change authentication token if pam_acct_mgmt() indicated
 323  * it was expired.  This needs to be called after an interactive
 324  * session is established and the user's pty is connected to
 325  * stdin/stout/stderr.
 326  */
 327 void do_pam_chauthtok(void)
 328 {
 329         int pam_retval;
 330
 331         do_pam_set_conv(&conv);
 332
 333         if (password_change_required) {
 334                 pamstate = OTHER;
 335                 pam_retval = pam_chauthtok(__pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 336                 if (pam_retval != PAM_SUCCESS)
 337                         fatal("PAM pam_chauthtok failed[%d]: %.200s",
 338                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 339         }
 340 }
 341
 342 /* Cleanly shutdown PAM */
 343 void finish_pam(void)
 344 {
 345         do_pam_cleanup_proc(NULL);
 346         fatal_remove_cleanup(&do_pam_cleanup_proc, NULL);
 347 }
 348
 349 /* Start PAM authentication for specified account */
 350 void start_pam(const char *user)
 351 {
 352         int pam_retval;
 353         extern ServerOptions options;
 354         extern u_int utmp_len;
 355         const char *rhost;
 356
 357         debug("Starting up PAM with username \"%.200s\"", user);
 358
 359         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &__pamh);
 360
 361         if (pam_retval != PAM_SUCCESS)
 362                 fatal("PAM initialisation failed[%d]: %.200s",
 363                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 364
 365         rhost = get_remote_name_or_ip(utmp_len, options.verify_reverse_mapping);
 366         debug("PAM setting rhost to \"%.200s\"", rhost);
 367
 368         pam_retval = pam_set_item(__pamh, PAM_RHOST, rhost);
 369         if (pam_retval != PAM_SUCCESS)
 370                 fatal("PAM set rhost failed[%d]: %.200s", pam_retval,
 371                     PAM_STRERROR(__pamh, pam_retval));
 372 #ifdef PAM_TTY_KLUDGE
 373         /*
 374          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 375          * and will fail in various stupid ways if they don't get one.
 376          * sshd doesn't set the tty until too late in the auth process and may
 377          * not even need one (for tty-less connections)
 378          * Kludge: Set a fake PAM_TTY
 379          */
 380         pam_retval = pam_set_item(__pamh, PAM_TTY, "NODEVssh");
 381         if (pam_retval != PAM_SUCCESS)
 382                 fatal("PAM set tty failed[%d]: %.200s",
 383                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 384 #endif /* PAM_TTY_KLUDGE */
 385
 386         fatal_add_cleanup(&do_pam_cleanup_proc, NULL);
 387 }
 388
 389 /* Return list of PAM enviornment strings */
 390 char **fetch_pam_environment(void)
 391 {
 392 #ifdef HAVE_PAM_GETENVLIST
 393         return(pam_getenvlist(__pamh));
 394 #else /* HAVE_PAM_GETENVLIST */
 395         return(NULL);
 396 #endif /* HAVE_PAM_GETENVLIST */
 397 }
 398
 399 /* Print any messages that have been generated during authentication */
 400 /* or account checking to stderr */
 401 void print_pam_messages(void)
 402 {
 403         if (__pam_msg != NULL)
 404                 fputs(__pam_msg, stderr);
 405 }
 406
 407 /* Append a message to buffer */
 408 void message_cat(char **p, const char *a)
 409 {
 410         char *cp;
 411         size_t new_len;
 412
 413         new_len = strlen(a);
 414
 415         if (*p) {
 416                 size_t len = strlen(*p);
 417
 418                 *p = xrealloc(*p, new_len + len + 2);
 419                 cp = *p + len;
 420         } else
 421                 *p = cp = xmalloc(new_len + 2);
 422
 423         memcpy(cp, a, new_len);
 424         cp[new_len] = '\n';
 425         cp[new_len + 1] = '\0';
 426 }
 427
 428 #endif /* USE_PAM */