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-pam.h"
  32 #include "servconf.h"
  33 #include "canohost.h"
  34 #include "readpass.h"
  35
  36 RCSID("$Id$");
  37
  38 #define NEW_AUTHTOK_MSG \
  39         "Warning: Your password has expired, please change it now"
  40
  41 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  42         struct pam_response **resp, void *appdata_ptr);
  43
  44 /* module-local variables */
  45 static struct pam_conv conv = {
  46         do_pam_conversation,
  47         NULL
  48 };
  49 static char *__pam_msg = NULL;
  50 static pam_handle_t *__pamh = NULL;
  51 static const char *__pampasswd = NULL;
  52
  53 /* states for do_pam_conversation() */
  54 enum { INITIAL_LOGIN, OTHER } pamstate = INITIAL_LOGIN;
  55 /* remember whether pam_acct_mgmt() returned PAM_NEWAUTHTOK_REQD */
  56 static int password_change_required = 0;
  57 /* remember whether the last pam_authenticate() succeeded or not */
  58 static int was_authenticated = 0;
  59
  60 /* Remember what has been initialised */
  61 static int session_opened = 0;
  62 static int creds_set = 0;
  63
  64 /* accessor which allows us to switch conversation structs according to
  65  * the authentication method being used */
  66 void do_pam_set_conv(struct pam_conv *conv)
  67 {
  68         pam_set_item(__pamh, PAM_CONV, conv);
  69 }
  70
  71 /* start an authentication run */
  72 int do_pam_authenticate(int flags)
  73 {
  74         int retval = pam_authenticate(__pamh, flags);
  75         was_authenticated = (retval == PAM_SUCCESS);
  76         return retval;
  77 }
  78
  79 /*
  80  * PAM conversation function.
  81  * There are two states this can run in.
  82  *
  83  * INITIAL_LOGIN mode simply feeds the password from the client into
  84  * PAM in response to PAM_PROMPT_ECHO_OFF, and collects output
  85  * messages with into __pam_msg.  This is used during initial
  86  * authentication to bypass the normal PAM password prompt.
  87  *
  88  * OTHER mode handles PAM_PROMPT_ECHO_OFF with read_passphrase(prompt, 1)
  89  * and outputs messages to stderr. This mode is used if pam_chauthtok()
  90  * is called to update expired passwords.
  91  */
  92 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  93         struct pam_response **resp, void *appdata_ptr)
  94 {
  95         struct pam_response *reply;
  96         int count;
  97         char buf[1024];
  98
  99         /* PAM will free this later */
 100         reply = malloc(num_msg * sizeof(*reply));
 101         if (reply == NULL)
 102                 return PAM_CONV_ERR;
 103
 104         for (count = 0; count < num_msg; count++) {
 105                 if (pamstate == INITIAL_LOGIN) {
 106                         /*
 107                          * We can't use stdio yet, queue messages for
 108                          * printing later
 109                          */
 110                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 111                         case PAM_PROMPT_ECHO_ON:
 112                                 free(reply);
 113                                 return PAM_CONV_ERR;
 114                         case PAM_PROMPT_ECHO_OFF:
 115                                 if (__pampasswd == NULL) {
 116                                         free(reply);
 117                                         return PAM_CONV_ERR;
 118                                 }
 119                                 reply[count].resp = xstrdup(__pampasswd);
 120                                 reply[count].resp_retcode = PAM_SUCCESS;
 121                                 break;
 122                         case PAM_ERROR_MSG:
 123                         case PAM_TEXT_INFO:
 124                                 if ((*msg)[count].msg != NULL) {
 125                                         message_cat(&__pam_msg,
 126                                             PAM_MSG_MEMBER(msg, count, msg));
 127                                 }
 128                                 reply[count].resp = xstrdup("");
 129                                 reply[count].resp_retcode = PAM_SUCCESS;
 130                                 break;
 131                         default:
 132                                 free(reply);
 133                                 return PAM_CONV_ERR;
 134                         }
 135                 } else {
 136                         /*
 137                          * stdio is connected, so interact directly
 138                          */
 139                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 140                         case PAM_PROMPT_ECHO_ON:
 141                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 142                                 fgets(buf, sizeof(buf), stdin);
 143                                 reply[count].resp = xstrdup(buf);
 144                                 reply[count].resp_retcode = PAM_SUCCESS;
 145                                 break;
 146                         case PAM_PROMPT_ECHO_OFF:
 147                                 reply[count].resp = xstrdup(
 148                                     read_passphrase(PAM_MSG_MEMBER(msg, count,
 149                                     msg), 1));
 150                                 reply[count].resp_retcode = PAM_SUCCESS;
 151                                 break;
 152                         case PAM_ERROR_MSG:
 153                         case PAM_TEXT_INFO:
 154                                 if ((*msg)[count].msg != NULL)
 155                                         fprintf(stderr, "%s\n",
 156                                             PAM_MSG_MEMBER(msg, count, msg));
 157                                 reply[count].resp = xstrdup("");
 158                                 reply[count].resp_retcode = PAM_SUCCESS;
 159                                 break;
 160                         default:
 161                                 free(reply);
 162                                 return PAM_CONV_ERR;
 163                         }
 164                 }
 165         }
 166
 167         *resp = reply;
 168
 169         return PAM_SUCCESS;
 170 }
 171
 172 /* Called at exit to cleanly shutdown PAM */
 173 void do_pam_cleanup_proc(void *context)
 174 {
 175         int pam_retval = PAM_SUCCESS;
 176
 177         if (__pamh && session_opened) {
 178                 pam_retval = pam_close_session(__pamh, 0);
 179                 if (pam_retval != PAM_SUCCESS)
 180                         log("Cannot close PAM session[%d]: %.200s",
 181                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 182         }
 183
 184         if (__pamh && creds_set) {
 185                 pam_retval = pam_setcred(__pamh, PAM_DELETE_CRED);
 186                 if (pam_retval != PAM_SUCCESS)
 187                         debug("Cannot delete credentials[%d]: %.200s",
 188                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 189         }
 190
 191         if (__pamh) {
 192                 pam_retval = pam_end(__pamh, pam_retval);
 193                 if (pam_retval != PAM_SUCCESS)
 194                         log("Cannot release PAM authentication[%d]: %.200s",
 195                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 196         }
 197 }
 198
 199 /* Attempt password authentation using PAM */
 200 int auth_pam_password(struct passwd *pw, const char *password)
 201 {
 202         extern ServerOptions options;
 203         int pam_retval;
 204
 205         do_pam_set_conv(&conv);
 206
 207         /* deny if no user. */
 208         if (pw == NULL)
 209                 return 0;
 210         if (pw->pw_uid == 0 && options.permit_root_login == 2)
 211                 return 0;
 212         if (*password == '\0' && options.permit_empty_passwd == 0)
 213                 return 0;
 214
 215         __pampasswd = password;
 216
 217         pamstate = INITIAL_LOGIN;
 218         pam_retval = do_pam_authenticate(0);
 219         if (pam_retval == PAM_SUCCESS) {
 220                 debug("PAM Password authentication accepted for "
 221                     "user \"%.100s\"", pw->pw_name);
 222                 return 1;
 223         } else {
 224                 debug("PAM Password authentication for \"%.100s\" "
 225                     "failed[%d]: %s", pw->pw_name, pam_retval,
 226                     PAM_STRERROR(__pamh, pam_retval));
 227                 return 0;
 228         }
 229 }
 230
 231 /* Do account management using PAM */
 232 int do_pam_account(char *username, char *remote_user)
 233 {
 234         int pam_retval;
 235
 236         do_pam_set_conv(&conv);
 237
 238         if (remote_user) {
 239                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 240                 pam_retval = pam_set_item(__pamh, PAM_RUSER, remote_user);
 241                 if (pam_retval != PAM_SUCCESS)
 242                         fatal("PAM set ruser failed[%d]: %.200s", pam_retval,
 243                             PAM_STRERROR(__pamh, pam_retval));
 244         }
 245
 246         pam_retval = pam_acct_mgmt(__pamh, 0);
 247         switch (pam_retval) {
 248                 case PAM_SUCCESS:
 249                         /* This is what we want */
 250                         break;
 251                 case PAM_NEW_AUTHTOK_REQD:
 252                         message_cat(&__pam_msg, NEW_AUTHTOK_MSG);
 253                         /* flag that password change is necessary */
 254                         password_change_required = 1;
 255                         break;
 256                 default:
 257                         log("PAM rejected by account configuration[%d]: "
 258                             "%.200s", pam_retval, PAM_STRERROR(__pamh,
 259                             pam_retval));
 260                         return(0);
 261         }
 262
 263         return(1);
 264 }
 265
 266 /* Do PAM-specific session initialisation */
 267 void do_pam_session(char *username, const char *ttyname)
 268 {
 269         int pam_retval;
 270
 271         do_pam_set_conv(&conv);
 272
 273         if (ttyname != NULL) {
 274                 debug("PAM setting tty to \"%.200s\"", ttyname);
 275                 pam_retval = pam_set_item(__pamh, PAM_TTY, ttyname);
 276                 if (pam_retval != PAM_SUCCESS)
 277                         fatal("PAM set tty failed[%d]: %.200s",
 278                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 279         }
 280
 281         pam_retval = pam_open_session(__pamh, 0);
 282         if (pam_retval != PAM_SUCCESS)
 283                 fatal("PAM session setup failed[%d]: %.200s",
 284                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 285
 286         session_opened = 1;
 287 }
 288
 289 /* Set PAM credentials */
 290 void do_pam_setcred(void)
 291 {
 292         int pam_retval;
 293
 294         do_pam_set_conv(&conv);
 295
 296         debug("PAM establishing creds");
 297         pam_retval = pam_setcred(__pamh, PAM_ESTABLISH_CRED);
 298         if (pam_retval != PAM_SUCCESS) {
 299                 if (was_authenticated)
 300                         fatal("PAM setcred failed[%d]: %.200s",
 301                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 302                 else
 303                         debug("PAM setcred failed[%d]: %.200s",
 304                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 305         } else
 306                 creds_set = 1;
 307 }
 308
 309 /* accessor function for file scope static variable */
 310 int is_pam_password_change_required(void)
 311 {
 312         return password_change_required;
 313 }
 314
 315 /*
 316  * Have user change authentication token if pam_acct_mgmt() indicated
 317  * it was expired.  This needs to be called after an interactive
 318  * session is established and the user's pty is connected to
 319  * stdin/stout/stderr.
 320  */
 321 void do_pam_chauthtok(void)
 322 {
 323         int pam_retval;
 324
 325         do_pam_set_conv(&conv);
 326
 327         if (password_change_required) {
 328                 pamstate = OTHER;
 329                 /* XXX: should we really loop forever? */
 330                 do {
 331                         pam_retval = pam_chauthtok(__pamh,
 332                             PAM_CHANGE_EXPIRED_AUTHTOK);
 333                         if (pam_retval != PAM_SUCCESS)
 334                                 log("PAM pam_chauthtok failed[%d]: %.200s",
 335                                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 336                 } while (pam_retval != PAM_SUCCESS);
 337         }
 338 }
 339
 340 /* Cleanly shutdown PAM */
 341 void finish_pam(void)
 342 {
 343         do_pam_cleanup_proc(NULL);
 344         fatal_remove_cleanup(&do_pam_cleanup_proc, NULL);
 345 }
 346
 347 /* Start PAM authentication for specified account */
 348 void start_pam(const char *user)
 349 {
 350         int pam_retval;
 351         extern ServerOptions options;
 352
 353         debug("Starting up PAM with username \"%.200s\"", user);
 354
 355         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &__pamh);
 356
 357         if (pam_retval != PAM_SUCCESS)
 358                 fatal("PAM initialisation failed[%d]: %.200s",
 359                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 360
 361         debug("PAM setting rhost to \"%.200s\"",
 362             get_canonical_hostname(options.reverse_mapping_check));
 363         pam_retval = pam_set_item(__pamh, PAM_RHOST,
 364                 get_canonical_hostname(options.reverse_mapping_check));
 365         if (pam_retval != PAM_SUCCESS)
 366                 fatal("PAM set rhost failed[%d]: %.200s", pam_retval,
 367                     PAM_STRERROR(__pamh, pam_retval));
 368 #ifdef PAM_TTY_KLUDGE
 369         /*
 370          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 371          * and will fail in various stupid ways if they don't get one.
 372          * sshd doesn't set the tty until too late in the auth process and may
 373          * not even need one (for tty-less connections)
 374          * Kludge: Set a fake PAM_TTY
 375          */
 376         pam_retval = pam_set_item(__pamh, PAM_TTY, "ssh");
 377         if (pam_retval != PAM_SUCCESS)
 378                 fatal("PAM set tty failed[%d]: %.200s",
 379                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 380 #endif /* PAM_TTY_KLUDGE */
 381
 382         fatal_add_cleanup(&do_pam_cleanup_proc, NULL);
 383 }
 384
 385 /* Return list of PAM enviornment strings */
 386 char **fetch_pam_environment(void)
 387 {
 388 #ifdef HAVE_PAM_GETENVLIST
 389         return(pam_getenvlist(__pamh));
 390 #else /* HAVE_PAM_GETENVLIST */
 391         return(NULL);
 392 #endif /* HAVE_PAM_GETENVLIST */
 393 }
 394
 395 /* Print any messages that have been generated during authentication */
 396 /* or account checking to stderr */
 397 void print_pam_messages(void)
 398 {
 399         if (__pam_msg != NULL)
 400                 fputs(__pam_msg, stderr);
 401 }
 402
 403 /* Append a message to buffer */
 404 void message_cat(char **p, const char *a)
 405 {
 406         char *cp;
 407         size_t new_len;
 408
 409         new_len = strlen(a);
 410
 411         if (*p) {
 412                 size_t len = strlen(*p);
 413
 414                 *p = xrealloc(*p, new_len + len + 2);
 415                 cp = *p + len;
 416         } else
 417                 *p = cp = xmalloc(new_len + 2);
 418
 419         memcpy(cp, a, new_len);
 420         cp[new_len] = '\n';
 421         cp[new_len + 1] = '\0';
 422 }
 423
 424 #endif /* USE_PAM */