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_NEW_AUTHTOK_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 = xmalloc(num_msg * sizeof(*reply));
 104
 105         for (count = 0; count < num_msg; count++) {
 106                 if (pamstate == INITIAL_LOGIN) {
 107                         /*
 108                          * We can't use stdio yet, queue messages for
 109                          * printing later
 110                          */
 111                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 112                         case PAM_PROMPT_ECHO_ON:
 113                                 xfree(reply);
 114                                 return PAM_CONV_ERR;
 115                         case PAM_PROMPT_ECHO_OFF:
 116                                 if (__pampasswd == NULL) {
 117                                         xfree(reply);
 118                                         return PAM_CONV_ERR;
 119                                 }
 120                                 reply[count].resp = xstrdup(__pampasswd);
 121                                 reply[count].resp_retcode = PAM_SUCCESS;
 122                                 break;
 123                         case PAM_ERROR_MSG:
 124                         case PAM_TEXT_INFO:
 125                                 if (PAM_MSG_MEMBER(msg, count, msg) != NULL) {
 126                                         message_cat(&__pam_msg,
 127                                             PAM_MSG_MEMBER(msg, count, msg));
 128                                 }
 129                                 reply[count].resp = xstrdup("");
 130                                 reply[count].resp_retcode = PAM_SUCCESS;
 131                                 break;
 132                         default:
 133                                 xfree(reply);
 134                                 return PAM_CONV_ERR;
 135                         }
 136                 } else {
 137                         /*
 138                          * stdio is connected, so interact directly
 139                          */
 140                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 141                         case PAM_PROMPT_ECHO_ON:
 142                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 143                                 fgets(buf, sizeof(buf), stdin);
 144                                 reply[count].resp = xstrdup(buf);
 145                                 reply[count].resp_retcode = PAM_SUCCESS;
 146                                 break;
 147                         case PAM_PROMPT_ECHO_OFF:
 148                                 reply[count].resp =
 149                                     read_passphrase(PAM_MSG_MEMBER(msg, count,
 150                                         msg), RP_ALLOW_STDIN);
 151                                 reply[count].resp_retcode = PAM_SUCCESS;
 152                                 break;
 153                         case PAM_ERROR_MSG:
 154                         case PAM_TEXT_INFO:
 155                                 if ((*msg)[count].msg != NULL)
 156                                         fprintf(stderr, "%s\n",
 157                                             PAM_MSG_MEMBER(msg, count, msg));
 158                                 reply[count].resp = xstrdup("");
 159                                 reply[count].resp_retcode = PAM_SUCCESS;
 160                                 break;
 161                         default:
 162                                 xfree(reply);
 163                                 return PAM_CONV_ERR;
 164                         }
 165                 }
 166         }
 167
 168         *resp = reply;
 169
 170         return PAM_SUCCESS;
 171 }
 172
 173 /* Called at exit to cleanly shutdown PAM */
 174 void do_pam_cleanup_proc(void *context)
 175 {
 176         int pam_retval = PAM_SUCCESS;
 177
 178         if (__pamh && session_opened) {
 179                 pam_retval = pam_close_session(__pamh, 0);
 180                 if (pam_retval != PAM_SUCCESS)
 181                         log("Cannot close PAM session[%d]: %.200s",
 182                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 183         }
 184
 185         if (__pamh && creds_set) {
 186                 pam_retval = pam_setcred(__pamh, PAM_DELETE_CRED);
 187                 if (pam_retval != PAM_SUCCESS)
 188                         debug("Cannot delete credentials[%d]: %.200s",
 189                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 190         }
 191
 192         if (__pamh) {
 193                 pam_retval = pam_end(__pamh, pam_retval);
 194                 if (pam_retval != PAM_SUCCESS)
 195                         log("Cannot release PAM authentication[%d]: %.200s",
 196                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 197         }
 198 }
 199
 200 /* Attempt password authentation using PAM */
 201 int auth_pam_password(Authctxt *authctxt, const char *password)
 202 {
 203         extern ServerOptions options;
 204         int pam_retval;
 205         struct passwd *pw = authctxt->pw;
 206
 207         do_pam_set_conv(&conv);
 208
 209         /* deny if no user. */
 210         if (pw == NULL)
 211                 return 0;
 212         if (pw->pw_uid == 0 && options.permit_root_login == PERMIT_NO_PASSWD)
 213                 return 0;
 214         if (*password == '\0' && options.permit_empty_passwd == 0)
 215                 return 0;
 216
 217         __pampasswd = password;
 218
 219         pamstate = INITIAL_LOGIN;
 220         pam_retval = do_pam_authenticate(
 221             options.permit_empty_passwd == 0 ? PAM_DISALLOW_NULL_AUTHTOK : 0);
 222         if (pam_retval == PAM_SUCCESS) {
 223                 debug("PAM Password authentication accepted for "
 224                     "user \"%.100s\"", pw->pw_name);
 225                 return 1;
 226         } else {
 227                 debug("PAM Password authentication for \"%.100s\" "
 228                     "failed[%d]: %s", pw->pw_name, pam_retval,
 229                     PAM_STRERROR(__pamh, pam_retval));
 230                 return 0;
 231         }
 232 }
 233
 234 /* Do account management using PAM */
 235 int do_pam_account(char *username, char *remote_user)
 236 {
 237         int pam_retval;
 238
 239         do_pam_set_conv(&conv);
 240
 241         if (remote_user) {
 242                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 243                 pam_retval = pam_set_item(__pamh, PAM_RUSER, remote_user);
 244                 if (pam_retval != PAM_SUCCESS)
 245                         fatal("PAM set ruser failed[%d]: %.200s", pam_retval,
 246                             PAM_STRERROR(__pamh, pam_retval));
 247         }
 248
 249         pam_retval = pam_acct_mgmt(__pamh, 0);
 250         debug2("pam_acct_mgmt() = %d", pam_retval);
 251         switch (pam_retval) {
 252                 case PAM_SUCCESS:
 253                         /* This is what we want */
 254                         break;
 255 #if 0
 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 #endif
 262                 default:
 263                         log("PAM rejected by account configuration[%d]: "
 264                             "%.200s", pam_retval, PAM_STRERROR(__pamh,
 265                             pam_retval));
 266                         return(0);
 267         }
 268
 269         return(1);
 270 }
 271
 272 /* Do PAM-specific session initialisation */
 273 void do_pam_session(char *username, const char *ttyname)
 274 {
 275         int pam_retval;
 276
 277         do_pam_set_conv(&conv);
 278
 279         if (ttyname != NULL) {
 280                 debug("PAM setting tty to \"%.200s\"", ttyname);
 281                 pam_retval = pam_set_item(__pamh, PAM_TTY, ttyname);
 282                 if (pam_retval != PAM_SUCCESS)
 283                         fatal("PAM set tty failed[%d]: %.200s",
 284                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 285         }
 286
 287         pam_retval = pam_open_session(__pamh, 0);
 288         if (pam_retval != PAM_SUCCESS)
 289                 fatal("PAM session setup failed[%d]: %.200s",
 290                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 291
 292         session_opened = 1;
 293 }
 294
 295 /* Set PAM credentials */
 296 void do_pam_setcred(int init)
 297 {
 298         int pam_retval;
 299
 300         if (__pamh == NULL)
 301                 return;
 302
 303         do_pam_set_conv(&conv);
 304
 305         debug("PAM establishing creds");
 306         pam_retval = pam_setcred(__pamh,
 307             init ? PAM_ESTABLISH_CRED : PAM_REINITIALIZE_CRED);
 308         if (pam_retval != PAM_SUCCESS) {
 309                 if (was_authenticated)
 310                         fatal("PAM setcred failed[%d]: %.200s",
 311                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 312                 else
 313                         debug("PAM setcred failed[%d]: %.200s",
 314                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 315         } else
 316                 creds_set = 1;
 317 }
 318
 319 /* accessor function for file scope static variable */
 320 int is_pam_password_change_required(void)
 321 {
 322         return password_change_required;
 323 }
 324
 325 /*
 326  * Have user change authentication token if pam_acct_mgmt() indicated
 327  * it was expired.  This needs to be called after an interactive
 328  * session is established and the user's pty is connected to
 329  * stdin/stdout/stderr.
 330  */
 331 void do_pam_chauthtok(void)
 332 {
 333         int pam_retval;
 334
 335         do_pam_set_conv(&conv);
 336
 337         if (password_change_required) {
 338                 pamstate = OTHER;
 339                 pam_retval = pam_chauthtok(__pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 340                 if (pam_retval != PAM_SUCCESS)
 341                         fatal("PAM pam_chauthtok failed[%d]: %.200s",
 342                             pam_retval, PAM_STRERROR(__pamh, pam_retval));
 343         }
 344 }
 345
 346 /* Cleanly shutdown PAM */
 347 void finish_pam(void)
 348 {
 349         do_pam_cleanup_proc(NULL);
 350         fatal_remove_cleanup(&do_pam_cleanup_proc, NULL);
 351 }
 352
 353 /* Start PAM authentication for specified account */
 354 void start_pam(const char *user)
 355 {
 356         int pam_retval;
 357         extern ServerOptions options;
 358         extern u_int utmp_len;
 359         const char *rhost;
 360
 361         debug("Starting up PAM with username \"%.200s\"", user);
 362
 363         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &__pamh);
 364
 365         if (pam_retval != PAM_SUCCESS)
 366                 fatal("PAM initialisation failed[%d]: %.200s",
 367                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 368
 369         rhost = get_remote_name_or_ip(utmp_len, options.verify_reverse_mapping);
 370         debug("PAM setting rhost to \"%.200s\"", rhost);
 371
 372         pam_retval = pam_set_item(__pamh, PAM_RHOST, rhost);
 373         if (pam_retval != PAM_SUCCESS)
 374                 fatal("PAM set rhost failed[%d]: %.200s", pam_retval,
 375                     PAM_STRERROR(__pamh, pam_retval));
 376 #ifdef PAM_TTY_KLUDGE
 377         /*
 378          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 379          * and will fail in various stupid ways if they don't get one.
 380          * sshd doesn't set the tty until too late in the auth process and may
 381          * not even need one (for tty-less connections)
 382          * Kludge: Set a fake PAM_TTY
 383          */
 384         pam_retval = pam_set_item(__pamh, PAM_TTY, "NODEVssh");
 385         if (pam_retval != PAM_SUCCESS)
 386                 fatal("PAM set tty failed[%d]: %.200s",
 387                     pam_retval, PAM_STRERROR(__pamh, pam_retval));
 388 #endif /* PAM_TTY_KLUDGE */
 389
 390         fatal_add_cleanup(&do_pam_cleanup_proc, NULL);
 391 }
 392
 393 /* Return list of PAM enviornment strings */
 394 char **fetch_pam_environment(void)
 395 {
 396 #ifdef HAVE_PAM_GETENVLIST
 397         return(pam_getenvlist(__pamh));
 398 #else /* HAVE_PAM_GETENVLIST */
 399         return(NULL);
 400 #endif /* HAVE_PAM_GETENVLIST */
 401 }
 402
 403 /* Print any messages that have been generated during authentication */
 404 /* or account checking to stderr */
 405 void print_pam_messages(void)
 406 {
 407         if (__pam_msg != NULL)
 408                 fputs(__pam_msg, stderr);
 409 }
 410
 411 /* Append a message to buffer */
 412 void message_cat(char **p, const char *a)
 413 {
 414         char *cp;
 415         size_t new_len;
 416
 417         new_len = strlen(a);
 418
 419         if (*p) {
 420                 size_t len = strlen(*p);
 421
 422                 *p = xrealloc(*p, new_len + len + 2);
 423                 cp = *p + len;
 424         } else
 425                 *p = cp = xmalloc(new_len + 2);
 426
 427         memcpy(cp, a, new_len);
 428         cp[new_len] = '\n';
 429         cp[new_len + 1] = '\0';
 430 }
 431
 432 #endif /* USE_PAM */