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 "servconf.h"
  31
  32 RCSID("$Id$");
  33
  34 #define NEW_AUTHTOK_MSG \
  35         "Warning: Your password has expired, please change it now"
  36
  37 /* Callbacks */
  38 static int pamconv(int num_msg, const struct pam_message **msg,
  39           struct pam_response **resp, void *appdata_ptr);
  40 void pam_cleanup_proc(void *context);
  41 void pam_msg_cat(const char *msg);
  42
  43 /* module-local variables */
  44 static struct pam_conv conv = {
  45         pamconv,
  46         NULL
  47 };
  48 static pam_handle_t *pamh = NULL;
  49 static const char *pampasswd = NULL;
  50 static char *pam_msg = NULL;
  51
  52 /* states for pamconv() */
  53 enum { INITIAL_LOGIN, OTHER } pamstate = INITIAL_LOGIN;
  54 /* remember whether pam_acct_mgmt() returned PAM_NEWAUTHTOK_REQD */
  55 static int password_change_required = 0;
  56 /* remember whether the last pam_authenticate() succeeded or not */
  57 static int was_authenticated = 0;
  58
  59 /* accessor which allows us to switch conversation structs according to
  60  * the authentication method being used */
  61 void pam_set_conv(struct pam_conv *conv)
  62 {
  63         pam_set_item(pamh, PAM_CONV, conv);
  64 }
  65
  66 /* start an authentication run */
  67 int do_pam_authenticate(int flags)
  68 {
  69         int retval = pam_authenticate(pamh, flags);
  70         was_authenticated = (retval == PAM_SUCCESS);
  71         return retval;
  72 }
  73
  74 /*
  75  * PAM conversation function.
  76  * There are two states this can run in.
  77  *
  78  * INITIAL_LOGIN mode simply feeds the password from the client into
  79  * PAM in response to PAM_PROMPT_ECHO_OFF, and collects output
  80  * messages with pam_msg_cat().  This is used during initial
  81  * authentication to bypass the normal PAM password prompt.
  82  *
  83  * OTHER mode handles PAM_PROMPT_ECHO_OFF with read_passphrase(prompt, 1)
  84  * and outputs messages to stderr. This mode is used if pam_chauthtok()
  85  * is called to update expired passwords.
  86  */
  87 static int pamconv(int num_msg, const struct pam_message **msg,
  88         struct pam_response **resp, void *appdata_ptr)
  89 {
  90         struct pam_response *reply;
  91         int count;
  92         char buf[1024];
  93
  94         /* PAM will free this later */
  95         reply = malloc(num_msg * sizeof(*reply));
  96         if (reply == NULL)
  97                 return PAM_CONV_ERR;
  98
  99         for (count = 0; count < num_msg; count++) {
 100                 switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 101                         case PAM_PROMPT_ECHO_ON:
 102                                 if (pamstate == INITIAL_LOGIN) {
 103                                         free(reply);
 104                                         return PAM_CONV_ERR;
 105                                 } else {
 106                                         fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 107                                         fgets(buf, sizeof(buf), stdin);
 108                                         reply[count].resp = xstrdup(buf);
 109                                         reply[count].resp_retcode = PAM_SUCCESS;
 110                                         break;
 111                                 }
 112                         case PAM_PROMPT_ECHO_OFF:
 113                                 if (pamstate == INITIAL_LOGIN) {
 114                                         if (pampasswd == NULL) {
 115                                                 free(reply);
 116                                                 return PAM_CONV_ERR;
 117                                         }
 118                                         reply[count].resp = xstrdup(pampasswd);
 119                                 } else {
 120                                         reply[count].resp =
 121                                                 xstrdup(read_passphrase(PAM_MSG_MEMBER(msg, count, msg), 1));
 122                                 }
 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                                         if (pamstate == INITIAL_LOGIN)
 129                                                 pam_msg_cat(PAM_MSG_MEMBER(msg, count, msg));
 130                                         else {
 131                                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 132                                                 fputs("\n", stderr);
 133                                         }
 134                                 }
 135                                 reply[count].resp = xstrdup("");
 136                                 reply[count].resp_retcode = PAM_SUCCESS;
 137                                 break;
 138                         default:
 139                                 free(reply);
 140                                 return PAM_CONV_ERR;
 141                 }
 142         }
 143
 144         *resp = reply;
 145
 146         return PAM_SUCCESS;
 147 }
 148
 149 /* Called at exit to cleanly shutdown PAM */
 150 void pam_cleanup_proc(void *context)
 151 {
 152         int pam_retval;
 153
 154         if (pamh != NULL)
 155         {
 156                 pam_retval = pam_close_session(pamh, 0);
 157                 if (pam_retval != PAM_SUCCESS) {
 158                         log("Cannot close PAM session[%d]: %.200s",
 159                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 160                 }
 161
 162                 pam_retval = pam_setcred(pamh, PAM_DELETE_CRED);
 163                 if (pam_retval != PAM_SUCCESS) {
 164                         debug("Cannot delete credentials[%d]: %.200s",
 165                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 166                 }
 167
 168                 pam_retval = pam_end(pamh, pam_retval);
 169                 if (pam_retval != PAM_SUCCESS) {
 170                         log("Cannot release PAM authentication[%d]: %.200s",
 171                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 172                 }
 173         }
 174 }
 175
 176 /* Attempt password authentation using PAM */
 177 int auth_pam_password(struct passwd *pw, const char *password)
 178 {
 179         extern ServerOptions options;
 180         int pam_retval;
 181
 182         pam_set_conv(&conv);
 183
 184         /* deny if no user. */
 185         if (pw == NULL)
 186                 return 0;
 187         if (pw->pw_uid == 0 && options.permit_root_login == 2)
 188                 return 0;
 189         if (*password == '\0' && options.permit_empty_passwd == 0)
 190                 return 0;
 191
 192         pampasswd = password;
 193
 194         pamstate = INITIAL_LOGIN;
 195         pam_retval = do_pam_authenticate(0);
 196         if (pam_retval == PAM_SUCCESS) {
 197                 debug("PAM Password authentication accepted for user \"%.100s\"",
 198                         pw->pw_name);
 199                 return 1;
 200         } else {
 201                 debug("PAM Password authentication for \"%.100s\" failed[%d]: %s",
 202                         pw->pw_name, pam_retval, PAM_STRERROR(pamh, pam_retval));
 203                 return 0;
 204         }
 205 }
 206
 207 /* Do account management using PAM */
 208 int do_pam_account(char *username, char *remote_user)
 209 {
 210         int pam_retval;
 211
 212         debug("PAM setting rhost to \"%.200s\"", get_canonical_hostname());
 213         pam_retval = pam_set_item(pamh, PAM_RHOST,
 214                 get_canonical_hostname());
 215         if (pam_retval != PAM_SUCCESS) {
 216                 fatal("PAM set rhost failed[%d]: %.200s",
 217                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 218         }
 219
 220         if (remote_user != NULL) {
 221                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 222                 pam_retval = pam_set_item(pamh, PAM_RUSER, remote_user);
 223                 if (pam_retval != PAM_SUCCESS) {
 224                         fatal("PAM set ruser failed[%d]: %.200s",
 225                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 226                 }
 227         }
 228
 229         pam_retval = pam_acct_mgmt(pamh, 0);
 230         switch (pam_retval) {
 231                 case PAM_SUCCESS:
 232                         /* This is what we want */
 233                         break;
 234                 case PAM_NEW_AUTHTOK_REQD:
 235                         pam_msg_cat(NEW_AUTHTOK_MSG);
 236                         /* flag that password change is necessary */
 237                         password_change_required = 1;
 238                         break;
 239                 default:
 240                         log("PAM rejected by account configuration[%d]: %.200s",
 241                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 242                         return(0);
 243         }
 244
 245         return(1);
 246 }
 247
 248 /* Do PAM-specific session initialisation */
 249 void do_pam_session(char *username, const char *ttyname)
 250 {
 251         int pam_retval;
 252
 253         if (ttyname != NULL) {
 254                 debug("PAM setting tty to \"%.200s\"", ttyname);
 255                 pam_retval = pam_set_item(pamh, PAM_TTY, ttyname);
 256                 if (pam_retval != PAM_SUCCESS) {
 257                         fatal("PAM set tty failed[%d]: %.200s",
 258                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 259                 }
 260         }
 261
 262         pam_retval = pam_open_session(pamh, 0);
 263         if (pam_retval != PAM_SUCCESS) {
 264                 fatal("PAM session setup failed[%d]: %.200s",
 265                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 266         }
 267 }
 268
 269 /* Set PAM credentials */
 270 void do_pam_setcred(void)
 271 {
 272         int pam_retval;
 273
 274         debug("PAM establishing creds");
 275         pam_retval = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 276         if (pam_retval != PAM_SUCCESS) {
 277                 if(was_authenticated) {
 278                         fatal("PAM setcred failed[%d]: %.200s",
 279                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 280                 } else {
 281                         debug("PAM setcred failed[%d]: %.200s",
 282                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 283                 }
 284         }
 285 }
 286
 287 /* accessor function for file scope static variable */
 288 int pam_password_change_required(void)
 289 {
 290         return password_change_required;
 291 }
 292
 293 /*
 294  * Have user change authentication token if pam_acct_mgmt() indicated
 295  * it was expired.  This needs to be called after an interactive
 296  * session is established and the user's pty is connected to
 297  * stdin/stout/stderr.
 298  */
 299 void do_pam_chauthtok(void)
 300 {
 301         int pam_retval;
 302
 303         if (password_change_required) {
 304                 pamstate = OTHER;
 305                 /*
 306                  * XXX: should we really loop forever?
 307                  */
 308                 do {
 309                         pam_retval = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 310                         if (pam_retval != PAM_SUCCESS) {
 311                                 log("PAM pam_chauthtok failed[%d]: %.200s",
 312                                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 313                         }
 314                 } while (pam_retval != PAM_SUCCESS);
 315         }
 316 }
 317
 318 /* Cleanly shutdown PAM */
 319 void finish_pam(void)
 320 {
 321         pam_cleanup_proc(NULL);
 322         fatal_remove_cleanup(&pam_cleanup_proc, NULL);
 323 }
 324
 325 /* Start PAM authentication for specified account */
 326 void start_pam(const char *user)
 327 {
 328         int pam_retval;
 329
 330         debug("Starting up PAM with username \"%.200s\"", user);
 331
 332         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &pamh);
 333
 334         if (pam_retval != PAM_SUCCESS) {
 335                 fatal("PAM initialisation failed[%d]: %.200s",
 336                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 337         }
 338
 339 #ifdef PAM_TTY_KLUDGE
 340         /*
 341          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 342          * and will fail in various stupid ways if they don't get one.
 343          * sshd doesn't set the tty until too late in the auth process and may
 344          * not even need one (for tty-less connections)
 345          * Kludge: Set a fake PAM_TTY
 346          */
 347         pam_retval = pam_set_item(pamh, PAM_TTY, "ssh");
 348         if (pam_retval != PAM_SUCCESS) {
 349                 fatal("PAM set tty failed[%d]: %.200s",
 350                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 351         }
 352 #endif /* PAM_TTY_KLUDGE */
 353
 354         fatal_add_cleanup(&pam_cleanup_proc, NULL);
 355 }
 356
 357 /* Return list of PAM enviornment strings */
 358 char **fetch_pam_environment(void)
 359 {
 360 #ifdef HAVE_PAM_GETENVLIST
 361         return(pam_getenvlist(pamh));
 362 #else /* HAVE_PAM_GETENVLIST */
 363         return(NULL);
 364 #endif /* HAVE_PAM_GETENVLIST */
 365 }
 366
 367 /* Print any messages that have been generated during authentication */
 368 /* or account checking to stderr */
 369 void print_pam_messages(void)
 370 {
 371         if (pam_msg != NULL)
 372                 fputs(pam_msg, stderr);
 373 }
 374
 375 /* Append a message to the PAM message buffer */
 376 void pam_msg_cat(const char *msg)
 377 {
 378         char *p;
 379         size_t new_msg_len;
 380         size_t pam_msg_len;
 381
 382         new_msg_len = strlen(msg);
 383
 384         if (pam_msg) {
 385                 pam_msg_len = strlen(pam_msg);
 386                 pam_msg = xrealloc(pam_msg, new_msg_len + pam_msg_len + 2);
 387                 p = pam_msg + pam_msg_len;
 388         } else {
 389                 pam_msg = p = xmalloc(new_msg_len + 2);
 390         }
 391
 392         memcpy(p, msg, new_msg_len);
 393         p[new_msg_len] = '\n';
 394         p[new_msg_len + 1] = '\0';
 395 }
 396
 397 #endif /* USE_PAM */