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