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