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         extern ServerOptions options;
 215
 216         debug("PAM setting rhost to \"%.200s\"",
 217             get_canonical_hostname(options.reverse_mapping_check));
 218         pam_retval = pam_set_item(pamh, PAM_RHOST,
 219                 get_canonical_hostname(options.reverse_mapping_check));
 220         if (pam_retval != PAM_SUCCESS) {
 221                 fatal("PAM set rhost failed[%d]: %.200s",
 222                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 223         }
 224
 225         if (remote_user != NULL) {
 226                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 227                 pam_retval = pam_set_item(pamh, PAM_RUSER, remote_user);
 228                 if (pam_retval != PAM_SUCCESS) {
 229                         fatal("PAM set ruser failed[%d]: %.200s",
 230                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 231                 }
 232         }
 233
 234         pam_retval = pam_acct_mgmt(pamh, 0);
 235         switch (pam_retval) {
 236                 case PAM_SUCCESS:
 237                         /* This is what we want */
 238                         break;
 239                 case PAM_NEW_AUTHTOK_REQD:
 240                         pam_msg_cat(NEW_AUTHTOK_MSG);
 241                         /* flag that password change is necessary */
 242                         password_change_required = 1;
 243                         break;
 244                 default:
 245                         log("PAM rejected by account configuration[%d]: %.200s",
 246                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 247                         return(0);
 248         }
 249
 250         return(1);
 251 }
 252
 253 /* Do PAM-specific session initialisation */
 254 void do_pam_session(char *username, const char *ttyname)
 255 {
 256         int pam_retval;
 257
 258         if (ttyname != NULL) {
 259                 debug("PAM setting tty to \"%.200s\"", ttyname);
 260                 pam_retval = pam_set_item(pamh, PAM_TTY, ttyname);
 261                 if (pam_retval != PAM_SUCCESS) {
 262                         fatal("PAM set tty failed[%d]: %.200s",
 263                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 264                 }
 265         }
 266
 267         pam_retval = pam_open_session(pamh, 0);
 268         if (pam_retval != PAM_SUCCESS) {
 269                 fatal("PAM session setup failed[%d]: %.200s",
 270                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 271         }
 272 }
 273
 274 /* Set PAM credentials */
 275 void do_pam_setcred(void)
 276 {
 277         int pam_retval;
 278
 279         debug("PAM establishing creds");
 280         pam_retval = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 281         if (pam_retval != PAM_SUCCESS) {
 282                 if(was_authenticated) {
 283                         fatal("PAM setcred failed[%d]: %.200s",
 284                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 285                 } else {
 286                         debug("PAM setcred failed[%d]: %.200s",
 287                                 pam_retval, PAM_STRERROR(pamh, pam_retval));
 288                 }
 289         }
 290 }
 291
 292 /* accessor function for file scope static variable */
 293 int pam_password_change_required(void)
 294 {
 295         return password_change_required;
 296 }
 297
 298 /*
 299  * Have user change authentication token if pam_acct_mgmt() indicated
 300  * it was expired.  This needs to be called after an interactive
 301  * session is established and the user's pty is connected to
 302  * stdin/stout/stderr.
 303  */
 304 void do_pam_chauthtok(void)
 305 {
 306         int pam_retval;
 307
 308         if (password_change_required) {
 309                 pamstate = OTHER;
 310                 /*
 311                  * XXX: should we really loop forever?
 312                  */
 313                 do {
 314                         pam_retval = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 315                         if (pam_retval != PAM_SUCCESS) {
 316                                 log("PAM pam_chauthtok failed[%d]: %.200s",
 317                                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 318                         }
 319                 } while (pam_retval != PAM_SUCCESS);
 320         }
 321 }
 322
 323 /* Cleanly shutdown PAM */
 324 void finish_pam(void)
 325 {
 326         pam_cleanup_proc(NULL);
 327         fatal_remove_cleanup(&pam_cleanup_proc, NULL);
 328 }
 329
 330 /* Start PAM authentication for specified account */
 331 void start_pam(const char *user)
 332 {
 333         int pam_retval;
 334
 335         debug("Starting up PAM with username \"%.200s\"", user);
 336
 337         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &pamh);
 338
 339         if (pam_retval != PAM_SUCCESS) {
 340                 fatal("PAM initialisation failed[%d]: %.200s",
 341                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 342         }
 343
 344 #ifdef PAM_TTY_KLUDGE
 345         /*
 346          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 347          * and will fail in various stupid ways if they don't get one.
 348          * sshd doesn't set the tty until too late in the auth process and may
 349          * not even need one (for tty-less connections)
 350          * Kludge: Set a fake PAM_TTY
 351          */
 352         pam_retval = pam_set_item(pamh, PAM_TTY, "ssh");
 353         if (pam_retval != PAM_SUCCESS) {
 354                 fatal("PAM set tty failed[%d]: %.200s",
 355                         pam_retval, PAM_STRERROR(pamh, pam_retval));
 356         }
 357 #endif /* PAM_TTY_KLUDGE */
 358
 359         fatal_add_cleanup(&pam_cleanup_proc, NULL);
 360 }
 361
 362 /* Return list of PAM enviornment strings */
 363 char **fetch_pam_environment(void)
 364 {
 365 #ifdef HAVE_PAM_GETENVLIST
 366         return(pam_getenvlist(pamh));
 367 #else /* HAVE_PAM_GETENVLIST */
 368         return(NULL);
 369 #endif /* HAVE_PAM_GETENVLIST */
 370 }
 371
 372 /* Print any messages that have been generated during authentication */
 373 /* or account checking to stderr */
 374 void print_pam_messages(void)
 375 {
 376         if (pam_msg != NULL)
 377                 fputs(pam_msg, stderr);
 378 }
 379
 380 /* Append a message to the PAM message buffer */
 381 void pam_msg_cat(const char *msg)
 382 {
 383         char *p;
 384         size_t new_msg_len;
 385         size_t pam_msg_len;
 386
 387         new_msg_len = strlen(msg);
 388
 389         if (pam_msg) {
 390                 pam_msg_len = strlen(pam_msg);
 391                 pam_msg = xrealloc(pam_msg, new_msg_len + pam_msg_len + 2);
 392                 p = pam_msg + pam_msg_len;
 393         } else {
 394                 pam_msg = p = xmalloc(new_msg_len + 2);
 395         }
 396
 397         memcpy(p, msg, new_msg_len);
 398         p[new_msg_len] = '\n';
 399         p[new_msg_len + 1] = '\0';
 400 }
 401
 402 #endif /* USE_PAM */