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 RCSID("$Id$");
  37
  38 #define NEW_AUTHTOK_MSG \
  39         "Warning: Your password has expired, please change it now"
  40
  41 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  42         struct pam_response **resp, void *appdata_ptr);
  43
  44 /* module-local variables */
  45 static struct pam_conv conv = {
  46         do_pam_conversation,
  47         NULL
  48 };
  49 static char *pam_msg = NULL;
  50 static pam_handle_t *pamh = NULL;
  51 static const char *pampasswd = NULL;
  52
  53 /* states for do_pam_conversation() */
  54 enum { INITIAL_LOGIN, OTHER } pamstate = INITIAL_LOGIN;
  55 /* remember whether pam_acct_mgmt() returned PAM_NEWAUTHTOK_REQD */
  56 static int password_change_required = 0;
  57 /* remember whether the last pam_authenticate() succeeded or not */
  58 static int was_authenticated = 0;
  59
  60 /* accessor which allows us to switch conversation structs according to
  61  * the authentication method being used */
  62 void pam_set_conv(struct pam_conv *conv)
  63 {
  64         pam_set_item(pamh, PAM_CONV, conv);
  65 }
  66
  67 /* start an authentication run */
  68 int do_pam_authenticate(int flags)
  69 {
  70         int retval = pam_authenticate(pamh, flags);
  71         was_authenticated = (retval == PAM_SUCCESS);
  72         return retval;
  73 }
  74
  75 /*
  76  * PAM conversation function.
  77  * There are two states this can run in.
  78  *
  79  * INITIAL_LOGIN mode simply feeds the password from the client into
  80  * PAM in response to PAM_PROMPT_ECHO_OFF, and collects output
  81  * messages with into pam_msg.  This is used during initial
  82  * authentication to bypass the normal PAM password prompt.
  83  *
  84  * OTHER mode handles PAM_PROMPT_ECHO_OFF with read_passphrase(prompt, 1)
  85  * and outputs messages to stderr. This mode is used if pam_chauthtok()
  86  * is called to update expired passwords.
  87  */
  88 static int do_pam_conversation(int num_msg, const struct pam_message **msg,
  89         struct pam_response **resp, void *appdata_ptr)
  90 {
  91         struct pam_response *reply;
  92         int count;
  93         char buf[1024];
  94
  95         /* PAM will free this later */
  96         reply = malloc(num_msg * sizeof(*reply));
  97         if (reply == NULL)
  98                 return PAM_CONV_ERR;
  99
 100         for (count = 0; count < num_msg; count++) {
 101                 if (pamstate == INITIAL_LOGIN) {
 102                         /*
 103                          * We can't use stdio yet, queue messages for
 104                          * printing later
 105                          */
 106                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 107                         case PAM_PROMPT_ECHO_ON:
 108                                 free(reply);
 109                                 return PAM_CONV_ERR;
 110                         case PAM_PROMPT_ECHO_OFF:
 111                                 if (pampasswd == NULL) {
 112                                         free(reply);
 113                                         return PAM_CONV_ERR;
 114                                 }
 115                                 reply[count].resp = xstrdup(pampasswd);
 116                                 reply[count].resp_retcode = PAM_SUCCESS;
 117                                 break;
 118                         case PAM_ERROR_MSG:
 119                         case PAM_TEXT_INFO:
 120                                 if ((*msg)[count].msg != NULL) {
 121                                         message_cat(&pam_msg,
 122                                             PAM_MSG_MEMBER(msg, count, msg));
 123                                 }
 124                                 reply[count].resp = xstrdup("");
 125                                 reply[count].resp_retcode = PAM_SUCCESS;
 126                                 break;
 127                         default:
 128                                 free(reply);
 129                                 return PAM_CONV_ERR;
 130                         }
 131                 } else {
 132                         /*
 133                          * stdio is connected, so interact directly
 134                          */
 135                         switch(PAM_MSG_MEMBER(msg, count, msg_style)) {
 136                         case PAM_PROMPT_ECHO_ON:
 137                                 fputs(PAM_MSG_MEMBER(msg, count, msg), stderr);
 138                                 fgets(buf, sizeof(buf), stdin);
 139                                 reply[count].resp = xstrdup(buf);
 140                                 reply[count].resp_retcode = PAM_SUCCESS;
 141                                 break;
 142                         case PAM_PROMPT_ECHO_OFF:
 143                                 reply[count].resp = xstrdup(
 144                                     read_passphrase(PAM_MSG_MEMBER(msg, count,
 145                                     msg), 1));
 146                                 reply[count].resp_retcode = PAM_SUCCESS;
 147                                 break;
 148                         case PAM_ERROR_MSG:
 149                         case PAM_TEXT_INFO:
 150                                 if ((*msg)[count].msg != NULL)
 151                                         fprintf(stderr, "%s\n",
 152                                             PAM_MSG_MEMBER(msg, count, msg));
 153                                 reply[count].resp = xstrdup("");
 154                                 reply[count].resp_retcode = PAM_SUCCESS;
 155                                 break;
 156                         default:
 157                                 free(reply);
 158                                 return PAM_CONV_ERR;
 159                         }
 160                 }
 161         }
 162
 163         *resp = reply;
 164
 165         return PAM_SUCCESS;
 166 }
 167
 168 /* Called at exit to cleanly shutdown PAM */
 169 void pam_cleanup_proc(void *context)
 170 {
 171         int pam_retval;
 172
 173         if (pamh) {
 174                 pam_retval = pam_close_session(pamh, 0);
 175                 if (pam_retval != PAM_SUCCESS)
 176                         log("Cannot close PAM session[%d]: %.200s",
 177                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 178
 179                 pam_retval = pam_setcred(pamh, PAM_DELETE_CRED);
 180                 if (pam_retval != PAM_SUCCESS)
 181                         debug("Cannot delete credentials[%d]: %.200s",
 182                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 183
 184                 pam_retval = pam_end(pamh, pam_retval);
 185                 if (pam_retval != PAM_SUCCESS)
 186                         log("Cannot release PAM authentication[%d]: %.200s",
 187                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 188         }
 189 }
 190
 191 /* Attempt password authentation using PAM */
 192 int auth_pam_password(struct passwd *pw, const char *password)
 193 {
 194         extern ServerOptions options;
 195         int pam_retval;
 196
 197         pam_set_conv(&conv);
 198
 199         /* deny if no user. */
 200         if (pw == NULL)
 201                 return 0;
 202         if (pw->pw_uid == 0 && options.permit_root_login == 2)
 203                 return 0;
 204         if (*password == '\0' && options.permit_empty_passwd == 0)
 205                 return 0;
 206
 207         pampasswd = password;
 208
 209         pamstate = INITIAL_LOGIN;
 210         pam_retval = do_pam_authenticate(0);
 211         if (pam_retval == PAM_SUCCESS) {
 212                 debug("PAM Password authentication accepted for "
 213                     "user \"%.100s\"", pw->pw_name);
 214                 return 1;
 215         } else {
 216                 debug("PAM Password authentication for \"%.100s\" "
 217                     "failed[%d]: %s", pw->pw_name, pam_retval,
 218                     PAM_STRERROR(pamh, pam_retval));
 219                 return 0;
 220         }
 221 }
 222
 223 /* Do account management using PAM */
 224 int do_pam_account(char *username, char *remote_user)
 225 {
 226         int pam_retval;
 227         extern ServerOptions options;
 228
 229         pam_set_conv(&conv);
 230
 231         debug("PAM setting rhost to \"%.200s\"",
 232             get_canonical_hostname(options.reverse_mapping_check));
 233         pam_retval = pam_set_item(pamh, PAM_RHOST,
 234                 get_canonical_hostname(options.reverse_mapping_check));
 235         if (pam_retval != PAM_SUCCESS)
 236                 fatal("PAM set rhost failed[%d]: %.200s", pam_retval,
 237                     PAM_STRERROR(pamh, pam_retval));
 238         if (remote_user) {
 239                 debug("PAM setting ruser to \"%.200s\"", remote_user);
 240                 pam_retval = pam_set_item(pamh, PAM_RUSER, remote_user);
 241                 if (pam_retval != PAM_SUCCESS)
 242                         fatal("PAM set ruser failed[%d]: %.200s", pam_retval,
 243                             PAM_STRERROR(pamh, pam_retval));
 244         }
 245
 246         pam_retval = pam_acct_mgmt(pamh, 0);
 247         switch (pam_retval) {
 248                 case PAM_SUCCESS:
 249                         /* This is what we want */
 250                         break;
 251                 case PAM_NEW_AUTHTOK_REQD:
 252                         message_cat(&pam_msg, NEW_AUTHTOK_MSG);
 253                         /* flag that password change is necessary */
 254                         password_change_required = 1;
 255                         break;
 256                 default:
 257                         log("PAM rejected by account configuration[%d]: "
 258                             "%.200s", pam_retval, PAM_STRERROR(pamh,
 259                             pam_retval));
 260                         return(0);
 261         }
 262
 263         return(1);
 264 }
 265
 266 /* Do PAM-specific session initialisation */
 267 void do_pam_session(char *username, const char *ttyname)
 268 {
 269         int pam_retval;
 270
 271         if (ttyname != NULL) {
 272                 debug("PAM setting tty to \"%.200s\"", ttyname);
 273                 pam_retval = pam_set_item(pamh, PAM_TTY, ttyname);
 274                 if (pam_retval != PAM_SUCCESS)
 275                         fatal("PAM set tty failed[%d]: %.200s",
 276                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 277         }
 278
 279         pam_retval = pam_open_session(pamh, 0);
 280         if (pam_retval != PAM_SUCCESS)
 281                 fatal("PAM session setup failed[%d]: %.200s",
 282                     pam_retval, PAM_STRERROR(pamh, pam_retval));
 283 }
 284
 285 /* Set PAM credentials */
 286 void do_pam_setcred(void)
 287 {
 288         int pam_retval;
 289
 290         debug("PAM establishing creds");
 291         pam_retval = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 292         if (pam_retval != PAM_SUCCESS) {
 293                 if (was_authenticated)
 294                         fatal("PAM setcred failed[%d]: %.200s",
 295                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 296                 else
 297                         debug("PAM setcred failed[%d]: %.200s",
 298                             pam_retval, PAM_STRERROR(pamh, pam_retval));
 299         }
 300 }
 301
 302 /* accessor function for file scope static variable */
 303 int pam_password_change_required(void)
 304 {
 305         return password_change_required;
 306 }
 307
 308 /*
 309  * Have user change authentication token if pam_acct_mgmt() indicated
 310  * it was expired.  This needs to be called after an interactive
 311  * session is established and the user's pty is connected to
 312  * stdin/stout/stderr.
 313  */
 314 void do_pam_chauthtok(void)
 315 {
 316         int pam_retval;
 317
 318         if (password_change_required) {
 319                 pamstate = OTHER;
 320                 /* XXX: should we really loop forever? */
 321                 do {
 322                         pam_retval = pam_chauthtok(pamh,
 323                             PAM_CHANGE_EXPIRED_AUTHTOK);
 324                         if (pam_retval != PAM_SUCCESS)
 325                                 log("PAM pam_chauthtok failed[%d]: %.200s",
 326                                     pam_retval, PAM_STRERROR(pamh, pam_retval));
 327                 } while (pam_retval != PAM_SUCCESS);
 328         }
 329 }
 330
 331 /* Cleanly shutdown PAM */
 332 void finish_pam(void)
 333 {
 334         pam_cleanup_proc(NULL);
 335         fatal_remove_cleanup(&pam_cleanup_proc, NULL);
 336 }
 337
 338 /* Start PAM authentication for specified account */
 339 void start_pam(const char *user)
 340 {
 341         int pam_retval;
 342
 343         debug("Starting up PAM with username \"%.200s\"", user);
 344
 345         pam_retval = pam_start(SSHD_PAM_SERVICE, user, &conv, &pamh);
 346
 347         if (pam_retval != PAM_SUCCESS)
 348                 fatal("PAM initialisation failed[%d]: %.200s",
 349                     pam_retval, PAM_STRERROR(pamh, pam_retval));
 350 #ifdef PAM_TTY_KLUDGE
 351         /*
 352          * Some PAM modules (e.g. pam_time) require a TTY to operate,
 353          * and will fail in various stupid ways if they don't get one.
 354          * sshd doesn't set the tty until too late in the auth process and may
 355          * not even need one (for tty-less connections)
 356          * Kludge: Set a fake PAM_TTY
 357          */
 358         pam_retval = pam_set_item(pamh, PAM_TTY, "ssh");
 359         if (pam_retval != PAM_SUCCESS)
 360                 fatal("PAM set tty failed[%d]: %.200s",
 361                     pam_retval, PAM_STRERROR(pamh, pam_retval));
 362 #endif /* PAM_TTY_KLUDGE */
 363
 364         fatal_add_cleanup(&pam_cleanup_proc, NULL);
 365 }
 366
 367 /* Return list of PAM enviornment strings */
 368 char **fetch_pam_environment(void)
 369 {
 370 #ifdef HAVE_PAM_GETENVLIST
 371         return(pam_getenvlist(pamh));
 372 #else /* HAVE_PAM_GETENVLIST */
 373         return(NULL);
 374 #endif /* HAVE_PAM_GETENVLIST */
 375 }
 376
 377 /* Print any messages that have been generated during authentication */
 378 /* or account checking to stderr */
 379 void print_pam_messages(void)
 380 {
 381         if (pam_msg != NULL)
 382                 fputs(pam_msg, stderr);
 383 }
 384
 385 /* Append a message to buffer */
 386 void message_cat(char **p, const char *a)
 387 {
 388         char *cp;
 389         size_t new_len;
 390
 391         new_len = strlen(a);
 392
 393         if (*p) {
 394                 size_t len = strlen(*p);
 395
 396                 *p = xrealloc(*p, new_len + len + 2);
 397                 cp = *p + len;
 398         } else
 399                 *p = cp = xmalloc(new_len + 2);
 400
 401         memcpy(cp, a, new_len);
 402         cp[new_len] = '\n';
 403         cp[new_len + 1] = '\0';
 404 }
 405
 406 #endif /* USE_PAM */