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