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