lib/libpam/modules/pam_ssh/pam_ssh.c

   1 /*      $NetBSD: pam_ssh.c,v 1.14 2007/09/15 14:30:56 ragge Exp $       */
   2
   3 /*-
   4  * Copyright (c) 2003 Networks Associates Technology, Inc.
   5  * All rights reserved.
   6  *
   7  * This software was developed for the FreeBSD Project by ThinkSec AS and
   8  * NAI Labs, the Security Research Division of Network Associates, Inc.
   9  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
  10  * DARPA CHATS research program.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. The name of the author may not be used to endorse or promote
  21  *    products derived from this software without specific prior written
  22  *    permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  */
  36
  37 #include <sys/cdefs.h>
  38 #ifdef __FreeBSD__
  39 __FBSDID("$FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.c,v 1.40 2004/02/10 10:13:21 des Exp $");
  40 #else
  41 __RCSID("$NetBSD: pam_ssh.c,v 1.14 2007/09/15 14:30:56 ragge Exp $");
  42 #endif
  43
  44 #include <sys/param.h>
  45 #include <sys/wait.h>
  46
  47 #include <errno.h>
  48 #include <fcntl.h>
  49 #include <paths.h>
  50 #include <pwd.h>
  51 #include <signal.h>
  52 #include <stdio.h>
  53 #include <string.h>
  54 #include <unistd.h>
  55
  56 #define PAM_SM_AUTH
  57 #define PAM_SM_SESSION
  58
  59 #include <security/pam_appl.h>
  60 #include <security/pam_modules.h>
  61 #include <security/openpam.h>
  62
  63 #include <openssl/evp.h>
  64
  65 #include "key.h"
  66 #include "buffer.h"
  67 #include "authfd.h"
  68 #include "authfile.h"
  69
  70 extern char **environ;
  71
  72 struct pam_ssh_key {
  73         Key     *key;
  74         char    *comment;
  75 };
  76
  77 static const char *pam_ssh_prompt = "SSH passphrase: ";
  78 static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
  79
  80 static const char *pam_ssh_keyfiles[] = {
  81         ".ssh/identity",        /* SSH1 RSA key */
  82         ".ssh/id_rsa",          /* SSH2 RSA key */
  83         ".ssh/id_dsa",          /* SSH2 DSA key */
  84         NULL
  85 };
  86
  87 static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
  88 static const char *pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL };
  89 static const char *pam_ssh_agent_envp[] = { NULL };
  90
  91 /*
  92  * Attempts to load a private key from the specified file in the specified
  93  * directory, using the specified passphrase.  If successful, returns a
  94  * struct pam_ssh_key containing the key and its comment.
  95  */
  96 static struct pam_ssh_key *
  97 pam_ssh_load_key(struct passwd *pwd, const char *kfn, const char *passphrase)
  98 {
  99         struct pam_ssh_key *psk;
 100         char fn[PATH_MAX];
 101         char *comment;
 102         Key *key;
 103
 104         if (snprintf(fn, sizeof(fn), "%s/%s", pwd->pw_dir, kfn) >
 105             (int)sizeof(fn))
 106                 return (NULL);
 107         comment = NULL;
 108         key = key_load_private(fn, passphrase, &comment);
 109         if (key == NULL) {
 110                 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn);
 111                 if (comment != NULL)
 112                         free(comment);
 113                 return (NULL);
 114         }
 115
 116         openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn);
 117         if ((psk = malloc(sizeof(*psk))) == NULL) {
 118                 key_free(key);
 119                 free(comment);
 120                 return (NULL);
 121         }
 122         psk->key = key;
 123         psk->comment = comment;
 124         return (psk);
 125 }
 126
 127 /*
 128  * Wipes a private key and frees the associated resources.
 129  */
 130 static void
 131 pam_ssh_free_key(pam_handle_t *pamh __unused,
 132     void *data, int pam_err __unused)
 133 {
 134         struct pam_ssh_key *psk;
 135
 136         psk = data;
 137         key_free(psk->key);
 138         free(psk->comment);
 139         free(psk);
 140 }
 141
 142 PAM_EXTERN int
 143 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
 144     int argc __unused, const char *argv[] __unused)
 145 {
 146         const char **kfn, *passphrase, *user;
 147         struct passwd *pwd, pwres;
 148         struct pam_ssh_key *psk;
 149         int nkeys, pam_err, pass;
 150         char pwbuf[1024];
 151
 152         /* PEM is not loaded by default */
 153         OpenSSL_add_all_algorithms();
 154
 155         /* get user name and home directory */
 156         pam_err = pam_get_user(pamh, &user, NULL);
 157         if (pam_err != PAM_SUCCESS)
 158                 return (pam_err);
 159         if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 ||
 160             pwd == NULL)
 161                 return (PAM_USER_UNKNOWN);
 162         if (pwd->pw_dir == NULL)
 163                 return (PAM_AUTH_ERR);
 164
 165         /* switch to user credentials */
 166         pam_err = openpam_borrow_cred(pamh, pwd);
 167         if (pam_err != PAM_SUCCESS)
 168                 return (pam_err);
 169
 170 #ifdef notyet
 171         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 172                 char path[MAXPATHLEN];
 173                 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn);
 174                 if (access(path, R_OK) == 0)
 175                         break;
 176         }
 177
 178         if (*kfn == NULL) {
 179                 openpam_restore_cred(pamh);
 180                 return (PAM_AUTH_ERR);
 181         }
 182 #endif
 183
 184         pass = (pam_get_item(pamh, PAM_AUTHTOK,
 185             (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS);
 186  load_keys:
 187         /* get passphrase */
 188         pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
 189             &passphrase, pam_ssh_prompt);
 190         if (pam_err != PAM_SUCCESS) {
 191                 openpam_restore_cred(pamh);
 192                 return (pam_err);
 193         }
 194
 195         /* try to load keys from all keyfiles we know of */
 196         nkeys = 0;
 197         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 198                 psk = pam_ssh_load_key(pwd, *kfn, passphrase);
 199                 if (psk != NULL) {
 200                         pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
 201                         ++nkeys;
 202                 }
 203         }
 204
 205         /*
 206          * If we tried an old token and didn't get anything, and
 207          * try_first_pass was specified, try again after prompting the
 208          * user for a new passphrase.
 209          */
 210         if (nkeys == 0 && pass == 1 &&
 211             openpam_get_option(pamh, "try_first_pass") != NULL) {
 212                 pam_set_item(pamh, PAM_AUTHTOK, NULL);
 213                 pass = 0;
 214                 goto load_keys;
 215         }
 216
 217         /* switch back to arbitrator credentials before returning */
 218         openpam_restore_cred(pamh);
 219
 220         /* no keys? */
 221         if (nkeys == 0)
 222                 return (PAM_AUTH_ERR);
 223
 224         pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
 225         return (PAM_SUCCESS);
 226 }
 227
 228 PAM_EXTERN int
 229 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
 230     int argc __unused, const char *argv[] __unused)
 231 {
 232
 233         return (PAM_SUCCESS);
 234 }
 235
 236 /*
 237  * Parses a line from ssh-agent's output.
 238  */
 239 static void
 240 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
 241 {
 242         char *line, *p, *key, *val;
 243         size_t len;
 244
 245         while ((line = fgetln(f, &len)) != NULL) {
 246                 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
 247                         continue;
 248
 249                 /* find equal sign at end of key */
 250                 for (p = key = line; p < line + len; ++p)
 251                         if (*p == '=')
 252                                 break;
 253                 if (p == line + len || *p != '=')
 254                         continue;
 255                 *p = '\0';
 256
 257                 /* find semicolon at end of value */
 258                 for (val = ++p; p < line + len; ++p)
 259                         if (*p == ';')
 260                                 break;
 261                 if (p == line + len || *p != ';')
 262                         continue;
 263                 *p = '\0';
 264
 265                 /* store key-value pair in environment */
 266                 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
 267                 pam_setenv(pamh, key, val, 1);
 268         }
 269 }
 270
 271 /*
 272  * Starts an ssh agent and stores the environment variables derived from
 273  * its output.
 274  */
 275 static int
 276 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd)
 277 {
 278         int agent_pipe[2];
 279         pid_t pid;
 280         FILE *f;
 281
 282         /* get a pipe which we will use to read the agent's output */
 283         if (pipe(agent_pipe) == -1)
 284                 return (PAM_SYSTEM_ERR);
 285
 286         /* start the agent */
 287         openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
 288         pid = fork();
 289         if (pid == (pid_t)-1) {
 290                 /* failed */
 291                 close(agent_pipe[0]);
 292                 close(agent_pipe[1]);
 293                 return (PAM_SYSTEM_ERR);
 294         }
 295         if (pid == 0) {
 296 #ifndef F_CLOSEM
 297                 int fd;
 298 #endif
 299                 /* child: drop privs, close fds and start agent */
 300                 if (setgid(pwd->pw_gid) == -1) {
 301                         openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)",
 302                             __func__, (int)pwd->pw_gid);
 303                         goto done;
 304                 }
 305                 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) {
 306                         openpam_log(PAM_LOG_DEBUG,
 307                             "%s: Cannot initgroups for %s (%m)",
 308                             __func__, pwd->pw_name);
 309                         goto done;
 310                 }
 311                 if (setuid(pwd->pw_uid) == -1) {
 312                         openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)",
 313                             __func__, (int)pwd->pw_uid);
 314                         goto done;
 315                 }
 316                 (void)close(STDIN_FILENO);
 317                 (void)open(_PATH_DEVNULL, O_RDONLY);
 318                 (void)dup2(agent_pipe[1], STDOUT_FILENO);
 319                 (void)dup2(agent_pipe[1], STDERR_FILENO);
 320 #ifdef F_CLOSEM
 321                 (void)fcntl(3, F_CLOSEM, 0);
 322 #else
 323                 for (fd = 3; fd < getdtablesize(); ++fd)
 324                         (void)close(fd);
 325 #endif
 326                 (void)execve(pam_ssh_agent,
 327                     (char **)__UNCONST(pam_ssh_agent_argv),
 328                     (char **)__UNCONST(pam_ssh_agent_envp));
 329 done:
 330                 _exit(127);
 331         }
 332
 333         /* parent */
 334         close(agent_pipe[1]);
 335         if ((f = fdopen(agent_pipe[0], "r")) == NULL)
 336                 return (PAM_SYSTEM_ERR);
 337         pam_ssh_process_agent_output(pamh, f);
 338         fclose(f);
 339
 340         return (PAM_SUCCESS);
 341 }
 342
 343 /*
 344  * Adds previously stored keys to a running agent.
 345  */
 346 static int
 347 pam_ssh_add_keys_to_agent(pam_handle_t *pamh)
 348 {
 349         AuthenticationConnection *ac;
 350         const struct pam_ssh_key *psk;
 351         const char **kfn;
 352         char **envlist, **env;
 353         int pam_err;
 354
 355         /* switch to PAM environment */
 356         envlist = environ;
 357         if ((environ = pam_getenvlist(pamh)) == NULL) {
 358                 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist",
 359                     __func__);
 360                 environ = envlist;
 361                 return (PAM_SYSTEM_ERR);
 362         }
 363
 364         /* get a connection to the agent */
 365         if ((ac = ssh_get_authentication_connection()) == NULL) {
 366                 openpam_log(PAM_LOG_DEBUG,
 367                     "%s: cannot get authentication connection",
 368                     __func__);
 369                 pam_err = PAM_SYSTEM_ERR;
 370                 goto end;
 371         }
 372
 373         /* look for keys to add to it */
 374         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 375                 const void *vp;
 376                 pam_err = pam_get_data(pamh, *kfn, &vp);
 377                 psk = vp;
 378                 if (pam_err == PAM_SUCCESS && psk != NULL) {
 379                         if (ssh_add_identity(ac, psk->key, psk->comment))
 380                                 openpam_log(PAM_LOG_DEBUG,
 381                                     "added %s to ssh agent", psk->comment);
 382                         else
 383                                 openpam_log(PAM_LOG_DEBUG, "failed "
 384                                     "to add %s to ssh agent", psk->comment);
 385                         /* we won't need the key again, so wipe it */
 386                         pam_set_data(pamh, *kfn, NULL, NULL);
 387                 }
 388         }
 389         pam_err = PAM_SUCCESS;
 390  end:
 391         /* disconnect from agent */
 392         if (ac != NULL)
 393                 ssh_close_authentication_connection(ac);
 394
 395         /* switch back to original environment */
 396         for (env = environ; *env != NULL; ++env)
 397                 free(*env);
 398         free(environ);
 399         environ = envlist;
 400
 401         return (pam_err);
 402 }
 403
 404 PAM_EXTERN int
 405 pam_sm_open_session(pam_handle_t *pamh, int flags __unused,
 406     int argc __unused, const char *argv[] __unused)
 407 {
 408         struct passwd *pwd, pwres;
 409         const char *user;
 410         const void *data;
 411         int pam_err = PAM_SUCCESS;
 412         char pwbuf[1024];
 413
 414         /* no keys, no work */
 415         if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS &&
 416             openpam_get_option(pamh, "want_agent") == NULL)
 417                 return (PAM_SUCCESS);
 418
 419         /* switch to user credentials */
 420         pam_err = pam_get_user(pamh, &user, NULL);
 421         if (pam_err != PAM_SUCCESS)
 422                 return (pam_err);
 423         if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 ||
 424             pwd == NULL)
 425                 return (PAM_USER_UNKNOWN);
 426
 427         /* start the agent */
 428         pam_err = pam_ssh_start_agent(pamh, pwd);
 429         if (pam_err != PAM_SUCCESS)
 430                 return pam_err;
 431
 432         pam_err = openpam_borrow_cred(pamh, pwd);
 433         if (pam_err != PAM_SUCCESS)
 434                 return pam_err;
 435
 436         /* we have an agent, see if we can add any keys to it */
 437         pam_err = pam_ssh_add_keys_to_agent(pamh);
 438         if (pam_err != PAM_SUCCESS) {
 439                 /* XXX ignore failures */
 440                 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent");
 441                 pam_err = PAM_SUCCESS;
 442         }
 443
 444         openpam_restore_cred(pamh);
 445         return pam_err;
 446 }
 447
 448 PAM_EXTERN int
 449 pam_sm_close_session(pam_handle_t *pamh, int flags __unused,
 450     int argc __unused, const char *argv[] __unused)
 451 {
 452         const char *ssh_agent_pid;
 453         char *end;
 454         int status;
 455         pid_t pid;
 456
 457         if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) {
 458                 openpam_log(PAM_LOG_DEBUG, "no ssh agent");
 459                 return (PAM_SUCCESS);
 460         }
 461         pid = (pid_t)strtol(ssh_agent_pid, &end, 10);
 462         if (*ssh_agent_pid == '\0' || *end != '\0') {
 463                 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid");
 464                 return (PAM_SESSION_ERR);
 465         }
 466         openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid);
 467         if (kill(pid, SIGTERM) == -1 ||
 468             (waitpid(pid, &status, 0) == -1 && errno != ECHILD))
 469                 return (PAM_SYSTEM_ERR);
 470         return (PAM_SUCCESS);
 471 }
 472
 473 PAM_MODULE_ENTRY("pam_ssh");