lib/pam_module/pam_ssh/pam_ssh.c

   1 /*-
   2  * Copyright (c) 2003 Networks Associates Technology, Inc.
   3  * All rights reserved.
   4  *
   5  * This software was developed for the FreeBSD Project by ThinkSec AS and
   6  * NAI Labs, the Security Research Division of Network Associates, Inc.
   7  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
   8  * DARPA CHATS research program.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. The name of the author may not be used to endorse or promote
  19  *    products derived from this software without specific prior written
  20  *    permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.c,v 1.40 2004/02/10 10:13:21 des Exp $
  35  * $DragonFly: src/lib/pam_module/pam_ssh/pam_ssh.c,v 1.2 2006/09/29 06:35:03 corecode Exp $
  36  */
  37
  38 #include <sys/param.h>
  39 #include <sys/wait.h>
  40
  41 #include <errno.h>
  42 #include <fcntl.h>
  43 #include <paths.h>
  44 #include <pwd.h>
  45 #include <signal.h>
  46 #include <stdio.h>
  47 #include <string.h>
  48 #include <unistd.h>
  49
  50 #define PAM_SM_AUTH
  51 #define PAM_SM_SESSION
  52
  53 #include <security/pam_appl.h>
  54 #include <security/pam_modules.h>
  55 #include <security/openpam.h>
  56
  57 #include <openssl/evp.h>
  58
  59 #include "buffer.h"
  60 #include "key.h"
  61 #include "authfd.h"
  62 #include "authfile.h"
  63
  64 extern char **environ;
  65
  66 struct pam_ssh_key {
  67         Key     *key;
  68         char    *comment;
  69 };
  70
  71 static const char *pam_ssh_prompt = "SSH passphrase: ";
  72 static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
  73
  74 static const char *pam_ssh_keyfiles[] = {
  75         ".ssh/identity",        /* SSH1 RSA key */
  76         ".ssh/id_rsa",          /* SSH2 RSA key */
  77         ".ssh/id_dsa",          /* SSH2 DSA key */
  78         NULL
  79 };
  80
  81 static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
  82 static const char *pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL };
  83 static char *const pam_ssh_agent_envp[] = { NULL };
  84
  85 /*
  86  * Attempts to load a private key from the specified file in the specified
  87  * directory, using the specified passphrase.  If successful, returns a
  88  * struct pam_ssh_key containing the key and its comment.
  89  */
  90 static struct pam_ssh_key *
  91 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase)
  92 {
  93         struct pam_ssh_key *psk;
  94         char fn[PATH_MAX];
  95         char *comment;
  96         Key *key;
  97
  98         if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
  99                 return (NULL);
 100         comment = NULL;
 101         key = key_load_private(fn, passphrase, &comment);
 102         if (key == NULL) {
 103                 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn);
 104                 return (NULL);
 105         }
 106
 107         openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn);
 108         if ((psk = malloc(sizeof(*psk))) == NULL) {
 109                 key_free(key);
 110                 free(comment);
 111                 return (NULL);
 112         }
 113         psk->key = key;
 114         psk->comment = comment;
 115         return (psk);
 116 }
 117
 118 /*
 119  * Wipes a private key and frees the associated resources.
 120  */
 121 static void
 122 pam_ssh_free_key(pam_handle_t *pamh __unused,
 123     void *data, int pam_err __unused)
 124 {
 125         struct pam_ssh_key *psk;
 126
 127         psk = data;
 128         key_free(psk->key);
 129         free(psk->comment);
 130         free(psk);
 131 }
 132
 133 PAM_EXTERN int
 134 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
 135     int argc __unused, const char *argv[] __unused)
 136 {
 137         const char **kfn, *passphrase, *user;
 138         struct passwd *pwd;
 139         struct pam_ssh_key *psk;
 140         int nkeys, pam_err, pass;
 141
 142         /* PEM is not loaded by default */
 143         OpenSSL_add_all_algorithms();
 144
 145         /* get user name and home directory */
 146         pam_err = pam_get_user(pamh, &user, NULL);
 147         if (pam_err != PAM_SUCCESS)
 148                 return (pam_err);
 149         pwd = getpwnam(user);
 150         if (pwd == NULL)
 151                 return (PAM_USER_UNKNOWN);
 152         if (pwd->pw_dir == NULL)
 153                 return (PAM_AUTH_ERR);
 154
 155         /* switch to user credentials */
 156         pam_err = openpam_borrow_cred(pamh, pwd);
 157         if (pam_err != PAM_SUCCESS)
 158                 return (pam_err);
 159
 160         pass = (pam_get_item(pamh, PAM_AUTHTOK,
 161             (const void **)&passphrase) == PAM_SUCCESS);
 162  load_keys:
 163         /* get passphrase */
 164         pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
 165             &passphrase, pam_ssh_prompt);
 166         if (pam_err != PAM_SUCCESS) {
 167                 openpam_restore_cred(pamh);
 168                 return (pam_err);
 169         }
 170
 171         /* try to load keys from all keyfiles we know of */
 172         nkeys = 0;
 173         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 174                 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase);
 175                 if (psk != NULL) {
 176                         pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
 177                         ++nkeys;
 178                 }
 179         }
 180
 181         /*
 182          * If we tried an old token and didn't get anything, and
 183          * try_first_pass was specified, try again after prompting the
 184          * user for a new passphrase.
 185          */
 186         if (nkeys == 0 && pass == 1 &&
 187             openpam_get_option(pamh, "try_first_pass") != NULL) {
 188                 pam_set_item(pamh, PAM_AUTHTOK, NULL);
 189                 pass = 0;
 190                 goto load_keys;
 191         }
 192
 193         /* switch back to arbitrator credentials before returning */
 194         openpam_restore_cred(pamh);
 195
 196         /* no keys? */
 197         if (nkeys == 0)
 198                 return (PAM_AUTH_ERR);
 199
 200         pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
 201         return (PAM_SUCCESS);
 202 }
 203
 204 PAM_EXTERN int
 205 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
 206     int argc __unused, const char *argv[] __unused)
 207 {
 208
 209         return (PAM_SUCCESS);
 210 }
 211
 212 /*
 213  * Parses a line from ssh-agent's output.
 214  */
 215 static void
 216 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
 217 {
 218         char *line, *p, *key, *val;
 219         size_t len;
 220
 221         while ((line = fgetln(f, &len)) != NULL) {
 222                 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
 223                         continue;
 224
 225                 /* find equal sign at end of key */
 226                 for (p = key = line; p < line + len; ++p)
 227                         if (*p == '=')
 228                                 break;
 229                 if (p == line + len || *p != '=')
 230                         continue;
 231                 *p = '\0';
 232
 233                 /* find semicolon at end of value */
 234                 for (val = ++p; p < line + len; ++p)
 235                         if (*p == ';')
 236                                 break;
 237                 if (p == line + len || *p != ';')
 238                         continue;
 239                 *p = '\0';
 240
 241                 /* store key-value pair in environment */
 242                 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
 243                 pam_setenv(pamh, key, val, 1);
 244         }
 245 }
 246
 247 /*
 248  * Starts an ssh agent and stores the environment variables derived from
 249  * its output.
 250  */
 251 static int
 252 pam_ssh_start_agent(pam_handle_t *pamh)
 253 {
 254         int agent_pipe[2];
 255         pid_t pid;
 256         FILE *f;
 257
 258         /* get a pipe which we will use to read the agent's output */
 259         if (pipe(agent_pipe) == -1) {
 260                 openpam_restore_cred(pamh);
 261                 return (PAM_SYSTEM_ERR);
 262         }
 263
 264         /* start the agent */
 265         openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
 266         pid = fork();
 267         if (pid == (pid_t)-1) {
 268                 /* failed */
 269                 close(agent_pipe[0]);
 270                 close(agent_pipe[1]);
 271                 return (PAM_SYSTEM_ERR);
 272         }
 273         if (pid == 0) {
 274                 int fd;
 275
 276                 /* child: drop privs, close fds and start agent */
 277                 setgid(getegid());
 278                 setuid(geteuid());
 279                 close(STDIN_FILENO);
 280                 open(_PATH_DEVNULL, O_RDONLY);
 281                 dup2(agent_pipe[1], STDOUT_FILENO);
 282                 dup2(agent_pipe[1], STDERR_FILENO);
 283                 for (fd = 3; fd < getdtablesize(); ++fd)
 284                         close(fd);
 285                 execve(pam_ssh_agent,
 286                     __DECONST(char * const *, pam_ssh_agent_argv),
 287                     pam_ssh_agent_envp);
 288                 _exit(127);
 289         }
 290
 291         /* parent */
 292         close(agent_pipe[1]);
 293         if ((f = fdopen(agent_pipe[0], "r")) == NULL)
 294                 return (PAM_SYSTEM_ERR);
 295         pam_ssh_process_agent_output(pamh, f);
 296         fclose(f);
 297
 298         return (PAM_SUCCESS);
 299 }
 300
 301 /*
 302  * Adds previously stored keys to a running agent.
 303  */
 304 static int
 305 pam_ssh_add_keys_to_agent(pam_handle_t *pamh)
 306 {
 307         AuthenticationConnection *ac;
 308         struct pam_ssh_key *psk;
 309         const char **kfn;
 310         char **envlist, **env;
 311         int pam_err;
 312
 313         /* switch to PAM environment */
 314         envlist = environ;
 315         if ((environ = pam_getenvlist(pamh)) == NULL) {
 316                 environ = envlist;
 317                 return (PAM_SYSTEM_ERR);
 318         }
 319
 320         /* get a connection to the agent */
 321         if ((ac = ssh_get_authentication_connection()) == NULL) {
 322                 pam_err = PAM_SYSTEM_ERR;
 323                 goto end;
 324         }
 325
 326         /* look for keys to add to it */
 327         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 328                 pam_err = pam_get_data(pamh, *kfn, (void **)&psk);
 329                 if (pam_err == PAM_SUCCESS && psk != NULL) {
 330                         if (ssh_add_identity(ac, psk->key, psk->comment))
 331                                 openpam_log(PAM_LOG_DEBUG,
 332                                     "added %s to ssh agent", psk->comment);
 333                         else
 334                                 openpam_log(PAM_LOG_DEBUG, "failed "
 335                                     "to add %s to ssh agent", psk->comment);
 336                         /* we won't need the key again, so wipe it */
 337                         pam_set_data(pamh, *kfn, NULL, NULL);
 338                 }
 339         }
 340         pam_err = PAM_SUCCESS;
 341  end:
 342         /* disconnect from agent */
 343         if (ac != NULL)
 344                 ssh_close_authentication_connection(ac);
 345
 346         /* switch back to original environment */
 347         for (env = environ; *env != NULL; ++env)
 348                 free(*env);
 349         free(environ);
 350         environ = envlist;
 351
 352         return (pam_err);
 353 }
 354
 355 PAM_EXTERN int
 356 pam_sm_open_session(pam_handle_t *pamh, int flags __unused,
 357     int argc __unused, const char *argv[] __unused)
 358 {
 359         struct passwd *pwd;
 360         const char *user;
 361         void *data;
 362         int pam_err;
 363
 364         /* no keys, no work */
 365         if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS &&
 366             openpam_get_option(pamh, "want_agent") == NULL)
 367                 return (PAM_SUCCESS);
 368
 369         /* switch to user credentials */
 370         pam_err = pam_get_user(pamh, &user, NULL);
 371         if (pam_err != PAM_SUCCESS)
 372                 return (pam_err);
 373         pwd = getpwnam(user);
 374         if (pwd == NULL)
 375                 return (PAM_USER_UNKNOWN);
 376         pam_err = openpam_borrow_cred(pamh, pwd);
 377         if (pam_err != PAM_SUCCESS)
 378                 return (pam_err);
 379
 380         /* start the agent */
 381         pam_err = pam_ssh_start_agent(pamh);
 382         if (pam_err != PAM_SUCCESS) {
 383                 openpam_restore_cred(pamh);
 384                 return (pam_err);
 385         }
 386
 387         /* we have an agent, see if we can add any keys to it */
 388         pam_err = pam_ssh_add_keys_to_agent(pamh);
 389         if (pam_err != PAM_SUCCESS) {
 390                 /* XXX ignore failures */
 391         }
 392
 393         openpam_restore_cred(pamh);
 394         return (PAM_SUCCESS);
 395 }
 396
 397 PAM_EXTERN int
 398 pam_sm_close_session(pam_handle_t *pamh, int flags __unused,
 399     int argc __unused, const char *argv[] __unused)
 400 {
 401         const char *ssh_agent_pid;
 402         char *end;
 403         int status;
 404         pid_t pid;
 405
 406         if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) {
 407                 openpam_log(PAM_LOG_DEBUG, "no ssh agent");
 408                 return (PAM_SUCCESS);
 409         }
 410         pid = (pid_t)strtol(ssh_agent_pid, &end, 10);
 411         if (*ssh_agent_pid == '\0' || *end != '\0') {
 412                 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid");
 413                 return (PAM_SESSION_ERR);
 414         }
 415         openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid);
 416         if (kill(pid, SIGTERM) == -1 ||
 417             (waitpid(pid, &status, 0) == -1 && errno != ECHILD))
 418                 return (PAM_SYSTEM_ERR);
 419         return (PAM_SUCCESS);
 420 }
 421
 422 PAM_MODULE_ENTRY("pam_ssh");