pam_ssh.c revision 1.12
1 /* $NetBSD: pam_ssh.c,v 1.12 2006/03/19 06:52:26 jnemeth 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 1.12 2006/03/19 06:52:26 jnemeth 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 "authfd.h" 67 #include "authfile.h" 68 69 extern char **environ; 70 71 struct pam_ssh_key { 72 Key *key; 73 char *comment; 74 }; 75 76 static const char *pam_ssh_prompt = "SSH passphrase: "; 77 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 78 79 static const char *pam_ssh_keyfiles[] = { 80 ".ssh/identity", /* SSH1 RSA key */ 81 ".ssh/id_rsa", /* SSH2 RSA key */ 82 ".ssh/id_dsa", /* SSH2 DSA key */ 83 NULL 84 }; 85 86 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 87 static const char *pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL }; 88 static const char *pam_ssh_agent_envp[] = { NULL }; 89 90 /* 91 * Attempts to load a private key from the specified file in the specified 92 * directory, using the specified passphrase. If successful, returns a 93 * struct pam_ssh_key containing the key and its comment. 94 */ 95 static struct pam_ssh_key * 96 pam_ssh_load_key(struct passwd *pwd, const char *kfn, const char *passphrase) 97 { 98 struct pam_ssh_key *psk; 99 char fn[PATH_MAX]; 100 char *comment; 101 Key *key; 102 103 if (snprintf(fn, sizeof(fn), "%s/%s", pwd->pw_dir, kfn) > 104 (int)sizeof(fn)) 105 return (NULL); 106 comment = NULL; 107 key = key_load_private(fn, passphrase, &comment); 108 if (key == NULL) { 109 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn); 110 if (comment != NULL) 111 free(comment); 112 return (NULL); 113 } 114 115 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn); 116 if ((psk = malloc(sizeof(*psk))) == NULL) { 117 key_free(key); 118 free(comment); 119 return (NULL); 120 } 121 psk->key = key; 122 psk->comment = comment; 123 return (psk); 124 } 125 126 /* 127 * Wipes a private key and frees the associated resources. 128 */ 129 static void 130 pam_ssh_free_key(pam_handle_t *pamh __unused, 131 void *data, int pam_err __unused) 132 { 133 struct pam_ssh_key *psk; 134 135 psk = data; 136 key_free(psk->key); 137 free(psk->comment); 138 free(psk); 139 } 140 141 PAM_EXTERN int 142 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 143 int argc __unused, const char *argv[] __unused) 144 { 145 const char **kfn, *passphrase, *user; 146 struct passwd *pwd, pwres; 147 struct pam_ssh_key *psk; 148 int nkeys, pam_err, pass; 149 char pwbuf[1024]; 150 151 /* PEM is not loaded by default */ 152 OpenSSL_add_all_algorithms(); 153 154 /* get user name and home directory */ 155 pam_err = pam_get_user(pamh, &user, NULL); 156 if (pam_err != PAM_SUCCESS) 157 return (pam_err); 158 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 159 pwd == NULL) 160 return (PAM_USER_UNKNOWN); 161 if (pwd->pw_dir == NULL) 162 return (PAM_AUTH_ERR); 163 164 /* switch to user credentials */ 165 pam_err = openpam_borrow_cred(pamh, pwd); 166 if (pam_err != PAM_SUCCESS) 167 return (pam_err); 168 169 #ifdef notyet 170 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 171 char path[MAXPATHLEN]; 172 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 173 if (access(path, R_OK) == 0) 174 break; 175 } 176 177 if (*kfn == NULL) { 178 openpam_restore_cred(pamh); 179 return (PAM_AUTH_ERR); 180 } 181 #endif 182 183 pass = (pam_get_item(pamh, PAM_AUTHTOK, 184 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 185 load_keys: 186 /* get passphrase */ 187 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 188 &passphrase, pam_ssh_prompt); 189 if (pam_err != PAM_SUCCESS) { 190 openpam_restore_cred(pamh); 191 return (pam_err); 192 } 193 194 /* try to load keys from all keyfiles we know of */ 195 nkeys = 0; 196 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 197 psk = pam_ssh_load_key(pwd, *kfn, passphrase); 198 if (psk != NULL) { 199 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 200 ++nkeys; 201 } 202 } 203 204 /* 205 * If we tried an old token and didn't get anything, and 206 * try_first_pass was specified, try again after prompting the 207 * user for a new passphrase. 208 */ 209 if (nkeys == 0 && pass == 1 && 210 openpam_get_option(pamh, "try_first_pass") != NULL) { 211 pam_set_item(pamh, PAM_AUTHTOK, NULL); 212 pass = 0; 213 goto load_keys; 214 } 215 216 /* switch back to arbitrator credentials before returning */ 217 openpam_restore_cred(pamh); 218 219 /* no keys? */ 220 if (nkeys == 0) 221 return (PAM_AUTH_ERR); 222 223 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 224 return (PAM_SUCCESS); 225 } 226 227 PAM_EXTERN int 228 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 229 int argc __unused, const char *argv[] __unused) 230 { 231 232 return (PAM_SUCCESS); 233 } 234 235 /* 236 * Parses a line from ssh-agent's output. 237 */ 238 static void 239 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 240 { 241 char *line, *p, *key, *val; 242 size_t len; 243 244 while ((line = fgetln(f, &len)) != NULL) { 245 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 246 continue; 247 248 /* find equal sign at end of key */ 249 for (p = key = line; p < line + len; ++p) 250 if (*p == '=') 251 break; 252 if (p == line + len || *p != '=') 253 continue; 254 *p = '\0'; 255 256 /* find semicolon at end of value */ 257 for (val = ++p; p < line + len; ++p) 258 if (*p == ';') 259 break; 260 if (p == line + len || *p != ';') 261 continue; 262 *p = '\0'; 263 264 /* store key-value pair in environment */ 265 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 266 pam_setenv(pamh, key, val, 1); 267 } 268 } 269 270 /* 271 * Starts an ssh agent and stores the environment variables derived from 272 * its output. 273 */ 274 static int 275 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 276 { 277 int agent_pipe[2]; 278 pid_t pid; 279 FILE *f; 280 281 /* get a pipe which we will use to read the agent's output */ 282 if (pipe(agent_pipe) == -1) 283 return (PAM_SYSTEM_ERR); 284 285 /* start the agent */ 286 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 287 pid = fork(); 288 if (pid == (pid_t)-1) { 289 /* failed */ 290 close(agent_pipe[0]); 291 close(agent_pipe[1]); 292 return (PAM_SYSTEM_ERR); 293 } 294 if (pid == 0) { 295 #ifndef F_CLOSEM 296 int fd; 297 #endif 298 /* child: drop privs, close fds and start agent */ 299 if (setgid(pwd->pw_gid) == -1) { 300 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 301 __FUNCTION__, (int)pwd->pw_gid); 302 goto done; 303 } 304 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 305 openpam_log(PAM_LOG_DEBUG, 306 "%s: Cannot initgroups for %s (%m)", 307 __FUNCTION__, pwd->pw_name); 308 goto done; 309 } 310 if (setuid(pwd->pw_uid) == -1) { 311 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 312 __FUNCTION__, (int)pwd->pw_uid); 313 goto done; 314 } 315 (void)close(STDIN_FILENO); 316 (void)open(_PATH_DEVNULL, O_RDONLY); 317 (void)dup2(agent_pipe[1], STDOUT_FILENO); 318 (void)dup2(agent_pipe[1], STDERR_FILENO); 319 #ifdef F_CLOSEM 320 (void)fcntl(3, F_CLOSEM, 0); 321 #else 322 for (fd = 3; fd < getdtablesize(); ++fd) 323 (void)close(fd); 324 #endif 325 (void)execve(pam_ssh_agent, 326 (char **)__UNCONST(pam_ssh_agent_argv), 327 (char **)__UNCONST(pam_ssh_agent_envp)); 328 done: 329 _exit(127); 330 } 331 332 /* parent */ 333 close(agent_pipe[1]); 334 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 335 return (PAM_SYSTEM_ERR); 336 pam_ssh_process_agent_output(pamh, f); 337 fclose(f); 338 339 return (PAM_SUCCESS); 340 } 341 342 /* 343 * Adds previously stored keys to a running agent. 344 */ 345 static int 346 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 347 { 348 AuthenticationConnection *ac; 349 struct pam_ssh_key *psk; 350 const char **kfn; 351 char **envlist, **env; 352 int pam_err; 353 354 /* switch to PAM environment */ 355 envlist = environ; 356 if ((environ = pam_getenvlist(pamh)) == NULL) { 357 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 358 __FUNCTION__); 359 environ = envlist; 360 return (PAM_SYSTEM_ERR); 361 } 362 363 /* get a connection to the agent */ 364 if ((ac = ssh_get_authentication_connection()) == NULL) { 365 openpam_log(PAM_LOG_DEBUG, 366 "%s: cannot get authentication connection", 367 __FUNCTION__); 368 pam_err = PAM_SYSTEM_ERR; 369 goto end; 370 } 371 372 /* look for keys to add to it */ 373 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 374 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 375 if (pam_err == PAM_SUCCESS && psk != NULL) { 376 if (ssh_add_identity(ac, psk->key, psk->comment)) 377 openpam_log(PAM_LOG_DEBUG, 378 "added %s to ssh agent", psk->comment); 379 else 380 openpam_log(PAM_LOG_DEBUG, "failed " 381 "to add %s to ssh agent", psk->comment); 382 /* we won't need the key again, so wipe it */ 383 pam_set_data(pamh, *kfn, NULL, NULL); 384 } 385 } 386 pam_err = PAM_SUCCESS; 387 end: 388 /* disconnect from agent */ 389 if (ac != NULL) 390 ssh_close_authentication_connection(ac); 391 392 /* switch back to original environment */ 393 for (env = environ; *env != NULL; ++env) 394 free(*env); 395 free(environ); 396 environ = envlist; 397 398 return (pam_err); 399 } 400 401 PAM_EXTERN int 402 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 403 int argc __unused, const char *argv[] __unused) 404 { 405 struct passwd *pwd, pwres; 406 const char *user; 407 void *data; 408 int pam_err = PAM_SUCCESS; 409 char pwbuf[1024]; 410 411 /* no keys, no work */ 412 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 413 openpam_get_option(pamh, "want_agent") == NULL) 414 return (PAM_SUCCESS); 415 416 /* switch to user credentials */ 417 pam_err = pam_get_user(pamh, &user, NULL); 418 if (pam_err != PAM_SUCCESS) 419 return (pam_err); 420 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 421 pwd == NULL) 422 return (PAM_USER_UNKNOWN); 423 424 /* start the agent */ 425 pam_err = pam_ssh_start_agent(pamh, pwd); 426 if (pam_err != PAM_SUCCESS) 427 return pam_err; 428 429 pam_err = openpam_borrow_cred(pamh, pwd); 430 if (pam_err != PAM_SUCCESS) 431 return pam_err; 432 433 /* we have an agent, see if we can add any keys to it */ 434 pam_err = pam_ssh_add_keys_to_agent(pamh); 435 if (pam_err != PAM_SUCCESS) { 436 /* XXX ignore failures */ 437 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 438 pam_err = PAM_SUCCESS; 439 } 440 441 openpam_restore_cred(pamh); 442 return pam_err; 443 } 444 445 PAM_EXTERN int 446 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 447 int argc __unused, const char *argv[] __unused) 448 { 449 const char *ssh_agent_pid; 450 char *end; 451 int status; 452 pid_t pid; 453 454 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 455 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 456 return (PAM_SUCCESS); 457 } 458 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 459 if (*ssh_agent_pid == '\0' || *end != '\0') { 460 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 461 return (PAM_SESSION_ERR); 462 } 463 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 464 if (kill(pid, SIGTERM) == -1 || 465 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 466 return (PAM_SYSTEM_ERR); 467 return (PAM_SUCCESS); 468 } 469 470 PAM_MODULE_ENTRY("pam_ssh"); 471
Indexes created Tue Sep 23 07:09:52 GMT 2025