pam_ssh.c revision 1.7
1 /* $NetBSD: pam_ssh.c,v 1.7 2005/03/14 05:45:48 christos 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 1.7 2005/03/14 05:45:48 christos 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 "auth.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 return (NULL); 112 } 113 if (!user_key_allowed(pwd, key)) { 114 openpam_log(PAM_LOG_DEBUG, "key from %s not authorized\n", fn); 115 goto out; 116 } 117 118 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn); 119 if ((psk = malloc(sizeof(*psk))) == NULL) { 120 out: 121 key_free(key); 122 free(comment); 123 return (NULL); 124 } 125 psk->key = key; 126 psk->comment = comment; 127 return (psk); 128 } 129 130 /* 131 * Wipes a private key and frees the associated resources. 132 */ 133 static void 134 pam_ssh_free_key(pam_handle_t *pamh __unused, 135 void *data, int pam_err __unused) 136 { 137 struct pam_ssh_key *psk; 138 139 psk = data; 140 key_free(psk->key); 141 free(psk->comment); 142 free(psk); 143 } 144 145 PAM_EXTERN int 146 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 147 int argc __unused, const char *argv[] __unused) 148 { 149 const char **kfn, *passphrase, *user; 150 struct passwd *pwd; 151 struct pam_ssh_key *psk; 152 int nkeys, pam_err, pass; 153 154 /* PEM is not loaded by default */ 155 OpenSSL_add_all_algorithms(); 156 157 /* get user name and home directory */ 158 pam_err = pam_get_user(pamh, &user, NULL); 159 if (pam_err != PAM_SUCCESS) 160 return (pam_err); 161 pwd = getpwnam(user); 162 if (pwd == NULL) 163 return (PAM_USER_UNKNOWN); 164 if (pwd->pw_dir == NULL) 165 return (PAM_AUTH_ERR); 166 167 /* switch to user credentials */ 168 pam_err = openpam_borrow_cred(pamh, pwd); 169 if (pam_err != PAM_SUCCESS) 170 return (pam_err); 171 172 #ifdef notyet 173 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 174 char path[MAXPATHLEN]; 175 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 176 if (access(path, R_OK) == 0) 177 break; 178 } 179 180 if (*kfn == NULL) { 181 openpam_restore_cred(pamh); 182 return (PAM_AUTH_ERR); 183 } 184 #endif 185 186 pass = (pam_get_item(pamh, PAM_AUTHTOK, 187 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 188 load_keys: 189 /* get passphrase */ 190 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 191 &passphrase, pam_ssh_prompt); 192 if (pam_err != PAM_SUCCESS) { 193 openpam_restore_cred(pamh); 194 return (pam_err); 195 } 196 197 /* try to load keys from all keyfiles we know of */ 198 nkeys = 0; 199 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 200 psk = pam_ssh_load_key(pwd, *kfn, passphrase); 201 if (psk != NULL) { 202 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 203 ++nkeys; 204 } 205 } 206 207 /* 208 * If we tried an old token and didn't get anything, and 209 * try_first_pass was specified, try again after prompting the 210 * user for a new passphrase. 211 */ 212 if (nkeys == 0 && pass == 1 && 213 openpam_get_option(pamh, "try_first_pass") != NULL) { 214 pam_set_item(pamh, PAM_AUTHTOK, NULL); 215 pass = 0; 216 goto load_keys; 217 } 218 219 /* switch back to arbitrator credentials before returning */ 220 openpam_restore_cred(pamh); 221 222 /* no keys? */ 223 if (nkeys == 0) 224 return (PAM_AUTH_ERR); 225 226 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 227 return (PAM_SUCCESS); 228 } 229 230 PAM_EXTERN int 231 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 232 int argc __unused, const char *argv[] __unused) 233 { 234 235 return (PAM_SUCCESS); 236 } 237 238 /* 239 * Parses a line from ssh-agent's output. 240 */ 241 static void 242 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 243 { 244 char *line, *p, *key, *val; 245 size_t len; 246 247 while ((line = fgetln(f, &len)) != NULL) { 248 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 249 continue; 250 251 /* find equal sign at end of key */ 252 for (p = key = line; p < line + len; ++p) 253 if (*p == '=') 254 break; 255 if (p == line + len || *p != '=') 256 continue; 257 *p = '\0'; 258 259 /* find semicolon at end of value */ 260 for (val = ++p; p < line + len; ++p) 261 if (*p == ';') 262 break; 263 if (p == line + len || *p != ';') 264 continue; 265 *p = '\0'; 266 267 /* store key-value pair in environment */ 268 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 269 pam_setenv(pamh, key, val, 1); 270 } 271 } 272 273 /* 274 * Starts an ssh agent and stores the environment variables derived from 275 * its output. 276 */ 277 static int 278 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 279 { 280 int agent_pipe[2]; 281 pid_t pid; 282 FILE *f; 283 284 /* get a pipe which we will use to read the agent's output */ 285 if (pipe(agent_pipe) == -1) 286 return (PAM_SYSTEM_ERR); 287 288 /* start the agent */ 289 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 290 pid = fork(); 291 if (pid == (pid_t)-1) { 292 /* failed */ 293 close(agent_pipe[0]); 294 close(agent_pipe[1]); 295 return (PAM_SYSTEM_ERR); 296 } 297 if (pid == 0) { 298 #ifndef F_CLOSEM 299 int fd; 300 #endif 301 /* child: drop privs, close fds and start agent */ 302 if (setgid(pwd->pw_gid) == -1) { 303 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 304 __FUNCTION__, (int)pwd->pw_gid); 305 goto done; 306 } 307 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 308 openpam_log(PAM_LOG_DEBUG, 309 "%s: Cannot initgroups for %s (%m)", 310 __FUNCTION__, pwd->pw_name); 311 goto done; 312 } 313 if (setuid(pwd->pw_uid) == -1) { 314 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 315 __FUNCTION__, (int)pwd->pw_uid); 316 goto done; 317 } 318 (void)close(STDIN_FILENO); 319 (void)open(_PATH_DEVNULL, O_RDONLY); 320 (void)dup2(agent_pipe[1], STDOUT_FILENO); 321 (void)dup2(agent_pipe[1], STDERR_FILENO); 322 #ifdef F_CLOSEM 323 (void)fcntl(3, F_CLOSEM, 0); 324 #else 325 for (fd = 3; fd < getdtablesize(); ++fd) 326 (void)close(fd); 327 #endif 328 (void)execve(pam_ssh_agent, 329 (char **)__UNCONST(pam_ssh_agent_argv), 330 (char **)__UNCONST(pam_ssh_agent_envp)); 331 done: 332 _exit(127); 333 } 334 335 /* parent */ 336 close(agent_pipe[1]); 337 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 338 return (PAM_SYSTEM_ERR); 339 pam_ssh_process_agent_output(pamh, f); 340 fclose(f); 341 342 return (PAM_SUCCESS); 343 } 344 345 /* 346 * Adds previously stored keys to a running agent. 347 */ 348 static int 349 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 350 { 351 AuthenticationConnection *ac; 352 struct pam_ssh_key *psk; 353 const char **kfn; 354 char **envlist, **env; 355 int pam_err; 356 357 /* switch to PAM environment */ 358 envlist = environ; 359 if ((environ = pam_getenvlist(pamh)) == NULL) { 360 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 361 __FUNCTION__); 362 environ = envlist; 363 return (PAM_SYSTEM_ERR); 364 } 365 366 /* get a connection to the agent */ 367 if ((ac = ssh_get_authentication_connection()) == NULL) { 368 openpam_log(PAM_LOG_DEBUG, 369 "%s: cannot get authentication connection", 370 __FUNCTION__); 371 pam_err = PAM_SYSTEM_ERR; 372 goto end; 373 } 374 375 /* look for keys to add to it */ 376 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 377 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 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; 409 const char *user; 410 void *data; 411 int pam_err = PAM_SUCCESS; 412 413 /* no keys, no work */ 414 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 415 openpam_get_option(pamh, "want_agent") == NULL) 416 return (PAM_SUCCESS); 417 418 /* switch to user credentials */ 419 pam_err = pam_get_user(pamh, &user, NULL); 420 if (pam_err != PAM_SUCCESS) 421 return (pam_err); 422 pwd = getpwnam(user); 423 if (pwd == NULL) 424 return (PAM_USER_UNKNOWN); 425 426 /* start the agent */ 427 pam_err = pam_ssh_start_agent(pamh, pwd); 428 if (pam_err != PAM_SUCCESS) 429 return pam_err; 430 431 pam_err = openpam_borrow_cred(pamh, pwd); 432 if (pam_err != PAM_SUCCESS) 433 return pam_err; 434 435 /* we have an agent, see if we can add any keys to it */ 436 pam_err = pam_ssh_add_keys_to_agent(pamh); 437 if (pam_err != PAM_SUCCESS) { 438 /* XXX ignore failures */ 439 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 440 pam_err = PAM_SUCCESS; 441 } 442 443 openpam_restore_cred(pamh); 444 return pam_err; 445 } 446 447 PAM_EXTERN int 448 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 449 int argc __unused, const char *argv[] __unused) 450 { 451 const char *ssh_agent_pid; 452 char *end; 453 int status; 454 pid_t pid; 455 456 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 457 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 458 return (PAM_SUCCESS); 459 } 460 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 461 if (*ssh_agent_pid == '\0' || *end != '\0') { 462 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 463 return (PAM_SESSION_ERR); 464 } 465 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 466 if (kill(pid, SIGTERM) == -1 || 467 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 468 return (PAM_SYSTEM_ERR); 469 return (PAM_SUCCESS); 470 } 471 472 PAM_MODULE_ENTRY("pam_ssh"); 473
Indexes created Sun Sep 28 16:09:52 GMT 2025