pam_ssh.c revision 1.6
1 /* $NetBSD: pam_ssh.c,v 1.6 2005/03/14 05:40:35 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 1.6 2005/03/14 05:40:35 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 "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(const char *dir, 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", dir, kfn) > (int)sizeof(fn)) 104 return (NULL); 105 comment = NULL; 106 key = key_load_private(fn, passphrase, &comment); 107 if (key == NULL) { 108 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn); 109 return (NULL); 110 } 111 112 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn); 113 if ((psk = malloc(sizeof(*psk))) == NULL) { 114 key_free(key); 115 free(comment); 116 return (NULL); 117 } 118 psk->key = key; 119 psk->comment = comment; 120 return (psk); 121 } 122 123 /* 124 * Wipes a private key and frees the associated resources. 125 */ 126 static void 127 pam_ssh_free_key(pam_handle_t *pamh __unused, 128 void *data, int pam_err __unused) 129 { 130 struct pam_ssh_key *psk; 131 132 psk = data; 133 key_free(psk->key); 134 free(psk->comment); 135 free(psk); 136 } 137 138 PAM_EXTERN int 139 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 140 int argc __unused, const char *argv[] __unused) 141 { 142 const char **kfn, *passphrase, *user; 143 struct passwd *pwd; 144 struct pam_ssh_key *psk; 145 int nkeys, pam_err, pass; 146 147 /* PEM is not loaded by default */ 148 OpenSSL_add_all_algorithms(); 149 150 /* get user name and home directory */ 151 pam_err = pam_get_user(pamh, &user, NULL); 152 if (pam_err != PAM_SUCCESS) 153 return (pam_err); 154 pwd = getpwnam(user); 155 if (pwd == NULL) 156 return (PAM_USER_UNKNOWN); 157 if (pwd->pw_dir == NULL) 158 return (PAM_AUTH_ERR); 159 160 /* switch to user credentials */ 161 pam_err = openpam_borrow_cred(pamh, pwd); 162 if (pam_err != PAM_SUCCESS) 163 return (pam_err); 164 165 #ifdef notyet 166 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 167 char path[MAXPATHLEN]; 168 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 169 if (access(path, R_OK) == 0) 170 break; 171 } 172 173 if (*kfn == NULL) { 174 openpam_restore_cred(pamh); 175 return (PAM_AUTH_ERR); 176 } 177 #endif 178 179 pass = (pam_get_item(pamh, PAM_AUTHTOK, 180 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 181 load_keys: 182 /* get passphrase */ 183 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 184 &passphrase, pam_ssh_prompt); 185 if (pam_err != PAM_SUCCESS) { 186 openpam_restore_cred(pamh); 187 return (pam_err); 188 } 189 190 /* try to load keys from all keyfiles we know of */ 191 nkeys = 0; 192 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 193 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase); 194 if (psk != NULL) { 195 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 196 ++nkeys; 197 } 198 } 199 200 /* 201 * If we tried an old token and didn't get anything, and 202 * try_first_pass was specified, try again after prompting the 203 * user for a new passphrase. 204 */ 205 if (nkeys == 0 && pass == 1 && 206 openpam_get_option(pamh, "try_first_pass") != NULL) { 207 pam_set_item(pamh, PAM_AUTHTOK, NULL); 208 pass = 0; 209 goto load_keys; 210 } 211 212 /* switch back to arbitrator credentials before returning */ 213 openpam_restore_cred(pamh); 214 215 /* no keys? */ 216 if (nkeys == 0) 217 return (PAM_AUTH_ERR); 218 219 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 220 return (PAM_SUCCESS); 221 } 222 223 PAM_EXTERN int 224 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 225 int argc __unused, const char *argv[] __unused) 226 { 227 228 return (PAM_SUCCESS); 229 } 230 231 /* 232 * Parses a line from ssh-agent's output. 233 */ 234 static void 235 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 236 { 237 char *line, *p, *key, *val; 238 size_t len; 239 240 while ((line = fgetln(f, &len)) != NULL) { 241 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 242 continue; 243 244 /* find equal sign at end of key */ 245 for (p = key = line; p < line + len; ++p) 246 if (*p == '=') 247 break; 248 if (p == line + len || *p != '=') 249 continue; 250 *p = '\0'; 251 252 /* find semicolon at end of value */ 253 for (val = ++p; p < line + len; ++p) 254 if (*p == ';') 255 break; 256 if (p == line + len || *p != ';') 257 continue; 258 *p = '\0'; 259 260 /* store key-value pair in environment */ 261 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 262 pam_setenv(pamh, key, val, 1); 263 } 264 } 265 266 /* 267 * Starts an ssh agent and stores the environment variables derived from 268 * its output. 269 */ 270 static int 271 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 272 { 273 int agent_pipe[2]; 274 pid_t pid; 275 FILE *f; 276 277 /* get a pipe which we will use to read the agent's output */ 278 if (pipe(agent_pipe) == -1) 279 return (PAM_SYSTEM_ERR); 280 281 /* start the agent */ 282 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 283 pid = fork(); 284 if (pid == (pid_t)-1) { 285 /* failed */ 286 close(agent_pipe[0]); 287 close(agent_pipe[1]); 288 return (PAM_SYSTEM_ERR); 289 } 290 if (pid == 0) { 291 #ifndef F_CLOSEM 292 int fd; 293 #endif 294 /* child: drop privs, close fds and start agent */ 295 if (setgid(pwd->pw_gid) == -1) { 296 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 297 __FUNCTION__, (int)pwd->pw_gid); 298 goto done; 299 } 300 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 301 openpam_log(PAM_LOG_DEBUG, 302 "%s: Cannot initgroups for %s (%m)", 303 __FUNCTION__, pwd->pw_name); 304 goto done; 305 } 306 if (setuid(pwd->pw_uid) == -1) { 307 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 308 __FUNCTION__, (int)pwd->pw_uid); 309 goto done; 310 } 311 (void)close(STDIN_FILENO); 312 (void)open(_PATH_DEVNULL, O_RDONLY); 313 (void)dup2(agent_pipe[1], STDOUT_FILENO); 314 (void)dup2(agent_pipe[1], STDERR_FILENO); 315 #ifdef F_CLOSEM 316 (void)fcntl(3, F_CLOSEM, 0); 317 #else 318 for (fd = 3; fd < getdtablesize(); ++fd) 319 (void)close(fd); 320 #endif 321 (void)execve(pam_ssh_agent, 322 (char **)__UNCONST(pam_ssh_agent_argv), 323 (char **)__UNCONST(pam_ssh_agent_envp)); 324 done: 325 _exit(127); 326 } 327 328 /* parent */ 329 close(agent_pipe[1]); 330 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 331 return (PAM_SYSTEM_ERR); 332 pam_ssh_process_agent_output(pamh, f); 333 fclose(f); 334 335 return (PAM_SUCCESS); 336 } 337 338 /* 339 * Adds previously stored keys to a running agent. 340 */ 341 static int 342 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 343 { 344 AuthenticationConnection *ac; 345 struct pam_ssh_key *psk; 346 const char **kfn; 347 char **envlist, **env; 348 int pam_err; 349 350 /* switch to PAM environment */ 351 envlist = environ; 352 if ((environ = pam_getenvlist(pamh)) == NULL) { 353 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 354 __FUNCTION__); 355 environ = envlist; 356 return (PAM_SYSTEM_ERR); 357 } 358 359 /* get a connection to the agent */ 360 if ((ac = ssh_get_authentication_connection()) == NULL) { 361 openpam_log(PAM_LOG_DEBUG, 362 "%s: cannot get authentication connection", 363 __FUNCTION__); 364 pam_err = PAM_SYSTEM_ERR; 365 goto end; 366 } 367 368 /* look for keys to add to it */ 369 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 370 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 371 if (pam_err == PAM_SUCCESS && psk != NULL) { 372 if (ssh_add_identity(ac, psk->key, psk->comment)) 373 openpam_log(PAM_LOG_DEBUG, 374 "added %s to ssh agent", psk->comment); 375 else 376 openpam_log(PAM_LOG_DEBUG, "failed " 377 "to add %s to ssh agent", psk->comment); 378 /* we won't need the key again, so wipe it */ 379 pam_set_data(pamh, *kfn, NULL, NULL); 380 } 381 } 382 pam_err = PAM_SUCCESS; 383 end: 384 /* disconnect from agent */ 385 if (ac != NULL) 386 ssh_close_authentication_connection(ac); 387 388 /* switch back to original environment */ 389 for (env = environ; *env != NULL; ++env) 390 free(*env); 391 free(environ); 392 environ = envlist; 393 394 return (pam_err); 395 } 396 397 PAM_EXTERN int 398 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 399 int argc __unused, const char *argv[] __unused) 400 { 401 struct passwd *pwd; 402 const char *user; 403 void *data; 404 int pam_err = PAM_SUCCESS; 405 406 /* no keys, no work */ 407 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 408 openpam_get_option(pamh, "want_agent") == NULL) 409 return (PAM_SUCCESS); 410 411 /* switch to user credentials */ 412 pam_err = pam_get_user(pamh, &user, NULL); 413 if (pam_err != PAM_SUCCESS) 414 return (pam_err); 415 pwd = getpwnam(user); 416 if (pwd == NULL) 417 return (PAM_USER_UNKNOWN); 418 419 /* start the agent */ 420 pam_err = pam_ssh_start_agent(pamh, pwd); 421 if (pam_err != PAM_SUCCESS) 422 return pam_err; 423 424 pam_err = openpam_borrow_cred(pamh, pwd); 425 if (pam_err != PAM_SUCCESS) 426 return pam_err; 427 428 /* we have an agent, see if we can add any keys to it */ 429 pam_err = pam_ssh_add_keys_to_agent(pamh); 430 if (pam_err != PAM_SUCCESS) { 431 /* XXX ignore failures */ 432 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 433 pam_err = PAM_SUCCESS; 434 } 435 436 openpam_restore_cred(pamh); 437 return pam_err; 438 } 439 440 PAM_EXTERN int 441 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 442 int argc __unused, const char *argv[] __unused) 443 { 444 const char *ssh_agent_pid; 445 char *end; 446 int status; 447 pid_t pid; 448 449 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 450 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 451 return (PAM_SUCCESS); 452 } 453 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 454 if (*ssh_agent_pid == '\0' || *end != '\0') { 455 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 456 return (PAM_SESSION_ERR); 457 } 458 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 459 if (kill(pid, SIGTERM) == -1 || 460 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 461 return (PAM_SYSTEM_ERR); 462 return (PAM_SUCCESS); 463 } 464 465 PAM_MODULE_ENTRY("pam_ssh"); 466
Indexes created Sun Sep 28 16:09:52 GMT 2025