pam_ssh.c revision 1.9
1 /* $NetBSD: pam_ssh.c,v 1.9 2005/03/17 01:14:40 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 1.9 2005/03/17 01:14:40 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(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 return (NULL); 111 } 112 113 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn); 114 if ((psk = malloc(sizeof(*psk))) == NULL) { 115 key_free(key); 116 free(comment); 117 return (NULL); 118 } 119 psk->key = key; 120 psk->comment = comment; 121 return (psk); 122 } 123 124 /* 125 * Wipes a private key and frees the associated resources. 126 */ 127 static void 128 pam_ssh_free_key(pam_handle_t *pamh __unused, 129 void *data, int pam_err __unused) 130 { 131 struct pam_ssh_key *psk; 132 133 psk = data; 134 key_free(psk->key); 135 free(psk->comment); 136 free(psk); 137 } 138 139 PAM_EXTERN int 140 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 141 int argc __unused, const char *argv[] __unused) 142 { 143 const char **kfn, *passphrase, *user; 144 struct passwd *pwd; 145 struct pam_ssh_key *psk; 146 int nkeys, pam_err, pass; 147 148 /* PEM is not loaded by default */ 149 OpenSSL_add_all_algorithms(); 150 151 /* get user name and home directory */ 152 pam_err = pam_get_user(pamh, &user, NULL); 153 if (pam_err != PAM_SUCCESS) 154 return (pam_err); 155 pwd = getpwnam(user); 156 if (pwd == NULL) 157 return (PAM_USER_UNKNOWN); 158 if (pwd->pw_dir == NULL) 159 return (PAM_AUTH_ERR); 160 161 /* switch to user credentials */ 162 pam_err = openpam_borrow_cred(pamh, pwd); 163 if (pam_err != PAM_SUCCESS) 164 return (pam_err); 165 166 #ifdef notyet 167 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 168 char path[MAXPATHLEN]; 169 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 170 if (access(path, R_OK) == 0) 171 break; 172 } 173 174 if (*kfn == NULL) { 175 openpam_restore_cred(pamh); 176 return (PAM_AUTH_ERR); 177 } 178 #endif 179 180 pass = (pam_get_item(pamh, PAM_AUTHTOK, 181 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 182 load_keys: 183 /* get passphrase */ 184 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 185 &passphrase, pam_ssh_prompt); 186 if (pam_err != PAM_SUCCESS) { 187 openpam_restore_cred(pamh); 188 return (pam_err); 189 } 190 191 /* try to load keys from all keyfiles we know of */ 192 nkeys = 0; 193 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 194 psk = pam_ssh_load_key(pwd, *kfn, passphrase); 195 if (psk != NULL) { 196 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 197 ++nkeys; 198 } 199 } 200 201 /* 202 * If we tried an old token and didn't get anything, and 203 * try_first_pass was specified, try again after prompting the 204 * user for a new passphrase. 205 */ 206 if (nkeys == 0 && pass == 1 && 207 openpam_get_option(pamh, "try_first_pass") != NULL) { 208 pam_set_item(pamh, PAM_AUTHTOK, NULL); 209 pass = 0; 210 goto load_keys; 211 } 212 213 /* switch back to arbitrator credentials before returning */ 214 openpam_restore_cred(pamh); 215 216 /* no keys? */ 217 if (nkeys == 0) 218 return (PAM_AUTH_ERR); 219 220 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 221 return (PAM_SUCCESS); 222 } 223 224 PAM_EXTERN int 225 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 226 int argc __unused, const char *argv[] __unused) 227 { 228 229 return (PAM_SUCCESS); 230 } 231 232 /* 233 * Parses a line from ssh-agent's output. 234 */ 235 static void 236 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 237 { 238 char *line, *p, *key, *val; 239 size_t len; 240 241 while ((line = fgetln(f, &len)) != NULL) { 242 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 243 continue; 244 245 /* find equal sign at end of key */ 246 for (p = key = line; p < line + len; ++p) 247 if (*p == '=') 248 break; 249 if (p == line + len || *p != '=') 250 continue; 251 *p = '\0'; 252 253 /* find semicolon at end of value */ 254 for (val = ++p; p < line + len; ++p) 255 if (*p == ';') 256 break; 257 if (p == line + len || *p != ';') 258 continue; 259 *p = '\0'; 260 261 /* store key-value pair in environment */ 262 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 263 pam_setenv(pamh, key, val, 1); 264 } 265 } 266 267 /* 268 * Starts an ssh agent and stores the environment variables derived from 269 * its output. 270 */ 271 static int 272 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 273 { 274 int agent_pipe[2]; 275 pid_t pid; 276 FILE *f; 277 278 /* get a pipe which we will use to read the agent's output */ 279 if (pipe(agent_pipe) == -1) 280 return (PAM_SYSTEM_ERR); 281 282 /* start the agent */ 283 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 284 pid = fork(); 285 if (pid == (pid_t)-1) { 286 /* failed */ 287 close(agent_pipe[0]); 288 close(agent_pipe[1]); 289 return (PAM_SYSTEM_ERR); 290 } 291 if (pid == 0) { 292 #ifndef F_CLOSEM 293 int fd; 294 #endif 295 /* child: drop privs, close fds and start agent */ 296 if (setgid(pwd->pw_gid) == -1) { 297 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 298 __FUNCTION__, (int)pwd->pw_gid); 299 goto done; 300 } 301 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 302 openpam_log(PAM_LOG_DEBUG, 303 "%s: Cannot initgroups for %s (%m)", 304 __FUNCTION__, pwd->pw_name); 305 goto done; 306 } 307 if (setuid(pwd->pw_uid) == -1) { 308 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 309 __FUNCTION__, (int)pwd->pw_uid); 310 goto done; 311 } 312 (void)close(STDIN_FILENO); 313 (void)open(_PATH_DEVNULL, O_RDONLY); 314 (void)dup2(agent_pipe[1], STDOUT_FILENO); 315 (void)dup2(agent_pipe[1], STDERR_FILENO); 316 #ifdef F_CLOSEM 317 (void)fcntl(3, F_CLOSEM, 0); 318 #else 319 for (fd = 3; fd < getdtablesize(); ++fd) 320 (void)close(fd); 321 #endif 322 (void)execve(pam_ssh_agent, 323 (char **)__UNCONST(pam_ssh_agent_argv), 324 (char **)__UNCONST(pam_ssh_agent_envp)); 325 done: 326 _exit(127); 327 } 328 329 /* parent */ 330 close(agent_pipe[1]); 331 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 332 return (PAM_SYSTEM_ERR); 333 pam_ssh_process_agent_output(pamh, f); 334 fclose(f); 335 336 return (PAM_SUCCESS); 337 } 338 339 /* 340 * Adds previously stored keys to a running agent. 341 */ 342 static int 343 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 344 { 345 AuthenticationConnection *ac; 346 struct pam_ssh_key *psk; 347 const char **kfn; 348 char **envlist, **env; 349 int pam_err; 350 351 /* switch to PAM environment */ 352 envlist = environ; 353 if ((environ = pam_getenvlist(pamh)) == NULL) { 354 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 355 __FUNCTION__); 356 environ = envlist; 357 return (PAM_SYSTEM_ERR); 358 } 359 360 /* get a connection to the agent */ 361 if ((ac = ssh_get_authentication_connection()) == NULL) { 362 openpam_log(PAM_LOG_DEBUG, 363 "%s: cannot get authentication connection", 364 __FUNCTION__); 365 pam_err = PAM_SYSTEM_ERR; 366 goto end; 367 } 368 369 /* look for keys to add to it */ 370 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 371 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 372 if (pam_err == PAM_SUCCESS && psk != NULL) { 373 if (ssh_add_identity(ac, psk->key, psk->comment)) 374 openpam_log(PAM_LOG_DEBUG, 375 "added %s to ssh agent", psk->comment); 376 else 377 openpam_log(PAM_LOG_DEBUG, "failed " 378 "to add %s to ssh agent", psk->comment); 379 /* we won't need the key again, so wipe it */ 380 pam_set_data(pamh, *kfn, NULL, NULL); 381 } 382 } 383 pam_err = PAM_SUCCESS; 384 end: 385 /* disconnect from agent */ 386 if (ac != NULL) 387 ssh_close_authentication_connection(ac); 388 389 /* switch back to original environment */ 390 for (env = environ; *env != NULL; ++env) 391 free(*env); 392 free(environ); 393 environ = envlist; 394 395 return (pam_err); 396 } 397 398 PAM_EXTERN int 399 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 400 int argc __unused, const char *argv[] __unused) 401 { 402 struct passwd *pwd; 403 const char *user; 404 void *data; 405 int pam_err = PAM_SUCCESS; 406 407 /* no keys, no work */ 408 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 409 openpam_get_option(pamh, "want_agent") == NULL) 410 return (PAM_SUCCESS); 411 412 /* switch to user credentials */ 413 pam_err = pam_get_user(pamh, &user, NULL); 414 if (pam_err != PAM_SUCCESS) 415 return (pam_err); 416 pwd = getpwnam(user); 417 if (pwd == NULL) 418 return (PAM_USER_UNKNOWN); 419 420 /* start the agent */ 421 pam_err = pam_ssh_start_agent(pamh, pwd); 422 if (pam_err != PAM_SUCCESS) 423 return pam_err; 424 425 pam_err = openpam_borrow_cred(pamh, pwd); 426 if (pam_err != PAM_SUCCESS) 427 return pam_err; 428 429 /* we have an agent, see if we can add any keys to it */ 430 pam_err = pam_ssh_add_keys_to_agent(pamh); 431 if (pam_err != PAM_SUCCESS) { 432 /* XXX ignore failures */ 433 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 434 pam_err = PAM_SUCCESS; 435 } 436 437 openpam_restore_cred(pamh); 438 return pam_err; 439 } 440 441 PAM_EXTERN int 442 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 443 int argc __unused, const char *argv[] __unused) 444 { 445 const char *ssh_agent_pid; 446 char *end; 447 int status; 448 pid_t pid; 449 450 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 451 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 452 return (PAM_SUCCESS); 453 } 454 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 455 if (*ssh_agent_pid == '\0' || *end != '\0') { 456 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 457 return (PAM_SESSION_ERR); 458 } 459 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 460 if (kill(pid, SIGTERM) == -1 || 461 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 462 return (PAM_SYSTEM_ERR); 463 return (PAM_SUCCESS); 464 } 465 466 PAM_MODULE_ENTRY("pam_ssh"); 467
Indexes created Sun Sep 28 16:09:52 GMT 2025