pam_ssh.c revision 1.8.2.3
1 /* $NetBSD: pam_ssh.c,v 1.8.2.3 2005/07/11 11:19:26 tron 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 1.8.2.3 2005/07/11 11:19:26 tron 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, pwres; 145 struct pam_ssh_key *psk; 146 int nkeys, pam_err, pass; 147 char pwbuf[1024]; 148 149 /* PEM is not loaded by default */ 150 OpenSSL_add_all_algorithms(); 151 152 /* get user name and home directory */ 153 pam_err = pam_get_user(pamh, &user, NULL); 154 if (pam_err != PAM_SUCCESS) 155 return (pam_err); 156 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 157 pwd == NULL) 158 return (PAM_USER_UNKNOWN); 159 if (pwd->pw_dir == NULL) 160 return (PAM_AUTH_ERR); 161 162 /* switch to user credentials */ 163 pam_err = openpam_borrow_cred(pamh, pwd); 164 if (pam_err != PAM_SUCCESS) 165 return (pam_err); 166 167 #ifdef notyet 168 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 169 char path[MAXPATHLEN]; 170 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 171 if (access(path, R_OK) == 0) 172 break; 173 } 174 175 if (*kfn == NULL) { 176 openpam_restore_cred(pamh); 177 return (PAM_AUTH_ERR); 178 } 179 #endif 180 181 pass = (pam_get_item(pamh, PAM_AUTHTOK, 182 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 183 load_keys: 184 /* get passphrase */ 185 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 186 &passphrase, pam_ssh_prompt); 187 if (pam_err != PAM_SUCCESS) { 188 openpam_restore_cred(pamh); 189 return (pam_err); 190 } 191 192 /* try to load keys from all keyfiles we know of */ 193 nkeys = 0; 194 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 195 psk = pam_ssh_load_key(pwd, *kfn, passphrase); 196 if (psk != NULL) { 197 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 198 ++nkeys; 199 } 200 } 201 202 /* 203 * If we tried an old token and didn't get anything, and 204 * try_first_pass was specified, try again after prompting the 205 * user for a new passphrase. 206 */ 207 if (nkeys == 0 && pass == 1 && 208 openpam_get_option(pamh, "try_first_pass") != NULL) { 209 pam_set_item(pamh, PAM_AUTHTOK, NULL); 210 pass = 0; 211 goto load_keys; 212 } 213 214 /* switch back to arbitrator credentials before returning */ 215 openpam_restore_cred(pamh); 216 217 /* no keys? */ 218 if (nkeys == 0) 219 return (PAM_AUTH_ERR); 220 221 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 222 return (PAM_SUCCESS); 223 } 224 225 PAM_EXTERN int 226 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 227 int argc __unused, const char *argv[] __unused) 228 { 229 230 return (PAM_SUCCESS); 231 } 232 233 /* 234 * Parses a line from ssh-agent's output. 235 */ 236 static void 237 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 238 { 239 char *line, *p, *key, *val; 240 size_t len; 241 242 while ((line = fgetln(f, &len)) != NULL) { 243 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 244 continue; 245 246 /* find equal sign at end of key */ 247 for (p = key = line; p < line + len; ++p) 248 if (*p == '=') 249 break; 250 if (p == line + len || *p != '=') 251 continue; 252 *p = '\0'; 253 254 /* find semicolon at end of value */ 255 for (val = ++p; p < line + len; ++p) 256 if (*p == ';') 257 break; 258 if (p == line + len || *p != ';') 259 continue; 260 *p = '\0'; 261 262 /* store key-value pair in environment */ 263 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 264 pam_setenv(pamh, key, val, 1); 265 } 266 } 267 268 /* 269 * Starts an ssh agent and stores the environment variables derived from 270 * its output. 271 */ 272 static int 273 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 274 { 275 int agent_pipe[2]; 276 pid_t pid; 277 FILE *f; 278 279 /* get a pipe which we will use to read the agent's output */ 280 if (pipe(agent_pipe) == -1) 281 return (PAM_SYSTEM_ERR); 282 283 /* start the agent */ 284 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 285 pid = fork(); 286 if (pid == (pid_t)-1) { 287 /* failed */ 288 close(agent_pipe[0]); 289 close(agent_pipe[1]); 290 return (PAM_SYSTEM_ERR); 291 } 292 if (pid == 0) { 293 #ifndef F_CLOSEM 294 int fd; 295 #endif 296 /* child: drop privs, close fds and start agent */ 297 if (setgid(pwd->pw_gid) == -1) { 298 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 299 __FUNCTION__, (int)pwd->pw_gid); 300 goto done; 301 } 302 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 303 openpam_log(PAM_LOG_DEBUG, 304 "%s: Cannot initgroups for %s (%m)", 305 __FUNCTION__, pwd->pw_name); 306 goto done; 307 } 308 if (setuid(pwd->pw_uid) == -1) { 309 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 310 __FUNCTION__, (int)pwd->pw_uid); 311 goto done; 312 } 313 (void)close(STDIN_FILENO); 314 (void)open(_PATH_DEVNULL, O_RDONLY); 315 (void)dup2(agent_pipe[1], STDOUT_FILENO); 316 (void)dup2(agent_pipe[1], STDERR_FILENO); 317 #ifdef F_CLOSEM 318 (void)fcntl(3, F_CLOSEM, 0); 319 #else 320 for (fd = 3; fd < getdtablesize(); ++fd) 321 (void)close(fd); 322 #endif 323 (void)execve(pam_ssh_agent, 324 (char **)__UNCONST(pam_ssh_agent_argv), 325 (char **)__UNCONST(pam_ssh_agent_envp)); 326 done: 327 _exit(127); 328 } 329 330 /* parent */ 331 close(agent_pipe[1]); 332 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 333 return (PAM_SYSTEM_ERR); 334 pam_ssh_process_agent_output(pamh, f); 335 fclose(f); 336 337 return (PAM_SUCCESS); 338 } 339 340 /* 341 * Adds previously stored keys to a running agent. 342 */ 343 static int 344 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 345 { 346 AuthenticationConnection *ac; 347 struct pam_ssh_key *psk; 348 const char **kfn; 349 char **envlist, **env; 350 int pam_err; 351 352 /* switch to PAM environment */ 353 envlist = environ; 354 if ((environ = pam_getenvlist(pamh)) == NULL) { 355 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 356 __FUNCTION__); 357 environ = envlist; 358 return (PAM_SYSTEM_ERR); 359 } 360 361 /* get a connection to the agent */ 362 if ((ac = ssh_get_authentication_connection()) == NULL) { 363 openpam_log(PAM_LOG_DEBUG, 364 "%s: cannot get authentication connection", 365 __FUNCTION__); 366 pam_err = PAM_SYSTEM_ERR; 367 goto end; 368 } 369 370 /* look for keys to add to it */ 371 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 372 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 373 if (pam_err == PAM_SUCCESS && psk != NULL) { 374 if (ssh_add_identity(ac, psk->key, psk->comment)) 375 openpam_log(PAM_LOG_DEBUG, 376 "added %s to ssh agent", psk->comment); 377 else 378 openpam_log(PAM_LOG_DEBUG, "failed " 379 "to add %s to ssh agent", psk->comment); 380 /* we won't need the key again, so wipe it */ 381 pam_set_data(pamh, *kfn, NULL, NULL); 382 } 383 } 384 pam_err = PAM_SUCCESS; 385 end: 386 /* disconnect from agent */ 387 if (ac != NULL) 388 ssh_close_authentication_connection(ac); 389 390 /* switch back to original environment */ 391 for (env = environ; *env != NULL; ++env) 392 free(*env); 393 free(environ); 394 environ = envlist; 395 396 return (pam_err); 397 } 398 399 PAM_EXTERN int 400 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 401 int argc __unused, const char *argv[] __unused) 402 { 403 struct passwd *pwd, pwres; 404 const char *user; 405 void *data; 406 int pam_err = PAM_SUCCESS; 407 char pwbuf[1024]; 408 409 /* no keys, no work */ 410 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 411 openpam_get_option(pamh, "want_agent") == NULL) 412 return (PAM_SUCCESS); 413 414 /* switch to user credentials */ 415 pam_err = pam_get_user(pamh, &user, NULL); 416 if (pam_err != PAM_SUCCESS) 417 return (pam_err); 418 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 419 pwd == NULL) 420 return (PAM_USER_UNKNOWN); 421 422 /* start the agent */ 423 pam_err = pam_ssh_start_agent(pamh, pwd); 424 if (pam_err != PAM_SUCCESS) 425 return pam_err; 426 427 pam_err = openpam_borrow_cred(pamh, pwd); 428 if (pam_err != PAM_SUCCESS) 429 return pam_err; 430 431 /* we have an agent, see if we can add any keys to it */ 432 pam_err = pam_ssh_add_keys_to_agent(pamh); 433 if (pam_err != PAM_SUCCESS) { 434 /* XXX ignore failures */ 435 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 436 pam_err = PAM_SUCCESS; 437 } 438 439 openpam_restore_cred(pamh); 440 return pam_err; 441 } 442 443 PAM_EXTERN int 444 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 445 int argc __unused, const char *argv[] __unused) 446 { 447 const char *ssh_agent_pid; 448 char *end; 449 int status; 450 pid_t pid; 451 452 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 453 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 454 return (PAM_SUCCESS); 455 } 456 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 457 if (*ssh_agent_pid == '\0' || *end != '\0') { 458 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 459 return (PAM_SESSION_ERR); 460 } 461 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 462 if (kill(pid, SIGTERM) == -1 || 463 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 464 return (PAM_SYSTEM_ERR); 465 return (PAM_SUCCESS); 466 } 467 468 PAM_MODULE_ENTRY("pam_ssh"); 469
Indexes created Mon Sep 29 21:09:56 GMT 2025