pam_ssh.c revision 1.15
1 /* $NetBSD: pam_ssh.c,v 1.15 2008/01/27 01:23:20 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 1.15 2008/01/27 01:23:20 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 "buffer.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 if (comment != NULL) 112 free(comment); 113 return (NULL); 114 } 115 116 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn); 117 if ((psk = malloc(sizeof(*psk))) == NULL) { 118 key_free(key); 119 free(comment); 120 return (NULL); 121 } 122 psk->key = key; 123 psk->comment = comment; 124 return (psk); 125 } 126 127 /* 128 * Wipes a private key and frees the associated resources. 129 */ 130 static void 131 pam_ssh_free_key(pam_handle_t *pamh __unused, 132 void *data, int pam_err __unused) 133 { 134 struct pam_ssh_key *psk; 135 136 psk = data; 137 key_free(psk->key); 138 free(psk->comment); 139 free(psk); 140 } 141 142 PAM_EXTERN int 143 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 144 int argc __unused, const char *argv[] __unused) 145 { 146 const char **kfn, *passphrase, *user; 147 struct passwd *pwd, pwres; 148 struct pam_ssh_key *psk; 149 int nkeys, pam_err, pass; 150 char pwbuf[1024]; 151 152 /* PEM is not loaded by default */ 153 OpenSSL_add_all_algorithms(); 154 155 /* get user name and home directory */ 156 pam_err = pam_get_user(pamh, &user, NULL); 157 if (pam_err != PAM_SUCCESS) 158 return (pam_err); 159 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 160 pwd == NULL) 161 return (PAM_USER_UNKNOWN); 162 if (pwd->pw_dir == NULL) 163 return (PAM_AUTH_ERR); 164 165 /* switch to user credentials */ 166 pam_err = openpam_borrow_cred(pamh, pwd); 167 if (pam_err != PAM_SUCCESS) 168 return (pam_err); 169 170 #ifdef notyet 171 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 172 char path[MAXPATHLEN]; 173 (void)snprintf(path, sizeof(path), "%s/%s", pwd->pw_dir, *kfn); 174 if (access(path, R_OK) == 0) 175 break; 176 } 177 178 if (*kfn == NULL) { 179 openpam_restore_cred(pamh); 180 return (PAM_AUTH_ERR); 181 } 182 #endif 183 184 pass = (pam_get_item(pamh, PAM_AUTHTOK, 185 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 186 load_keys: 187 /* get passphrase */ 188 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 189 &passphrase, pam_ssh_prompt); 190 if (pam_err != PAM_SUCCESS) { 191 openpam_restore_cred(pamh); 192 return (pam_err); 193 } 194 195 /* try to load keys from all keyfiles we know of */ 196 nkeys = 0; 197 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 198 psk = pam_ssh_load_key(pwd, *kfn, passphrase); 199 if (psk != NULL) { 200 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 201 ++nkeys; 202 } 203 } 204 205 /* 206 * If we tried an old token and didn't get anything, and 207 * try_first_pass was specified, try again after prompting the 208 * user for a new passphrase. 209 */ 210 if (nkeys == 0 && pass == 1 && 211 openpam_get_option(pamh, "try_first_pass") != NULL) { 212 pam_set_item(pamh, PAM_AUTHTOK, NULL); 213 pass = 0; 214 goto load_keys; 215 } 216 217 /* switch back to arbitrator credentials before returning */ 218 openpam_restore_cred(pamh); 219 220 /* no keys? */ 221 if (nkeys == 0) 222 return (PAM_AUTH_ERR); 223 224 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 225 return (PAM_SUCCESS); 226 } 227 228 PAM_EXTERN int 229 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 230 int argc __unused, const char *argv[] __unused) 231 { 232 233 return (PAM_SUCCESS); 234 } 235 236 /* 237 * Parses a line from ssh-agent's output. 238 */ 239 static void 240 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 241 { 242 char *line, *p, *key, *val; 243 size_t len; 244 245 while ((line = fgetln(f, &len)) != NULL) { 246 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 247 continue; 248 249 /* find equal sign at end of key */ 250 for (p = key = line; p < line + len; ++p) 251 if (*p == '=') 252 break; 253 if (p == line + len || *p != '=') 254 continue; 255 *p = '\0'; 256 257 /* find semicolon at end of value */ 258 for (val = ++p; p < line + len; ++p) 259 if (*p == ';') 260 break; 261 if (p == line + len || *p != ';') 262 continue; 263 *p = '\0'; 264 265 /* store key-value pair in environment */ 266 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 267 pam_setenv(pamh, key, val, 1); 268 } 269 } 270 271 /* 272 * Starts an ssh agent and stores the environment variables derived from 273 * its output. 274 */ 275 static int 276 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 277 { 278 int agent_pipe[2]; 279 pid_t pid; 280 FILE *f; 281 282 /* get a pipe which we will use to read the agent's output */ 283 if (pipe(agent_pipe) == -1) 284 return (PAM_SYSTEM_ERR); 285 286 /* start the agent */ 287 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 288 pid = fork(); 289 if (pid == (pid_t)-1) { 290 /* failed */ 291 close(agent_pipe[0]); 292 close(agent_pipe[1]); 293 return (PAM_SYSTEM_ERR); 294 } 295 if (pid == 0) { 296 #ifndef F_CLOSEM 297 int fd; 298 #endif 299 /* child: drop privs, close fds and start agent */ 300 if (setgid(pwd->pw_gid) == -1) { 301 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%m)", 302 __func__, (int)pwd->pw_gid); 303 goto done; 304 } 305 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 306 openpam_log(PAM_LOG_DEBUG, 307 "%s: Cannot initgroups for %s (%m)", 308 __func__, pwd->pw_name); 309 goto done; 310 } 311 if (setuid(pwd->pw_uid) == -1) { 312 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%m)", 313 __func__, (int)pwd->pw_uid); 314 goto done; 315 } 316 (void)close(STDIN_FILENO); 317 (void)open(_PATH_DEVNULL, O_RDONLY); 318 (void)dup2(agent_pipe[1], STDOUT_FILENO); 319 (void)dup2(agent_pipe[1], STDERR_FILENO); 320 #ifdef F_CLOSEM 321 (void)fcntl(3, F_CLOSEM, 0); 322 #else 323 for (fd = 3; fd < getdtablesize(); ++fd) 324 (void)close(fd); 325 #endif 326 (void)execve(pam_ssh_agent, 327 (char **)__UNCONST(pam_ssh_agent_argv), 328 (char **)__UNCONST(pam_ssh_agent_envp)); 329 done: 330 _exit(127); 331 } 332 333 /* parent */ 334 close(agent_pipe[1]); 335 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 336 return (PAM_SYSTEM_ERR); 337 pam_ssh_process_agent_output(pamh, f); 338 fclose(f); 339 340 return (PAM_SUCCESS); 341 } 342 343 /* 344 * Adds previously stored keys to a running agent. 345 */ 346 static int 347 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 348 { 349 AuthenticationConnection *ac; 350 const struct pam_ssh_key *psk; 351 const char **kfn; 352 char **envlist, **env; 353 int pam_err; 354 355 /* switch to PAM environment */ 356 envlist = environ; 357 if ((environ = pam_getenvlist(pamh)) == NULL) { 358 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 359 __func__); 360 environ = envlist; 361 return (PAM_SYSTEM_ERR); 362 } 363 364 /* get a connection to the agent */ 365 if ((ac = ssh_get_authentication_connection()) == NULL) { 366 openpam_log(PAM_LOG_DEBUG, 367 "%s: cannot get authentication connection", 368 __func__); 369 pam_err = PAM_SYSTEM_ERR; 370 goto end; 371 } 372 373 /* look for keys to add to it */ 374 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 375 const void *vp; 376 pam_err = pam_get_data(pamh, *kfn, &vp); 377 psk = vp; 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, pwres; 409 const char *user; 410 const void *data; 411 int pam_err = PAM_SUCCESS; 412 char pwbuf[1024]; 413 414 /* no keys, no work */ 415 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 416 openpam_get_option(pamh, "want_agent") == NULL) 417 return (PAM_SUCCESS); 418 419 /* switch to user credentials */ 420 pam_err = pam_get_user(pamh, &user, NULL); 421 if (pam_err != PAM_SUCCESS) 422 return (pam_err); 423 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 424 pwd == NULL) 425 return (PAM_USER_UNKNOWN); 426 427 /* start the agent */ 428 pam_err = pam_ssh_start_agent(pamh, pwd); 429 if (pam_err != PAM_SUCCESS) 430 return pam_err; 431 432 pam_err = openpam_borrow_cred(pamh, pwd); 433 if (pam_err != PAM_SUCCESS) 434 return pam_err; 435 436 /* we have an agent, see if we can add any keys to it */ 437 pam_err = pam_ssh_add_keys_to_agent(pamh); 438 if (pam_err != PAM_SUCCESS) { 439 /* XXX ignore failures */ 440 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 441 pam_err = PAM_SUCCESS; 442 } 443 444 openpam_restore_cred(pamh); 445 return pam_err; 446 } 447 448 PAM_EXTERN int 449 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 450 int argc __unused, const char *argv[] __unused) 451 { 452 const char *ssh_agent_pid; 453 char *end; 454 int status; 455 pid_t pid; 456 457 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 458 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 459 return (PAM_SUCCESS); 460 } 461 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 462 if (*ssh_agent_pid == '\0' || *end != '\0') { 463 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 464 return (PAM_SESSION_ERR); 465 } 466 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 467 if (kill(pid, SIGTERM) == -1 || 468 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 469 return (PAM_SYSTEM_ERR); 470 return (PAM_SUCCESS); 471 } 472 473 PAM_MODULE_ENTRY("pam_ssh"); 474
Indexes created Mon Sep 22 10:09:38 GMT 2025