1 /* $NetBSD: pam_ssh.c,v 1.3 2005/01/03 03:08:40 lukem 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 1.3 2005/01/03 03:08:40 lukem 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 pass = (pam_get_item(pamh, PAM_AUTHTOK, 166 (const void **)__UNCONST(&passphrase)) == PAM_SUCCESS); 167 load_keys: 168 /* get passphrase */ 169 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 170 &passphrase, pam_ssh_prompt); 171 if (pam_err != PAM_SUCCESS) { 172 openpam_restore_cred(pamh); 173 return (pam_err); 174 } 175 176 /* try to load keys from all keyfiles we know of */ 177 nkeys = 0; 178 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 179 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase); 180 if (psk != NULL) { 181 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 182 ++nkeys; 183 } 184 } 185 186 /* 187 * If we tried an old token and didn't get anything, and 188 * try_first_pass was specified, try again after prompting the 189 * user for a new passphrase. 190 */ 191 if (nkeys == 0 && pass == 1 && 192 openpam_get_option(pamh, "try_first_pass") != NULL) { 193 pam_set_item(pamh, PAM_AUTHTOK, NULL); 194 pass = 0; 195 goto load_keys; 196 } 197 198 /* switch back to arbitrator credentials before returning */ 199 openpam_restore_cred(pamh); 200 201 /* no keys? */ 202 if (nkeys == 0) 203 return (PAM_AUTH_ERR); 204 205 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 206 return (PAM_SUCCESS); 207 } 208 209 PAM_EXTERN int 210 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 211 int argc __unused, const char *argv[] __unused) 212 { 213 214 return (PAM_SUCCESS); 215 } 216 217 /* 218 * Parses a line from ssh-agent's output. 219 */ 220 static void 221 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 222 { 223 char *line, *p, *key, *val; 224 size_t len; 225 226 while ((line = fgetln(f, &len)) != NULL) { 227 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 228 continue; 229 230 /* find equal sign at end of key */ 231 for (p = key = line; p < line + len; ++p) 232 if (*p == '=') 233 break; 234 if (p == line + len || *p != '=') 235 continue; 236 *p = '\0'; 237 238 /* find semicolon at end of value */ 239 for (val = ++p; p < line + len; ++p) 240 if (*p == ';') 241 break; 242 if (p == line + len || *p != ';') 243 continue; 244 *p = '\0'; 245 246 /* store key-value pair in environment */ 247 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 248 pam_setenv(pamh, key, val, 1); 249 } 250 } 251 252 /* 253 * Starts an ssh agent and stores the environment variables derived from 254 * its output. 255 */ 256 static int 257 pam_ssh_start_agent(pam_handle_t *pamh) 258 { 259 int agent_pipe[2]; 260 pid_t pid; 261 FILE *f; 262 263 /* get a pipe which we will use to read the agent's output */ 264 if (pipe(agent_pipe) == -1) { 265 openpam_restore_cred(pamh); 266 return (PAM_SYSTEM_ERR); 267 } 268 269 /* start the agent */ 270 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 271 pid = fork(); 272 if (pid == (pid_t)-1) { 273 /* failed */ 274 close(agent_pipe[0]); 275 close(agent_pipe[1]); 276 return (PAM_SYSTEM_ERR); 277 } 278 if (pid == 0) { 279 #ifndef F_CLOSEM 280 int fd; 281 #endif 282 283 /* child: drop privs, close fds and start agent */ 284 setgid(getegid()); 285 setuid(geteuid()); 286 close(STDIN_FILENO); 287 open(_PATH_DEVNULL, O_RDONLY); 288 dup2(agent_pipe[1], STDOUT_FILENO); 289 dup2(agent_pipe[1], STDERR_FILENO); 290 #ifdef F_CLOSEM 291 (void)fcntl(3, F_CLOSEM, 0); 292 #else 293 for (fd = 3; fd < getdtablesize(); ++fd) 294 close(fd); 295 #endif 296 execve(pam_ssh_agent, (char **)__UNCONST(pam_ssh_agent_argv), 297 (char **)__UNCONST(pam_ssh_agent_envp)); 298 _exit(127); 299 } 300 301 /* parent */ 302 close(agent_pipe[1]); 303 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 304 return (PAM_SYSTEM_ERR); 305 pam_ssh_process_agent_output(pamh, f); 306 fclose(f); 307 308 return (PAM_SUCCESS); 309 } 310 311 /* 312 * Adds previously stored keys to a running agent. 313 */ 314 static int 315 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 316 { 317 AuthenticationConnection *ac; 318 struct pam_ssh_key *psk; 319 const char **kfn; 320 char **envlist, **env; 321 int pam_err; 322 323 /* switch to PAM environment */ 324 envlist = environ; 325 if ((environ = pam_getenvlist(pamh)) == NULL) { 326 environ = envlist; 327 return (PAM_SYSTEM_ERR); 328 } 329 330 /* get a connection to the agent */ 331 if ((ac = ssh_get_authentication_connection()) == NULL) { 332 pam_err = PAM_SYSTEM_ERR; 333 goto end; 334 } 335 336 /* look for keys to add to it */ 337 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 338 pam_err = pam_get_data(pamh, *kfn, (void **)__UNCONST(&psk)); 339 if (pam_err == PAM_SUCCESS && psk != NULL) { 340 if (ssh_add_identity(ac, psk->key, psk->comment)) 341 openpam_log(PAM_LOG_DEBUG, 342 "added %s to ssh agent", psk->comment); 343 else 344 openpam_log(PAM_LOG_DEBUG, "failed " 345 "to add %s to ssh agent", psk->comment); 346 /* we won't need the key again, so wipe it */ 347 pam_set_data(pamh, *kfn, NULL, NULL); 348 } 349 } 350 pam_err = PAM_SUCCESS; 351 end: 352 /* disconnect from agent */ 353 if (ac != NULL) 354 ssh_close_authentication_connection(ac); 355 356 /* switch back to original environment */ 357 for (env = environ; *env != NULL; ++env) 358 free(*env); 359 free(environ); 360 environ = envlist; 361 362 return (pam_err); 363 } 364 365 PAM_EXTERN int 366 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 367 int argc __unused, const char *argv[] __unused) 368 { 369 struct passwd *pwd; 370 const char *user; 371 void *data; 372 int pam_err; 373 374 /* no keys, no work */ 375 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 376 openpam_get_option(pamh, "want_agent") == NULL) 377 return (PAM_SUCCESS); 378 379 /* switch to user credentials */ 380 pam_err = pam_get_user(pamh, &user, NULL); 381 if (pam_err != PAM_SUCCESS) 382 return (pam_err); 383 pwd = getpwnam(user); 384 if (pwd == NULL) 385 return (PAM_USER_UNKNOWN); 386 pam_err = openpam_borrow_cred(pamh, pwd); 387 if (pam_err != PAM_SUCCESS) 388 return (pam_err); 389 390 /* start the agent */ 391 pam_err = pam_ssh_start_agent(pamh); 392 if (pam_err != PAM_SUCCESS) { 393 openpam_restore_cred(pamh); 394 return (pam_err); 395 } 396 397 /* we have an agent, see if we can add any keys to it */ 398 pam_err = pam_ssh_add_keys_to_agent(pamh); 399 if (pam_err != PAM_SUCCESS) { 400 /* XXX ignore failures */ 401 } 402 403 openpam_restore_cred(pamh); 404 return (PAM_SUCCESS); 405 } 406 407 PAM_EXTERN int 408 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 409 int argc __unused, const char *argv[] __unused) 410 { 411 const char *ssh_agent_pid; 412 char *end; 413 int status; 414 pid_t pid; 415 416 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 417 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 418 return (PAM_SUCCESS); 419 } 420 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 421 if (*ssh_agent_pid == '\0' || *end != '\0') { 422 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 423 return (PAM_SESSION_ERR); 424 } 425 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 426 if (kill(pid, SIGTERM) == -1 || 427 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 428 return (PAM_SYSTEM_ERR); 429 return (PAM_SUCCESS); 430 } 431 432 PAM_MODULE_ENTRY("pam_ssh"); 433