1 /*- 2 * Copyright (c) 2003 Networks Associates Technology, Inc. 3 * Copyright (c) 2004-2011 Dag-Erling Smørgrav 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by ThinkSec AS and 7 * NAI Labs, the Security Research Division of Network Associates, Inc. 8 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. The name of the author may not be used to endorse or promote 20 * products derived from this software without specific prior written 21 * permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 */ 35 36 #include <sys/cdefs.h> 37 __FBSDID("$FreeBSD$"); 38 39 #include <sys/param.h> 40 #include <sys/wait.h> 41 42 #include <errno.h> 43 #include <fcntl.h> 44 #include <paths.h> 45 #include <pwd.h> 46 #include <signal.h> 47 #include <stdio.h> 48 #include <string.h> 49 #include <unistd.h> 50 51 #define PAM_SM_AUTH 52 #define PAM_SM_SESSION 53 54 #include <security/pam_appl.h> 55 #include <security/pam_modules.h> 56 #include <security/openpam.h> 57 58 #include <openssl/evp.h> 59 60 #include "key.h" 61 #include "buffer.h" 62 #include "authfd.h" 63 #include "authfile.h" 64 65 #define ssh_add_identity(auth, key, comment) \ 66 ssh_add_identity_constrained(auth, key, comment, 0, 0) 67 68 extern char **environ; 69 70 struct pam_ssh_key { 71 Key *key; 72 char *comment; 73 }; 74 75 static const char *pam_ssh_prompt = "SSH passphrase: "; 76 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 77 78 static const char *pam_ssh_keyfiles[] = { 79 ".ssh/identity", /* SSH1 RSA key */ 80 ".ssh/id_rsa", /* SSH2 RSA key */ 81 ".ssh/id_dsa", /* SSH2 DSA key */ 82 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 83 NULL 84 }; 85 86 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 87 static char *const pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL }; 88 static char *const 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", fn); 109 return (NULL); 110 } 111 112 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", 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 const void *item; 144 struct passwd *pwd; 145 struct pam_ssh_key *psk; 146 int nkeys, nullok, pam_err, pass; 147 148 nullok = (openpam_get_option(pamh, "nullok") != NULL); 149 150 /* PEM is not loaded by default */ 151 OpenSSL_add_all_algorithms(); 152 153 /* get user name and home directory */ 154 pam_err = pam_get_user(pamh, &user, NULL); 155 if (pam_err != PAM_SUCCESS) 156 return (pam_err); 157 pwd = getpwnam(user); 158 if (pwd == NULL) 159 return (PAM_USER_UNKNOWN); 160 if (pwd->pw_dir == NULL) 161 return (PAM_AUTH_ERR); 162 163 nkeys = 0; 164 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 165 item != NULL); 166 load_keys: 167 /* get passphrase */ 168 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 169 &passphrase, pam_ssh_prompt); 170 if (pam_err != PAM_SUCCESS) 171 return (pam_err); 172 173 if (*passphrase == '\0' && !nullok) 174 goto skip_keys; 175 176 /* switch to user credentials */ 177 pam_err = openpam_borrow_cred(pamh, pwd); 178 if (pam_err != PAM_SUCCESS) 179 return (pam_err); 180 181 /* try to load keys from all keyfiles we know of */ 182 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 183 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase); 184 if (psk != NULL) { 185 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 186 ++nkeys; 187 } 188 } 189 190 /* switch back to arbitrator credentials */ 191 openpam_restore_cred(pamh); 192 193 skip_keys: 194 /* 195 * If we tried an old token and didn't get anything, and 196 * try_first_pass was specified, try again after prompting the 197 * user for a new passphrase. 198 */ 199 if (nkeys == 0 && pass == 1 && 200 openpam_get_option(pamh, "try_first_pass") != NULL) { 201 pam_set_item(pamh, PAM_AUTHTOK, NULL); 202 pass = 0; 203 goto load_keys; 204 } 205 206 /* no keys? */ 207 if (nkeys == 0) 208 return (PAM_AUTH_ERR); 209 210 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 211 return (PAM_SUCCESS); 212 } 213 214 PAM_EXTERN int 215 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 216 int argc __unused, const char *argv[] __unused) 217 { 218 219 return (PAM_SUCCESS); 220 } 221 222 /* 223 * Parses a line from ssh-agent's output. 224 */ 225 static void 226 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 227 { 228 char *line, *p, *key, *val; 229 size_t len; 230 231 while ((line = fgetln(f, &len)) != NULL) { 232 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 233 continue; 234 235 /* find equal sign at end of key */ 236 for (p = key = line; p < line + len; ++p) 237 if (*p == '=') 238 break; 239 if (p == line + len || *p != '=') 240 continue; 241 *p = '\0'; 242 243 /* find semicolon at end of value */ 244 for (val = ++p; p < line + len; ++p) 245 if (*p == ';') 246 break; 247 if (p == line + len || *p != ';') 248 continue; 249 *p = '\0'; 250 251 /* store key-value pair in environment */ 252 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 253 pam_setenv(pamh, key, val, 1); 254 } 255 } 256 257 /* 258 * Starts an ssh agent and stores the environment variables derived from 259 * its output. 260 */ 261 static int 262 pam_ssh_start_agent(pam_handle_t *pamh) 263 { 264 int agent_pipe[2]; 265 pid_t pid; 266 FILE *f; 267 268 /* get a pipe which we will use to read the agent's output */ 269 if (pipe(agent_pipe) == -1) 270 return (PAM_SYSTEM_ERR); 271 272 /* start the agent */ 273 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 274 pid = fork(); 275 if (pid == (pid_t)-1) { 276 /* failed */ 277 close(agent_pipe[0]); 278 close(agent_pipe[1]); 279 return (PAM_SYSTEM_ERR); 280 } 281 if (pid == 0) { 282 int fd; 283 284 /* child: drop privs, close fds and start agent */ 285 setgid(getegid()); 286 setuid(geteuid()); 287 close(STDIN_FILENO); 288 open(_PATH_DEVNULL, O_RDONLY); 289 dup2(agent_pipe[1], STDOUT_FILENO); 290 dup2(agent_pipe[1], STDERR_FILENO); 291 for (fd = 3; fd < getdtablesize(); ++fd) 292 close(fd); 293 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp); 294 _exit(127); 295 } 296 297 /* parent */ 298 close(agent_pipe[1]); 299 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 300 return (PAM_SYSTEM_ERR); 301 pam_ssh_process_agent_output(pamh, f); 302 fclose(f); 303 304 return (PAM_SUCCESS); 305 } 306 307 /* 308 * Adds previously stored keys to a running agent. 309 */ 310 static int 311 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 312 { 313 AuthenticationConnection *ac; 314 const struct pam_ssh_key *psk; 315 const char **kfn; 316 const void *item; 317 char **envlist, **env; 318 int pam_err; 319 320 /* switch to PAM environment */ 321 envlist = environ; 322 if ((environ = pam_getenvlist(pamh)) == NULL) { 323 environ = envlist; 324 return (PAM_SYSTEM_ERR); 325 } 326 327 /* get a connection to the agent */ 328 if ((ac = ssh_get_authentication_connection()) == NULL) { 329 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent"); 330 pam_err = PAM_SYSTEM_ERR; 331 goto end; 332 } 333 334 /* look for keys to add to it */ 335 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 336 pam_err = pam_get_data(pamh, *kfn, &item); 337 if (pam_err == PAM_SUCCESS && item != NULL) { 338 psk = item; 339 if (ssh_add_identity(ac, psk->key, psk->comment)) 340 openpam_log(PAM_LOG_DEBUG, 341 "added %s to ssh agent", psk->comment); 342 else 343 openpam_log(PAM_LOG_DEBUG, "failed " 344 "to add %s to ssh agent", psk->comment); 345 /* we won't need the key again, so wipe it */ 346 pam_set_data(pamh, *kfn, NULL, NULL); 347 } 348 } 349 pam_err = PAM_SUCCESS; 350 end: 351 /* disconnect from agent */ 352 if (ac != NULL) 353 ssh_close_authentication_connection(ac); 354 355 /* switch back to original environment */ 356 for (env = environ; *env != NULL; ++env) 357 free(*env); 358 free(environ); 359 environ = envlist; 360 361 return (pam_err); 362 } 363 364 PAM_EXTERN int 365 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 366 int argc __unused, const char *argv[] __unused) 367 { 368 struct passwd *pwd; 369 const char *user; 370 const void *data; 371 int pam_err; 372 373 /* no keys, no work */ 374 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 375 openpam_get_option(pamh, "want_agent") == NULL) 376 return (PAM_SUCCESS); 377 378 /* switch to user credentials */ 379 pam_err = pam_get_user(pamh, &user, NULL); 380 if (pam_err != PAM_SUCCESS) 381 return (pam_err); 382 pwd = getpwnam(user); 383 if (pwd == NULL) 384 return (PAM_USER_UNKNOWN); 385 pam_err = openpam_borrow_cred(pamh, pwd); 386 if (pam_err != PAM_SUCCESS) 387 return (pam_err); 388 389 /* start the agent */ 390 pam_err = pam_ssh_start_agent(pamh); 391 if (pam_err != PAM_SUCCESS) { 392 openpam_restore_cred(pamh); 393 return (pam_err); 394 } 395 396 /* we have an agent, see if we can add any keys to it */ 397 pam_err = pam_ssh_add_keys_to_agent(pamh); 398 if (pam_err != PAM_SUCCESS) { 399 /* XXX ignore failures */ 400 } 401 402 openpam_restore_cred(pamh); 403 return (PAM_SUCCESS); 404 } 405 406 PAM_EXTERN int 407 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 408 int argc __unused, const char *argv[] __unused) 409 { 410 const char *ssh_agent_pid; 411 char *end; 412 int status; 413 pid_t pid; 414 415 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 416 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 417 return (PAM_SUCCESS); 418 } 419 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 420 if (*ssh_agent_pid == '\0' || *end != '\0') { 421 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 422 return (PAM_SESSION_ERR); 423 } 424 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 425 if (kill(pid, SIGTERM) == -1 || 426 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 427 return (PAM_SYSTEM_ERR); 428 return (PAM_SUCCESS); 429 } 430 431 PAM_MODULE_ENTRY("pam_ssh"); 432